Laboratory Manual Colloid Chemistry - Forgotten Books

Copyright, 1922,

By HARRY N . HOLMES

PREFACE

TH IS manual was written at the request of the Colloid Com

mittee of the National Research Council.

M ost of the experiments have been tested in the laboratory

course given at Oberlin for the past six years, while others have

been contributed by the leading colloid chemists of this country .

There has long been need of a suitable laboratory manual

to advance the teaching of colloid chemistry,and for lack of such a

book instruction has lagged . Lecture courses in plenty are given

at various universities, but in very few institutions is there a

real laboratory course in the subject . It is the laboratory method

of instruction that has advanced science so wonderqy in the last

half century ; obviously, instruction in colloids must develop in

the same way .

The general interest in the subj ect grows apa ce . Not only

theoretical chemists but industrial men as well are expressing the

belief that a great many of their problems are colloidal . Hun

dreds of able chemists would study colloid chemistry in their

private laboratories if a self-tea ching manual were available . To

meet this demand th is manual offers a large amount of text mate

rial in the way of comment and explanation . The carefully

selected references for collatera l reading will guide the experi

menter and enable him to pursue his studies with a minimum of

wasted effort . I t is,as the author knows from persona l experi

ence,very difficult for the beginner in the subj ect to know what

to read first,or wha t experiments are worth performing .

Twenty years ago,when colloid chemistry was still in its

swaddling clothes,chemists concerned themselves too much

with the mere preparation of new colloids,just as organic chemists

once prided themselves too much on the mere prepara tion of new

compounds . Now we are making genuine progress by a more

intensive study of the properties of material in the colloid state,iii

iv PREFACE

by discovering general principles and by the use ofquantitativemethods .

In preparing this manual the author has been greatly helped

by advice and criticism from Mr . Jerome Alexander of the Uniform

Adhesive Co .,Professor W . D . Bancroft of Cornell University

,

Dr. Martin H . Fischer. of the Cincinnati General Hospital, Dr.

Leon Parsons and M r. Robert E . Wilson of M assachusetts Insti

tute of Technology, Dr. Ellwood Spear of the Goodyear Rubber

Co.,Dr. S . E . Sheppard of the E astman Kodak Co .

,Dr. J . A .

Wilson of the Gallun Tanneries at Milwaukee, and Professor

J . H . Mathews of the University ofWisconsin .

A number of detailed experiments were generously given by

Mr . Alexander (on the ultramicroscope) , by Professor Bancroft

(on dyeing) , by Dr. Spear (on rubber) , by Dr. Sheppard (on silver

nuclei) , by Dr . J . A . Wilson (on tanning) and by Dr. Parsons

(on varied topics) .

Most of the ch apter on Adsorption of Gases was used by per

missmn of the S11ica Gel Co. of Baltimore and represents the work

of Dr. Patrick. Cuts were loaned by D .r M artin H . Fischer,the

Central ScientificCo. and the Telling-Belle Vernon Co.

HARRY N . HOLMES .

OBERLIN, OHIO,March,“1922 .

SELECTIONS FOR SPECIAL COURSES

IT is not expected that any one student shall perform all the

experiments in this manual . If he did he would probably spend

two full days each week for a year in the colloid laboratory .

The teacher must use judgment m selecting representative

experiments from each chapter to suit the time allowed for the

course . There is a distinct gain in general interest if similar

experiments are given to different students rather than to give

all exactly the same drill .

Again we must admit that a single definite list of experiments

does not meet equa lly well the needs of students interested in a

general fundamental course, in medical work, in agriculture and

ceramics,in geology and in industrial work . To meet these dif

ferent demands the author suggests the following courses based

on a time allowance of at least twelve clock-ho‘urs per week for

one semester

A Genera l Course — Experiments 1 , 2, 5, 6, 7, 10, 12, 15, 17,

67, 68 , 69, 71 , 74, 76, 78 , 84, 89, 91 , 94, 95, 96, 98, 100, 101 , 103,

165—166, 167— 174

,175, 176, 177, 18 1 , 184,

A Course for'

M edica l Students — Experiments 1,6,8,1 1

,12,

64, 65, 67, 68 , 69, 71 , 73, 80, 8 1, 82, 83, 84, 85, 86, 89, 91,

92,93

, 95, 96, 98 , 99, 101 , 104, 1 10, 1 12, 1 15, 1 19, 126, 133, 135,

144,148

,150

,153-159, 182 .

A Course for Students ofAgriculture or Ceramics — Experiments

1,4, 6, 10, 12, 13, 17, 21 , 25, 31 , 39, 40, 44, 46, 47, 48 , 49, 50, 56,

57,58 , 59, 63, 65, 67, 68 , 69, 72, 80, 84 ,

91, 94,95, 96, 98 , 100, 101 ,

104, 105, 1 12, 1 15, 122, 123, 133, 134, 144, 147, 148 , 153

— 159, 162,

163,164, 182, 184 .

vi SELECTIONS FOR SPECIAL COURSES

A Course for Students of Geology.

— Experiments l, 3, 4, 10, 12,

13, 17, 21, 25, 31 , 40, 46,47

,48

,49

,50

,56

,57

,58 , 59, 63,

65, 67, 68 , 69, 71 , 72, 84, 91 , 95, 100, 106 , 1 15, 122, 123, 125, 127,

128 , 133, 134, 144— 152

,159—164 , 182, 184.

A Course for Students of I ndustrial Chemistry.

— Experiments

1,2,3,10

,12

,13

,16

,21

,25

,31

,41

,42

,46, 47, 48 , 50, 55, 56, 57,

58 , 59, 65, 67 68, 69, 70, 72, 79, 8 1 , 84 ,

85,86

,90

,91 , 94, 95, 96,

137, 138 , 139, 140, 141 , 144 ,148

,153-159

,160, 161 , 165, 166 , 167

174,177

,178 , 180, 185, 186 .

Quantitative experiments for a course in Physical Chemistry

are scattered throughout the book and may readily be selected .

TABLE OF CONTENTS

INTRODUCTION (SELECTION OF COURSES)

CHAPTER I

SUSPENSIONS— COARSE AND FINERa te Of Settling Of Particles Of Different SizesSurfa ce and SolubilityTynda ll ConeThe Colloid Chemistry Of Feh ling ’s TestsVon Weimarn

’

s Law

CHAPTER II

DIALYSIS AND DIFFUSIONBottle D ia lyzersParchment Cup Dia lyzersCollodion M embranesIdentification of Colloids by Dia lysisHot Dia lysisChromium Hydroxide by Hot DialysisDiffusion Tests“ PatriotiC Tl lb e 0 0 0

CHAPTER

CONDENSATION M ETHODS OF PREPARATION

ReductionGold by Zsigmondy ’s M ethodGo ld by TanninGreen Gold (by Pyrocatech in)Koh lsch iitter

’

s SilverSilver by Tannin

o o o o o o o o o o ooo o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o

viii CONTENTS

Hydroxides and OxidesFerric Hydroxide .

Chromium HydroxideMolybdenum Blue .

M anganese DioxideSulfides ofAn timony, Arsenic, Mercury and CopperSilicic AcidTungstic Acid

StaM iC ACid 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

CHAPTER IV

D ISPERSION METHODS OF PREPARATION— PEPTIZATIONBredig

’

s M ethod

Behavior of Gum Arabic with Alcohol and WaterPeptization Of Cadm ium SulfideSilver Iodide Sols .

Prussian BlueFerric Arsenate .

Peptization ofChromium Hydroxide in Presence ofFerric Hydroxide

CHAPTER V

COAGULATIONHardy ’s Rule ofVa lencePrecipitation Of a Negative ColloidDetermination Of the Nature Of the Charge on ColloidsPrecipitation of Fa ctory Wastes .

Stabiliz ing Influence Of Ions Of the Same Charge as the Colloid .

Replacement of the Coagulating Ion .

References to Literature on CoagulationCoagulation by Heat and PressureSa lting OutFractiona l Precipitationc ataphoreSE t t l t ’ O 0 0 0 0 0 0 0 0 0 0

CHAPTER VI

Gelatin as a Protective Colloid .

CONTENTS

Gold NumberCarey Lea ’s SilverGela tin in M ilk and Ice Cream

Color ofPhotographic Images in Relation toDispersity ofSilver .

CHAPTER VI I

Distinction between Suspensoids and EmulsoidsGels

,Jellies and Gelatinous Precipitates

Solid AlcoholSilicic Acid JellyVibra ting GelsBarium Sulfa te GelsSoapsHydration of SoapsSoap in AlcoholsGel StructureThe Use Of Indicators in Soap SolutionSoap-Oil GelsPectin JelliesDi—benzoyl Cystine GelCellulose Hydra ted by Action Of Hydroch loric AcidCellulose Dissolved by Neutra l Sa ltsProtein SwellingGelatin

CHAPTER VIII

Drop SpreadDu Nouy ApparatusSoap FilmsStab ilization Of FoamS O O O O O Q O O 0 0 0 0 0 0 0 0 0

CHAPTER IX

ReferencesSoap as Emulsifying Agent

ix

X CONTENTS

Oil-in-Wa ter and Wate r-in-Oil EmulsionsMayonna isePharma ceutica l EmulsionsPickering ’s EmulsionsAdsorption FilmsFroth Concentration Of a DyeComparison Of Theories .

Use Of Donnan ’s Pipette in Emulsion Studies .

Creaming .

How to Recognize Emulsion Types .

Cellulose Nitrate as an Emulsifying AgentA Lubricating Grease .

Transparent EmulsionsChromatic Emulsions (Structural Color) .

CHAPTER X

V ISCOSITY .

Viscosity of GelatinViscosity Change Of Benzopurpurin with AgeEffect Of Concentration upon the Viscosity of an EmulsionViscosity Of Soap at Different ConcentrationsViscous and Plastic Flow

CHAPTER XI

ADSORPTION FROM SOLUTIONAdsorption Of GlueAdsorption OfDyes .

Spring ’ s Soap Cleansing ExperimentAdsorption by Barium SulfateAdsorption of the Base from Potassium SaltsAdsorption by HumusAdsorption Of an Indica torCoarse Particles Coated by Fine .

Lloyd ’s Reagent as an Adsorbent for Alka loidsFuller ’s Earth .

Capillary Rise in PaperThe Adsorption Isotherm

CHAPTER XII

ADSORPTION OF GASESCompression Of Adsorbed Gases .

CONTENTS

Cocoanut Charcoa lPreparation of Silica GelProperties Of Silica GelActiva tion

Apparatus and M ethods ofWorkStatic and Dynamic M ethodsFerric Hydroxide Gel for Solvent Recovery .

Fuller’s Earth as an Adsorbent

CHAPTER X III

R EACTIONS IN GELsM ethods ofWorkLead Iodide Crysta lsCopper Crysta lsLead TreeTheory of Formation Of Crysta ls in GelsCrysta ls without a GelRh

'

ythmic Banding or Liesegang ’s RingsM ercuric Iodide BandsCopper Chromate BandsGold BandsBasic M ercuric Ch lorideTheory of Banding .

CHAPTER X IV

EX PERIMENTS WI TH THE ULTRAM ICROSCOPE

Brown ian MovementCrysta lloid vs . Colloid SolutionPrecip itation and ProtectionEnzyme ActionMutua l CoagulationsBlood o o o o o q 0 a c

CHAPTER XV

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O

Determin ing the Amount of Colloida l M a teria l in ClaysUltra Clay

The Effect Of Sodium Hydroxide on ClaysM easurement Of Plasticity Of ClayAdsorption OfWa ter Vapor by Soils .

The Effect ofVariations in Humidity upon Soils

xii CONTENTS

CHAPTER XVI

SPECIAL TOPICS

Dyeing with a Direct or Substantive DyeDyeing with an Acid Dye and the Effect of Glauber

’

s SaltRubberTa ckinessSwelling, SolvationRubber Sols .

Precipitation ofRubberRubber as a So lventRubber as an Emulsifying Agent .

Preparation of HopcaliteCata lysis Of the Rea ction be tween Carbon Monoxide and Oxygen .

Colloida l Platinum as a Cata lyst for Reduction by HydrogenLubrica tionMechanism Of LubricationFlotation ExperimentsColloida l GardenCarrying Mercury on an Iron GauzeUltrafiltration

Imbibition of Gela tin .

Chrome TanningMethods in Genera l

BIBLIOGRAPHY

AUTHOR INDEX

SUBJECT INDEX .

COLLOID LABORATORY MANUAL

CHAPTER I

SUSPENSIONS— COARSE AND FINE

EXp. 1 .—With three sieves, of 50-Inesh , 100-mesh and ZOO-mesh , sift any

suitable powder,such as quartz flour

,clay or starches, into three grades Of

particles . Suspend about 1 g . of ea ch in test tubes Of distilled water andnote the time of settling . Make Observations on the portions that settlerapidly. In each case a very sma ll fra ction is slow to settle .What has mere size Of particle to do with time Of settling"Exp. 2.

— Precipitate barium sulfate cold and attempt to filter it . Now

precipitate the sa lt by mixing the proper hot solutions and keeping hot an

hour . Will a filter paper reta in the precipitate"The solubil ity of sma ll particles

,slight though it may be, is greater than

that Of larger particles (greater surfa ce) . This solubil ity is increased by risein temperature

,so the sma ller particles dissolve and the dissolved sa lt deposits

on the larger particles which are in conta ct with their own saturated solution .

Exp. 3. Surface and Solub ility.

— Kenrick (Jour . Phys . Chem .,16, 515,

1912) outlines a . convincing demonstration Of the difference between the

solubility Of sma l l particles and that Of larger particles :Make a norma lly saturated solution of ca lcium sulfate by stirring gently,

for some hours, 30 g . Of coarsely powdered gypsum in 300 cc . Of distilled water .

The finer particles must previously have been rinsed away with water . Th issaturated solution may well be kept in conta ct with the crystals . NOW grindsome gypsum to an impa lpable powder in an agate mortar . To one of twobeakers conta ining about 50 cc . Of the previously made normally saturatedgypsum add about g . Of the gypsum powder . Shake a moment and filtertwice if not clear. With the greater surfa ce more gypsum dissolves, a lthoughthe solution was saturated with the larger particles .

Aduplicate Of the“ norma lly satura ted” solution is filtered at the same time

(both portions handled rapidly) . TO 20 cc . Of ea ch filtrate is added 10 cc .Of a solution prepared as follows : 100 g. Na zHPO4 12H20 and g . NaOH

made up to 1000 cc . and 29 cc . (exa ct amount to be found by titration) ofth is are colored a deep pink with phenolphtha lein and diluted to 100 cc .

The liquid shaken with the finer powder turns colorless, b ut the otherrema ins pink . An a ctua l titration would Show a difference of 10 per cent in

2 COLLOID LABORATORY MANUAL

the concentration of calcium sulfate. If the difference in color is not sharpwith addition of 10 cc . try cc .

Exp . 4.

—Problem in ana lysis : To titrate any unused Ca (OH) z whencarbon dioxide is run into clear limewater . Hydroch loric a cid neutral iz esunused Ca (OH) 2 and then atta cks the precipitated CaCOs.

First try h ea ting this limewater, with its suspended CaCOg, for fifteenminutes at about The CaCOa particles grow in size, probably becomingcrysta ll ine and compa ct, Offering far less surfa ce to atta ck the a cid . In fa ctthey settle out rapidly. They now dissolve so slowly in dilute a cid that theend point with phenolphtha lein can be secured before the CaCOa is atta ckednoticeably .

Exp. 5 .— Proj ect a powerful beam Of light from some source into a sma ll jar

or flask conta ining an A828 3 sol (or any colloid at hand) and note whether thepath of the beam becomes strongly lum inous . Luminosity Of the path of

the beam is known as the Tynda ll effect and indicates the presence Of sus

pended particles,provided that this luminosity is not due to fluorescence .

Insert a Nicol prism between the l ight source and the colloida l suspensionand rotate the prism . Note whether there is any change in the intensityof the luminosity as the Nicol is rotated . Such a change in luminosity is tobe expected if the luminosity is due to the Tynda ll effect, because the lightis polarized by reflection from the surfa ces of the suspended particles

,b ut

it will not be observed if the luminosity is due to fluorescence . (J . H .

M atthews . )Compare the Tynda ll cone in ordinary water and the same wa ter from

which a gelatinous precipitate of has settled . Square bottles orsma ll

,flat battery jars are suitable for th is experiment . What is optically

clea r wa ter"Exp. 6 .

— Pour 2 cc . ofa 10% a lcoholic solution Ofrosin ormastic into 100 cc .of water and get a suspension of minute solid particles of mastic in water .Pour an a cetone solution of any liquid fat into water and get a suspension of

minute liquid particles of fat in water . It is a genera l principle that if A issoluble in B b ut is insoluble in C ,

A will be thrown into suspension, frequently

colloidal, when a solution of A in B is added to an excess Of C (if B and C are

miscible) .

The color change is explained by the reaction

3CaSO4+2Na2HPO4 Ca3(PO4) 2+2Na 2SO4+H280 4

The more calcium sulfate there is in solution,the more sulfuric

acid is set free to react with the small amount Of base present.

Of course , the exact amount Of base must be carefully adjusted

to show the difference expected .

Hulett (Zeit . phys . Chem .,37

,385

,1901) found that a coarsely

crystalline calcium sulfate (1 .8p ) was soluble mg . per literat while the solubility of the same gypsum ground in an

SUSPENSIONS— COARSE AND FINE 3

agate mortar to rose to mg. per liter . Red mer

curic oxide becomes yellow on grinding, and its solubility in

creases threefold .

f Surface increases enormously with subdivisi on, and all surface

phenomena become greatly magnified . A cube, 1 cm . on edge,

when subdivided into cubes 10W on edge,would possess a total .

surface Of 600 square meters, and the num ber of particles would

be 101 8

Interesting experiments may be devised for the use Of the

Kober nephelometer in determining the amount Of suspended

material . Read the excellent discussion Of nephelometry by

Kober and Graves (Jour . Ind . Eng . Chem ., 7, 843,

Exp. 7 .

— Add a saturated solution Of mercuric ch loride to colloidal silverwhich the instructor has previously prepared . The da rk color disappears,and a milkiness, due to the precipitation ofwh ite mercurous ch loride and silverch loride

,appears .

Ag—f-HgClz AgCH—HgCl

Th is rea ction becomes apparent when silver in colloida l form ,with enor

mous surfa ce,is used a lthough

,Of course

,some reduction must occur when

silver foil is used .

THE COLLOID CHEM ISTRY OF FEHLING ’

S TESTS l

Exp. 8 .

—When Feh ling’s solution is treated with a reducing substanceit is genera lly expected that a bright-red precipitate will be obta ined . Pre

quently,however

,an orange or yellow precipita te is Obta ined

,and in certa in

instances nothing b ut a yellowish-green discoloration results .These color changes are coincident with differences in Size Of particles of

the cup rous oxide formed . The smallest particles are yellowish green ; as

they grow in size they become yellow,then orange

,and when very coa rse they

are red . When the brigh t-blue Feh ling’s solution is mixed with a little dextrosesolution

,or some diabetic urine

,and the mixture is not boiled as ordinarily

,

but is a llowed to stand severa l hours at room temperature,th is series of color

changes,beginning with bluish green and ending with red

,is Observed .

Drops Of these suspensions examined under the microscope Show the corresponding growth in size of particle .

Mix cold cc . Of Feh ling’s solution and 20 cc . of 2 per cent dextrose .

In 30 minutes the colors cha nge from green to yellow to orange and in 7 hoursto red .

1 Adapted from Martin H . Fischer,Science

,45, 505, 1917 . See a lso

Journa l of Laboratory and Clinica l M edicine,


In the action of the a lkali ofFeh ling’s solution upon dextrose, for example,there are produced, from a chemica l point of view

,not only the various

degradation products wh ich are responsible for the reduction of the coppersa lt, b ut from a colloid point Of view, certa in hydroph ilic colloids wh i ch tendto inh ibit a precipita tion of the cuprous oxide in coarse form .

To a llow adequate time for the growth of the cuprous oxide particles to thered form

,it is better to make reductions at low temperatures than at h igher

ones .With much sugar present the number of points at wh ich the copper sa lt is

atta cked and reduced will evidently be much larger than when less sugar isadded . Al l the ava ilable copper sa lt for further growth of the particles will,therefore

,have been exhausted when the copper oxide particles are stil l small .

Therefore too much reducing sugar is likely to yield only the greenish discoloration . In such cases dilution or reduction and long standing at roomtemperature may help .

It might be well,before testing for sugar

,to boil and filter urine in order

to remove any albumin present . Albumin is a protective colloid .

An interesting presentation Of von Weimarn’s law is found

in Ostwald ’s Theoretical and Applied Colloid Chemistry ” and

in Washburn ’s Principles of Physical Chemistry,

”432

,1921 ,

pages 24—33. As demonstrated with Prussian blue and with

barium sulfate the size Of precipitated particles is greatest when

medium concentrations Of the two reacting solutions are used .

With very low or very high concentrations the precipitated par

ticles are smaller .

Exp . 9.— TO 10 cc . of M /200 FeCls add 10 cc . of M/200 K4Fe (CN)6 solu

tion ; dilute to about 100 cc . and note whether the solution is clear . Repea tthe experiment, us ing M / 10 solutions and expla in the difference in the phenomena Observed .

Add 5 cc . Of a practically saturated solution of FeCl;; to 10 cc . Of a practis

cally sa turated solution Of K4Fe (CN)6 . Take a sma ll quantity of the geland stir up in water . Prove by filtering that the resulting suspension is colloidal.

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removed,and the cup holds its shape perfectly . The cord must

be left on the cup to support the sides . Two holes may be punched

near the top of the paper and a string attached like the handle Of

a pail . SO tough is the paper that a parchment cup holding a

liter Of water may be carried without tearing or collapsing . Trim

ming the upper edges Of the cup gives a neater appearance . Three

cords may be attached by wire clips as an improvement on the

pail .When such a dialyzer is to be used it is nearly filled with the

colloidal solution and suspended In a large vessel Of pure water .

Remova l Of ions is ex

tremely rapid,in spite

Of the fact that parchment

is inferior as a mem

brane to gold-beater ’s

skin . It is evident that

with a given membrane

the rate Of dia lysis is pro

portional to the effective

surface of the membrane .

In this form the bottom

and sides Of the cup are

all effective .

The rate of dialysis

may be doubled if two

such cups are used , the

smaller inside the larger .

F I G . 1 .

— Parchment dia lyzing cup .

The inner CUP hOldS pure

water and the other the

colloidal solution,while the combination Of cups is hung in a

larger vessel of pure water . This arrangement gives dialyzing

surface outside and inside the colloidal solution . The water may

be changed as desired .

”

In dialysis it must be remembered that the non—colloids

will diffuse back through the semi-permeable membrane unless

the outside water is changed frequently or continuously . A

constant level siphon,as shown in Fig . 1

,is useful . For many

purposes a few days ’ dia lysis may serve ; but for very accurate

work dia lysis must be continued for a few weeks . Hot dialysis ,by increasing the speed Of diffusion

,hastens removal of impurities .

DIALYSIS AND DIFFUSION 7

It is a good plan to soak parchment paper in three or more

changes Of distilled water before use . In th is way the sulfates

left.

from the manufacture Of the paper (treatment with sulfuric

acid) are removed . Some colloids are easily precipitated by

sulfates .

Exp. 1 1 .— TO make collodion

—

dialyzers,dip a dry test tube into a solution

of collodion in a mixture of dry eth er and absolute a lcohol,dra in for two

minutes,and dry by revolving in air . When it no longer sticks to the finger

on a light touch , immerse in warm water a few minutes . Ca reful ly peel itOff. Keep it in water . Orfill a dry tube or an Erlenmeyer flask, invert, andclamp to dra in for a few minutes . When no ether is noticeable

,fill with

warm water and carefully loosen membrane . By using beakers,larger cups

may be made . Permeability depends on the extent Of drying before wa teris added to loosen the film .

M ake your own collodion solution . Dry the pyroxylin, dissolve 3or 4 g.

In 100 cc . (25 cc . a lcohol+75 cc . ether) by first soaking for fifteen minutes inthe a lcohol and then adding the ether . Stir .Flat films 1 are made on a glass plate or on mercury .

J. M . Looney (Jour . Biol . Chem . 50, 1 , 1922) outlines a method of preparing very flexible collodion membranes . The usua l membranes Of th istype become brittle and stiff if a llowed to dry completely so they are keptwet . Looney prepared collodion membranes that were very flexible aft-er

drying for two weeks and still reta ined their permeability .

Place 5 g . of“ Anthony ’s Negative Cotton

,

” wh ich has been dried 48hours over concentrated sulfuric a cid

,in a very clean and dry Erlenmeyer

flask . Add 25 cc . of absolute ethyl a lcohol and agitate so that all the cottonis moistened . Now add 75 cc . Of ether wh ich has been distilled over sodium

,

and shake until the cotton has completely dissolved . Next add 15 cc . Of

dry ethyl a cetate with shaking to secure complete mixing of the solvents .Let the solution stand overnigh t and then decant the clean supernatantliquid into another flask .

Pour th is solution into a large test tube or Erlenmeyer flask (clean and

dry) and dra in ba ck into the conta iner by holding the flask at an angle Of60

°and rotating to secure uniform th ickness of film . When the liquid no

longer drips freely,clamp th e flask vertically and let stand until perfectly

dry . Then peel Off the top of the film from the neck of the flask and loosenby pouring a gentle stream Of water between the membrane and the side Ofthe flask . Carefully pul l out the membrane and test for pin holes by fillingwith a solution of Congo red and hanging in pure water . Permeability may

be tested by noting the readiness with which a solution of potassium ferrocyanide diffuses through into pure water.R . E .Wilson and Leon W. Parsons modify the method OfWm . Brown (Jour .

1 An egg membrane can be secured by dissolving off the shell in dilute a cidViscose bottle caps

,holding about 100 cc .

,can be secured from Antoine Ch iris

Co .,20 Platt St .

, New York City. They are good dia lyzers .


B iol . Chem . 9, 320, 1915) in order to prepare suitable large sheets of collodionmembrane . A 4 per cent solution of collodion in a mixture of three partsether to one part absolute a lcohol is poured onto a clean, level, glass plate,covering this over

,with a frame immediately to restrict evapora tion Of the

solvent . When the film is dry enough to strip it is cut away with a knifeand carefully removed . It is immersed at once in 80 per cent a lcohol . Aftersoaking in th is for twenty-four hours it is removed and washed for a day insevera l changes of pure cold water . Such a membrane is very permanentin a cid or neutra l solution b ut dissolves in a lka li .These membranes may be made in b ag form by sewing the edges and

then pa inting them’

with collodion solution .

Bartel and Carpenter will soon publish a paper on “ Anoma lous Osmosewith Collodion M embranes in which variations in the permeability of suchmembranes will be discussed .

Get Ansco ’s

“ negative cotton from Ansco Co ., B inghamton, N . Y .,

or

Parlodion from Du Pont,Wilm ington

,Del .

Read Bigelow and Gemberling, Jour . Am . Chem . Soc .,29,

1576 Walpole,in Biochem . Jour .

,9, 284 Brown

,

in Biochem . Jour .,9, 320, 591 Farmer

,Jour . Biol . Chem .

32, 447 Schoep, Koll .-Zeit . , 8 , 80

Exp. 12.—Make colloida l Fe (OH) 3 by pouring a concentrated solution of

FeCls into a beaker conta ining 300 cc . boiling water. A rich red solution,wh ich is very stable, is formed instantly .

3HCl+Fe (OH)3

When it is cold,dialyze portions in different dialyzers

,noting the time Of

appearance of ch loride ions in the dia lysates . (AgNOa test . )Dia lyze 200 cc . with frequent changes Of water until nearly free from

ch loride ions . Preserve for Coagulation chapter.A convenient °

support for large dia lyzing tubes may be made by. cuttinga hole in a sheet Of heavy cardboard so that the tube may be held tigh tly inthe hole . With the cardboard on th e top of a beaker the tube may be adjustedso that th e membrane does not rest on the bottom of the beaker. Still better

,

a circle having the same diameter as the tube may be outl ined and five orsix radia l cuts made with a knife . The triangular proj ections of cardboard

,

when bent out and reinforced with a rubber band,h elp to hold the dia lyzing

tube .Exp . 13.

— Try to dia lyze (sma l l tubes ) solutions of blue Congo-red a cid(a cidified dye ) , nigh t blue, safranine, fluorescein, sugar, copper sulfate, coffeeand other substances . Wh ich h ave colloida l properties"

Exp. 14 .—Dia lyze a solution Of castile soap (about per cent) aga inst a

relatively sma l l amount Of water . DO not change th e dia lysa te . After a

few days shake some of the dia lysa te in a test tube . Does it froth like soapsolutions" Was any appreciable amount of th e soap in true solution at roomtemperature"

DIALYSIS AND DIFFUSION 9

Exp. 15.

— Dialyze th in starch paste . Test the dialysate for starch and

glucose . Now add diastase (or Fa irch ild’s Dia zyme to the starch and

keep on testing samples Of the dia lysate for glucose, using Feh ling’s solution .

Exp . 16 .—Dialyzers for Non-aqueous Sols .— W0 . Ostwa ld in a report

before the Faraday Society and the Physica l Society of London ( 1920) described a useful method of non-aqueous dia lysis . Prepare Lottermoser

’s

colloida l mercuric sulfide by passing a brisk stream Of wash ed and dried Has

for 10 minutes into an‘

a lcoholic solution Of Hg (CN) 2 Of any concentration

. The a lcohol, however, must be 97 per cent, not stronger . A deepbrown sol forms . It may be diluted with more 97 per cent a lchool and

stabilized with more 11 28 . In a closed bottle th is keeps for weeks .Compare the dia lysis of th is colloid (an a lcosol) with that of nigh t blue

dissolved in 97 per cent a lcohol . Alcohol must be used on both sides Of themembrane . Nigh t blue is a colloid in water b ut is molecularly dispersed in97 per cent a lcohol . M embranes suitable for alcohol dia lysis are parchment,collodion

,and gelatin hardened with a lcohol . Soak paper th imbles in 97

per cent a lcohol and then pour into the th imbles ordinary 4 per cent pharmaceutical collodion . Dra in and dry quickly in warm air until dry to thetouch and until the smell of ether is gone . Pour in collodion solution aga in,dra in and dry . The membrane is now ready . During dia lysis the alcosols

must be kept covered to prevent evapora tion and the levels Of the liquidoutside and in the th imble must be kept the same .

SO far,” writes Ostwa ld,

“ we have not found any substance, spontaneously soluble in 97 per cent alcohol, wh ich would not dia lyze or diffuse to aperceptible degree . Even resins such as copa l

,mastic

,dammar and dragon ’s

blood dia lyzed in 97 per cent a lcohol,as did a lcoholic linseed Oil, beeswax,

lard,a luminum Oleate , etc .

” Even th e zein of corn diffused .

Permeability is tested by dropping the dia lysate into a beaker Of water ora solution Of a lum . After 24 hours some milkiness is a lways Observed . Anycollodion precipitated appears in films or sca les, not as a milky suspension .

HOT DIALYSIS 1

The Speed of dialysis depends upon the following factors

First,the nature of the membrane ; second , the area Of the mem

brane which is in contact with liquid on both Sides ; th ird , the

difference in concentration of diffusible substances in internal and

externa l liquids close to the membrane fourth,the temperatures

of the internal and externa l liquids .

Hot dialysis, with its greater speed Of diffusion, enables us tohasten greatly the purification Of colloids . A parchm ent paper

sack, A (prepared wet) , of about 1 liter capa city, is nearly filled

1 Method of Marks Neidle,Jour . Am . Chem . Soc .,

38 , 1270 39,

7 1


with distilled water and then suspended in a 2-liter beaker containing 500—1000 cc . Of the solution to be dialyzed . Distilled

water is run through the sack at a rate of about 2 liters per hour,

the level being kept constant by means Of an automatic siphon .

The folded neck Of the paper sack is tied to the flanged end Of a

glass tube (15 cm . long and 2 cm . in diameter) . The colloidal

solution in the beaker is heated, usually to

Pressure d ialysisto prevent d ilution.

F IG . 2 .

-Hot dia lysis . F IG . 3.

By placing the colloidal solution to be dialyzed in the outer

vessel,the large increase in volume, due to osmosis, is avoided .

Evaporation balances the effect of osmotic flow .

A colloidal solution Of high purity may be Obtained by this

method in eight to ten days, while the usual method may require

a month . For most experiments even this time Of dialysis is

excessive .

DIALYSIS AND DIFFUSION 1 1

Exp. Chromium Hydroxide Purified by Hot Dialysis — Add 49 cc .of N ammonium hydroxide to 162 cc . of N chromium ch loride with vigorousshaking . Th is amount Of ammonium hydroxide is equiva lent to less than ha lfof the chromium ch loride , so the hydroxide precipitated at first is peptized

(subdivided) by the a ction Of the rema ining chromium ch loride .

Let stand twenty minutes, or until the precipitate disappears . The

resulting clear green solution is diluted to 400 cc . and dia lyzed for th irty-fourhours at 75

° That a nearly pure ch romium hydroxide is secured isshown by ana lysis . The ratio Of

'

chromium to ch lorine has been found byNeidle to be 65 : 1 . I f the dia lysis is carried on near the boiling point

,the

colloid secured in ten hours will be as pure as that resulting from seventythree days ’ cold dia lysis .

The volumes given above represent an a ctual experiment by

Neidle and may be varied somewhat .

DIFFUSION

Exp. 18 .

—Let solutions Of Congo red,beet juice, colloida l Fe (OH)3, nigh t

blue,coffee

,safranine and fluorescein,

as well as colored sa lts,diffuse into

j ellies Of 3per cent gelatin or 2 per cent agar . Use test tubes more than ha lffull of j elly . Wh ich are colloids

,as shown by speed Of diffusion" Jellies are

th ick membranes .Exp . 19. Alexander’s Patriotic Tube . — Fill a test tube two-th irds full

with sligh tly alka line solution of agar conta ining enough -phenolphtha lein toturn it pink

,and a little K 4Fe (CN) 4. After the agar has set to a solid

,a

dilute solution of FeCls is carefully poured on top . The ion forms,with the

ferrocyanide,a slowly advancing band of blue

,before wh ich the more rapidly

diffusing HCl spreads a wh ite band as it discharges the pink Of the indicator .In a few days the tube is about equa lly banded in red, wh ite and blue .The agar may be a lka line as

'

purcha sed . Acetic a cid may be added untilthe pink color Of the phenolphtha lein is just discharged . Then the colormay be brought back with a trace of a lkali .

CHAPTER III

CONDENSATION METHODS OF PREPARATION

REACTION between dissolved substances may yield precipitates

or may yield those aggregates of a few hundred or thousand

molecules that we term colloidal . In the latter case colloidal

suspensions are formed by condensation Of smaller particles into

larger ones .

In the following work distilled water must be used . Since on

long storage it may take up impurities from the container or from

the air,there are times when freshly distilled water may be neces

sary . Resistance glass vessel s must be used for all work . Inferior

results are Obtained with the vessels Of more soluble glass .

Small Erlenm eyer flasks are useful . The utmost cleanlinessmust be Observed . Glass is best cleaned with warm chromic

acid solution,rinsed with tap water and finally with distilled

water . If necessary,the glass should be steamed out .

Dialyzing membranes are used the second time only for puri

fication of the same colloid, and only if they have been kept wet .

REDUCTION

Exp. 20. Preparation of Gold Hydrosol . (Zsigmondy’s M ethod) .— Thewater used for solutions should be distilled twice through a block tin coilcondenser . The best American resistance glass, thoroughly cleaned, shouldbe used for all conta iners .

. Three solutions are necessary : (1 ) 6 g . AuCls-HC1 °3H20 dissolved and

made up to 1 liter with conductivity water ; (2) one liter of N KzCO

and (3) a per cent solution Offormaldehyde .

According to Zsigmondy, 120 cc . of wa ter prepared as above are hea ted ,

and cc . of gold ch loride solution added, then cc . K2C0 3 solution .

This is st irred to insure uniformity and h ea ted to 100° C . It is removed fromthe hea ter

,and 3 to 5 cc . of the forma ldehyde solution are added with lively

stirring .

S . E . Sheppard and F . A . Ell iott find a much smaller amount Of formalde

hyde quite sufficient . They added forma ldehyde solution per cent, madeb y adding cc . of ordinary formal in to 100 cc . of water) a drop at a time,

12


Exp. 25. Sulfur.

—Pass hydrogen sulfide (washed) into sulfur d ioxidewater until all odor of sulfur dioxide is gone . (DO not do th is in the colloidlaboratory . )

2s +80 2 2H20 +3S

Precipitate th is colloidal sulfur by addition of powdered sodium chloride,

shaking . Filter . Wa sh on the filter until all sodium ch loride is removed .

The sulfur begins to run through the filter in a good suspension . Acidified

hypo ” yields colloida l sulfur,as do most oxidizing agents on hydrogen

sulfide water . The author found gleaming crystals Of sulfur in an Old suspension Of colloida l sulfur . Th is would seem to indicate a sligh t solubility Of

sulfur to make possible the change from the colloid to the crysta lloid state .

HYDROXIDES AND OXIDES

(Although for convenience we write Fe (OH)3, it is probable

that we deal with different degrees of hydration of F8 20 3.)

Exp . 26. Ferric Hydroxide .— The addition of a few cc . of concentratedFeC13 to much boiling water has a lready been given as one method Of preparing ferric hydroxide .

We may a lso boil ferric a cetate (made from wa shed ferrichydroxide and

a cetic a cid) until no more a cetic a cid passes off, and get the colloid, an exampleof hot hydrolysis. (Péan de St . Gille

’s method .)

Read : Jour . Phys . Chem .,232 Make Krecke ’s colloid

by hydrolysis of per cent FeClg ; also by hydrolysis of

per cent FeC13 at 87° and also by hydrolysis of per cent

FeC13 at

These represent different degrees of hydration Of F6 20 3.

The color differences are similar to those in hematite and limonite

iron ores .

Exp . 27. Chromium Hydroxide — TO remove the tra ce of sulfate in most

C. P . chromium ch loride,”add a little barium ch loride to the boil ing solution .

Dilute greatly and then add ammonia to the boiling-hot chromium ch lorideto precipitate chromium hydroxide . Boil off the excess ammonia (test byodor) , let settle, filter and wash the precipitate . Dissolve it in boiling 6Nhydroch loric a cid and evaporate the resulting solution Of chromium ch lorideto a sma ll volum e to get the last Of the precipitate into solution . Morehydroxide should then be added . Filter

,and dia lyze . A beautiful, clea r,

green sol is Obta ined .

Exp. 28 . M olybdenum Blue (M 0 30 3) .— Add 5 g . ammonium molybdateand 30 cc . Of 4 N sulfuric a cid to 150 cc . Of water . Wh ile it is boiling hot

,

reduce with a rapid stream Of hydrogen sulfide (Hood ) . Dialyze . Dye a

strip of wh ite silk with the blue colloid .

CONDENSATION METHODS OF PREPARATION 15

Th is was reduction in a strongly acid solution (Dumanski’s method) .

Repeat the experiment, using only one drop Of sulfuric a cid instead Of 30 cc .Note the difference in color of the colloid wh ich is probably a different oxideOfmolybdenum .

Exp. 29. M anganese D ioxide .1 Potassium permanganate is a powerful

but relatively slow oxidizing agent and does not rea ct at a measurablerate with ammonium hydroxide at ordinary temperatures . I f

,however

,to a

hot concentrated potassium permanganate solution ammonium hydroxide isadded , ammonia is oxidized to nitrogen and manganese dioxide is precipitated .

I f; to a fa irly dilute solution Of potassium permanganate , concentrated ammonium hydroxide is added slowly

,manganese dioxide does not precipitate , b ut

rema ins in the colloida l form . After trying various concentrations of potassium permanganate and Of ammonium hydroxide we Obta ined the best resultsby the following method :

“ Heat a M / IGO permanganate solution to boiling . Then wh ile stirring,add concentrated ammonium hydroxide

,one drop every three minutes . At

no time should anyth ing but the fa intest smell Of ammonia be perceptible .

The solution should be kept at about It turns wine-red and fina lly coffeebrown by transmitted ligh t and a bluish-brown 0 i color by reflected light .To test if all the permanganate has been reduced

,a portion Of the colloida l

solution can be coagulated by the addition Of sa lt,to Show the presence Of

any violet color wh ich may have been masked by the dioxide .

(About 10 cc . ammonia may be added, 1 drop per second .)As will be seen from the equation

2KMnO4+2NH3 N2+2MnOg+2KOH+2HgO

in the fina l colloid there is present,beside the dioxide

,only some potassium

hydroxide,wh ich has a sma ll

,if any,

coagulating effect . Marck has foundthe colloid is coagulated by conta ct with filter paper or parchment

,so it cannot

be dialyzed unless very specia l precautions are taken . Alcohol does notcoagulate the solution .

Colloidal manganese dioxide can also be made by reductionof potassium permanganate with hydrogen peroxide (M arck) ;by reduction with sodium th iosulfate (Spring and de Boeck) ;and by reduction with arsenious acid (Deisz) . Fremy (Compt .

rend .

, 82, 1231 , 1876) Obtained a red solution by treating potas

sium permanganate with concentrated sulfuric a cid (cautionD.

It is safer to leave Premy ’s experiment alone unless the exact

directions are at hand . See page 1 10.

Exp. 30.— Mix 60 cc . Of per cent potassium permanganate with 20 cc .

of H20 2 (commercia l 3 per cent plus an ,equal volume of water) . A brown

form of colloida l managanese dioxide is secured and is stable for weeks .

1 Eustace J . Cuy, Jour. Phys . Chem .,25, 415


SULFIDES

Exp. 31 . Arsenic Trisulfide .-Mix equa l volumes of l per cent arsenic

trioxide solution (prepared hot and fil tered cold) and saturated hydrogensulfide water . Or simply pass washed hydrogen sulfide through a solution Ofarsenious a cid . Boil Off the excess hydrogen sulfide or remove it cold with a

stream of hydrogen .

2As (OH)3+3H28 6H20 +ASzSa

Compare with the product obta ined by passing s into AsCls. Whythe difference" Write the equation .

Exp. 32. Antimony Trisulfide .

— From a dropping funnel drop a 1 per centtartar emetic solution into water through which washed 11 28 is pa ssing . Abeautiful, rich orange-red sol forms . Dia lyze . It may remain in suspensionsevera l weeks .Exp. 33. M ercuric Sulfide — Mix 200 cc . of M/8 mercuri c cyanide solu

tion and 200 cc . of saturated hydrogen sulfide water.Note that mercuric cyanide is but slightly ionized and therefore there are

almost no Hg ions to coagulate the negative colloid . All sulfides in water arenegatively charged and hence easily discharged by positive ions

,especially

by those of h igher va lance .

As stated in the previous experiment, the negatively charged

sulfides are best prepared in the colloidal form if polyvalent positive

ions are absent,or present in a very low concentration . To form

copper sulfide we need some copper ions,but our needs are safely

met if a poorly ionized Copper complex is formed . Then,as fast

as the few copper ions present react with sulfide ions,equilibrium

is disturbed and more copper ions form . The tartrates and citrates,

or even ammonia, tie up copper ions to suit our needs .

Exp. 34. Copper Sulfide — TO 100 cc . of water add 4 cc . of 1 per centblue vitriol ” and enough dilute ammonia to form the a zure-blue solublecomplex. Then add 4 cc . of dilute Rochelle salts solution . Pass washedhydrogen sulfide into th is solution wh ile it is on the dia lyzer . Dia lyze untilthe dia lysate is nearly free from sulfates . The colloida l sulfide is bluish byreflected light and green by transmitted light . It may rema in in suspensiona few months.

A richer blue,b ut a less stable colloid

,is Obta ined by using only 1 cc . of

Rochelle sa lts . It is well to remove any excess of hydrogen sulfide with a

stream of hydrogen . I f satisfa ctory results are not obta ined vary the amountof Rochelle salts used.

CONDENSATION METHODS OF PREPARATION 17

ACIDS

Exp. 35. Silicic Acid — Dilute commercia l water glass to a density of

about Since carbon dioxide has a coagulating influence on Silicic a cid,

it is well to use fresh ly boiled distilled water for dilution . Keep in a rubberstoppered bottle . Pour 75 cc . Of th is into a mixture of 25 cc . concentratedHCl and 100—150 cc . Ofwater, and dia lyze . I f it is dia lyzed too far a gel may

precipitate on the membrane . Rather unstable ; easily coagulated by phos

phates, etc .

Precipitate a gel of Silicic a cid, by pouring stronger a cid into the waterglass and let stand until a gel (j elly) sets . Wash the lumps thorough ly withmany changes Of water and note how little NaOH is required to peptize (seepage 18 ) into the sol form . The amount Of NaOH required to peptiz e thegel is far less than the amount called for by chemica l rea ction .

Read Zsigmondy’s “Chemistry of Colloids

,

” page 134 .

Exp. 36. Tungstic Acid — Add a 5 per cent solution of ammonium or so

dium tungstate to a sligh t excess of dilute HCl . Dia lyze . Add a little HClevery day or two

,until all the a lka li is removed . Save a portion Of the sol .

Evaporate on the wa ter bath until flakes form . These are reversible,that is

,

they may be redissolved in water . Or peptize a fresh ly precipitated tungstie acid with oxa lic a cid, and dia lyze . M olybdic a cid is handled in the sameway .

Exp. 37 . Stannic Ac id.— Zsigmondy dilutes a solution of stannic ch loride

so that the sa lt is hydrolyzed a lmost completely . The gel is then washed bydecantation and peptized by a very little ammonia . The excess ammonia isboiled away . Such a sol has been kept for years . When precipitated bypotassium hydroxide or sodium ch loride

,th e stannic a cid goes ba ck into

solution on wash ing out the electrolyte,yet coagulation with a cids is

irreversible .

CHAPTER IV

DISPERSION METHODS OF PREPARATION

PEPTIZATION

DISPERSION methods Of preparation are exactly the opposite

Of condensation methods : larger particles are broken down into

smaller . This may be done by grinding,electrical disintegration

,

the action Of various liquids,adsorption Of ions

,and sometimes by

washing out the excess Of adsorbed ions from precipitates .

Exp . 38 . Bredig’s Arc M eth od — M ake and break an are under wa ter in a

sma ll crysta lliz ing dish,using gold wires run through glass tubes for handles .

I f the water is about N with NaOH the results are better . Any currentof 30—1 10 volts and 5 to 10 amperes is suitable . When the water is wellcolored

,filter and keep the filtrate . Try wires Of platinum

,copper or silver .

TO prove tha t some oxide is formed,as well as meta l, add HCl to some

Pt suspension . Then pass in 11 28 . A dark sta in and minute precipitate Ofthe platinum sulfide could not have formed if only the meta l were present .Of course , it is conceivable that colloidal platinum might be attacked byhydroch loric a cid . The more a ctive meta ls form more oxide .

I f the gold,made as above , is blue , try heating to see if it turns red . The

particles of red gold are sma ller than those Of blue gold .

PEPTIZATION

Exp. 39.

— Heat dilute egg-wh ite to Opa lescence (due to a partia l coagulation ) . Now add pepsin and a tra ce Of hydroch loric a cid to peptize the

protein . Th is experiment illustrates the origin Of the term . Graham ca lledit peptonization because he first used the process to break down proteininto peptones (as in digestion) . The term now used by all colloid chemists ispeptization.

Glue , gelatin , soap , gum arabic and dextrin are said to be

soluble in water . In reality they are merely peptized by water

they are subdivided into particles far larger than molecules . Of

course,in hot water some soap is in true solution , and probably

a little may be molecularly dispersed in cold water . Even gun

18

DISPERSION METHODS OF PREPARATION 19

cotton is merely peptized by amyl acetate or by a mixture of

alcohol and ether .

At this point it is worth while to read pages 166—171 inBancroft’s Applied Colloid Chemistry .

” A quotation from his

Colloid Problems (NO. 38) follows :

(38) Behavior of G'

um Arab ic with Alcohol and Water.

It is not very easy to peptize gum arabic by grinding with water

because the water does not displace the air readily from the gum .

If the gum is ground for a moment with a lcohol,water then

wets it readily . This is surprising because water peptizes thegum and alcohol does not ; one would consequently have expected

the water to be adsorbed more strongly than the a lcohol . By

shaking the gum a rabic with aqueous a lcohol,it should be an

easy matter to tell whether the alcohol or the wa ter is adsorbed

the more strongly . I t is possible tha t there may be a film Of grease

on the gum wh ich is removed by the a lcohol . I t is possible that

alcohol displa ces the air more rapidly because it adsorbs the air

more strongly than does water .”

Peptization Of precipitates by adsorbed ions is common .

Whenever one ion Of an electrolyte is more strongly adsorbed

than the other,the particles of a precipitate become positively

or negatively charged,as the case may be, and repel each other .

This disintegrating effect makes for suspension in the colloid

form . Clays are kept in suspension in water much longer if a

very low concentration Of some base is present . Preferentia l

adsorption Of hydroxyl ions explains the fact .

Exp. 40. Peptization of Cadmium Sulfide — Precipitate cadmium sulfidewith ammonium sulfide

,filter

,wash and suspend in water. Pass in enough

hydrogen sulfide to peptize the precipitate . When suspension is completeboil Off the excess Of hydrogen sulfide . All sulfides are not peptized by adsorption Of an excess Of sulfide ion

,b ut the sulfides of cadmium and nickel are— a

fact that must be remembered in qualitative analysis .

SILVER HALIDE SOLS

Adsorption of Different Ions

Exp. 41 .— Prepare N solutions of silver nitrate and potassium

iodide . From a burette add,while stirring

,20 cc . of the silver nitrate solu

tion to 20 cc . Of the potassium iodide solution,

an equiva lent amount .If the precipitated silver iodide does not settle soon, shake the mixture .


To another beaker containing a slight excess Of silver nitrate solution,for

example , cc .,add 20 cc . Of potassium iodide solution . Prepare a series of

mixtures,each conta ining 20 cc . Of potassium iodide with cc . Of silver

nitrate or any other sma ll excess of the latter solution . The silver iodiderema ins in suspension as a positive colloid

,hav ing been stabilized by the

adsorption of the excess of silver ions . The question is asked at once,Why

is the negative nitrate ion not adsorbed" Th is is merely a case Of preferentia ladsorption of silver ions . Yet there is some adsorption Of nitrate ions andwhen the concentration Of the negative ions becomes great enough the colloida lsilver iodide is dis charged and precipitated .

For a similar series add 20 cc . of s ilver nitrate to varying excesses of

potassium iodide . Adsorption Of th e iodide ion gives the silver iodide a negative charge (How test for th is charge") and thus stabilizes the colloida l suspension . Read Experiments 128 , 129 and 130 . Washburn states that silveriodide is best peptized by potassium iodide of a concentration Of 0 .3N .

Exp. 42.-M ake colloida l Fe (OH) 3 by digesting precipitated and washed

Fe (OH) 3with FeCls. Dia lyze . Peptization is due to adsorbed ferric ions .

Cautiously add very dilute NH 4OH or (NH 4) 2CO3 to dilute FCC13. Th isneutra lizes the HCl liberated by hydrolysis and disturbs the equilibrium .

Shake until the precipitate is just redissolved . Add a little more FeCla ifnecessary to peptize the last of the precipitate .

It is possible to get a concentration Of g . of FezOg per

liter . If the last traces of chloride ions are removed by dialysis "

the colloid is less stable .

The hydroxides of alum inum and chromium may be peptized

by the proper chlorides in a similar manner. The author once

attempted to precipitate aluminum hydroxide by adding ammonia

to the hot solution of the chloride . It was kept hot too long and

could not be filtered . The suspension was set aside and dated .

It did not settle for nearly three years .

Freshly precipitated Al (OH)3 is peptized by one-tenth Of an

equiva lent amount Of hydrochloric acid .

Exp. 43.— Insoluble hydroxides of the type M (OH) 2, when digested

with excess FeC13 Of medium concentration and dialyzed yield only colloida lFe (OH) 3. This is due to mass a ction . Of course the ferric ch loride is hydrolyzed .

Try Cu(OH) 2 as a typ e . 0 110 12 goes through membrane .Exp . 44 . Prussian Blue — Pour a 3 per cent solution Of potassium ferro

cyanide slowly into a 3 per cent solution of ferric ch loride . After a few

minutes,filter and wash well . Pour through the filter a 5 per cent solution

CHAPTER V

COAGULATION

MANY colloids are sensitive to the addition of smallquantitiesof electrolytes, first becoming turbid and then coagulating .

Such colloidal suspensions owe part of their stability to the like

charges carried by their particles . When these charges are neu

tralized by ions of opposite charge, precipitationmay occur .

Rapid addition Of an excess of a precipitating salt often carries

a suspension past the precipitating point and gives it an opposite

charge with a certain stability . Hardy Observed that a colloid

was most unstable at the isoelectric point. This point was recog

nized by a failure to migrate in an electric field (cataphoresis)and showed electric neutrality .

Hardy ’s rule Of valence (Schulze’s law) , that the precipitating

power Of an electrolyte towards a given colloid depends largely

upon the valence of the ion Of charge opposite to that Of the colloid,

is useful in detecting the charge on a colloid .

Hatschek reports an experiment that illustrates this point .

Charge Precipitation Concentration in M illimols per Liter

NaCl CaClz AlCla

NaCl K280 4 0 .20 Still less K4Fe (CN)6would have served .

Evidently the precipitating power Of the is hundreds

of times as great as that Of the Na+ towards a negative colloid .

We might have expected it to be only three times as great . Simi

larly,the precipitating power (the reciprocal Of the concentration)

of the SO4 is about fifty times as great as that of Cl “

,towards

a positive colloid . The Fe (CN) 6 is still more powerful .

Svedberg states that the concentration of K+,Bait + and

required to aggregate particles of Aszs3 to the same degree

stand In the ratio Of 1 : W Im

22

COAGULATION 23

To determine the nature of the charge, then, on any colloid,we need only compare the concentrations of various electrolytes

needed to produce turbidity . For comparison , the different salt

solutions must be added at the same rate with the same sort of

stirring and the same degree of turbidity secured . Since the

precipitation depends on the concentration in the mixture,it is

well to add rather small volumes of salt solution to much larger

volumes of colloid .

Exp. 47 . Precipitation of a Negative Colloid — Van Klooster suggests anexperiment that is worth repeating .

Pour 100 cc . ea ch of the following solutions into seven beakers . Add toeach 25 cc . of dialyzed colloidal ASzSa, as a typica l negative colloid .

milli-equiva lents AlCl3 per liter1 5 M gC12

60 0 NaCl*400 0 NaCl

60 0 Na 280 4

*400 0 Na 280 4

Only the starred concentrations produce clouding and coagulation during the working period . Interpret the results .

Exp. 48 .—Using equiva lent b ut very dilute concentrations of NaCl,

BaClz and AlCl3 for one series, and NaCl, Na 2S0 4 and Na gHPO4 for another,measure the minima l precipitating (or clouding) concentrations of theseelectrolytes towards suspensions of Prussian blue

,silver

,nigh t blue

,chro

mium hydroxide and ferric hydroxide . From the results state the nature ofthe charge on each colloid .

From Hardy ’s rule it may be assumed that HCl,NaCl

,KCl

,

RbCl and other electrolytes with a univalent cation must have

the same precipitating power towards negative colloids . This

is only approximately true . Ions must be adsorbed before they

can discharge colloid particles ; therefore, the univa lent ions that

are most strongly adsorbed by the colloid have the greatest precipitating power . This holds for a similar series of negativeions

,etc .

M anufacturing concerns are often anxious to precipitatefactory wastes and are given to trusting blindly to alum . Th is

is not a bad guess,for most suspensions in water are negative ;

hence with its positive valence of three must be powerful

in precipitation . On the other hand,sulfa te ions are strongly

adsorbed by a large number of colloids,and

,being negative

,must


tend to peptize a negatively charged aggregate— the Opposite of

coagulation . Therefore,tests on preferential adsorption are in

order in many cases .

H+ and OH “ are powerqy adsorbed, as a rule ; hence the

coagulating power ofacids and bases is not quite of the same order

as that of salts in the same valence series . For example,KC ]

and KOH have different effects on a negative colloid . The

coagulating action of K+ is partly counterbalanced by the great

adsorption,and consequent peptizing action

, ofOH“

.

Exp. 49.— Compare the precipitating power of equivalent concentrations

of KOH and KCl on a suspension of Aszss or of mastic .

So well is H+ adsorbed that Hardy coagulated a mastic sus

pension by a much lower concentration of HCl than of KCl.

This suggests an extension of Exp . 49.

Organic anion s are generally strongly adsorbed ; hence, they

have high precipitat ing value on positive colloids . Sodium acetate

has ten times as great precipitating power towards Fe (OH)3 as

has sodium chloride .

Linder and Pi cton (Jour . Chem . Soc .,67, 63, 1895) found that

when Ba+ + precipitated AszSg the barium could not be washed

out of the precipitate . Yet,by continued treatment with a more

powerfully adsorbed ion (in excess) , such as NH4+,the Ba+ +

was completely replaced by an equivalent amount of NH4+ .

Exp. 50.

— Divide a suspension of clay or kaol in into two portions . Adda few drops of a solution of a lum to one . Does the difference in time of

settling suggest a use of a lum in water purification" What must be theeffect of sa lt water in the Gulf of Mexico on the suspended soil carried by theMississippi"Exp. 51 .

—Coagulate HgS by the dye, auramine,which is strongly

adsorbed . On long standing the colloid becomes crysta lline,thus exposing

infinitely less surfa ce . I f the cogulated and washed dye is left in clear waterit will fina lly be seen diffusing away from the crysta lline mercuric sulfide .

Read in th is connection Freundlich "s paper, in Zeit . phys . Chem .

,85, 660

A splendid paper on the mechanism of coagulation was pub

lished by Kruyt and van der Spek in Koll .-Zeit . , 25, 1—20

A good résumé of this is found in Chemical Abstracts,14, 1472

Read the coagulation rules of Burton and Bishop (Jour . Phy.

COAGULATION 25

Chem . 27, 701 , Weiser'

and Nicholas (Jour . Phy. Chem .

25, 742, 1921) show that these rules are of limited application .

Wo . Ostwald ’ s thorough study of the colloidal dye, Congo

Rubin (Koll . Beihefte, 10, 179, 1919) is a useful contribution

to the subj ect of coagulation .

There is a se cond class of colloids not coagulated by elec

trolytes in low concentration . This class includes glue,gelatin

,

agar, a lbumin and j elly-like or gummy substances . Th ey can,

however,be salted out by h igh concentrations of ammonium

sulfate,for example, or coagula ted in some instances by heat or

by certain a cids . Here we must be careful in making exact

general statements . Bridgman (Jour . Biol . Chem .,19, 577, 1914)

sta tes that egg a lbumin is coagulated at some temperatures by a

pressure of 7000 atmospheres .

Exp. 52. Coagulation by Heat — Heat 20 cc . of dilute egg-albumin toboiling . Some of it coagulates . The coagulation can be completed by addition of 2—4 drops of a cetic a cid while boiling .

Exp. 53 —With a pipette,cautiously introduce a little album in solution

into an inclined tube conta ining a few cc . Of concentrated nitric a cid . Atthe zone Of conta ct a wh ite layer of precipitated a lbumin appears . Th is is avery delicate test for a lbumin .

Exp. 54.— Add saturated ammonium sulfate solution to a dilute solution

of a lbumin . There is no precipitation until an equa l volume has been added ,and it is not complete until more is added

,or until 10 cc . of th e mixture

conta ins cc . of the saturated ammonium sulfate solution .

Solid ammonium sulfate may be added direct to the a lbumin solutionuntil saturated (below When water is added to the coagulated a lbumin(thus diluting the ammonium sulfate) the albumin goes into suspension aga in .

In other words, it is reversible .

An interesting precipitation and crysta lli zation method of

purifying albumin is found in Taylor’s Chemistry of Colloids

,

”

page 1 14

Duclaux and Wollman (Bull . Soc .,Chem . 27, by

frac tiona l precipitation of an a cetone solution of cellulose nitrate

with cautious addition of water secured fractions of different

viscosities b ut constant nitrogen content .

Read Bancroft ’s Applied Colloid Chemistry, pages 212—223,as a reference for this entire chapter .

Exp. 55. Cataph oresis . — The nature of the charge on suspended particlesmay be determined by their migration in an electric field (ma croscopica lly orultra-microscopica lly) . Coehn (Zeit . Elektrochemie, 15, 653, 1909) used a


large Us haped tube with two stopcocks of the same bore as the tube itself.

The tube was filled with the suspension,stopcocks closed, the ends rinsed and

filled with water . After platinum or silver electrodes were hung in the water,

the stopcocks were opened and a direct current of 100—200 volts turned on.

I f the color boundary surfa cemoved slowly to the anode the colloid was negative

,etc . Carbon electrodes may be used .

A simple devi ce may be prepared from a U-tube with an inlet tube at thebottom and a funnel a tta ched to it with a rubber tube , wh ich may be closedwith a screw clamp . In filling

,great caution is necessary to prevent mixing

of the colloid with the water layer above in ea ch arm of the U . Read Z sigmondy

’s

“ Chemistry of Colloids,” pages 44—50.

FI G . 4.

— Cataphoresis.

CHAPTER VI

PROTECTIVE COLLOIDS

Exp. 56. Protected Silver Bromide — Mix 20 cc . of N silver nitratewith 20 cc . of N potassium bromide . Set aside until the silver bromideprecipitate settles out . To 20 cc . Of the same silver nitrate add 2 cc . of

1 per cent gelatin and then 20 cc . of the potassium bromide . Compare th etwo suspensions as to time of settling .

Exp . 57 .— Repeat Bechold ’

s experiment with ma stic (Zeit . Phy . Chem48 , 408 , To 1 cc . of a mastic suspension (see Exp . 6) mixed with1 cc . of M M gSO4 add 1 cc . of water . Coagula tion will be complete in15 minutes . Now add 2 drops of 1 per cent gelatin solution to a mixtureof the mastic and M gS4 solution before diluting with water . There shouldbe no precipita tion in 24 hours . Also try addition of the gelatin directly tothe mastic before m lxmg with MgSO4.

Such substances as gelatin,ca sein

,albumin

, agar,dextrin

,

gum arabic and glue interfere with the precipita t ion of manyinsoluble compounds . In fact when added in absolutely small

but relatively large amounts to a colloidal suspension they pro

tect that colloid from the precipitating a ction of electrolytes,

up to a certain point wh ich can be determined accurately . H‘

énce

the name, protective colloids .

In relatively small amounts they cause precipitation. if they

have the Opposite sign . Yet Clayton coagulated severa l emul

soids by the addition of a relatively small amount of starch pa ste,a lthough these colloids carried a charge of the same sign as the

starch .

Exp. 58 .— Prevent the precipitation of a number of the usual compounds

so familiar in qualitative analysis by adding a little of any of the protectivecolloids named above to one of the sa lt solutions before mixing with the othersalt solution . Why do you destroy organic matter before proceedingfar in ana lysis of some mixtures"

Exp. 59.

— To 50 cc . of colloida l Fe (OH) 3 add 2 cc . of 1 per cent gelatin ,and compare th e volumes of N sodium sulfate required to precipitate thecolloid with th e amounts that precipitate unprotected Fe (OH ) 3.

27


Zsigmondy measures protective power by the gold number .The following quotation is taken from his Chemistry of Col

loids

By the gold number we shall understand the maximum

number of milligrams of protective colloid that may be added to

10 cc . of gold solution without preventing a chang e from red to

violet by 1 cc . of a 10 per cent solution of sodium chloride,wh ere

the Change would take place if no protective colloid were added .

For the determination of the gold number,hydrosols pre

pared by the formaldehyde method,having particles lying between

20 and 30W ,are the most suitable . The correct degree of sub

division may be known by a faint brownish Opa lescence in incident

ligh t ; in transmitted light the solution must be deep red and clear .

If the protective effect of the colloid in question is approximately

known,it is wise to dilute until a few tenths of a cubic centimeter

will prevent the color change . If the effect is quite unknown it

should be roughly determined before accurate measurements are

attempted .

”

TABLE I

Reciproca lCollo id Gold Number

Gold Number

Gelatin and gluesIsinglassCasein .

Gum a rabic,poor

Sodium oleate .

Traga canth

Potato starchSilicic a cid .

Aged stannic a cid

Exp. 60. Gold Number. and 1 cc . of the solution whose protective effect

'

is to be determined (a , b and c ) are put into three small beakersand thoroughly mixed with 10 cc . of gold Zsigmondy ’s gold ’

) solution .

At the end of three minutes 1 cc . of a 10 per cent sodium ch loride solution isadded to ea ch , and the contents well mixed . Assuming that there is a colorchange in (a ) but not in (b) nor (c) , the gold number must lie between and


It is probable that protective colloids are present in many alloys .

The la cta lbumin ofmilk has a high protective va lue,of importance

in coagulation . M other ’s milk has a higher percentage Of lac

talbumin than has cow ’s milk— a significant fact . Jerome

Alexander and others advocate the addition of a very little gelatin

or gum arabic to cow ’s milk used in infant feeding . After such

addit ion the coagulated curd formed in digest ion is of a looser

texture and more readily digested .

Exp . 63. Selenium .-D issolve 1 g . selenium dioxide in 500 cc . of water .

To 50 cc . of th is solution (hot ) add 10 cc . of 1 per cent gelatin and then , dropby drop

,60 cc . of hydra zine hydrate ( 1 : 2000 of water) . Keep just below

the boiling point for fifteen minutes . A beautiful soft pea ch-pink color appears . Without the protective a ction of the gelatin the colloid soon prec ipitates, b ut when made as above it may be kept for years .

Exp. 64. Color of Ph otographic Images in Rela tion to Dispersity of Silverand Initial Nucleation .

1 — As Zsigmondy showed,the initiation of reduction

in gold or silver conta ining reduction mixtures is cata lytica lly a ccelerated bythe addition of colloida l gold

,in such a way that, by the addition of gold

sols of different dispersity to the reduction mixture,sols of very different

dispersity (subdivision) are obta inable .

Li'

I ppO-Cramer

,in the Kollo id Zeitschrift

,drew attention to these experi

ments and confirmed them for the case of colloid silver a ction on a silver-reducing mixture in gelatin .

The gelatin is purified,by ten wash ings with distilled water

,from elec

trolytes, especia lly ch lorides . The colloid silver used is prepared a ccordingto Carey Lea ’s dextrin method and purified by precipitation with a lcohol

,

as in the preparation of colloida l gold .

In ea ch experiment , 100 cc . of 10 per cent gelatin extra ct are diluted with400 cc . of water ; dayligh t is then excluded, and 20 cc . of 10 per cent silvernitrate are added to th e solution at and the solution is divided into 5parts of about 100 cc . ea ch . Th en port ions of per cent colloid silver areadded as follows

,4 cc . of 10 per cent a lcoholic hydroquinone being added to

each

Mixture Color(a ) NO colloid Ag . Blue-gray(b) cc . Blue(0) cc . Blue-violet(d) cc . Ruby-red(6) cc . Yellow-brown to yellow (diluted)

The reduction is more rapid, a ccording to the silver added . Resultsmay be Observed after th irty minutes . Dilute

,if necessary , to see the colors .

The results are still better seen if the S0 1 is fina lly diluted with an equa l

1 Contribution by S . E . Sheppard, Eastman Kodak Co .

PROTECTIVE COLLOIDS 31

volume of 10 per cent gelatin and coated as a th in layer on glass . On drying,the color changes observed by Kirchner and Zsigmondy (Anna len der Physik,15, 573, Schaum and Sch loemann and others with Lippman emulsions

,

etc .,are observed .

On dryingYellow red blueOn moistening

The addition of colloid gold in increa sing proportions has a similar effectin that an even greater a cceleration is produced ; b ut the color stages are thesame as for Silver additions . Luppo-Cramer points out that not all photographic developers are suitable for the experiments.

From these experim ents, it follows that the color of reduced

silver pa sses,with increasing amount of nuclear materia l from

blue violet red yellow . The deduction is sim ple . In the

mixture with most nuclear materia l,the na scent silver finds the

greatest number of aggregation (crysta lli za t ion) centers . As the

amount of silver formable by reduction is limited,the increase in

number of centers can only be at the expense of the size of particle .

Since,however

,with increasing number of nuclei the color passes

from blue red yellow,the particle size must increase from

yellow red blue , which agrees with photographic experience .

CHAPTER VII

SOLVATED COLLOIDS

Wo . OSTWALD classifies colloids as suspensoids and emulsoids .Suspensoids are dispersions of solid particles in a liquid

, and

emulsoids,he states

,are dispersions of a liquid in a liquid . Ostwald

divides emulsoids into two subdivisions, the ordinary type of

emulsions and the type represented by gelatin,agar

,glue

,albumin

,

alkali soaps and Silicic a cid .

This latter cla ss is distinguished by relatively high viscosity

as compared with equal concentrations of suspensoids,and by

comparative indifference to low concentrations of electrolytes .

The classification given here is challenged by a num ber of chem

ists, but it is difficult to draw hard and fast lines . The smaller a

drop Of liquid the more rigid it is,fina lly taking on the properties

of a solid particle . Some substances may be prepared in both

the suspensoid and the emulsoid sta te . Even barium sulfate

has been prepared as a j elly .

The emulsoids of h igh viscosity are hydrated,or solvated

,since

other liquids than water may be used . How else could we secure

solid j ellies with less than 1 per cent of the colloid and over 99

per cent of water,as has been done in some instances" In fa ct

,

Gortner prepared a j elly, discussed later in the chapter, containing

per cent water . By solvation we mean that much of the

solvent is firmly held by the colloid . It is not necessary to assume

that a compound is formed,but merely that liquid is powerfufly

adsorbed . It seems to the author that adsorption of water,for

instance,may hold layers of water in a condition approaching the

solid state . Such adsorption greatly increases the bulk of emulsoid

particles,and if by this means the remaining inter-part icle space

is reduced to capillary dimensions still more solvent may be

loosely held .

When viscosity is plotted against concentration,we find that

a straight line represents the suspensoids and a curve the emulsoids .The straight line falls well below the curve since at e qual con

32

SOLVATED COLLOIDS 33

centrations the emulSOids are far more viscous than the suspen

soids .

Solvated colloids are often ca lled hydrophile (water-loving) or,in genera l, lyophile . Typical non-solvated suspensoids are called

lyophobe .

Concentration

F I G . 5 .

— Viscosity curves for emulsoids and suspensoids .

Bancroft uses the term gel to include both gelatinous precipiitates and j ellies . He considers that a gelat inous precipitate is

a lways viscous, conta ins liquid and settles out at once,leaving

supernatant liquid . A jelly, he affirms, does not separate liquid

at first,although it may in time .

Without doubt, j ellies have a regular structure of some kind,usually requiring a very appreciable time to develop . Gelatinous

precipita tes form instantly and have but little regularity of strue

ture and but lit tle opt ica l clearness as compared with j ellies .

M oreover,j ellies possess some rigidity and ela st icity .

When a suitable mixture of sodium silica te and a cid is dialyzed

while fresh,Silicic acid passes through the membrane for a time

,

showing that at first the Silicic a cid is molecular . Later the

mixture loses its wa ter clearness and,still la ter

,sets to a solid

j elly. This gives a clue to structure . The highly hydrated aggre

gates are probably roughly spherical,since there is but little

chance of orientation with SiOg . With soap gels,however, and

gelatin , too , a filamentOus or forked-chain structure is possible and

probable . The Unlike groups in long molecules may join .

Exp . 65. Solid Alcohol .— Baskerville patented a clever process of makingsolid a lcohol . M ix

,by tossing from one beaker to another and ba ck aga in

,


90 cc . of 95 per cent alcohol and 10 cc . of a saturated aqueous solution of

calcium a cetate . A jelly sets instantly . Cut out a cube and set fire to it .

Let some of the j elly stand in a corked bottle . In a day or two it breaksdown into little granules floating around in liquid . Th is suggests that theorigina l j elly was made up of h igh ly solvated coa lescing sph eres . Volumesof 85 and 15 cc . will serve as well . In fa ct

,some other liquids may be sub sti

tuted for a lcohol . Try a cetone,methyl a cetate

,etc . But the solution of

ca lcium a cetate must be saturated,beyond question . Baskerville stabilizes

his j elly by addition of per cent of stearic a cid .

Exp. 66 .—Heat 5 cc . of aniline with 95 cc . of water to There is b ut

one phase . On cooling,minute drops conta ining over 90 per cent anil ine

(wet aniline) separate, and a milky emulsion results . Now heat very diluteagar . Examine a little as it cools

,under the microscope . M inute drops

appear . I f more concentrated agar is used,these minute drops coalesce to

a sort of network th rough wh ich the rest of the liquid can freely pa ss . Wa lkerstates (Physica l Chemistry, 231 ) tha t these drops are a solution of agar moreconcentrated than the surrounding liquid . Hardy considers a concentratedgelatin j elly as a system of drops of water in a gelatin—rich pha se .

M artin Fischer cons iders that hydrated colloid particles separa te fromwater conta ining little colloid but drops of water conta ining colloid separatefrom wa ter conta ining a much h igher concentration of the colloid .

Exp. 67 . Silicic Acid Jelly.— Dilute commercia l water glass ( lNa zO

3.5Si0 2) of about density to 1 : 10 density . Pour some of th is into anequa l volume of N a cetic a cid . M ix qui ckly and let stand . Note the Opa lescence preceding the set to a j elly . M ake 100 cc . of th is

,cut it out carefully

and a llow to dry for weeks . Observe the changes . In th is connection,read

Zsigmondy ’s Chemistry of Colloids,

137—152,and Bancroft ’s “ Applied

Colloid Chemistry,

”246— 251 . An a rticle on Silicic Acid Gels

,by the

author of the present volume,in Jour . Phys . Chem .

,22

, 510 may beuseful .

Exp . 68 . Vibrating Gels — Pour water glass diluted to densityinto an equa l volume of 6 N HCl. M ix quickly and pour into test tubes orinto 100 cc . bottles so th at th ey are only ha lf full . Cork the tubes . After afew days

,see if the bottles vibrate musica lly on being held lightly by the

top and tapped smartly aga inst wood . Test tubes are rapped on the top withthe fingers .

Try the same experiment after first greasing the tubes or bottles heavilywith melted vaseline . Compare th ese j ellies with the above after a week or

so . All tubes must be corked to check evaporation . See Syneresis inthe article mentioned below .

Th e pitch of vibration varies inversely as th e diameter of the tubes ; thatis,the gel vibra tes as a rigid body, as a suspended b ar of iron would do when

struck with a hammer . The vibrations are transverse . Rigidity is securedby tension . The gel adheres strongly to the glass tube and thus , in attemptingto contra ct

,must be under considerable tension . Silicic a cid does not adhere

to a vaselined surfa ce ; hence , in the greased tubes , the gel is free to contra ctand does so

,to an astonish ing extent . For further deta ils

,read the paper by

Holmes,Kaufmann and Nicholas, Jour . Am . Chem . Soc . ,

41 , 1329

SOLVATED COLLOIDS

Exp ; 69. Syneresis.— The gels in the va selined tubes of the p receding

experiment separated considerable water, or rather a solution of everyth ing inthe gel . Th is spontaneous separation of liquid from gels is ca lled syneresis .All gels exh ibit the ph enomenon , b ut it is more extreme in some instances thanin others . The formation of

“ curds and whey ” from a uniform gel is a

familiar instance .

M ix equa l volumes of a water glass of density and N citric a cidand let stand in a corked tube to set and synerize .

”

Further discussion of syneresis may be found in th e reference given in thepreceding experiment .

Exp. 70 . Barium Sulfate Gels .— Von Weimarn states that any very difficultly soluble salt will separate as a gel if made by mixing sufficiently concentrated solutions . It is essentia l that enough of th e sa lt be precipitatedin a medium in wh ich its solubility is sufficiently slight . Th is sligh t solubilitymay be secured in some cases by addition of considerable a lcohol to th eaqueous solutions .M ix equiva lent quantities of saturated aqueous solutions of barium

th iocyanate and manganese sulfate . On long standing,th e gel changes to the

usua l form .

SOAPS

The brilliant work ofM artin H . Fischer on the colloid chemistry

of soaps has been brought together in a recently published book,

Soaps and Proteins (John Wiley Sons) . M ost of the

material in this section has been taken from that book .

FI G . 6 .

— Water-holding capacities of the palmitates of potassium,ammonium,

Sodium, magnesium,barium and lead .

Exp. 71 .— Determine the water-holding capa city of sodium steara te and

of sodium olea te as described by Fischer .

“

Unless otherwise noted, weprepa red:

all. our soaps in e xa ctly the same way,by neutra lizing a defin ite

weight (one mol) of the pure fatty a cid with a chemica lly equ iva lent amount


of the hydroxide, oxide, or carbonate in a unit volume (one liter) of water,keeping the whole mixture at the temperature of a boiling-water bath untilunion between the a cid and base had been a ccomplished . Care was takento prevent or make good any loss of water from the rea ction mixture whi lein the ba th . Th is gives us a unit weigh t of pure soap in the presence of aunit weigh t of wa ter . The mixture was cooled to 18 °

and the yield of soapWeighed. When the entire mixture became gelatinous or solid we consideredtha t all the wa ter had been absorbed ’ by the soap . (This sta tement isqua lified elsewhere . ) When ‘free water began to appear above the soap ,the weigh t of the theoretica l yield of dry soap was subtra cted from the

weigh t of the soap as produced,the difference being expressed as per cent

of water absorbed ’ by the soap in terms of the weight of the theoretica ldry yield .

Sodium caproate may be taken as the first soap in the series (a cetic a cidseries) to show any water-holding power .

1 mol sodium laurate holds 4 liters of water1 mol sodium myristate holds 12 l iters of water1 mol sodium pa lmitate holds 20 liters of water1 mol sodium margarate holds 24 liters of water1 mol sodium stearate holds 27 liters of water1 mol sodium ara ch idate holds 37 l iters of water

The water-holding power of the oleic a cid series is much less . One .

gram-molecule of sodium oleate holds only one liter of water,as does one

gram-molecule of sodium linoleate .”

F IG . 7 — Water-holding capacities of the oleates of ammonium, potassium,

sodium,lith ium

,magnesium

,calcium

,mercury

,lead and barium . One

mol of soap to one liter of water.

Exp. 72.— Test part of th is experiment . We added water to 1 g . ea ch

of carefully dried soaps until, after solution in a hot-water bath , a dry gelwas no longer obta ined on reducing the temperature of the mixture toThe a ctua l amounts of water taken up by the h igher members of the seriesper gram of soap are shown graph ically in Fig . 1 1 .

Exp . 73. Soap with Alcohol. —Add to unit weights of fatty a cid the necessary ch emical equiva lent of N sodium hydroxide in absolute alcohol . Keep


Exp. 75.— Place a drop of phenolphthalein on a sodium stearate/water

gel . It rema ins uncolored . Squeeze the gel to break the structure of the

encircling hydrated sodium stearate film . As the enclosed solution of soap-inwater is squeezed out, the spot turns red . Any other soap-water systembehaves in similar fash ion . Make the gel about 10% soap .

Warm a concentrated sodium oleate solution,which at ordinary tempera

tures fa ils to color phenolphtha lein . On being warmed, it turns pink . Th ismay be sa id to be due to increased hydrolysis ; yet such a temperature marks adispla cement in the system from a solution of the solvent in the soap to one ofthe soap in the solvent .Add a drop of phenolph tha lein to an ordinary ( 15—30 per cent ) solu

tion of sodium or pota ssium oleate in water . Is there any color" Nowpour water down the side of the inclined tube producing a graded dilutionof the soap solution .

” What happens"

Read page 88 in Fisch er ’ s Soaps and Proteins for the dis

cussion ofmixtures of soaps ; pages 1 10—1 16 on the salt ing out

of soaps ; pages 150—160 on the foaming, emulsifying and cleansing

properties of soaps ; and pages 163—201 on the colloid chemistry

of soap manufacture .


Fischer mentions a number of other liquids, in addition to

water and the various alcohols, that solvate soap . The author

of the present volume has made many very beautiful j ellies

using soaps in some of the common lubricating oils .

Exp. 76 . Soap-oil Gels . —Dry sodium stearate (any hard wh ite b athsoapwill serve) at 90

° in an air bath . M ake a per cent solution in the com

mercia l lubrica ting oil ca lled Veedol or in any petroleum fra ction of a

h igh flash point . Hea t to 200 ° if necessary to get a clear liquid . Comparewith a per cent solution of sodium oleate in Veedol or in Arctic oil .When these solutions cool

,solid gels of beautiful clearness are Obta ined .

M cBain and his associates have published va luable papers on

the soaps . Read his chapter in the Third Report on Colloid

Chemistry published by the Brit ish Association . M cBain and

M art in (Jour. Chem . Soc .

,1 19, 1369, 1921) determined the degree

of hydration of soap curd by salting out the curd in the presence

of a known concentra t ion of sodium sulfate and determining the

increa se in ' concentration of the sodium sulfa te . This increase was

due to the fa ct that soap abstra cted some of the water from the

solution,in other words

,became hydrated .

This method of investiga t ion,a lthough tedious in the ca se of

soap solut ions,is worthy of a more genera l app lica tion to the

study of solvated colloids .

M cBain also believes th at the degree of hydration of the fibers

of soap curd depends a lmost entirely upon the vapor pressure of

the solution with which it has been in conta ct,being lea st for the

most concentrated brines . His dew-point method for mea suring

vapor pressure is given in Jour . Am . Chem . Soc .,42

, 426 (1920)and in Proc . Roy . Soc .

,97 "A] , 44

M cBain and Salmon proved t hat the concentration of OH

in soap solutions is only of the order of G.OO1N . They furth er

state that the conductivity of soap solutions is due to the ioniza t ionof the s oap itself . In dilute solutions soap is in true solut ion .

M artin H . Fischer ’ s papers in Science,48 , 143 (1918) and 49,

615 (1919) give a brief summary of a number Of his findings .

Exp . 77. Pectin Jelly.— The white rinds of citrus fruits

,apples and a

number of other fruits are rich in a carbohydrate-called pectin . It may be

isolated as a wh ite powder,soluble in hot water .

Boil th e wh ite peel of any citrus fruit in water . Filter and coagulate thepectin with a lcohol . Wash and dry . M ake an imitation fruit j elly by boilinga few minutes water conta ining 1 per c ent pectin

,per cent tartaric a cid


and three-fourths of th is volum e of dry sugar. Fruit j ellies need pectin, ana cid and cane sugar . Boil until the temperature rea ch esRead : Jour . Ind . Eng . Chem .

,12

, 558 (1920) Jour . Phys . Chem .,20, 633

Jour . Ind . Eng . Chem .,1 , 333 2, 457

C . A . Peters states tha t when the a cid concentration is equ iva lent toper cent sulfuric a cid he gets the best gel structure . Less a cid is poor

,

and more is no better than per cent . A definite ratio of sugar to pectinis desirable . As th e percentage Of pectin increases

,so does the amount of

suga r needed to make the stiffest gel . One volume, or less, of 95 per centa lcohol coagulates a concentrated pectin solution .

Di-benzoyl Cystine Gel. -Theories of gel structure must take

account of the remarkable di-benzoyl cystine gel recently prepared

by Ross Aiken Gortner and Walter F . Hoffman . Brenzinger

(Zeit . physiol . Chemie, 16, 537, 1892) was the first to study thisgel .

Cystine is prepared from human hair by hydrolysis with hydro

chloric a cid . Suspend 2 g . of cystine in 100 cc . of water and add

10 per cent sodium hydroxide until the amino acid dissolves .

Then add 10 g . of benzoyl chloride and enough sodium hydroxide

solution to make a total Of 6 g . Shake vigorously until all odor of

benzoyl chloride is gone .

Acidify with hydrochl oric acid . The solution sets to a stiff

gel whi ch should be broken up by agitation“ and drained by suctionon a Buchner funnel for several hours . Wa sh the felt Of crystals

with water . Recrysta llize from diluted alcohol . Long,silky

needles,melting at 180

°—18 1°

are secured .

These needles are insoluble in water and do not conta in waterof crysta lli zation . They are soluble in most organic solvents .

Brenzinger states that if the a lka line solut ion from 2 g . of

di-benzoyl cystine, as above noted, is diluted to 3 liters and then

acidified with hydrochloric acid a rigid gel results,with no free

water to pour off. Brenzinger claims a good gel in wh ich only

of 1 per cent is di-benzoyl cyst ine and the rest is water .

This is startling, considering that the substance has no hydrophylic properties .

Exp . 78 .— Cortner ’s method is different . He dissolves g . of pure

di-benzoyl cystine in 5 cc . of 95 per cent a lcohol . He adds hot water slowly(keeping the so lution boil ing) to a volume of 100 cc . The beaker is coveredand set aside to cool . In two to th ree hours a transparent gel

,as rigid as 5 per

cent gelatin,is formed . After severa l days opaque nuclei of stellate groups

of needles appear,and syneresis is noticeable .


This gel reminds us of Wo . Ostwa ld ’s statement that castorOil soap forms almost a solid gel in water at per cent coneen

tration if a certa in amount of a lkali is present . Further examples

of this sort are deta iled by W . Dohle, Koll .-Zeitschr.,12, 73, 1913.

Cuprimucate Gels.

— Pickering (Trans . Chem . Soc . 99, 176,

191 1) prepared and studied a most interesting gel offi-cuprimucate .

The precipitate,made by simple double decomposition, was prae

tica lly insoluble in water . On being heated to it reta ined

4HzO,but at 120

° it became anhydrous .

On the addition of a solution of potassium hydroxide, a blue

solution slowly forms . About equiva lents of the base for

each copper atom must be added before any a lka linity is Shown .

Unless very dilute,th is solution turns into a gel in a few minutes .

Only when the percentage of copper is or less can the gel be

filtered,even if hot . It may be boiled without decomposition .

Alcohol coagulates the blue solution .

When a weak gel is filtered under pressure it passes through thepaper

,forming a slightly cloudy filtra te

,which gelatinizes aga in

in a day or two . The same cloudy solution may be secured by

merely shaking a weak gel .

A lump of the gel on a porous t ile loses liquid,but a solid residue

rema ins . The gel disintegrated by shaking is completely adsorbed

by the porous tile .

Cupriquinate gel is discussed by Pickering in the above

reference .

Ceric hydroxide gel is described by Fernan and Pauli (Koll .Zeit .

,20, 20,

CELLULOSE SALTS

Exp . 79. Saturate concentrated hydroch loric a cid at 0° with additiona l

hydrogen ch loride . Th is yields a 43 or 44 per cent solution . Stir dryshredded filter paper into th is solution . It dissolves (probably as an oxoniumsa lt) . Even a cid of density dissolves cotton or paper in 10 secondsat room temperatures and more slowly a t

Th is is an example of equil ibrium,for in any concentra tion of th e a cid

below 40 per cent the cellulose does not dissolve . The ma ss a ction of sufficienthydrogen ch loride is necessa ry to overcome hydrolysis .After fifteen minutes pour a portion of the solution into an excess ofwater .

A colloida l precipitate of hydrated cellulose is produced,due

,Of course

,to

hydrolysis of the oxonium salt . After th irty minutes pour another portionof the origina l solution into water . The amount of precipitate is much lessbecause of a change to dextrin and dextrose (a mere depolymerization of the


cellulose) . After one hour pour another portion into water,and after two

hours repeat the experiment . Examine the series of products thus obta inedfor dextrose

,by Feh ling ’s test . After two hours ’ hydrolysis all the cellulose

has been converted into dextrose . Adapted from Willstatter and Zechmeister (Ber . 46, 2401 ,

Th is is the reversa l of photosynthesis, by which plants build

forma ldehyde into sugars and these into starch and cellulose .

A paper by H . E . Williams,Theory of the Solvent Action

of Aqueous Solutions of Neutral Salts on Cellulose ”

(M emoirs

and Proceedings of the M anchester Literary and Philosophical

Society,65, II , No . 12

,1921) is so striking that it was felt worth

wh ile to quote at some length . Not one but many interesting

experiments m ay be devised by the student from the suggestions

in the paper . Viscosity may be plotted aga inst boiling points

with convincing effect .

The solution of cellulose in an aqueous solution of a neutra l

sa lt is independent of the chemical nature of the salt, but is largely

dependent upon the physica l properties of the sa lt solution . For

such a solution to dissolve cellulose it must consist of a liquid

hydrate— an associated molecular complex of sa lt and water .

But th is complex must be of such an order that it has a viscosity

above a certa in minimum and a positive heat of dilution between

well-defined limits .

Before an aqueous solution can dissolve cellulose it must

have a boiling point of 133° C . or over and a viscosity at 100°

of times tha t of water at“ Solution of chemica l wood pulp may be obtained in most

cases below the boiling point of the salt solution,b ut in all cases

it is necessary to heat the mixture to a minimum tempera turevarying from 90 depending on the particular sa lt used .

With pure neutral ca lcium thiocyanate solution boiling at

solution of cellulose may be obta ined by hea ting to 90°

Solutions of calcium chloride can be made which have the

necessary viscosity and boiling point but they do not dissolve

cellulose .

“ If one of the necessary preliminary conditions before the

cellulose dissolves is the hydration of the cellulose,it is evident

that if the water present in the aqueous solution is atta ched to

the sa lt with too great an affinity it will not hydrate the cellulose

and no solution of the cellulose can result .


Concentrated calcium chloride solution has a very high heat

of dilution , therefore it has too strong a dehydrating a c tion to

dissolve cellulose .

Since Ca lcium chloride with so large a hea t of dilution was

a non-solvent for cellulose, it was thought possible tha t if a cal

cium th iocyanate solution could be made concentrated enough,a point should be rea ched when its heat of dilution would be so

great that it would cease to be a cellulose solvent . Experimenta l

evidence showed this to be true for a solution concentrated to

a boiling point of 150° and over . At this point no cellulose was

dissolved even after heating for some time . The addition of a

very small amount of wa ter, sufficient to drop the boiling point

of the solution to 148° caused the cellulose to dissolve rapidly .

A solution of sodium th iocyanate fails to become a cellulose

solvent because of its low viscosity . The addition of other salts

that will either not affect, or will not increase the heat of dilution ,and at the same time will increase v iscosity, should convert the

solution of sodium thiocyanate into a cellulose solvent . A very

large number of such additions can be made, such as sodium zinc

th iocyanate, sodium manganese th iocyanate, aluminium thiocya

nate or by dissolving lead thiocyana te in the solution . All these

additions increase the viscosity of the solution and a t the same

time convert the sodium th iocyanate solution into a cellulose

solvent .

Lithium thiocyanate solution does not dissolve cellulose

until it is concentra ted to a boiling point of the viscosity

being too low for all concentrations below this boiling point ; but

when the viscosity of the solution is increased by additions of

other soluble compounds (manganese, calcium or a luminium

thiocyanates or even hexamethylenetetramine, dicyanam ide or

thiourea) , a cellulose solvent may“

be obta ined boiling 30° lower .

Each Of these solutions has a positive heat of dilution when con

centrated .

I t is thus seen tha t there is a definite connection between the

boil ing point, the viscosity and the hea t of dilution of a solution

salt and its solvent power for cellulose .

Both calcium chloride and magnesium chloride solution when

concentrated to the required viscosity have too great a heat of

dilution to dissolve cellulose . Additions,therefore

,wh ich lower

the heat of dilution , and either”

increase or do not lower the vis


cosity should convert these solutions into cellulose solvents . This

may be a ccomplished by dissolving mercuric chloride in these

solutions to form the double ca lcium mercuric chloride and the

magnesium mercuric chloride respectively .

If the solutions (any given above) are made acid by a weak

acid such as acetic,the cellulose is more readily dissolved and

in much grea ter amounts .

Both stannic and ferric hydroxides begin to dissolve when

a calcium thiocyana te solution is concentrated until the composi

tion of the solution corresponds with the liquid hydra te,

Ca (CNS) 2 10HzO

This is the lowest concentration that will dissolve cellulose .

As an aqueous sa lt solution having the necessary viscosity

and boiling point, b ut wh ich is not hydrated or only partially

hydrated in solution,and therefore contains free water , is a non

solvent for cellulose,it is evident that the combined water plays

an important part in the solution of the cellulose,the solution

being brough t about by means of the combined water,or the

capacity of the sa lt for taking up water . The combination of

the salt and water must,however

,be of a certain order

,that is

to say,the water must be bound to the salt between the limits of

a maximum and minimum intensity,above or below which no

solution of the cellulose can take pla ce on heating .

“ A simple and possible explanation of the solvent action on

cellulose of these sa lt solutions,wh ich fulfils the prescribed con

ditions,may be stated thus : The hydroxyl groups of the cellulose

unit link up with the salt complex in place of the water molecules

acting in the manner of a substituted wa ter group,thus causing the

fibre to swell considerably . The cellulose unit is brought by this

means into molecular range with the water molecules combined with

the sa lt . By ra ising the tempera ture the union between the salt

and water molecules will weaken and they tend to part from

the parent molecule . The water thus freed migrates to the cellu

lose by which it'

is imbibed,causing further swelling of the fibre

,

which increases as the progressive hydration proceeds . The highly

swollen fibre in the gela tinous condition then peptizes,and passes

into colloidal solution .

”


GELATIN

Gelatin is far from ash free as purchased,and may be

purified by soaking in several changes of dist illed water, so that

the salts dia lyzeout . Or it may be placed in water in the middle

compartment of a glass box which is cut into three compartmentsby two porous clay slabs . Electrodes dip into the water of the

end compartments . When a direct current is turned on,the

electrolytes move out and the gelatin is washed by electric osmose .

A water solution of gelatin may be poured into alcohol and the

gelatin precipitated . This coagulum may then be wa shed and

dissolved again in water at with further purification by

reprecipitation .

Jacques Loeb (Jour . Am . Chem . Soc 44, 213, 1922) prepares

ash-free gelatin by bringing it to the isoelectric point and then

washing sufficiently with cold water . He states that at the

isoelectric point an amphoteric electrolyte like gelatine cannot

combine with anion or cation . C . R . Smith (Jour . Am . Chem .

Soc . 43, 1350, 1921) also presents a method of making ash-free

gelatin . Pauli Colloid Chemistry of the Proteins ”) states

that a gelatin studied by him was isoelectric at a H+ concentra

tion of for 1 per cent gelatin .

Exp. 87. Efiect of Salts on Setting of Gelatin and Agar.— Hatschek out

lines a useful experiment to demonstrate the effect of sa lts on gelatin and agar .Prepare 250 cc . of 10 per cent gelatin (dissolved at and an equa l volumeOf 1 per cent agar (dissolved at the boiling point) . In ea ch of three 100 cc .

beakers pla ce enough sodium sulfate, sodium ch loride and sodium sulfocyanate

(or the potassium sa lts) to make the 50 cc . of gelatin solution to be addedN . Of course

,only one sa lt is added to ea ch beaker . A fourth beaker

conta ins merely gelatin for comparison . A similar series is prepared withagar . The salts are dissolved at 40

° in the gelatin and at 100° in the agar .

Note the order in wh ich the gels set on cool ing. What is Hofmeister’s series"

Gelatin is very sensitive to treatment . For example,Elliott

and Sheppard autoclaved gelatin for four hours at 60 lbs . and

secured a liquid with the viscosity Of water . Gelatin,heated

repeatedly above lose s the power of j ellying on cooling ; C .

R . Smith states that ash-free gelatin does not set to a j elly in

cold water b ut comes out as a precipita te .

Ja cques Loeb considers that gelatin forms salts (gelatin chloride,sodium gelatinate

,etc .) which form true solutions . His experi


ments are given in Jour . Biol . Chem .

,31 , 343, 1917. His work on

the effect of hydrogen ion is found in Jour . Gen . Physiol .,1 , 39,

237,353, 483, 559 ( 1918 His paper on “ The Proteins and

Colloid Chemistry (The Physics and Chemistry of Colloids, a

Report by the Faraday Society and the Physical Society of

London,Oct . 1920) is a summary of the work described in

severa l previous papers .

The idea that a lka lies or acids unite with protein to form new

compounds is, by itself, not new . It was early expressed by S .

Bugarsky (Pfluger’s Ar ch . 72, 51 , 1898) and has since been con

firmed and developed by Hardy,Pauli

,Van Slyke

,Robertson

and others .

Exp. 88 . Ferric Arsenate Jellies — When ferric arsenate (or phosphate)is peptized by a sligh t excess of ferric ch loride and dialyzed

,beautiful j ellies

form on th e dia lyzer . Remova l of the peptizing ions, at a sufficiently Slowrate, a llows precipitation of ferric arsenate in a hydrated form of the regularstructure we ca ll a j elly . For details

,see Holmes and Arnold

,Jour . Am .

Chem . Soc ., 40, 1014 Holmes and Fall, ibid .,41 , 763

Exercise — From the experiments in this chapter develop a

classifica t ion of the ways in which j elly structure may be obtained .

A useful chapter by Stocks on several common solvated

colloids is found in the First Report on Colloids (46— 78) issued bythe British Association .

CHAPTER V I I I

SURFACE TENSION

THE surface film of a liquid is in a state of tension due to the

unbalanced attractions between molecules at the surfa ce as com

pared with those wh ich are entirely surrounded by other molecules .

The molecules in the surfa ce layer of liquid are attra cted only

downward and sideways,not upward, since there are no liquid

molecules above them . Consequently,

the surface molecules a ct as if they

formed a tightly stretched but elastic

skin over the surface of the liquid .

As a result of this surfa ce tension,

every liquid tends to assume the

spherical shape because the sphere,

of all shapes,has the least surfa ce .

When a liquid wets the wa lls of a

glass capillary tube,the surface is

0 concave and the liquid rises to a

8 height inversely proportiona l to the

0diameter of the tube . The unit surface

F IG . 10 ,

— Liquids 0 f 10w_ and tension is the tension across a line 1

h igh-surface tension . cm . in length .

“ If we denote the va lue of surfa ce

tension by y ,writes Findlay

,and by h the height in centi

meters to which a liquid of density 3 rises in a tube of radius r

cm .,we obtain the expression

7 ihrsg

where g is the value of gravity (98 1 dynes) . We then Obtain thevalue of the surfa ce tension in absolute units (dynes per centi

meter) . The va lue Of 7 is dependent on the nature of the liquid

and also on the temperature, rise of temperature being a ecom

panied by a decrease of the surfa ce tension .

48

SURFACE TENSION 49

By the drop weight method we determine the weight of a drop

of liquid falling freely from the end of a tube .

Or,with Traube ’s sta lagmometer, We count the number of

drops formed by a given volume of liquid . From this we can

calculate surfa ce tension . For working directions on the capillary

rise method and drop weight method, read Findlay’s Practica l

Physica l Chemistry,

” pages 89—96

The sta lagmometer is used to determine surface tension of

liquid aga inst air,but it may be modified to determine surfa ce

tension of one liquid aga inst another . In connect ion with the

chapter on Emulsions we sha ll find this method

very useful . Surface tens10n Is not absolutely

inversely proportiona l to the drop number,

but it approximates it well enough to make

the method worth wh ile .

Harkins (Jour . Am i Chem . Soc .

,

1919) determines surfa ce tension with great

accuracy and discusses the theory in deta il .

Exp . 89. Use of Donnan ’ s Pipette .—Since surfa ce

tension lowering is a factor in emulsification,it is of

importance to have a method ofmeasuring the changein surfa ce tension between the’ two liquids to be emulsified . Donnan devised a pipette with which he

a llowed a definite volume of l iquid A to run into liquidB or into liquid C

,etc . Th e lower the surfa ce tension

between the two liquids the greater the number of

drops . Therefore,merely counting th e number of F I G 1 1 Donnan

drops gives an approximate measure of surfa ce tensions . pipette (improvedShorter’ s modification of th is pipette is very useful . by Shorter) .

Use a capillary tube of 1 mm . bore . Blow a bulbat C holding 1 or 2 cc . To regulate the flow

,a short piece drawn down to

a ha ir Opening at A is connected to the pipette by the rubber tubing B .

The tip D is shown magnified at E .

Drops sometimes widen at their point of atta chment,changing their size .

By using heavy glass and grinding the end level,it is easy to detect such a cci

denta l distortion and to discard the reading . Readings are taken betweenF and G

,marks on the tube . Determine the drop numbers of benzene (or

any hydrocarbon) against water,1 per cent sodium ch loride

,1 per cent

sodium oleate,1 per cent sodium hydroxide and 1 per cent sulfuric a cid .

Draw conclusions .

Drop Spread — The surfa ce tension of mercury is 436 (atof wa ter (at and of ether (at Which of these

COLLOID LABORATORY MANUAL

liquids should give the flattest, thinnest drop on a gla ss or porcela in

plate" Test your opinion . Wo . Ostwald observes that a gla ss

tube may be drawn out to a tip of such aperture that ether runs :

through it in a stream while mercury runs through in droplets .

Explain .

Exp. 90.—From a heigh t of 1 cm . (for example) let cc . of water fa ll

from a burette on a thorough ly cleaned glass plate . M easure the “ dropSpread in millimeters as soon as the maximum width of the spot is rea ched .

Compare with the drop spread of a 1 per cent solution of sodium oleate .

Th is is a rough method of measuring surfa ce tension, useful at tim es if precautions are taken to prevent evaporation .

(The following is taken from P. Lecompte du Nouy by the author ’ s

permission from The Journal of General Physiology,-7,

The importance of the act ion of surface tension in biological

phenomena is well known,but all the techniques of mea surement

are either complicated (sta t ic methods : capillary undula t ions,drop rebounding

,capillary j ets, re bounding j ets) , or long (drop

method) ; and it is desirable to have a Simple apparatus by means

ofwhich the surface tension, and especially the varia tion of surface

tension of a given liquid,can be readi ly.

mea sured, with sufficient

a ccuracy. For this reason the apparatus to be described has been

designed . There is no new principle in it ; it is based upon adher

enCe of a ring, or of any Other design, to the liquid (Weinberg) .

It is simply a torsion balance, but instead ofmea suring the tension

by means of weights (which is time-consuming, and makes two

readings necessary) , it makes use of the torsion of the wire to

counteract the tension of the liquid film and to break it . A single

reading on a dia l indicating the degree of torsion of the wire

gives a figure,which

,if the appara tus has been previously standard

ized with water, gives the surface tension of the liquid by a sirnple

proportion . From the fact tha t the torsion of the wire for wa ter,which has the highest surface tension, is only we can assume

that,within these limits

,the strain of the wire is proport iona l to

the angle of torsion , so that no table of correction is needed .

”

The instrument consists essentia lly of a stand provided at

the top with a fine steel wire stretched between end supports .

One end of the wire is tightly clamped , the other being attached

to a worm wheel controlled by thumb—screw (b) . To the worm

SURFACE TENSION 51

wheel is a lso attached a pointer (a ) which moves over a metal

sca le graduated in degrees . To the middle of the wire is clamped

a hollow,light a luminum lever (d) with a sma ll hook in the outer

end . A stirrup a tta ched to this hook carries a carefully made

loop (h) of platinum-iridium wire with a periphery exactly 4 cm .

in length .

The wa tch glass,or other vessel conta ining the liquid whose

surfa ce tension is to be determined , is pla ced on the platform (9)and carefully ra ised by means of the adjusting screw until the

pla t inum loop has made conta ct with the liquid . The pointer (a )having been previously set at zero

,the torsion of the wire is gradu

ally increased by means of the thum b-screw (b) controlling theworm gear

,until the loop Of wire tearsloose from the liquid . The

number of degrees is then read from the sca le and by a Simple

ca lcula t ion is converted directly into dynes per cent imeter .

This instrument provides the most rapid and direct-reading

device for measuring surfa ce tension which has yet been produced .

The method is Simple, yet capable of the h ighest degree of precision

in mea surement . Th is is the only device by which the surfa ce

tension of colloida l liquids can be a ccura tely determined . A

feature of specia l importance is the fa ct that a complete determina

tion can be made in from fifteen to th irty seconds, and result s can

be duplicated over and over with perfect ag reement . Another

interest ing feature of the instrument is the sma ll amount of liquid

required,1 cc . being sufficient . Th is perm its a wide use

, particu

larly with biologica l fluids, wh ich are usua lly ava ilable only in

sma ll quantit ies . The instrument can be readily and quickly

standardized by the use of pure wa ter at 20°

C .

The first precaut ion to take is to clean thoroughly the

pla tinum wire (h) , by flaming it,or by wa shing it in a solution of

10 cc . of saturated potassium dichroma te solution in 990 cc . of

sulfuric a cid,and rinsing it carefully under a flow of ordinary tap

wa ter,running from the stopcock, unless very pure distilled water

conta ined in clean and grea seless bot tles can be provided .

The same thing must be done with the watch glass, or the

beaker used for conta ining the liquid,the surfa ce tension Of which

is to be measured . It is advisable to a llow them to boil for five

minutes in the above-ment ioned solut ion, in order to remove the

slightest trace of grease .

These parts are then put in place, without being touched


with the fingers ; that is, the platinum loop (h) hooked to the

lever (d) and the watch glass containing the liquid on the table (g)“ The zero is now determined . For this

,the needle (a) is

brought by means of the knob (5) just in front of the point 0 on

the dial . Then,by means of the adjusting screw (f) , the torsion

of the wire is modified until the lever (d) is just above the resting

platform (e) , the distance between them not exceeding a smallfraction of a millimeter ; for instance, the thickness of a piece of

very thin paper . The screw (c) being fixed in position,one will

—Du Nouy surface tension apparatus .

observe that an imperceptible movement of the knob (b) will

bring the lever in conta ct with the platform (e) , practi ca llywithout changing the reading on the dial . The apparatus is now

ready for use .

The table (9) is raised slowly by means of the adjustingscrew until the liquid touches the platinum ring (h) . One must

be sure that a perfect contact exists . Then by turning the knob

(b) , the torsion of the wire is controlled , and one keeps on turning

until the ring is suddenly separated from the liquid , by the tearing

off of the film . The reading is made . One can rapidly check

this reading by one or two others .

The figure read being carefully noted,the liquid is lowered


Exp. 91 .—With the Du Nouy apparatus , measure the surfa ce tension of

water, of a 1 per cent aqueous solution of nigh t blue, of a lcohol and of a 1 percent a lcoholic solution of nigh t blue .

Nigh t blue is colloida lly dispersed in water and molecularly dispersed ina lcohol . Draw your own conclusions . With the same apparatus lea rn ifthere is any difference in the surfa ce-tension lowering caused by suspensoidsand emulsoids .

J . Willard Gibbs (Scientific Papers, I , 219) taught that any

dissolved substance lowering surfa ce tension must concentra te in

the surfa ce layer . Th is important sta tement applied to true

solutions ; yet it is a fa ct that some colloids concentrate at the

surfa ce far more then called for by the formula . The surfa ce

tension of a fresh solution is often very different from tha t of an

older solution . In some instances it requires apprec iable time to

reach equilibrium between the change in surfa ce tension and the

osmotic pressure difference of surfa ce film and mass of solut ion .

SURFACE PHENOM ENA CONNECTED WITH SOAP SOLUTIONS 1

Change of Surface Tension of Soap Solutions with Tim e

Obj ect.—Simple method for determining surfa ce tension of soap solutionsand varia tion with time.

Exp. 92 . Procedure .—M ake up a dilute solution of sodium stearate

( 1 part in by diluting the stock solution conta ining gr . cc . withthe required amount of distilled water . Pipette a portion into a watch glassand immediately mea sure surface tension by Du Nouy surfa ce tensimeter (or ahome—made apparatus similar to th is ) . Continue the readings once everyminute for ha lf an hour . Repea t with sodium oleate . Record variations withtime and expla in them .

Surface Films on Soap Solutions .

Obj ect. -To demonstrate the presence of a surfa ce film on soap solution .

Exp . 93. Procedure .— Allow a dilute solution of sodium stearate

,on the

surfa ce of wh ich ta lc has been dusted, to stand severa l minutes in an opendish . Dip a fine glass point into the surfa ce

,observ ing the movement of the

surfa ce as the point is moved to and fro . Repeat the above experiment,

using sodium oleate . Compare results .

1 Contributed by Leon W . Parsons and R . E . Wilson , of Massa chusettsInstitute of Technology .

SURFACE TENSION 55

We quote from NO. 182 of Bancroft ’s Two Hundred Colloid

Problems .”

Stab ilization of Foam To get a foam the only essentia l is

that there sha ll be a distinct surface film ; in other words, that theconcentration in the surfa ce layer shall differ perceptibly from

tha t in the mass of the liquid . All true solut ions will, therefore,foam if there is a ma rked change of surface tension with change of

concentra t ion,regardless of whether the surfa ce tension increases

or decrea ses . All colloida l solutions will foam if the colloid con

centrates in the interfa ce or if it is driven away from the interfa ce .

To get a fa irly permanent foam the surface film must either be

sufficiently viscous in itself or must be stabilized in some way.

Th is can be done by introducing a solid powder into the interfa ce .

Exp. 94. Solutions of aqueous a lcohol,a cetic a cid

,sodium ch loride and

sulfuric acid all foam when shaken ; b ut the foam is unstable . Soap solutionsfoam when shaken and th e foam is

,or may be, qu ite stable, owing to the

v iscosity of the soap film . With saponin th e surfa ce film is even more stable .

I f we add to aqueous a lcohol some substance like lycopodium powder wh ichgoes into th e interfa ce

,we get a stabilized foam . We can do the same

th ing with aqueous a cetic a cid by adding lampbla ck . The presence of enoughof a finely divided solid in the interfa ce will make th e film so viscous that thefoam will be quite stable . Grease will h elp stabilize a foam in some casesand it has been cla imed erroneously that the foaming of sulfuric a cid solutionsis due to grease .

”

R . E . Wilson and Leon Parsons believe that stable foams are

produced only when the surface layer has the properties of a

pla stic solid ra ther than Of a viscous liquid .

Surface Tension and Surfa ce Energy by Willows and

Ha tschek is a book of 80 pages published (1915) by Blakistons.

CHAPTER IX

EMULSIONS

BEFORE performing the experiments of this chapter read most

of the references following :

W . D . Bancroft,Applied Colloid Chemistry

,161

,260-273;

Martin H . Fischer,Fats and Fatty Degenera tion

,1— 16 (John

Wiley Sons) ; Emulsions, Jour . Ind . Eng . Chem .,12, 177

Pickering ’s paper,Jour . Chem . Soc .

,91 , 2001 (1907) Clowes ’

paper,Jour . Phys . Chem .

,29, 407

There are conflicting views in these various articles,but they

are all stimulating .

Emulsions are,of course

,dispersions of minute drops of one

liquid in another . Two mutua lly insoluble liquids may be emul

sified by mechanical agitation, but they soon separate into two

layers of the original liquids . Such emulsions are not stable when

they contain more than 1 per cent of the dispersed phase . Poor

emulsions of this type may be secured by pouring 10 cc . of a 1 per

cent solution of any oil in a cetone (or a lcohol) into 1000 cc . of

water . Stable emulsions of two pure liquids cannot be made .

A third substance,usua lly colloidal

,is necessary to stabilize

emulsions . This is often present as an unsuspected impurity .

The exact manner in which this third substance, the emulsifying

agent,

” funct ions is in dispute . The different theories are illus

trated in the following experiments .

Exp. 95. Soap as Emul sifying Agent.— Shake together oil (kerosene willdo) and water . A temporary emulsion forms . Now shake 20 cc . of oil with60 cc . of 1 per cent sodium oleate . Let it stand . The soap has lowered thesurfa ce tension of the wa ter

,probably concentrating as a film around ea ch

Oil globule, and it has bound all the water . These points represent threeth eories of emulsifica tion . All may apply in certa in cases . In other casesa single influence is predominant .A “ cream rises to the top in soap emulsions . Th is cream is much

richer in oil than is the l iquid below . To prove th is,separa te the two layers

with a pipette and break the emulsions with any a cid . Th is l iberates free

56

EMULSIONS 57

fatty acid wh ich has no emulsifying power . Compare volumes of the oil

layers separating .

Agitation is necessary to break at least one liquid into drops . Briggs

(Jour . Phys . Chem .,24, 120, 1920) insists tha t intermittent shaking is better

than continuous shaking . Agitation may be secured by hand shaking, shakingma ch ines, egg-beaters, mortar grinding or by air stirring as with Hatschek

’s

device,Fig . 13. The flow of oil from th e pipette is regulated by a screw clamp,

so that 50 cc . of kerosene would be delivered in th irtyminutes . Th is oil is dropped into a long-stemmedth istle tube wh ich admits a ir at th e same time . The

lower tip of th is th istle tube (rea ching nearly to thebottom of the cylinder) should be only 1 mm . in diameter

,for the best results . The rubber stopper in the

top of th e cylinder fits tigh tly,so that the suction

from the air pump can draw air and Oil down theth istle tube . The cylinder conta ins one-fourth of itsvolume of soap water (usua lly 1 per cent sodiumoleate) . To prevent froth being carried over, a fewsheets of loosely crumpled filter paper are push ed intothe upper part of the cylinder . Before the apparatus isset up , the th istle tube must be wet with oil . To doth is

,pour a little oil through the tube

,wh ile tilting giftgipni

’

iierand rotating it .A counter-current beater is very useful in agitating

liquids . It consists of two propeller blades atta chedto the same shaft so that one is inverted, each throwinga current of liquid aga inst the other . Cut a slot in abrass shaft and solder in two copper blades wh ichhad previously been bent to shape . The whole deviceshould be nickel-plated . The shaft may be set in a

rubber tube as a bush ing .

Exp . 96 .— With Ha tschek

’s emulsifier, see if you

can make a 90 per cent emulsion of cotton oil in 1 mulsion

per cent sodium oleate or in potassium oleate .

Exp . 97 . Gelatin as an Emulsifying Agent — Useany good gela tin, a lthough we prefer Difeo

,

” madeby Digestive Ferments Co . of Detroit . Difeo gelatinhas an ash content of per cent and sets to a j elly F I G . 13.

— Hatschek’s

at a concentration'

of per cent or less . M ake a emulsifier .per cent solution of gelatin in water at

Place 10 cc . in a 125 cc . oil sample bottle and add 5 cc . of kerosene at atime, with intermittent shaking . It is possible to add a tota l of30 cc . ormore of oil , making a 75 per cent emulsion . Holmes and Ch ild, J . Am .

Chem . Soc .

, 42, 2049, 1920 .

Emulsion Th eories — Plateau and Q uincke believed that sur

face-tension lowering by the emulsifying agent was its most

important funct ion . Since the a lkali soaps lower the surface


tension ofwater greatly, they have been favored as aids to emulsi

fication. Yet M art in Fischer holds that the a lka li soaps are

effective rather because they are solvated colloids and thus

bind the water . Read “ The Argument ,” pages 1— 15, in his

Fats and Fatty Degeneration,” for further statements on his

theory .

In the more common type of emulsions drops of oil are dis

persed in water (oil-in-water) yet the opposite type is well known .

Drops of water may be dispersed (with the aid of the proper

emulsifying agent) in oil forming wa ter-in-oil emulsions .

The heavy-metal soaps are notgood emulsifyingagents for theoil

in-‘water type . Yet they are good emulsifying agents for the wa ter

in-oil type,Fischer holds

,

because they are not hy

drated to any marked extent . ‘

Gum arabic, gela tin, a lbumin

and all the solvated colloids

are useful emulsifying agents .

We have used gelatin in theOil in Water Water in on previous experiment with

F I G 14 — *Emulsi0 n types good results . The norma lly

present proteins of egg yolk

keep the 30 per cent of fat of the yolk in emulsified form . Still

more fat may be added as when mayonnaise is made . Acid

casein and alkali casein both hydrate well,and SO yield good

emulsions of oil-in-water . But when either is exactly neutral

ized,neutral casein

,a slightly hydrated substance

,results and

the emulsion breaks . Potassium soaps are better emulsifying

agents than sodium soaps,because their films are softer at room

temperatures .

Pickering made good emulsions of oil-in-water by using basic

copper sulfate as the emulsifying agent . Thus he rea soned that

oil globules, or drops, could be kept apart by small discrete part icles

of an insoluble substance . It is true in a few instances,but his

theory is not of general application . We give his experiment below .

Bancroft considers that a tough ela st ic film around ea ch oil drop

is necessary to stabili ty. He thinks that the good emulsifying

agents are those colloids that are concentrated at the liquid

liquid interface by strong adsorption . Froth concentration of a

dye,as ou tlined below,

throws light on this theory .

EMULSIONS 59

Exp. 98 . M ayonna ise .

—Beat the whole egg to a froth and then add

cottonseed oil (or olive oil) , a t first drop by drop and then a few cc . at a time,

up to 100 cc . Of course,the egg-beater or other stirring device is used a lmost

constantly . Now add 2 cc . Of strong vinegar,more oil up to 100 co. and fina lly

the rest of the vinegar . Sa lt (5 g . ) with other seasoning is added later inthe process . I f oil is steadily worked in until the tota l volume of Oil usedis 250 cc .

,a very good mayonna ise results . The yolk of egg may be used

as the emulsifying agent . M ore than 15 cc . of vinegar may interfere withthe proper consistency of the mayonna ise

,or make it “ cra ck ” because

the a cid dehydra tes some of the hydrated protein colloids (globulins) . But

more is often used to suit the taste of the cook .

Exp. 99. Ph armaceutica l Emul sions .— C osper (Jour . Ind . Eng . Chem .,9,

156,1917 ; ibid .

,9, 966, 1917) observes that some pharma cists, instead of

adding the oil last in their a cacia (gum arabic) emulsions, start out with a

nucleus,such as 4 parts Olive oil (cottonseed oil is cheaper) , 2 parts powdered

a ca cia and 3 pa rts wa ter . Th is is ground in a mortar until it takes ” toa cream and may then be diluted (grinding) with more oil or water . In someinstances it takes better after standing a few hours .

Exp . 100. Pickering ’ s Emul sions . —Churn 50 cc . of a petroleum distillateheavier than kerosene into a mixture of 134 cc . limewater and 1 g . CuSO4 5H20 ,

dissolved in as little water as possible,adding oil all at once . Here a plastic

film of separate,minute solid particles of basic copper sulfate covers ea ch

oil drop .

Read Jour . Chem . Soc .,91 , .

200 1 ( 1907) for further directions and comment .

Exp. 101 . Ad sorption Film s — Peptize a ir-dried cellulose nitrate ( 1 1 percent nitrogen) by a mixture of 1 part of amyl a cetate and 3parts of benzene,making it about a 2 per cent solution . Pour enough of th is into a sma llbeaker to give a layer nearly 1 cm . deep . With a pipette

,add a very large

drop,or globule

,of wa ter and watch it for a few minutes . A v isible film

quickly forms . Gently tilt the beaker and distort the drop by rolling itaround . Wrinkles in the film demonstrate its toughness and elasticity .

Th is film of cellulose nitrate has lowered the surfa ce tension of its solvent andthus concentrated at the interfa ce . Similar films m ay form in other instancesbut may la ck visibility because of an equa l ity of indices of refra ction of all

the substances present . This experiment supports Bancroft ’s theory,in th is

instance, at least . If it fa ils use much more benzene .

Froth Concentration of a Dye .-Another example of the con

centration of dissolved substances at surfaces is found.

in the

frothing of an aqueous solution of methyl violet . Here the interfa ce is between water and air. M iss Benson (Jour . Phys . Chem .

,

7 , 532, 1903) first demonstrated that such a froth of aqueous amyl

a lcohol showed a h igher concentration than did the solution

beneath ; but we give experimenta l details from Kenrick (Jour .Phys . Chem .

,16, 517,


Exp. 102.— Shake a solution of g . ofmethyl violet in 300 cc . ofwater

in a 1000 cc . separatory funnel . After a good froth is secured let stand aboutfour minutes . Dra in Off the clear liquid . In about four minutes longer

,the

foam in the funnel will subside to liquid . I f not,add a drop of ether to break

the froth . Dra in off 1 cc . and dilute with 20 cc . of wa ter . Also dilute 1 cc .

of the origina l solution with 20 cc . of water . Compare the two samples inin depth of color before the lantern . The solution prepared from the foamis darker than the other, thus showing a greater concentration of dye .

Concentration at the Interface .

— The following is quoted from a

pamphlet issued by the Sharples Specialty Co

When crude corn Oil is agitated with hot water a thick white

emulsion forms . When this emulsion is pa ssed through the

Sharples Super-Centrifuge at a moderate rate of flow,some of the

Oil separates and is discharged as a clear yellow oil . The rest of the

emulsion is discharged in a highly emulsified condition .

The oil separated in this way will not form a stable emulsion

when aga in agitated with hot wa ter,because the emulsifying agent

has been extracted . But when the discharged emulsion is broken

by any chemica l means the separated oil is ea sily emulsified again .

”

This seems to be a good illustration Of concentration of the

emulsifying agent at the oil-water interface .

A Compari son of Th eories— Harkins

,Davis and Clark (Jour .

Am . Chem . Soc .,39, think that the best emulsifying

agents have long molecules with a polar a ctive group at one end of

the molecule . (Polar groups such as COOR— COOH .) Langmuir

(Jour . Am . Chem . Soc .

,34, 1848 , 1917) believes that the organic

groups strike inward into the fatty globules,while the COOH,

SogH ,etc .

,are outside in the water phase . There is probably

no real clash between the solvated colloid idea and the suggestion

of adsorption films around drops of the dispersed liquid . If there

is not enough colloid to be uniformly distributed in the liquid that

peptized it,some Of the adsorption film will be peptized back into

the liquid . Doubt less the film is essential ; b ut its existence in the

right physica l condition depends upon the peptizing a ction

of the one liquid on the film . Solva ted colloids are the best

emulsifying agents .

Having studied the action of cellulose nitra te as an emulsifying

agent (Jour . Am . Chem . Soc . 44, 66, 1922) the author believes

that the ideal film for an emulsion must be one that forms readily

and comes quickly to an equilibrium between the peptizing


0 0 1, (at some definite tempera ture) until a drop released from a pipetteneither sinks nor rises in the soap water used . M ake an emulsion and it willnot cream .

Emulsions conta ining drops suffi ciently sma ll never cream . Homogenizedmilk illustrates this point .

WATER-IN-OIL EMULSIONS

The ordinary emulsions,and those previously discussed in this

chapter consist of drops of oil (meaning any liquid insoluble

in water) dispersed in water . All of these were made by the use ofa colloid emulsifying agent peptized by the water. Yet if a

colloid peptized by the oil and not by water is used,the pha ses

are reversed and the wa ter is dispersed in drops throughout the

oil. For example,the alka li soaps are more soluble in wa ter than

in oil,hence they always aid in formation of the usua l type of emul

sions,oil-in-water . On the other hand

,the soaps of the alka line

earths and heavy meta ls are generally more readily pept ized (hot)by oils than by water, and thus aid in the formation of the unusua l

and less stable type of emulsions . It may even be sa id that anysubstance more readily wetted by one liquid than by another

favors dispersion of the second liquid in the first . Clowes (Jour .

Phys . Chem .

,20, 407, 1916) considers that the determina t ion of

phase depends upon the convex or concave bending of the liquid

interface as influenced by surfa ce-tension lowering caused by the

emulsifying agent . Newman ’ s work with the oleates ofmagnesium

and calcium (Jour . Phys . Chem .,17, 501 , 1913) shows the influence

of the two classes of soaps .

When Nujol is shaken with water conta ining about 1 percent sodium oleate as the emulsifying agent

,the oil is dispersed

in the water . Al so,when a Nujol solut ion of a suitable emulsi

fying agent, such as magnesium oleate, is shaken with water, it is

the water that is dispersed in the oil. Newman (Jour. Phys .

Chem .

,18 , 40, 1914) observed that when mixtures of these two

soaps were present the emulsion was oil-in-water with an excess

of sodium oleate and water-in-oil with an excess of magnesium

oleate .

Exp. 106 . A Four-layer Emulsion .— Leon W . Pa rsons finds tha t when

a Nujol solution of ma gnesium olea te is shaken with an equa l volume ofwater conta ining an approxima tely equiva lent amount of sodium oleate

,and

EMULSIONS 63

allowed to stand, a four-layer emulsion results . The top layer is Nujol,and the bottom layer is water ; b ut between these there is a double layer, theupper part of wh ich is an emulsion (or cream) of water-in-oil, and th e lowerpart a cream of oil-in-water . These layers may be removed with a pipetteand examined by the usua l tests .

Glycerol and wa ter are cla ssed together as regards their

insolubility in most other liquids ; so by the phrase water-in

oil we may really mean glycerol-in-oil. Cellulose nitrate is

readily pept ized by a number of liquids in which glycerol is insolu

ble,and hence aids in the format ion of water-in-oil.”

Exp. 107 .—To a 2 per cent solution of cellulose nitrate in amyl a ceta te , add

glycerol in sma ll portions with much shaking . An excellent creamy emul sionresults . The glycerol is dispersed in drops .M ake an emulsion of water-in-toluene by shaking water with a 2 per cent

solution of raw crepe rubber in toluene .

Exp . 108 . How to Recognize Emul sion Types — Heat powdered rosin ina heavy minera l oil until nearly 1 per cent has dissolved . Grind (or beat )water into th is . Is it an emulsion of Oil-in-water (th e usua l type) or waterin-oil"

Test th is by attempting to dilute portions'

with water ; with oil . Additionof the continuous phase gives ready mixing . M ixing does not occur if thedispersed phase is added in excess . Or put a little emulsion on a gla ss plateand add one drop of either pha se . Wh ichever one spreads must be identica lwith the continuous phase .

A minute fragment of a fa t-soluble dye, such as Sudan III or Scarlet R,

gives a spreading color in an emulsion of water-in—o il b ut not in the othertype . Try all these tests on some of your emulsions . Oil-in—water is a

better conductor of hea t and electricity than water-in-oil . Why"Exp . 109. A Lubricating Grea se .

— To 100 cc . of some heavy petroleum fraction add 20 g . of dry ca lcium oleate . Heat to 200 ° or h igher

,until th e soap

dissolves . Now cool with constant stirring,and as soon as the temperature

fa lls below 100°

add 5 cc . of wa ter,continuing the stirring until the mixture

is cold . An emuls ion of water-in—oil is obta ined,with a smooth

,sa lve-l ike

structure suited for cup lubrica tion .

Ra pe oil may be saponified with lime to furnish a good soap for th e grea se .

Aluminum oleate is often used and a sma ll amount of a sodium soap added toth e other soap .

Transparent Emulsions — Usua lly,when two transpa rent

liquids are emulsified,a milky-white mixture results . Kerosene

shaken with wa ter gives such an emulsion ; yet transparent

emulsions can readily b e prepared . Transparency depends uponthe relative indices of refra c tion of the two liquid phases . Ifboth pha ses have the same refractive index there will be neither


reflection nor refraction,and the system will appear homogeneous

and entirely transparent .

Exp. 1 10.— M ake a 2—4 per cent solution of dry ca lcium oleate in carbon

tetra ch loride (warming) . D isperse glycerol in this by shaking . A goodtransparent emulsion is possible .

Shake a solution of 2 per cent raw crepe rubber in Nujol with an equa lvolume of glycerol . What typ e is th is"

Exp. 1 1 1 .— Chromatic Emul sions (Holmes and Cameron, Jour. Am . Chem .

Soc . 44, 71 ,— Shake 4 volumes of gycerol with 4 volumes of a 2-3 per

cent solution of dry cellulose nitra te (1 1 per cent nitrogen) in amyl a cetate .

Add 10 volumes of benzene with shaking ; then more glycerol, until ratherviscous ; then still more benzene in small additions, shaking, until colorappears . The whole chromatic

,

” sca le of colors may be secured by the addition of increasing amounts of benzene . The colors reappear in reverse orderon the addition of more amyl a cetate . Tempera ture changes change thecolors . Such an emulsion is viewed best if a 125 cc . Oil specimen bottle isused as a conta iner and h eld some distance from the source of light . Asingle source is best

,as one window in a room or a Single strong light a t nigh t .

On long standing these emulsions cream downwards, a lthough vigorous

shaking restores much of their beauty . The cream often sets to a rea l j elly .

To secure such structura l color emulsions it is necessary to have twomutua lly soluble liquids for the continuous pha se, one of them of h igh refrac

tive index and h igh dispersive power (as a prism disperses ligh t) . On carefuladdition of th is liqu id to a milky emul sion a lready prepared

,it is possible to

change gradua lly both the refra ctive index and th e dispersive power . Th isinsures th e chromatic range of colors . Carbon disulfide may be used insteadof benzene, rubber for the cellulose nitrate] and water solutions for th e

glycerol . Any constituent may be varied .

If carbon disulfide be used instead of benzene th e emulsions are morebeautiful and do not cream so soon . A much sma ller volume of carbondisulfide than of benzene is used in bringing out the colors .

CHAPTER X

VI SCOSITY

THE Ostwald viscometer is a suitable instrument for laboratory

mea surem ent of viscosit ies . It consists of a U-shaped tube with

a sm all bulb emptying into a capillary for one arm and a much

wider tube for the other arm . For ordinary viscosities the bulb

should hold 2—3 cc . The capillary Should have

a diameter of about mm . and a length

of about 6 cm . The rema ining sect ions Of the

tube in the cap illary arm should have a diam

eter of about 4— 5 mm .

Since viscosity changes with the tempera ture,the viscometer should be read in a thermosta t .

Of course absolute cleanliness of the capillary

is essent ia l . The tube should be trea ted with

warm chromic a cid solut ion,rinsed with water,

a lcohol and ether and dried with a current of

warm air which has been freed from dust by

passing through glass wool .

The liquid to be measured is pipetted into

the larger arm and then carefully drawn above

the bulb . As it falls (viscometer quite vert i

ca l) the stop wa tch is sta rted as the liquid

pa sses the upper mark and is stopped as itF I G . 16 .

— Ostwa ldpasses the lower mark . viscometer .

A simple 5 cc . pipet te with a tip drawn out

sufficiently small may be used for rough comparative work, and

the time of outflow taken as a mea sure of viscosity. Even the

t ime of fa ll of steel bicycle ba lls in viscous media may serve

where only approxima te results are wanted .

A very good commercia l viscom eter,now much used

,is the

Improved M a cM ichael instrument . It operates on the principleofmeasuring by the angular torque of a standardized wire

,the force

65


required to cause two surfaces,1 cm . apart, to move past each

other at the rate of 1 cm . per second, overcoming the interna l

friction of the liquid aga inst itself throughout the spa ce between

the surfa ces,a film of liquid moving with each surface and the

layers of liquid between shearing past each other .

Bingham ’s new viscometer gives excellent results .

Viscosity of G elatin .

— Davis, Oakes and Browne (Jour . Am .

Chem . Soc .,43, 1526, 1921) show how the viscosity of gelatin

solutions is influenced by age of the solution,concentration

,

temperature Of preparation and chara cter of the gelatin . They

report a maximum viscosity at an age of twenty-four hours .

Hydrolysis of gelatin by OH “ is quite marked . Bacteria l decom

position has a strong influence . A good gelatin,after boiling a

few minutes,is no better than a poor grade . It was their pra ct ice

to bring all solutions to 75°

for concordant results . Hydrolysis

was usua lly slow at that temperature . Their directions for a

measurement follow .

Exp . 1 12 .

—Bring the gelatin and wa ter (with a cid or base if desired )to 75 ° in twenty minutes

,stirring frequently . Filter through glass wool and

place in a thermostat a t Pipette 5 cc . into an Ostwa ld viscometer andimmerse in the thermostat for ten minutes . Draw the solution into the bulbof th e viscometer and make the run wh ile in the thermostat

,timing the flow

with the stop-watch . The density is determined with a pycnometer . The

viscosity coefficient is ca lculated a ccording to the customary formula .

N (gela tin) =Ntime in for gel . solution

Flow time in see . for waterX density water

N for water is taken as absolute unit .M easure the viscosities of per cent gelatin aged 5

,30

,60 and 120 minutes

(or longer) and plot th e curve .

Exp . 1 13. Viscosity Ch ange of Benzopurpurin with Age .— M easure

rough ly with a pipette the time change in viscosity of a per cent solutionof benzopurpurin at Plot age of the solution in minutes aga inst time ofoutflow in seconds .

Exp . 1 14. Effect of Concentration upon th e Viscosity of an Emul sion .

Using any convenient oil, prepare 5, 10, 20 and 30 per cent emulsions of oilin 3per cent aqueous gum arabic . Plot viscosity aga inst concentration of theoil. Note the similarity to solvated colloids in th is respect .

Exp . 1 15. Viscosity of Soap at Difi erent Concentrations — With a pipette,make rough mea surements a t 20° of the viscosities of N

,N

,N

and N solutions of pota ss ium oleate (or sodium oleate) . Plot time of

flow in seconds aga inst concentration . Th is curve is typica l of the solvated

VISCOSITY 67

Fischer ’s diagrams Soaps and Proteins,70

,throw light

on viscosity studies .

Ha tschek sta tes tha t if suspended part icles do not rest on ea chother the viscosity-concentra tion curve is a stra igh t line .

Wo . Ostwa ld believes that,other conditions being constant a

dispersoid reaches its highest viscosity at a medium degree of

dispersion . Jerome Alexander (Jour . Am . Chem . Soc .

,43, 434,

1921) enlarges upon this view with his discussion of the zone of

maximum colloidality .

” He sta tes that clays hold increa sing

amounts of water as their particles become sma ller . In tha t

event the particles must a ct as liquids rather than as solids .

Bingham ’s work on viscous and pla stic flow is published in

book form by the M cGraw-Hill Book Co . and is worth reading .

He makes the interesting distinction that a viscous liquid will

Pressure Pre ssureF IG . 17 .

— Viscous flow . F I G . 18 .

— Plastic flow .

start to flow , no ma tter how sma ll a pressure is applied,while

with pla stic materials no flow takes place until after the pressure

has exceeded a certa in definite yield va lue . Plast ic sub

stances he classifies as solids ; and he insists tha t pa ints are not

viscous liquids but highly mobile plastic solids . Even a veryviscous substance, such as pit-ch , flows, under a very slight pressure,like water or any fluid .

Bingham sta tes that the melt ing point of gelatin and other gels

is the point where viscous flow changes to plastic flow . This

suggests possible experiments with solvated colloids .Bingham ’s elaborate but a ccurate viscometer and pla stometer

are now on the market .The falling-sphere viscometer was used to mea sure the V iscosi ty

of cellulose nitra te solutions by Gibson and Ja cobs (Jour . Chem .

Soc . 1 17, 472, 1920) and by Gibson , Spencer and M cCall (Jour .

Chem . Soc . 1 17 , 484,

CHAPTER X I

ADSORPTION FROM SOLUTION

IT seems that every solid surfa ce has an attraction for other

substances,greater for some than for others . This holding to a

surface we call adsorption,and we differentiate it from chemical

rea ction or solid solution . It may be due to free valence of the

surface atoms ; but, whatever it is, we are able to measure it and

study it . Some solids have far greater adsorbing power than

o thers,and a given adsorbent shows preferential adsorption .

”

Of course,the finer a solid is

,the greater

.its surfa ce area and the

grea ter its adsorbing effect per gram . Bone char is used to adsorb

coloring matter from sugar solutions in refineries,fabrics adsorb

dyes (in many instances) , and most precipitates adsorb ions fromsolution . When glues adhere to a solid they must be power

fully adsorbed . Adsorption may be considered a concentra

tion of dissolved or dispersed substance upon the solid or liquid

or ga seous adsorbing surface . After concentrating there the

adsorbed substance may rea ct or polymerize or dissolve or be

coagula ted or it may crystallize slowly .

Exp . 1 16 . Adsorption of Glue .

— Dissolve 10 g . of dry glue in 30 cc . ofhot water . Pour it into a 100 cc . beaker and set aside for a week or more todry . As the glue contra cts it pulls in the wa lls of the beaker, so powerfullydoes it adsorb the glass .

Exp. 1 17 .— Filter nigh t blue

.

sol through a 15 cm . layer of precipitatedand oven-dried silica . Use a tube 1 or 2 cm . in diameter . Th is suggests theuse of sand filters in adsorbing ba cteria from water .

Exp . 1 18 .—Shake crysta l violet (or other dyes) , 2 mg . to 100 cc . ofwater,

with 2 g . of powdered charcoa l (blood charcoa l is excellent) or fullers’earth .

Is the solution colorless after settling" Pour off the liquid and add a lcohol ora cetone to th e mud . What about th e equilibrium concentration in th e twoca ses"

Exp. 1 19. Spring’s Soap Cleansing Experiment.— Wa sh anima l carbon

with a lcohol and ether (to remove grease) . Dry. Rub th e carbon on the

outside of a folded filter,shaking off all loose materia l . Rub a lso on the

inside of another filter . Pour water through ea ch . Repeat with 1 per cent

68


Exp. 124. Adsorption of an Indicator.— Shake finely powdered orthoclase(or other similar rock powder) with wa ter to wh ich has been added a very littlephenolph tha lein . A fa ilure to develop pink color does not mean an absenceof a lkalinity . Decant the clear solution after complete settling of the rockpowder and add to the solution more ph enolph tha lein . A distinct pink colorappears . Now add a little more rock powder to th is pink solution and the

color disappears .

Clarke showed the a lka linity of water in which rock powders

have been in suspension (Bull . 167, U . S . Geol Survey,156

,

Yet some powdered rocks in aqueous suspension show no red color

with ph enolphthalein . Of course,this is due to the adsorption of

the color by the powder . Therefore,the test of alka linity of a solu

tion by phenolphthalein cannot properly be made if there are

present in suspension finely divided pa rt icles whi ch have the power

of adsorbing the indicator .

Hulett and Duschak (Zeit . anorg . Chem .,40, 196, 1904) have

investigated the nature of barium sulfa te precipitates,which are

nearly always found to weigh too much,and attribute the

results observed by them to the formation of a compound,

BaCl-HSO4 . On long standing or heating of the precipitate,

hydrochloric acidwas given off— wh ich indicates that hydrochloricacid was adsorbed on the surfa ce of the precipitate and escaped

when the area of surfa ce was reduced . Barium sulfate has been

found to adsorb many compounds from solution . Vanino and

Ha rtl (Ber . , 37, 3620, 1904) observed that this precipita te adsorbs

colloidal meta ls from solut ion . Patten (Jour . Am . Chem . Soc .

,

25, 186, 1903) found that barium sulfate adsorbs salts of nickel,coba lt

,chromium

,iron and manganese .

Exp. 125. Coarse and Fine Powders — Fink (Jour . Phys . Chem .,21

, 32,

1917 ) and Briggs (ibid .,22

,2 16

,1918 ) point out tha t fine powders adhere to

coarser particles when mixed . A coarse red powder mixed with a very finewh ite powder looks wh ite . Also

,a fine red powder mixed with a coarse wh ite

powder looks red . Obviously, this interests the man wish ing to use cheapfillers in commercia l products .M ix about g . of dry Prussian blue with 10 g . of dolomite (or some

convenient wh ite powder) that pa sses a 40-mesh sieve b ut not a 100-meshsieve . Wha t is the genera l color effect" Now mix the same weights

,b ut use

dolomite that passes a 200-mesh sieve . Expla in the difference . Rouge or

larnpb la ck may be substituted for the Prussian blue .

I n a somewha t similar fash ion , larger particles settling in a coarse sus

pension drag down the sma ller particles with them .

ADSORPTION FROM SOLUTION 71

Exp . 126. Adsorption of Alka loids by Lloyd ’

s Reagent.— Dissolve 1 g.

of quinine bisulfate in 80 cc . of wa ter and add g . of Lloyd ’s reagent (ahydrous a luminum sil icate prepared from fullers ’ earth ) . Shake well andfilter . Test the filtrate for quinine by M ayer ’s test or any of the usua l tests .Expla in the result . Now wash well with water, dry and extra ct the powderwith fra ctions of 100 cc . ammonia ca l ch loroform . Test the ch loroform extra ctfor quinine . Draw conclusions . We are indebted to . John Uri Lloyd of

Cincinnati for th is experiment .Exp . 127 . Use of Fullers ’ Earth in Adsorption Filtration .

— Fill twotubes

,one conta ining ful lers ’ earth previously heated to 300 °

and the oth erconta ining fullers ’ earth hea ted to red heat , with a heavy

,dark

,cylinder oil

wh ich has been warmed to 100 °

C .,providing tubes with exit stopcocks or

clamps . Allow to stand overnigh t ; then run off effluent oil and note fina lcolor .

Exp. 128 . Water R ings and Capillary Spread .

— M ake a dilute solutionof copper sulfate and cadmium sulfate . Add ammonia until alka line

,and

dilute until the blue color is scarcely visible . Let severa l drops fa l l on thecenter of a piece of fil ter paper and hold thepaper over the mouth of a bottleof ammonium sulfide . Three rings appear— an outer water ring

,a yellow

ring of cadmium sulfide and a centra l bla ck ring of mixed copper sulfide andcadmium sulfide .

The copper sa lt is most strongly adsorbed by the paper and hence diffusedonly a short d istance ; wh ile the cadmium sa lt diffuses farther because it isless strongly adsorbed by th e paper .Th is method has been used for the ana lytica l separation of copper and

cadmium . Ba iley found that with increasing dilution the amount of separation became greater .

CAPILLARY RISE OF DYES

References : Pelet-Jolivet in Koll .-Zeit, 5, 238 ( 1909 ) Chem . Abs ., 3,

839 4, 829

Exp . 129 .— The capillary rise of dye solutions

,on strips of l inen

,wool or

silk,shows that capillarity is least when the dye is fixed directly by the ma teria l .Dye bases rise less than dye a cids . With methylene b lue

, addition of an

a cid increases the capillary rise of th e dye and addition of a base decreases it .Try th is and compare with ponceau .

Does increased depth of immersion in th e dye solution affect the rise"Try both methylene blue and crysta l violet .

What is the influence of concentration on rise of color" Learn by experi

ment if capillary rise occurs when the dye is dissolved in a cetone,a lcohol or

other non-aqueous solvents .There is evidently a close relation between capillarity and the electric

charge on particles .Exp. 130.

— Capillary rise of dyes in strips of filter paper increases as

adsorption of the dye decreases . Basic dyes are strongly adsorbed ; therefore direct dyes show weak capillarity

, increasing with the concentration of


the dye . Acid dyes exhibit strong capillarity,not increased by concentra

tion .

Positive colloids are like the basic dyes in strong adsorption and weakcapillarity . Try severa l . To one of these colloida l suspensions add lessthan enough hydroch loric a cid to coagulate it

,and note the change in rise .

To a portion of the same suspension add sodium hydroxide,and measure the

cha nge in capillarity. (Molybdenum blue is a negative colloid wh ile methylene blue is a positive colloid only in strongly a lka line solution .

Exp .—Sahlb om (Kolloidchem .

,Beihefte 2

, 79, 1910) followed the

membrane hydrolysis of aqueous solutions of ferric ch loride by noting thecapillary rise of dia lyzing solution after dia lysis had continued for twentyfour hours

,two days

,three days

,etc . The molecularly dispersed ferric ch loride

rose h igh in a strip of filter paper ; but as colloida l ferric hydroxide formed onprolonged dia lysis

,the rise of iron compounds decreased as shown by color .

Such a positive colloid would,of course

,be discharged and coagulated by the

negative fil ter paper .Represent graph ica lly th is difference in capil lary rise in the paper strips .Exp . 132 .

— Hang strips of filter paper in colloida l ferric hydroxide and incolloida l Prussian blue . Expla in th e difference in rise . Remember thatPrussian blue is a nega tive colloid and that the charge on paper in water isnegative .

It has been urged byWo . Ostwa ld that th is capil lary rise method should beused as a method of determining the sign of the electric charge on colloidparticles . Thoma s and Garard, in a paper well worth reading (Jour .

.

Am .

Chem . Soc .

,40, 101 , 1918 ) take issue with Ostwa ld . They contend th at the

heigh t of rise is Wholly a matter of concentra tion, presence of electrolytes, theatmosph eric conditions and the nature of the paper .

H . B . Weiser sta te s that electrolytes with anions that arenotreadily adsorbed precipita te the positively charged colloids in

h igh concentration and the precipitates are readily reconverted

to the colloida l state by washing on account of the ease with

wh i ch the precipitating electrolytes are removed . Electrolytes

with readily adsorbed anions precipita te in low concentra t ion and

th is precipitation is irreversible since the strongly adsorbed anions

are not readily removed by washing .

Th e Adsorption Isotherm .

— Freundlich has stated that the

quantitative adsorption of dissolved substances in relation to the

end concentration can be expressed by the formula

where x is the amount adsorbed by one gram of the adsorbing

material C is the end or equilibrium concentration in the liquid

ADSORPTION FROM SOLUTION 73

after adsorption,and a and n are constants depending on the

nature of the solution and adsorbent .

The va lue of Freundlich states,va ries from to

while a varies much more . The amount of adsorpt ion by a given

substance varies with the solvent, as shown by the fa ct tha t certa in

dyes powerfully adsorbed by gla ss from wa ter solution may not

be wa shed off completely by water,while alcohol quickly cleans

the gla ss .

When we plot 51: against C,tha t is

,adsorption aga inst the

equilibrium concentration,the curve becom es a parabola (or

FI G . 19.

— Adsorption isotherm .

approximately so) . The logarithm of the equa t ion should plot as astra ight line, but in pra ctice it usually misses th is ideal somewhat .In some instances the solvent is adsorbed as well as the solute

,

and th is complicates ma tters . Adsorption is proportiona lly

greater from very dilute solut ions than from more concentrated

solutions,which is certa inly not true of rea ctions .

Exp . 133.— Freundlich (Zeit . phys . Ch em .

,57, 385, 1906) states that if

1 g . of charcoa l or other adsorbent carbon be shaken twenty minutes by handthe system approa ch es the same equilibrium as that rea ched after twentyone hours ’ shaking . Q uick surfa ce adsorption is the ma in fa ctor

,not slow

diffusion into the interior of pa rticles .Shake 1 g . of blood carbon with 100 cc . of N a cetic a cid for six minutes

(using a 300 cc . Erlenmeyer flask) . Let settle overnight and remove a convenient fraction w ith a pipette . Titra te with a standard base and record thea cid concentra tion as C. Try similar experiments with a series of differentconcentrations, such as N,

N, N

,N

,1 N

,2 N

,etc .


Plot 2: against C. I f the curve is noth ing like a parabola, use more dilute or

more concentrated solutions to extend the curve .

Since oxalic acid is adsorbed by charcoa l and is easily titrated

In very dilute solution by potassium permanganate,an exper iment

can be managed very well in much the same way as with acetic

acid . The solutions of oxa li c acid should vary from per cent

to 3 per cent,and

“

extremely dilute potassium permang anate

solut ion should be used in titration .

Concentration

F I G . 20 .

— Curves for adsorption, reaction and solid solution .

Wa lker and Appleya rd (Jour . Chem . Soc .,69, 1336, 1896)

outline a very good experiment on the adsorption of picric a cid

by silk . It is best to heat the silk in the ba th only to as it

becomes tender after a few hours at

In the same paper,Walker and Appleyard report an interesting

experiment w ith picric acid and diphenylamine to show the dif

ference between an adsorption curve and a reaction curve .

CHAPTER X I I

ADSORPTION OF GASES

FIR ST read the chapters on Adsorption in Bancroft ’s

Applied Colloid Chemistry .

”

The tenacity with which gla ss vessels reta in a film of air when

evacuated,even at elevated temperatures

,shows us that a layer

of gas molecules may be powerfully adsorbed by solid surfaces .

Fine powders surge when poured,and run a lmost like water

if heated . Ea ch solid particle is cush ioned on a film of air . We

have all not iced that phosphorus pentoxide smoke ” may pass

through water,an a stounding fact . In this case a strongly ad

sorbed film of air interferes with conta ct between the pentoxide

and the water .

Carbon black, states Cabot , may occupy only 5 per cent of

its own apparent volume,the rest being adsorbed air

,and air

free to move between particles .

Exp. 134.— Find the density of quartz (or any suitable solid) and then

weigh 100 cc . of the same solid in finely powdered form . Ca lculate th evolume of a ir present in the 100 cc .To be exa ct

,a ir is compressed by adsorption . Bancroft suggests a good

experiment to demonstrate th is .Exp. 135.

— Fill a 50 cc . vessel with cocoanut charcoa l and add water .Catch the air displa ced by the water . It m ay amount to 150—200 cc .

An excellent discussion of adsorption by cocoanut charcoa l in

gas masks is found in the report by Lamb , Chaney and Wilson,

Jour . Ind . Eng . Chem .

,1 1

,420 They state that 1 cc . of

war charcoa l has a surfa ce of 1000 square meters .

Langmuir ’ s oriented adsorption theory is widely a ccepted .

Particular groups in a compound m ay be strongly adsorbed by

particular solid surfac es , thus placing the adsorbed molecules in

a regularly arranged layer .


ADSORPTION BY SILICA GEL ‘

Exp . 136 . Preparation of th e Ge1.— According to United States Patenta h igh ly adsorbent gel is secured after mixing (with constant stirring)

hot solutions of hydroch loric a cid conta ining 10 per cent of the gas byweigh t and an equa l volume of sodium silicate of about specific gravity .

Th is mixture sets to a gel in about one hour. The gel is broken into sma llpieces and washed free from a cid and sa lt . Hot wash wa ter hastens the process . It is essentia l that the wa ter be removed slowly in the drying opera tion .

The gel is first dried in a stream of air a t 75° to The tempera ture is

then slowly increased up toThe fina l product is a hard, transparent substance resembling gla ss in

appearance .

Propertie s of Silica Gel

Chemically,silica gel is a hydrated form of pure silica and is

accordingly extremely resistant to most reagents . The material

as shipped from the factory conta ins approximately 18 per cent

water by weight . The wa ter content is not fixed,since on exposure

to air at ordinary temperatures, it will either take up or give off

water,depending upon the water content of the gel and the

humidity Of the air.

Physically, it is a hard, semi-transparent glassy substance .

Its hardness on the minera l sca le is about 5,and it undergoes

but little abrasion with ordinary handling . It is capable of use

either in powdered or granular form . The materia l as furnished

to the trade does not undergo any volume change with variation

in water content or when used to adsorb gases and vapors .

The paragraphs which follow are written with particular

reference to the use of granular gel, the size of granules ranging

from 8 to 14 mesh .

Activation

The gel,as furnished to customers

,must be activated before

use . This may be readily accomplished by heating to a modera te

tempera ture in a stream of air for a few hours . For the activation

of small quantities of gel (200 grams or less) , a satisfactory pro

cedure is as follows

Exp. 137 .— Pla ce th e gel in a tube not more than inch es in diameter,

bent as shown in Fig . 1,immerse th e tube in an oil bath at 150

° C . and pass

1 Adapted from bulletins issued by the Silica Gel Corpora tion ofBa ltimore .


at various temperatures,the relation between the quantity of

sulfur dioxide adsorbed and the partia l pressure or concentration

of sulfur dioxide gas in the space surrounding the gel .

A statement of three general principles will help in the under

standing of these curves

1 . The process of adsorption of a gas or vapor in silica gel is a

reversible one .

2 . Silica gel containing a definite amount of adsorbed gas or

vapor at a given tempera ture will be in equilibrium with respect

to a particular concentration of this gas or vapor in the spa ce

surrounding the gel .

3. The system made up of silica gel and gas (or vapor) havingrea ch ed equilibrium at a particular temperature and concentra tion

,

this equilibrium will be disturbed by any change, either in tempera

ture or in the concentra tion of the gas (or vapor) in the spa ce

surrounding the gel,and the gel will in consequence either liberate

some of its adsorbed materia l or take up more . The accompany

ing curves indicate clearly the direction which such change will

take .

If,for example

,we pass over the gel at 100

°

C .,a mixture of

sulfur dioxide and air conta ining 4 per cent of the former by

volume,adsorption will stop when the gel has taken up about

per cent of its weight of sulfur dioxide . After this amount has

been adsorbed,the gas emerging from the gel chamber will have

the same amount of sulfur dioxide as that entering the gel chamber .

In other words,at 100

°

C .

, gel containing per cent of its

weight of adsorbed sulfur dioxide will be in equilibrium with

respect to a mixture of th is gas and air conta ining 4 per cent by

volume of the former . I f, however, we work at 40

°

C .,the

equilibrium point is reach ed only when the gel has adsorbed about

per cent of its own weight of sulfur dioxide . At 30°

C . the

equilibrium point is reached at 5 per cent adsorption, and at

0°

C . at 14 per cent adsorption .

These curves also make clear to what extent the quantity of

sulfur dioxide taken up by the gel is a function of the concentration

of sulfur dioxide in the space surrounding the gel .

The effect of temperature is shown by the following : From a

mixture of sulfur dioxide and air, containing 4 per cent by volume

of sulfur dioxide (part ial pressure about 30 the gel takes up

4 per cent , 6 per cent , per cent and per cent sulfur dioxide

ADSORPTION OF GASES

Partia l Pre ssure s-Mill imeters

Percent Concentra tion of Entering Gases

F I G . 21 .

— Adsorption of SO) .

79


by weight at 20°

and respectively . The effect Of

concentration may be illustrated by the following : At 30°

the

gel takes up per cent,6 per cent

, per cent and 8 per cent

by weight of sulfur dioxide from mixtures conta ining 1 per cent,

4 per cent,6 per cent and 8 per cent, respectively.

Since adsorption is a reversible process,it is clear that

,having

saturated the gel at a given temperature with respect to a particula r

concentration Of sulfur dioxide,and keeping the tempe rature con

stant,if we reduce the concentration of gas in the spa ce surround

ing the gel the latter will . give up its adsorbed materia l till a new

condition of equilibrium is established with reference to the

a ltered concentration . If at the same time we ra ise the tempera

ture,the new equilibrium is rea ched more quickly and

,at equilib

rium, the gel will have less adsorbed materia l than at the lower

tempera ture .

In pra ctice,for the recovery of material which has been

adsorbed in the gel at a comparatively low temperature,we do

both ; that is, we raise the temperature and reduce the partial

pressure or concentration of the gas or vapor in the space surround

ing the gel .

Working tempera tures— I t will be clear from the curves tha t

,

for adsorption,the lower the temperature the better . In practice

we genera lly adsorb at room temperature . For libera t ion of

adsorbed materia l we work at temperatures ranging from 100°

C .

to 150°

C .

,depending on the volatility of the substance in question .

For the liberation of such liquids as ether,ethyl and methyl

a lcohols,benzene and water

,1 10

°

to 125°

C . is ample . For

high-boiling liquids,correspondingly high temperatures are re

quired .

We may reduce the concentration of the gas or'

vapor in the

space surrounding the gel in either of two ways :

1 . By pa ssing through the gel bed a stream of pure air,steam

or other vapor .

2 . By exhausting the vessel conta ining the gel .

By either of these methods we may bring about rapid liberation

of adsorbed materia l at the temperatures given above .

It has been found that liquids of high boiling point are more

strong ly adsorbed than vapors from a liquid of low boiling point .

Furthermore,

adsorption decreases with rise in temperature .

Also,the greater the partia l pressure of vapor being adsorbed , the

ADSORPTION OF GASES 8 1

greater is the extent of the adsorption . All these facts suggest the

idea of condensation of the vapor in the adsorbent .

All adsorbents are porous, with a large internal volume com

posed Of exceedingly fine pores . Since a liquid in a sma ll tube

(capillary) possesses a lower vapor pressure than the norma l vapor

pressure,it must be easier to condense a vapor into a sma ll capillary

than on to a level surfa ce .

Silica gel is used successfully at ordinary temperatures and

under atmospheric pressure to remove from air the vapors of any

liquid mix ed with air in any proportions, provided the liquid boils,under atmospheric pressure, above 10

°

Apparatus and M ethod of Work

ADSORPTION

The apparatus required for a laboratory study of adsorption,

by silica gel,of ga ses and vapors when mixed with air or other

permanent gas consists essentia lly of the following :

1 . M eans of a ccura tely measuring and controlling gas volumes

passing through the apparatus tra in .

2 . M eans of mixing air and vapors in any desired proportions .

3. The adsorption appara tus proper .

4 . M eans of ana lysis of the gas mixture before and after it

pa sses through the absorber .

For measuring the volumes of air or other non-corroding gas,we may use an ordinary gas meter . For a ccura cy

,ease of control

and convenience,the type of flowmeter and a ccessories employed

by the Research Division of The Chemica l Warfare Service is

recommended . Th is appara tus has been fully described in a

number of places,and a brief description of certa in adaptations

made by the Davison Chemica l Company will suffice for our

present purpose .

The essentials of an air flowmeter, with means of control and

ca libration,are illustrated in Fig . 22 . Air enters at A under a

pressure sligh tly greater than the head of water in F,and con

sequently a portion of it goes to waste through 0 . The balance,

which is to be metered,passes through the stopcock K to the

flowmeter,consisting essentia lly of a capillary tube D spanning

the two ends of a U containing water or other liquid . The


pressure drop through the capillary is indicated by the difference

in level of the liquid in the two arms of the U. The pressure in

G'

,and consequently the pressure drop through D, is regulated

by the stop cock K . The pressure on the left side of K should be

slightly greater than the desired flowmeter differential . This

pressure may be regulated by adjusting the head of water in F

and,to a certain extent

,by varying the volume of air going to

waste through C. The head of water in F may be regulated by

Air— a,

Flowmeter

F I G . 22 .

— Pressure regula tor .

raising or lowering the adjustable tube B or,more conveniently

,

by means of an adjustable reservoirJ. The flowmeter differential

should not be less than 10 cm . for the smallest volume of gas to be

metered .

Fig. 22 also illustrates a convenient method of ca librating a

flowmeter. The ca libration consists in determining the relation

between pressure drop and volume of gas passing through the

fiowmeter in unit time. If we mainta in a constant pressure in G,

as may be readily done by means of the arrangement shown,and

draw off water at H at such a rate that the levels of liquid in the

two limbs of the manometer I remain always the same, the air

ADSORPTION OF GASES 83

will have passed through the flowmeter at a uniform rate and its

total volume will be equa l to the volume of water drawn off.

In this way we a scerta in the volum e of air, in cubic centimeters

per minute,wh ich will pa ss through the flowmeter w ith the

particular pressure differentia l employed , and we have one pointon the calibration curve . By ra ising or lowering the adjustable

tube B or the reservoir J,we can alter the pressure in G at will

,

and so determine as many points on the ca libra t ion curve as‘

desired .

A flowmeter calibrated as above may be used as a standard in

calibrating other flowmeters of approximately the same capacity .

Silica gel

C D E P

Benz eneif desired

for d ilution

F I G . 23.

— Gas adsorption tra in .

The method described above is also applicable in ca librating

flowmeters for gases other than air,provided a liquid is used in

which the gas in quest ion is only slightly soluble . For ca librating

a flowmeter for sma ll volum es (1 to 10 cc . per minute) of such a

gas as sulfur dioxide, for example, ana lysis is preferable to themethod described above .

The capa city of the flowmeter will,of course

,depend on the

size and length of the capillary D and th e height of the U-tube E .

Fig . 23 gives the essentia l fea tures of an apparatus for studyingthe adsorption of the vapor of a volatile liquid . A certa in

definite and constant volume of air per minute,dried at N and

metered through B , is saturated at a desired temperature with

vapor by being bubbled successively through at lea st three bottles,


C,D and E, containing the liquid whose vapor is to be adsorbed .

The liquid in the saturators must, of course, be kept at a constant

temperature by means of a properly regulated bath . A fourth

bottle,P

,should be loosely pa cked with glass wool to prevent

liquid spray from being carried over . The mixture of air and vapor

thus obtained pa sses into the mixer F,where it may or may not be

diluted by mixing with a known volume Of fresh air,metered

separately and admitted at M . The gas mixture thus obta ined

passes from F to the absorberK . The three-way stopcocks,0 and L,

permit the taking of samples for ana lysis . The air admit ted at M

may be dried,or any desired amount of moisture may be intro

duced at this point . It is clear that by varying the temperature

of the bath H ,the relative volumes of air admitted through B

and ill,and the humidity of the air admit ted at M

,we can

,in a

V ery simple way, study adsorpt ion in K under a wide variety of

conditions .

This arrangement of the appara tus is intended for use when

the air is saturated with vapor at a temperature below that of the

room . If it is desired to saturate the air above room temperature,

the mixer F should be pla ced in the same ba th with the saturators

C,D and E’

,and all connections submerged beneath the surfa ce

of the liquid in the bath .

For a study of the adsorption, by silica gel, of gases, instead of

vapors Of liquids,mixed with air, the air and the gas in question

are metered separately in the desired proportions, mixed in a bottle

or a vessel similar to F (Fig . 23) and are passed through the gel as

before . Provision must,of course

,be made for analysis Of the

mixture before and after it passes through the absorber.

RELAT ION BETW EEN WE IGHT OF GEL AND VOLUME OF GAs

The relation between the weight of gel in the absorber and the

volume of gas passing per minute is, of course, subj ect to variation .

We express this relation in terms of cubic centimeters per minute

per gram of gel . M ost of the work on which this discussion is

based has been carried out with rates of gas flow ranging between

40 cc . and 100 cc . per m inute per gram of gel . If granular gel is

used,and the particles range in size from 8 to 14 mesh , a practical

rate for adsorption in genera l is 50 cc . per minute per gram Of gel .


the thermostat, and passing through the gel at a given temperature

a definite mixture of sulfur dioxide and air . The air and sulfur

dioxide are metered separately through carefully calibrated flow

meters similar to those used by the Chemical Warfare Service,

passing first into a mixing chamber and thence over the gel .

Under these conditions the gel adsorbs the sulfur dioxide com

pletely for a certain period . At theend Of th is period a trace ofgas begins

to come through,the percentage of

sulfur dioxide in the exit gas increas

ing rapidly,becoming finally equal

to that of the entering gas. This cor

responds to the point of saturation for

this part icular mixture and temper

ature .

A simple form of appa ra tus for

carrying out this operation in the

laboratory is shown in Fig . 5 .

The gel tube B with its adsorbed

material is immersed in bath C,and

when the temperature of the gel

rea ches 100° C . steam is admitted at

A . The mixed vapors are condensed

in D and collected in receiver E . To

F I G . 24 .

-Tube of a ctive silicaminimize by evaporation through

gel . vent , etc .

,we water should c irculate

through the condenser and the re

ceiver should be surrounded by ice water . After displacement

of the adsorbed materia l by steam,the gel

,before being used

again for adsorption, should be rea ctivated in an air steam as

already described .

The method just described is in principle perfectly adapted to

the recovery of liquids which, like ether, benzene , etc . , are but

slightly soluble in water, and do not react chemically with it .

For substances which, like acetone and alcohol, are miscible with

water,the distillate may require subsequent fractiona tion . For

this class of liquids,recovery by evacuation instead of steam dis

placement may be preferable, from a practica l standpoint . Steam

displacement may also prove impracticable for esters,such as

ethyl and methyl acetates , on account of hydrolysis , with forma

ADSORPTION OF GASES 87

tion of acetic acid and alcohol . If for any reason steam displace

ment is impossible,the adsorbed material may be liberated by

vacuum or by displacement with a vapor other than steam .

— Recovery of adsorbed ga ses .

Read a more detailed article on adsorption by M cGavack and

Patrick,Jour . Am . Chem . Soc .

, 42, 946

A series of experiments with silica gel,ferric oxide gel (as

prepared by R . E . Wilson and Leon Parsons at M assachusetts

0dilution, if desired ,Cap illary Insert H se cond flowm eter

Flowmeter

F I G . 26 .

—Gas adsorption tra in .

Institute ofTechnology) or similar gels may be performed with theapparatus described in Fig . 26 . I t is worth while to study the

ga in in weight of the gel at different temperatures,as well as at


different partial pressures Of the gas adsorbed . Curves may then

be plotted .

In Fig . 26 is represented an apparatus with which it is easy

to determine when the active material is saturated (under thegiven condit ions) , or nearly so .

Sulfur dioxide is led through the train of 100 cc . bottles,D

,C,

B and A by opening and closing the proper screw clamps atJ, etc .

D is a safety trap ; C is partly filled with water ; and B and A

contain a solution of sodium hydroxide to prevent sulfur dioxide

from poisoning the air of the room .

’

As soon as the water in C

is saturated,the bubbles per second or minute are counted . Then

the gas is shut Off from this tra in of bottles and led through the

flowmeter at E . It is warmed (if desired) by passing through the

tube F filled with glass wool , and is adsorbed by the active gel in G.

F I G . 27 .

— Capillary for flowmeter.

Some unadsorb ed gas passes on through the train of bottles,

D,C,B

, A . I f the origina l rate of flow was 100 bubbles per

unit of time and after passing over the adsorbent it is only 50

bubbles,it is evident that half the gas is being adsorbed . When

no more is adsorbed the ra te of bubbling rises to 100 again and the

tube G may be weighed . A connection may be made at I with a

second flowmeter from which air may be drawn for . any desired

dilution . A mixing bottle should then be placed at I . In this

case the flowmetersare useful in showing the maintenance of flow

of the gas. The capillary insert at H should have a fine Opening

barely large enough to be easily visible . The best arrangement

of the capillary insert is magnified in Fig . 27 .

EXPERIMENTS ON FERRIC HYDROXIDE GEL

"Contributed by Dr. Leon W . Parsons of M assa chusetts Institute of

Technology . ]

Preparation of Ferric Hydroxide Gel

Exp . 138 .— M ix 6 per cent solution of ferric ch loride with 6 per cent solu

tion of sodium hydroxide at 40° C . with vigorous agitation . Allow the pre


g. and add to the above mixture of pinene and xylol, noting the temperature rise . Hea t another g . portion to 1 10° C . for a short period

,noting

the tempera ture rise on mixing with the pinene and xylol . Has the adsorp

tion of a film of wa ter made the earth more or less a ctive"Exp. 143.

— Heat a sample of ful lers ’ earth at about 300 °—400°until it

conta ins, say, 8 per cent of water. Now h eat another sample much hotteruntil it conta ins decidedly less water. Then let it stand in moist air untilits moisture content is a lso 8 per cent . Experiment will show that it is lessa ctive than the first sample . Why"

CHAPTER X III

REACTIONS IN GELS

THIS chapter is largely composed of quotations from the

author ’s own papers : Jour . Am . Chem . Soc .

,40, 1 187

Jour Phys . Chem .,21 , 709 and Jour . Franklin Institute

,

184, 743

The student Should repea t a suitable number of the experi

ments,including at least those with gold, copper chromate and

lead iodide .

As a prefa ce to a study of crysta l forma t ion in gels, we must

note their retardation of the rates of diffusion of a cids,ba ses and

sa lts,and their proh ibition of diffusion of colloids . The mesh

structure of gels must be pra ct ically equiva lent to a network of

capillary channels filled with the less concentrated pha se . It

follows,then

,that the presence of substances affecting the dis

tribution of water between the two phases must affect the size

of these channels and change the rates of diffusion above men

tioned . For example, Hatschek sta tes that such sa lts as citrates

and sulfa tes produce more rigid gels, but iodides and sulfo

cyanates retard or prevent gel forma t ion . Bechhold adds that

sulfates,glucose

,alcohol and glycerol retard diffusion

,while

urea,iodides and chlorides accelerate it .

The influence of certa in gels— or j ellies— on crysta l growth is

illustra ted by many crysta lline minera ls . It is probable tha t

gelatinous Silicic a cid was the ancestor of vein quartz and by

gradua l dehydration became hard silica rock . In the gelatinous

medium,rea ctions took place under conditions favoring the forma

tion of crysta ll ine veins . For example,the reduction of gold sa lts

produced crysta ls of gold,veining the gel, wh ich later became

quartz . A convincing part of this development can be repro

duced in the labora tory .

To the geologist,a working method of duplicating many such

processes of nature must be of -great va lue . To the chemist, a

91


study of reactions in gels gives a useful control of relative con

centrations and velocity of rea ctions . The pathologist finds in

the subj ect some relation to the formation of crystalline material

in animal tissue .

METHODS OF WORK

The author found it convenient to mix equal volumes of solu

tions of sodium silicate and some acid,pouring the water glass into

the acid and mixing quickly and thoroughly . Before the Silicic

acid set to a solid,one of the reacting salts was mixed with this

solution,which was then poured into test tubes . After the gel

set, the other salt solution designed to react with the first was

poured on top . The solution on top should have a greater osmotic

pressure than the gel,to insure rea ction with in the gel instead

Of above the surfa ce .

The water gla ss used was a commercia l grade known as water

white,

” with a density of The ratio of the NazO to the

SiOz was 1 to When diluted to a density of and titrated

against hydroch loric acid,phenolphtha lein being used as an in

dicator,it was equivalent to N a cid . With methyl red as

indicator the normality was

Pouring the mixture, before it solidifies, into the bend of a

U-tube gives the experimenter excellent control of conditions .

The two rea c ting solut ions,poured separately into the arms of the

U-tube,slowly diffuse through the gel and meet

,often forming a

sharp precipitation band . Any amount of either solution can be

used in this method .

Hatschek,in some of his work

,directs that the mixture of

water gla ss and a cid be dia lyzed to free it from excess a cid and

sa lts . The addition of a very lit tle ammonia sets the gel . In

other experiments he did not dia lyze . The author does not find

it necessa ry or desirable to dia lyze out the a cid and sa lts,as their

influence on crysta l formation or development of banding is

beneficia l in most instances . In a number of experiments he used

a large excess of acid, and in others he added salts or non-elec

trolytes to secure certa in effects .

Pringsheim states that when two salt. solutions diffuse into a

gel in opposite directions the reaction does not proceed beyond a

thin film,if the solutions are isotonic . A hypertonic solution con


dichromate,1 cm . in length . Similar experiments

,although not

so striking,were performed with barium sulfate powder, flowers of

sulfur and closely packed a sbestos . In repeat ing such experi

ments the difference in concentra tion of the solutions in the two

arms of the U-tube should be varied throughout a series .

Without doubt,any compact mass of insoluble discrete particles

with proper-sized capillaries will funct ion as a gel in favoring the

forma tion of crysta ls . Other influences may be present in a true

gel . Adsorption,pressure and solubility effects may greatly

influence the capillary Spa ce results . A ra ther amorphous insoluble

compound,first formed by the meeting of two rea cting substances

in a relatively narrow channel,may further regulate the rates of

diffusion in such a way as to give tim e for crysta l format-ion of

more of the same insoluble compound . In th is suggestion the

geologist may possibly find an explanation of the marked crystal

line nature of some minera l veins . The pa thologist,too

,may

obta in some light on the a ccumulat ion of crysta lline deposits in

anima l tissue .

Exp. 147 . Crysta l s with out a Gel .— To test the theory,the mouth of a

10 cc . specimen tube was covered with a sheet of gold-beater ’s skin,held on

firmly with a rubber band . The tube had first been filled with a solution of

N potassium iodide . Care was taken to leave no a ir bubbles on the

under side of the membrane and to rinse the outside of the tube . The tubewas then immersed in a sma ll beaker of saturated lead a cetate solution .

At once an a lmost amorphous precipitate of lead iodide appeared on the

under Side of the membrane,and in less than a minute crysta ls of lead iodide

fell in a beautiful gleaming shower,rapidly increasing in amount . It is

very easy to secure gleaming crysta ls of lead iodide by cooling its hot solution,b ut in th is experiment the solutions were cold . I f th e same solutions aremixed in a test tube without the use of a membrane

,a yellow powder results .

When the more concentra ted solution was pla ced inside the

specimen tube,the crystals formed on the upper surface of the

membrane . Th is is in a ccord with the osmotic difference rule of

Pringsheim . With less difference in concentration of the rea cting

substances in the solutions,the reac t ion was much Slower.

Sepa rating solutions of silver nitrate and pota ssium dichromate

in this way,it was a simple matter to make a gram or two of

brilliant crysta ls of silver dichrom ate which settled to the bottom

of the tube . Possibly th is method may be of some use in the

prepara tion of pure compounds,since the crystals are not mixed

with an annoying gel . Other thin,semi-permeable membranes

REACTIONS IN GELS 95

serve . Parchment paper is good , but gold-beater’ s skin is most

suitable .

To carry the theory further, the only need of the gold—beater’s

skin is to prevent sudden wholesa le mixing of the solutions and

mechanica lly susta in the ra ther amorphous precipita te first formed,which then func tions a s the rea l a ctive membrane . This theory

is not universa l in its applica tion, for in gels excellent c rysta ls of

a number of substances formed without the appearance of a pre

limina ry compa ct layer of precipita te . In these instances only thegel functions in regula ting diffusion . The theory does apply,however

,in the absence of a gel and in a ll instances where a

compact precipitation band is formed .

RHYTHM IC BANDING

Rhythmic banding of precipita tes was first Observed and

recorded by Liesegang,hence the name Liesegang ’ s rings . His

origina l experiment dea lt with the rhythmic precipita tion of silver

chroma te in gela t in . A solution of silver nitrate was poured on a

solid gel conta ining dilute pota ssium chroma te . The precipita te

of silver chromate formed was not continuous but marked by gaps

or empty spaces at regula r interva ls .

Exp. 148 . Liesegang ’s R ings . —Prepare a gela tine gel conta ining 4 g . of

gelatin , g . of potassium dichromate and 120 cc . of wa ter . Let it cool inthe ice-box . When it is firm

,carefully remove from the beaker and immerse

in a solution of g . silver nitrate in 100 cc . of wa ter . The gel must becompletely covered with solution . Repla ce in the ice-box for a day or two andthen pour off the silver nitrate ; rinse and cut a slice through the middle Of thegel . Remarkable bands of silver dichroma te are seen . Th is experiment isfrom Liesegang and W0 . Ostwa ld .

Exp . 149. M ercuric Iodide .

— A tube of Silicic a cid gel (from mixing equa lvolumes of density wa ter glass and N a cetic a cid) was made N withrespect to potassium iodide and covered with N mercuric ch loride . In a

few days,bands of red crysta lline mercuric iodide began to appear . These

bands were not sharply marked for the first cm . or two below the surfa ce ofthe gel

,b ut below that depth were excellent . In some tubes there were 40

bands , rather sharply marked , in a distance of 8 cm . The spa ces betweenthe th in disks conta ined many scattered crysta ls .In a U-tube with a gel filling the bend

,N mercuric chloride in one

arm and N potassium iodide in the other,th e sharp red bands of

mercuric iodide followed th e curve like ranks of soldiers pivoting in regularformation . The excess of mercuric ch loride diffusing into the gel rea ctedwith the red mercuric iodide

,forming a soluble colorless double sa lt

,leaving

96 COLLOID”

LABORATORY MANUAL

the gel somewhat clearer where the red bands had b een. Th is gave theappearance of shadow bands following in the rea r .

The presence of glucose in the gel made the bands very much sharper .Sodium chloride

,on the other hand

,diminished the tendency to band and

in sufficient concentration prevented it a ltogether . In a gel of the com

position described above b ut conta ining an added 10 per cent of sodium ch loride

,the mercuric iodide formed

,

not in the usua l red needles,but

in much larger crysta ll ine aggre

gates,and very few bands appeared .

The crysta ls were scattered in an

irregular way . The addition of

sodium ch loride to the amount Of25 per cent of the weight of thegel caused the appearance of stilllarger widely sca ttered crystallineaggregates . Neither needles norbands were in evidence . Since a

gel made from sodium silicate andhydroch loric a cid conta ins consid

erab le soluble ch loride,no sharp

banding ofmercuric ch loride couldbe expected under such conditions .Th is may expla in why earlier investigators in th is field fa iled torecord the beautiful examples of

banding possible with mercuric

F IG . 28 .

— Rhythmic bands ofmercuric iodide . It is worthy Of note tha tiodide in a silicic a cid gel . when mercuric nitrate was sub sti

tuted for mercuric ch loride stillfiner banding was obta ined . Th is may be due to the absence of ch lorides orin part to the fa ct that mercuric ch loride is less ionized than mercuric nitrate .

Exp . 1 50. Copper Chromate — The banding of copper chroma te in a

Silicic a cid gel of very sligh tly basic rea ction affords the best ma teria l for a

deta iled study of the phenomenon . Gold banding is Often more beautiful,

b ut the remarkable sharpness of the layers of copper ch romate and the perfectclearness of the gaps excel all other examples .A gel from mixing equal volumes of density wa ter glass and N

a cetic a cid was made N with respect to pota ssium ch romate (beforesolidifying) and was later covered with N copper sulfate . In a day or

two,bands of apparently amorphous copper chroma te formed . The first

layer was often ra ther deep , 1 cm . or more , then a clear gap with no tra ce ofa precipitate of copper chromate , below that a much th inner band, more gapsand bands , the gaps widening steadily .

These relative distances varied not only with the initial con

centrations of the reacting solutions , but also with the volumes of

the potassium chromate solution in the gel and the copper sulfate


Working with a cetic acid as in the first experiments discussed,

the effect of increased alkalinity was studied . In a gel made from

equal volumes of density water gla ss (as compared wi th the

usual density) and N acetic a cid,the copper chromate

bands were much closer together,greatly resembling an aga te .

Thirty in a distance of 3 cm . were Obtained . With a gel from

density wa ter gla ss and N acetic a cid the bands were still more

compact . It is evident that an increase in the excess of sodium

Silicate,with its resulting a lka linity

,brings the bands of Copper

chromate closer together.

Addition of sugar to the usual gels made the bands thinner.Urea had the Opposite effect . The influence of gravity was shown

by corking tubes and inverting . The bands were irregular and

made up of crescent-shaped fragments . I t is noteworthy that the

final condition of many tubes showed the blue of the copper sulfate

in all the clear gaps— even below the last band .

Exp. 151 . Gold .

— To 25 cc . of a mixture of equa l volumes of densitywater glass and 3N sulfuric a cid was added 1 cc . of 1 per cent gold ch loride .

The solid gel formed in a day or two and was then covered with a saturatedsolution of oxa l ic a cid (about 8 per cent) . AS the oxa l ic a cid diffused into thegel the gold ch loride was reduced . A wonderfully beautiful series of coloredbands of colloida l gold developed

,with sparkling golden crysta ls sca ttered

throughout the gel . The upper layer of the first bands was red,the next blue

and the next green . A comparatively clear gap below th is series was followedby anoth er red-blue-green zone . Usually after the first few ra inbows thered was omitted . A dozen or more such complex bands in an ordinary testtube were not uncommon

,the upper bands measuring about 1 cm . in depth .

These concentrations of the gold chloride and the oxa lic a cid

were varied somewhat,with no improvement in results . However

,

when the gel was made from density water glass and 3 N

sulfuric acid (setting in about one week) no bands of colored

colloidal gold appeared— or only traces of them— b ut great num

bers of gleaming yellow crystals of g old formed throughout the

gel— strikingly beautiful in a beam of sunlight .

These bands have been obta ined before,but the author found

the use Of sulfuric acid in making the gel a very great improve

ment . When hydrochloric acid was used the colored bands were

quite inferior . With acetic acid instead of sulfuric,no bands

appeared,b ut the gel was colored uniformly with violet-blue

colloidal gold . However, loading an acetic acid gel with consider

REACTIONS IN GELS 99

able sodium sulfate developed a few shadowy bands . Evidently

the influence of sulfates was a factor of importance .

Exp. 152. Basic M ercuric Ch loride — The author poured a basic gel,

wa ter-glass N a cetic into a test tube and,with no other added sa lt

,

covered the gel with saturated mercuric ch loride solution . Shining redbrown leaves appeared . Since they could not be obta ined in a gel of a cidreaction nor with any sa lt other than mercuric ch loride, they were evidentlyone of the ba sic mercuric chlorides . A search of the literature justified th istheory . Different basic chlorides are on record

,but the description of

HgClz 2HgO agrees perfectly with the crysta ls obta ined above .

Gels of different basicity were covered with mercuric ch loride solutionand the crystals compared . With water-glass N a cetic (very slightlybasic) the crysta ls were more widely scattered and

,at a distance of a few

centimeters from the surfa ce of the gel, were excellent . Th is particular gelcaused the most remarkable banding of the basic ch loride . With a verybasic gel the crysta ls were sma l ler and formed in a rather compa ct ma ss . Afew grams of glucose in 25 cc . of a sligh tly basic gel changed the results decidedly. Instead of the brown-red leaves

,a gray mass of closely pa cked bands

,

sh arply marked,appeared . In a distance of 8 cm . over one hundred of these

bands were counted .

Th eory

The experimental evidence given above justifies the advance

ment of a more detailed theory of rhythm ic banding . For the

clearest illustration,consider the Copper chromate banding.

The gel (a Silicic a cid gel of slightly basic reaction) conta ins adilute solution of a chromate and

,above it in the tube

,a solution

Of a copper salt . The copper ions diffuse into the gel,meet the

chromate ions and form a layer of insoluble Copper chromate atthe surface of the gel . The chromate ions immediately below

this precipita tion zone diffuse into this region,now depleted of

chromate ions,and meet the advancing copper ions

,thus thicken

ing the layer of copper chromate . According to Fick ’s law of

diffusion,the rate of diffusion is greatest where the difference in con

centration of the chromate ions in two contiguous layers is greatest,

that is,just below the front of th is thickening band of copper

chromate . As a result,the region near the band decreases in con

centration of the chromate ions faster than does the space b elow .

Finally the Copper ions have to advance some distance beyond the

band to find such a concentration of ch romate ions that the

solubility product of copper chromate may be exceeded and a new


band formed . This repeats again and again . Of course, if the

copper ions were retarded sufficiently there would be time for the

concentration of the chromate ions again to become uniform

throughout the remaining clear gel, and no gap would occur.Hence

,if the diffusion of the copper ions is retarded by any means

,

the clea r gaps decrease in

depth— the bands are closer

together. If coppe r ferrocyanide bands are formed in a

sim ilar manner they almostmerge after the first layer

reaches a thickness of a few

centimeters . Yet‘

they are

distinct and agate-like . A

precipitate of Copper ferrocyanide greatly retards the diffu

sion of the ions that form it ;hence we have here the proper

condition to reduce the clear

gaps to a minimum depth .

The permeability of the

gel,as influenced by the pres

ence of va rious salts,and

FIG . 30 .

— The influence of ch lorides sugars

,for example

,was found

on the distr ibution of mercuri ciodide . The tube on the left con to be 81

}Important fa°t0 r

.

ln

ta ins sodium ch loride— the others rhythm l c b and lng . Wlth

do not . mercuric iodide in a silicic

acid gel,the presence of suffi

cient sodium chloride entirely prevented the arrangement of the

crysta ls in bands . On the other hand,glucose in a similar gel

greatly favored the banding of mercuric iodide . In another

experiment glucose produced a great increase in the number of

bands of basic mercuric chloride . This marked influence of some

salts gives importance to the selection of the acid used in making

the gel . ‘Hydrochloric acid is a poor choice when experimenting

with mercuric iodide banding .


benzopurpurin solution prepared as in Exp . 1 . After the diffusion currentscea se

,watch the gradua l aggregation of ultramicrons . At first they form

groups of two or three . AS the groups increase in size their motion diminishes,

until fina llv there are large motionless or Slowly floating grape-like clustersor ma sses . By using very dilute solutions and weak a cid

,the time of coagu

lation may be extended to ha lf an hour or more .

Now add some warm gelatin or gum a rabic solution to the dilute milk or

benzopurpurin,and observe that the coagulating a ction of the a cid may be

partia l ly or entirely prevented, most or all of the ul tramicrons ma intainingtheir isolated a ctive motion .

Note a lso by test-tube experiment tha t the addition of HCl to b enzopur

purin solution produces a color change from red to blue, a ccompanied byprecipita tion . (The dy e is a soluble sodium sa lt

,and the precipita te the

insoluble color ba se .) I f a protective colloid (gela tin or gum arabic) beadded to the benzopurpurin solution prior to the addition of the a cid

,the

color remains red or reddish-brown even though enough a cid is added toproduce marked turbidity . Compare the ma croscopic with the ultramicroscopic findings . (See Jour . Soc . Chem . Ind .

,30, 517,

Exp. 156 . Enzyme Action — Observe the a ction of diastase on starch,

and Of pepsin on partia lly coagulated dilute egg-a lbumen solution . (See Jour .

Am . Chem . Soc .,32, 682,

Exp. 157 . Mutua l Coagulation.— Observe the mutua l coagulation of

colloida l gold and colloida l AszS3. (Diph theria toxin is precipita ted bydiph th eria antitoxin

,but not by tetanus antitoxin

,wh ich

,however

,coa gulates

tetanus toxin . These rea ctions may be followed ultramicroscopica l ly ; b utit should be remembered tha t the toxins are h igh ly poisonous ; the sma llesttra ce in a scratch may produce serious if not fata l consequences . )

Exp . 1 58 . Blood — Examine fresh blood,observing colloida l blood

dust and red blood corpuscles for comparative motion . Watch fibrinformation or coagulation .

N0 TE .

— Read King’s Short article on Ultramicroscopy, pages 31—4 1 of

the Th ird Report on Colloid Chemistry,” published in 1920 by the British

Associa tion ; a lso pages 122-127 in Bechhold ’s

“ Colloids in B iology and

M edicine .

’

CHAPTER XV

SOILS AND CLAYS

THE productivity of a soil is Closely related to its colloid con

tent . Weathering of feldspa r yields much colloida l materia l in

the form of a lumina and silicic acid . This,with colloida l hydra ted

oxides Of iron and humus,gives soil the proper physica l condition .

Permeability,capilla rity

,adsorption and moisture content

depend more upon the physica l sta te of a soil than upon its chem

ical condition . J . M . van Bemmelen (Die Absorption , Dresden,1910) states that the ability of soils to take up sa lts of alka line

earth s and alka lies from solution is due to the content of ba sic

silicates,soluble in hydrochloric a cid

,wh ich act by an exchange of

ba ses .

Humus is an indefinite mixture of organic substances,the

debris of bacteria,plants and anima ls . M anure

,plowed-under

crops and sods increase the humus content . This humus ac ts

as a protect ive colloid tending to keep much of the soil in the

hydrosol state . It is opposed by the coagula ting tendency of

an excess of salts,by heat with drying and evapora tion

,and by

freez ing .

Soils have been ruined by a flood of sea water and by an overdose

of fertiliz ing salts . On the other hand,Cameron and his assistants

found that a certa in non-product ive soil was improved by treat

ment with tannin . Th is is a rem inder of Egyptianized clay

and of Acheson ’s graphite in wh ich tannin a cted as a dispersing

or peptizing agent .

The ceramic chemist calls a clay weak,lean or sandy and

lacking in pla sticity if it has too li ttle colloida l ma terial . I f ithas too much he calls it fat

,strong and sticky. A modera te

plasticity is desirable for his purposes . Highly colloida l clays

Shrink too much on drying and firing .

It has been found that clays may be given the fluidity needed

for proper pouring into molds by the peptizing action of hydroxyl

103


ions from a little sodium carbonate . Then,on drying

,there is less

water to evaporate and consequently less shrinkage .

Cushm an (Jour. Am . Chem . Soc .

,25

,451

,1903) Shows that the

cementing power of rock powders is due to the formation of

gelatinous silica,ferric oxide

,etc .

M any soils adsorb the base from blue litmus more readily

than the acid and give a fa lse impression (due to the reddening of

the blue paper in contact with soil) that a free acid was present

in the soil . Cameron showed that moist cotton in contact with

blue litmus does the same thing .

Exp. 1 59. (1 ) Determ ining th e Amount of Colloida l M atter in Clays.

Moore,Fry and M iddleton (Jour . Ind . Eng . Chem .

,13, 527, 1921 ) separated

the colloida l materia l from clay by the use of a Sharples centrifugetimes the force of gravity) . Th is “

ultra clay consists ma inly of hydra teda luminum silicate mixed with ferric hydroxide, silicic a cid

,organic ma tter

and possibly a luminum hydroxide . Suspended in wa ter,it exh ibits good

Brownian movement . As a binding materia l it is much stronger than Portlandcement

,when dry.

Their method of determining the adsorptive power of ultra clay towa rdsammonia may well be applied to studies of other solid materia ls and othergases .

Ultra clay was dried in an oven a t 1 10° C . for twenty-four hours . It wasimmediately transferred

,wh ile still hot

,to a Schwartz U-tube, and weigh ed,

and the'

tube was pla ced in a tra in of drying appara tus . The Schwartz tubewas then immersed in boil ing wa ter and thorough ly evacuated with an oilpump . The U-tube was next pla ced in an ice ba th

,and dry ammonia gas

was passed over the ultra clay until it would adsorb no more under a pressureof one atmosphere . The current of gas was then shut off and the apparatusa llowed to stand for one hour to inake sure tha t equilibrium had been rea chedas shown b v a manometer atta ched to a U-tube . The next step was to drawoff the ammonia and collect it in a tra in of absorption apparatus filled with a

sa turated boric a cid solution . When a good dea l of ammonia had beendrawn off

,the U-tube was aga in pla ced in boiling water and the residua l

ammonia displa ced with a current of air . The ammonium bora te solutionwas titrated with O. I /N sulfuric a cid, using methyl orange as indica tor .

”

The adsorptive power of soils towards gases is undoubtedly due largelyto their colloid content ultra clay The authors quoted above destroyedthe colloida l condition of a certa in clay by heating to 1 130° C . and then measured its gas-adsorptive power . A careful microscopic examination showed noevidence of fusion even on sharp edges .

1 cc . ultra clay (heated to adsorbed cc . NH3

1 cc . clay soil (heated to adsorbed cc . NH3

1 cc . clay soil (hea ted to adsorbed cc . NH3


number of soils in the air and a para llel series at Use such soils as

qua rtz sand,clay soil

,loam

,very heavy clay and humus . Weigh out a

convenient sample (100 g . to 200 g .) Of ea ch soil on a sha llow dish and pla cein the moist atmosphere of the desiccators for twenty-four hours . Weighaga in and compare the speed with wh ich ea ch soil takes up moisture . Sinceth is is the reverse of drying out

,it is a mea sure of the strength with wh ich

water is held by ea ch soil .

From these results it may be concluded that the adsorptive

capacity of soil for water vapor is generally higher the finer the

texture of the soil and the grea ter its content of humus . It appears

,too

,that productive soils have a very considerable capacity

for water vapor while the poor soils range much lower.

Exp. 163. Th e Effect of Variations in Hum idity upon Soils.

1— The effectof atmospheric humidity changes upon soils may be experimenta lly reproducedby pla cing severa l equa l portions of a soil of known moisture content indesiccators whose individua l atmospheric humidity is ma inta ined pra ctica llyconstant by sulfuric a cid, differing in strength for ea ch desiccator and thusgiving a range of hum idity from the very low partia l pressure of concentra teda cid to the vapor pressure of water at the tempera ture chosen for theexperiments .

Hea t changes may be studied by running equilibrium experiments similarto those just described

,b ut at different temperatures

,and comparing the

quantities of moisture in soil and in vapor above it at ea ch tempera ture .

One of Patten and Gal lagher ’s experiments is graph ica lly presented here .

Exp . 164 .— Test Fickendey

’s sta tement that more a lkal i is required to

precipitate (floc culate) natura l clay than kaolin on a ccount of the protectivea ction of humus .

For other soil exp eriments see the chapter on adsorption from solution,Experiments 120

,121

,122 .

ADDITIONAL REFERENCES

Russel,Second Report on Colloid Chemistry by the British Association

,

pages 70—8 1 .

Patten and Waggaman,Bul letin 52

, U. S . Bureau of Soils .Cushman; Jour . Am . Chem . Soc .

,30, 779

Cushman,Bulletin 104

,U . S . Bureau of Soils .

1 Adapted from Patten and Ga l lagher,Bureau of Soils Bulletin No . 31 .

CHAPTER X VI

SPECIAL TOPICS

EXPERIMENTS ON DYEING 1

Exp . 165. Dyeing with a Direct or Sub stantive Dye .—After thorough ly

shaking the standard direct dye solution 2 found on the reagent shelf, transferfour 40 cc . portions to beakers or flasks . Add 10 cc . of water to three of

th e solutions . To the fourth add 10 cc . of a saturated solution of sodiumch loride . To the second and th ird dye baths add cc . and cc . of the

saturated NaCl,respect ively . Label the solutions so that you will know the

amount of sa lt in each,and then heat them to boiling . Pla ce a piece of

cotton or woolen cloth,1 inch square

,in ea ch bath and a llow the solutions

to simmer for twenty minutes . Remove the cloth , rinse once in cold waterand dry . Compare the different pieces . How does the intensity of the

color vary with the amount of NaCl present in the bath " The direct dyesare in colloida l solution . Can you expla in your results in terms of colloidchem istry"Reference : Pelet-Jolivet, Z eitschr . Chem . Ind . Kolloid

,5, 235

Chemica l Abstra cts,4, 829

The dye taken up will pass through a maximum as the amount of NaCl

or other ' sa lt added is increased . The reason seems to be tha t the dye isdestabilized by the added sa lt before coagula tion takes place . Decreasingthe peptizing or stripping a ction of the solvent means increased adsorption .

Exp . 166. Dyeing with an Acid Dye and th e Effect of Glaub er ’s Sa lt.3

Into ea ch of four 250 cc . beakers or flasks mea sure 25 cc . of ' the standarda cid-dye solution 4 found on the rea gent shelf. Then add exa ctly cc .of N hydroch loric acid 5 to two of the solutions and exa ctly cc . of

1 Contributed by Professor W . D. Bancroft,Cornell University .

2 The direct dye standard solution should be a per cent solution or

suspension of any of the usua l direct dyes . Erie Red 4B Conc .,Buffa lo D irect

Blue G Cone . and Erie D irect Green are typica l examples .3Contributed by Professor W. D . Bancroft

,Cornell University

4 The standard dye solution may be made up from any a cid dye which ispresent in true solution . Orange II

,Lake Scarlet

,Croceine Orange

,Acid

Green or Crysta l Ponceau are typica l examples . The standa rd shouldcontain grams of dye per liter .

5 It will be best to supply the labora tory with a bottle of th is a cid connected with a burette

,so that amounts can be mea sured a ccurately . The

acid need only be approximately N.

107


N hydrochloric a cid to ea ch of the other two . Twenty-five cc . of Nsodium sulfa te are then added to one of the solutions conta ining the cc . of

a cid and to one of the solutions conta ining cc . of the a cid . Add wa ter to a llfour dye baths until the tota l volume in ea ch ca se is 125 cc . Heat the foursolutions to boiling and then add a ha lf gram of wool yarn to each bath

,

making sure that the wool is thoroughly wetted by the solutions } Cover th edishes with watch glasses to prevent excessive evaporation and ma inta inat a slow boil for thirty minutes . Remove the wool samples before the bathcools and rinse them once quickly in cold water . Dry and compare theresulting shades and a lso compare the intensity of the partia lly exhausted dyeba ths . Expla in your results .

References : Bancroft,Applied Colloid Chemistry

,1 15 Jour .

Phys . Chem .,18 , 10 Davison

,Jour . Phys . Chem .

,1 7, 737

RUBBER 2

Rubber latex is a colloidal suspension or emulsion of caoutchouc

in a watery liquid with protein as the emulsifying agent . Coagu

lation is produced by evaporation,by smoking

,or by adding certa in

reagents which change the physica l condition Of the protein films .

Vulcanization by heating with sulfur is probably a colloidal process,

although some chemists dispute this .

Rubber exhibits the ordinary properties of gels,often to an

extraordinary degree .

NOTE .

— A short disserta tion on rubber will be found on pages 251—262of The Chemistry of Colloids

,

” by Zsigmondy and Spea r (John WileySons) . Simmon ’s book on Rubber Manufa cture (D . Van Nostrand isa lso useful .

Exp. 167 . Tackine ss , Pla sticity .— Pla ce a strip of raw rubber about

1 inch wide upon a wooden block and pound the rubber severely with a ham

mer. Note the rise of tempera ture . Touch two portions of the poundedsurfa ce together . It has become sticky, or ta cky

,

”and more plastic . In

this sta te it can be easily molded by pressure . Th is property is made use of

in the production ofmost rubber goods .We are not sure of the reasons for th is extraordinary ch ange of properties

brought about by mechanica l manipulation . It is ascribed to a depolymeriza

tion of the rubber, but whether th is is due to a mechanica l subdivision Of theparticles , or to a readjustment with in the molecule is not known .

Exp . 168 . Elongation of Rubber Which Has Been Cured (vulcanized

1 Instead of being weighed out,the wool can be measured by length if in

the form of yarn . A heavy knitting worsted will require about 50 inches fora ha lf gram .

2 Contributed by Ellwood B . Spea r,Goodyea r Rubber Co .

1 10 COLLOID LABORATORY MANUAL

Exp . 174.— Rub ber as an Emulsifying Agent. —Shake various liquids with

any convenient rubber solution (such as 2 per cent rubber in benzene ) . I f

emulsions are formed let them stand,and note time of creaming and time of

breaking . Is the benzene the continuous or the dispersed ph ase" Why"

HOPCALITE

CATALYSIS OF THE REACTION BETWEEN CARBON MONOXIDE ANDOXYGEN

Exp . 175 . Hopca lite,

as developed during th e Great War by J . C . W .

Fra zer,A . B . Lamb and W . C . Bray

,for gas ma sks, was a mixture of Mn0 2,

50 per cent ; CuO,30 per cent ; C0 20 3, 15 per cent ; and Ag gO,

5 per cent .Th e process of manufa cture involved the separate precipitation and wash ingof the manganese dioxide

,copper oxide and coba ltic oxide and the subsequent

precipitation of the silver oxide in the mixed sludge . After further wash ing,

the sludge was filtered,kneaded

,dried and ground to such Sizes tha t 52 per

cent passed th rough an 8-12 mesh screen,a lthough not more than 6 per cent

passed a 14—16 mesh screen .

The cata lytic a ctivity of the mixture depends in large mea sure on themethod Of preparation of the manganese dioxide . The first rea lly a ctivemanganese dioxide was made by reduc ing a cold solution of ammoniumpermanganate with methyl a lcohol . A large-sca le process used depended on

th e rea ction between pota ssium permanganate and anhydrous manganesesulfa te in the presence of fa irly concentrated sulfuric a cid; When preparedby oxida tion of a manganous sa lt in neutra l or alka l ine solution

,the man

ganese dioxide was not cata lytic (or, rather, Hopca lite conta ining it was not) .Fremy

’s method (Compt . rend .

,82, 1231 , 1876) furnished th e best m an

ganese dioxide . To 150 g . of pota ssium permanganate was added a cooledmixture of 500 g . of concentrated sulfuric a cid with 150 g . of water

,and the

mixture was a llowed to stand severa l days, during wh ich time the permanganica cid was slow ly decomposed with evolution Of oxygen . The mixture wasthen poured into a large volume of water and th e resulting finely dividedmanganese dioxide “ wash ed

,first by decantation and then on a filter

,until th e

filtrate showed no test for sulfate . The precipitated oxides of manganese,

copper and coba lt , were suspended uniformly in water and added,with stirring,to a Silver nitrate solution conta ining suffi cient silver nitra te to give thedesired amount of silver oxide . Sodium hydroxide solution was then added

,

with vigorous stirring, until a distin ct a lka l ine rea ction was observed . Afterthorough wash ing the mixture may be collected as a filter cake on a Buchnerfunnel . The materia l was dried on a water bath

,broken up , then slowly

heated to 120° meshed,and finally dried for a short time a t

Prolonged heat treatment at ‘

a h igh temperature spoils these ca ta lysts,

presumably on a ccount of the destruction of the porous na ture of the granul es .Wa ter vapor poisons this cata lyst ; therefore the mixture must be h ea ted

a few hours to about 150° before use,to a ctivate it . In the gas masks, the

air was dried by granular calcium ch loride before coming in conta ct with theHopca l ite .

SPECIAL TOPICS 1 1 1

Exp. 176 .— Pa ss a stream of air

,dried over anhydrous ca lcium ch loride

,

through a pyrex tube (1 cm . diameter) conta ining a 2—3cm . layer ofHopca lite .

The ca ta lyst may be held in pla ce by means of copper gauze plugs . Watergas (because of its carbon monoxide content) , or even prepared carbon monox

ide, may be introduced into the air stream,and as the concentration of the

iGas

Hopc alite

H W EZJ 00 0 0 0 0 0 0 :

Ca Cl0 O o O 0 o 2

Copper g auze

FI G. 31 .

— Ca ta lysis with Hopca lite .

carbon monoxide is increa sed the conta ct layer becomes warm . I f the concentration is sufficiently h igh the conta ct materia l will rea ch a red heat .Test the issuing gas for carbon dioxide .

The author is indebted to A . T . La rson, of the Fixed Nitrogen

Resea rch Laboratory, for suggestions on th is experiment .'

Much

materia l was taken directly from the paper by Lamb,Bray and

Fra zer in Jour. Chem . Ind . Eng .

,12, 213, 1920 .

CATALYTIC REDUCTION

We quote from page 192 of Cata lysis in Theory and Pra ctice,

by Ridea l and Taylor, The M a cmillan Co .

The theoretical investigations of Paa l and his cO-workers,

of Willstatter and others have demonstrated conclusively that

numerous hydrogenations can be effected in presence of finely

divided platinum or of colloida l palladium as ca ta lyst . In

genera l,it was found necessary to stabilize the colloidal meta l

,

and various protective colloids were employed to effect this .

Skita , who in his book Uber Kata lytische Reduktionen

Organischer Verbindungen (F . Enke,Stuttgart . 1912) has de

ta iled in a comprehensive manner the literature of the subj ect,

employed an a cid— stable protec tive colloid such as gum arabic

in pla ce of the agents used by Paa l . Solutions of platinum or

pa lladium chloride in presence of such protective agents are

reduced to stable colloida l solutions of the meta l by means of

hydrogen in the cold . The protective colloid a lso has the power

of preventing the precipitation of the hydroxide of the meta l

when sodium carbonate is added to the solutions, the meta l

rema ining in colloida l suspension . Such colloida l suspensions

have proved to be excellent hydrogen carriers for hydrogenation

of both aromatic and aliphatic unsaturated compounds .”


Lochte,Bailey and W . A . Noyes

,Jour . Am . Chem . Soc . (43,

2597, 1921) used colloidal platinum in'

reduction .

The Skita apparatus (Ber . 45, 3578 and 3589, 1912) is used ,the container for the reduction mixture being a l

'

ter fla sk . This

bottle is charged with 25 g . of hydrazine hydrate in 100 cc . of

water . To this is added amixture of g . of gum arabic dissolved

in 50 cc . of wa ter and 10 cc . of chloroplatinic acid . The seed

ing colloid is next prepared by mixing 10 cc . of wa ter,a few drops

of gum arabic solution,5 cc . of chloroplatinic acid

,cc . of

30 per cent sodium hydroxide,and a few crysta ls of the hydro

chloride of symmetrica l di—isopropyl-hydraz ine,or some equally

good reducing agent . On heating this mixture reduct ion of the

platinum begins at once . The hot mixture is rapidly added to

the solution in the flask,to which are then added

,under thorough

shaking of the flask, 100 cc . of per cent hydrochloric a cid

and finally 100 cc . of acetone. The flask is then connected to

the apparatus, the system evacuated and filled with hydrogen

from a cylinder,until the apparatus is under a total pressure of

two atmospheres . The hydrogen cylinder should be supplied

with a reducing valve to prevent a ccidents and damage to the

appara tus in filling the reservoir and fla sk .

The room temperature,hydrogen pressure

,atmospheric

pressure and gage readings are now recorded and the shaker

started . During the few minutes required for the reduction of

the chloroplatinic a cid the absorption is relatively slow,but as

reduction of the pla tinum proceeds the ra te of absorption increases

until the gas is used up at the rate of 8 to 12 liters an hour . AS

reduction proceeds the absorption of hydrogen gradually slows

down and comes to a complete step at the end of 3 to 4 hours,when the theoretica l amount of hydrogen has been absorbed .

In ca se of poisoning of catalyst or other causes of slow redue

tion an additiona l 5 cc . of chloropla t inic acid is sometimes required

to complete the reduction .

”

In the above experiment the purpose was to reduce hydrozine

hydra te to symmetrica l di-isopropyl-hydra zine .

T . B . Johnson and E . B . Brown will soon publish a description

of their pra ctical appara tus for reduction Of large quantities of

reagents on a quantitative basis . They do not use any promoter

other than hydrogen to prepare their colloidal platinum .


atmospheres the viscosity of vegetable and animal oils increases

fourfold while that of mineral oils increases sixteenfold . Hence,

viscosity is not the most important factor in difficult lubrication .

Oiliness is attributed to adhesion or chemical affinity between

the metal and the lubricant . The addition of 1 per cent free fatty

acids of rape Oil to a certa in mineral Oil lowered the friction coeffi

cient from to equa l to the benefit from the addition

of 60 per cent neutra l rape oil

An excellent abstract of a Discussion on Lubrication held at

the Imperia l College of Science and Technology was written by

Bingham for Chemical Abstracts,14, 1475

FLOTATION

Read Jour . Ind . Eng . Ch em .,M ay Jour . Phys . Chem . ,

19, 275

any volume of Trans . Am . Inst . M . E . Flotation,

” by Rickard and

Ra lston ; Flotation,

” by M cGraw ; Flotation,

” by Taggart .Exp. 178 .

-Clean a needle in soda solution (handling with pincers) .Dry on a clean cloth . Lay on a floating tissue paper . Depress th e papergently with a stick . The paper sinks and th e needle floats on the surfaceskin of the water . I f greased

,a larger needle can be floated . A glass rod

of the same diameter,b ut l igh ter

,sinks because it is easily wetted by water

wh ile the steel needle is not . Grease the glass rod and it floats . Glass andsteel typify th e gangue and sulfide of flotation ores .

Exp . 179.

— By addition of enough oil,surfa ce tens ion is lowered from

73 to 14 dynes per linear centimeter . Lay a match on the surface of water,

then a drop of olive oil near the match . The match draws away because theoil has reduced the tension of part of the water surfa ce, and therefore the purerwater on the other side pulls away .

Exp. 180.—Drop oil on wet galena . Oil displa ces the water. Drop oil

on wet quartz . There is no displa cement .Drop water on oiled quartz . Water displa ces the oil. Wh ich l iquidwets quartz" Wh ich wets ga lena "Exp . 181 .

— Grind quartz and a sulfide ore (CuS or ZnS) to pass a 48-meshsieve . Flotation ores are usua lly ground wet in pra ctice . Pour into a

sepa ratory funnel, add more water and Shake . There is no froth . Now add

a drop or so of creosote oil. Violent shaking should produce a good froth ,carrying the sulfide . Run out the liquid and sludge

, put the froth on a hot

pla te to dry, and examine with the microscope or ana lyt ica lly to see if the“ floa ted materia l is richer than the ore .

A simple laboratory experiment with hand shaking of flasks is describedby W . H . Cogh ill in Chem . M et . Eng . 20

,537

,1919.

It may be seen from the above experiments that sulfides (and

other minera ls of metallic luster) may be separated cheaply from

SPECIAL TOPICS 1 15

the waste rock (gangue) in which they occur. Preferential wetting

of the sulfide by the oily froth ba lloons the heavy sulfide particles

to the floa ting froth while preferential wet ting of the gangue bywa ter ca rries gangue particles to the bottom . The froth is then

skimm ed off and broken . Air is beaten into the wet pulp of

ground ore and water to which a very little pine oil or other oil has

been added to secure a froth . Over tons of ore a re

floated in th is way every year and the recovery is much higher

than by Older methods .

Exp . 182 . Colloida l Garden .— Dilute ordinary commercia l water—glass

Syrup with a nearly equa l volum e ofwater and put into a ta ll,wide-mouthed

bottle . Drop in solid fragments (about ha lf the size of a pea ) of ferric ch lorideand coba lt ch loride (be sure to use these two) , as well as sa lts of nickel, copperand manganese . As th e solids dissolve

,the solution rea cts with sodium silicate

to form gelatinous membranes of copper silicate, etc . The little sa ck is,of

course,filled with a very concentra ted solution of copper sa lt of h igher osmotic

pressure than the solution outside . Natura lly,water enters the sa ck faster

th an it leaves,and bursts th e sack (upwards because there is less hydrostatic

pressure at greater heights) . New membrane forms,and the fina l growth is

tree-like in appearance . Ferric ch loride trees grow rapidly, a matter of inchesin a few minutes

,and coba lt ch loride trees make noticeable growth .

’

The

others are much Slower .

Exp. 183. Carrying of M ercury on Iron Gauz e (No . 40 of Bancroft’sColloid Prob lems ) .— Lord Rayleigh (Scientific Papers , 4, 430, 1903) presseda piece of iron gauze down on the flat bottom of a gla ss vessel holding a sha llowlayer of mercury, and found tha t the gauze rema ined on the bottom of the

vessel and did not rise through the mercury . The rea son for th is is tha t themercury does not wet the iron . A corollary from th is

,wh ich has not been

tested experimentally,is that one Should be able to carry mercury in an iron

sieve just as one can carry water in an oiled sieve (Chwolson,Traité de Phy

sique,1 , III, 613, Since sodium ama lgam wets iron

,a dilute sodium

ama lgam should run through an iron sieve wh ich would stop pure mercury .

Also, Rayleigh

’s experiment would not succeed if a sodium ama lgam were

substituted for the mercury .

ULTRAFILTRATION

Read Bechhold,95-102 ; Zsigmondy, 38—39; Alexander, 26—28 ;

Hatschek’

s Labora tory M anua l,69—76 ; Schoep, Kolloid-Z eit

schrift,8 , 80 Schoep used collodion to which castor Oil

and glycerin had been added . Paper thimbles were soaked in

this . They became more permeable as the content of glycerin

and oil increased . No extra pressures were needed .


Exp. 184 .— A sim ple ultrafilter may be prepared by pouring a 4 per cent

collodion solution on a wet filter paper, folded in the funnel . Tilt to securea uniform coating, pour out the excess , add a

fresh solution, and repeat . A film of cellulosenitrate is precipitated in such form that it servesfor some colloid separations . Schoep

’s device of

tying a collodion sa ck to the flanged end of a

funnel,so that it hangs inside a filter flask , is

useful . Th is introduces some pressure .

IMBIBITION OF GELATIN 1

Exp . 185.—Cut th in sheets of the purest

commercia l gela tin (such as Coignet ’s) intopieces about 1 inch square . Determine the

moisture and ash contents of the gela t in and

a ssume the rest to be dry gelatin . Weigh exa ctlythe equiva lent of 1 g . dry gelatin into ea ch of

12 wide-mouthed 6-oz . bottles and add 100 cc . of

FIG . 32 .

— Schoep’s

HCl,using a different strength for ea ch ; use the

ultrafilter following norma l ities :and

Let stand for forty-eigh t h ours and keep at a tempera ture notexceeding preferably a t constant temperature . Then carefully removethe gelatin plates from the solutions

,by means ofa wide spatula

,blot off adher

ing moisture with filter paper, pile on to a watch glass,and weigh . Then

put the gelatin pla tes, as quickly as possible, into clean , dry bottles, add moredry NaCl than will dissolve

,and let stand for another forty-e igh t hours .

In the meantime,calculate

,from the increa se in weigh t of the gelatin

plates, V ,the number of cc . of a cid solution wh ich the gelatin has absorbed .

Titrate a liquots of the rema ining a cid solutions to obta in 33,the concentra tion

of HCl in the externa l solution . Plot V aga inst 2: and note the peculiarnature of the curve . Why is th is preferable to plotting V aga inst the initia lconcentration of a cid , as is sometimes done"From ( 100 V )x, the milligram-equiva lents of a cid not absorbed, and th e

quantity of a cid used initia lly,ca lculate a

,the quantity absorbed . Plot a

'

aga inst th e initia l concentra tion of a cid and compare with any so-ca l ledadsorption curves .

At the end of the second forty-e igh t-hour period,remove the gelatin pla tes

from the saturated sa lt solutions,and weigh . Ca lculate the volume of sa lt

solution in the gelatin . Titrate the salt solutions in the bottles,using methyl

orange as indicator, and record as b the quantity of a cid removed from the

gelatin by sa lt . Assume (not strictly true) that the sa lt solution rema iningin the gelatin has the same concentra tion of a cid as that titrated

,and ca l culate

c,the quantity of free a cid still left inthe gelatin . I f the quantity (b+c)represents the free a cid in the absorbed solution before adding sa lt

,its con

centration was (b+0) V ,or y. What relation does y bear to x" Subtra ct

1 Contributed by John Arthur Wilson, of Ga llun Co .,M ilwaukee .


Osmotic Pressure of Colloids — For a very complete discussion

of osmotic pressure Of colloids,read Ostwald ’ s “ Handbook of

Colloid Chemistry,”231—262 ; also Zsigmondy

’ s Chemistry of

Colloids,38 .

Glues — The Technica l Notes of the Forest Products Labora

tory at M adison,Wis .

,give a va st amount of valuable information

On glues and glue testing .

A useful paper on glues by R . H . Bogue is found in Chemica l

Age,30, 103, 1922 .

Pure Fib rin .

—For the prepara tion of pure fibrin, read a paper

by A . W . Bosworth (Jour . Biol . Chem .

Pure Casein .

— Van Slyke and Baker,Jour . Biol . Chem .

,35

,

127 give an excellent method for the preparation of pure

casein .

Photometric M ethods — Sheppard and Elliott,Jour . Am .

Chem . Soc .

,43, 531 outline some useful photometric

methods and apparatus for the study of colloids .

In Chem . Met . Eng ,23, 1005 (1920) Alsberg presents some

suggestive colloid problems .

BRIEF BIBLIOGRAPHY

1 . Jerome Al exander : “ Colloid Chemistry . 90 pp . D. Van NostrandCo .

,New York City

,1 919 . Dea ls largely with the pra ctica l applica tions of

the science .

2 . Plimmer : “ Pra ctica l Organic and Bio-Chemistry,”Longmans, Green

Co .

,New York

,1918 . In pages 374—391 is given a clearly-written intro

duction to colloid chemistry .

3. Emil Hatschek : “ An Introduction to the Physics and Chemistry of

Colloids .

”172 pp . P . BlakiSton ’

s Son Co .

,Ph iladelphia , 1922 . Ba sed

on a course of ten lectures . A useful introduction to colloids . Th ird edition .

4. Wolfgang Ostwa ld : Theoretica l and Applied Colloid Chemistry .

”

Translated by M artin Fischer . 232 pp . John Wiley Sons,Inc .

,New York

City,1917 . Revision of a course of five lectures given in the United Sta tes

a few years ago . A very stimulating book . Second edition in press .

5 . Zsigmondy The Chemistry of Colloids . Translated by Spear .288 pp . John Wiley Sons

,Inc . , New York City, 1917 . One of th e most

useful books of its size on the subj ect yet published . Conta ins 33pp . on the

industria l applications of colloids .6 . W . D . Bancroft : “ Applied Colloid Chemistry . 345 pp . M cGraw

Hill Book Co .,Inc .

,1921 . Written at the request of the Committee on the

Chemistry of Colloids . A stimulating book,full of illumina ting comments

on the work recorded in the literature . Especia lly strong in trea tment ofadsorption . Every colloid chemist sh ould own th is book .

7 . Freundlich : Kapillarchemie .

”591 pp . Leipzig . 1909 . Thegrea t

est classic in the literature of colloids .

8 . Wolfgang Ostwa ld : “ Handbook of Colloid Chemistry . Translatedby M artin Fischer . 284 pp . P . Blakiston

’s Son Co .

,Ph iladelph ia

,1919 .

Gives va luable references to the literature . A translation of Ostwa ld ’ sGrundriss der Kolloidchemie . Second edition .

9 . Bechhold : Colloids in Biology and M edicine . fi anslated by Bullowa from second German edition . 464 pp . D . Van Nostrand Co .

, New

York City,1919 . A useful book

,somewhat specia lized as the title indicates,

b ut va luable to any student of colloids . Conta ins 40 pp . on M eth ods ofColloida l Research

,

” including much of th e author ’s own work on

ultrafiltration .

10 . Taylor : Colloids .” 327 pp . Longmans,Green Co New York

City . Not very well arranged . Conta ins some useful directions for the

preparation of colloids . Should be used only as a reference book on isolatedpoints .

1 1 . Burton : Physica l Properties of Colloid Solutions . 197 pp . Longmans

,Green Co .

,New York City, 1916 . Contains a good bibliography .

Rather physica l in treatment .

120 BRIEF BIBLIOGRAPHY

12. The Svedberg : Herstellung Kolloider Lesungen . 507 pp . TheodorSteinkopf, Dresden, 1909 . A classic . Gives ful l directions for preparinghundreds of colloids . Conta ins a va luable bibliography .

13. Trivelli and Sheppard : “The Silver Bromide Gra in of Photograph ic

Emulsions .

”143pages . D . Van Nostrand Co .

,New York City . A splendid

monograph,the first of a series .

14. M a rtin Fischer : (Edema and Neph ritis . 3d ed . 922 pp . JohnWiley Sons

,Inc . New York City

,1920 . Outlines and defends a treatment

of disease ba sed on the principles of colloid chemistry .

15 . First, Second and Th ird Reports on Colloid Chemistry and Its Genera land Industria l Applica tions, by the British Association for the Advancement ofScience . At H . M . Sta tionery Offi ce

,128 Abingdon St .

,London

,S . W . 1 .

Ea ch report (about 160 pp . ) conta ins chapters on specia l fields by eminentauthorities . Thorough reviews

,numerous references . An inva luable colloid

library . Ea ch report costs 2 6d .

16 . The Physics and Chemistry of Colloids (report of a genera l discussion held by the Faraday Society and the Physica l Society of London

,Oct .

Gels are discussed at length . Published by His M a j esty ’s StationeryOffice

,London .

17 . M artin Fischer Soaps and Proteins . 272 pp . John WileySons

,New York City

,1921 . A study of soaps as solvated colloids . Their

similarity to proteins in many respects is pointed out for the benefit of thephysician . Yet the commercia l side of soap manufa cture is not neglected .

A brilliant production .

18 . M art in Fischer and M arian Hooker : Fats and Fatty Degeneration .

146 pp . John Wiley Sons,Inc . , New York City

,1917 . Theories of emul

sification discussed, especially in relation to body tissues .

19 . U . S . Bureau of Soils,Bulletin 52; Absorption by Soils . 95 pp .

1908 . Very useful .20 . U . S . Bureau of Soils

,Bulletin 51 ;

“ Absorption of Vapors and Gasesby Soils .” 1908

21 . Ash ley : Techn ica l Control of the Colloida l M atter of Clays .U . S . Bureau of Standards

,Technologic Paper 23. 1 15 pp . Written in 191 1 .

22 . Bancroft : “ Applied Colloid Chemistry .

” Chem . M et . Eng .

,23

,

454 A brief survey of the field .

23. W . C . M cC . Lewis : Some Technica l Applications ofCapillary andElectrocapillary Chemistry,

” M et . Chem . Eng .,15, 253

—259 a lsoJour . Soc . Chem . Ind . M ay 31 , 1916 . Somewhat l ike the book by Al exander

(No .

24 . Whitney and Ober : Jour . Am . Ch em . Soc . ,23, 856

—863

Gives an excellent bibliography, with brief comment, of colloid work publishedbefore 1901 . Nearly 150 references .

25 . A . Muller : Bibliography of Colloid Chemistry,Zeit . anorg . Chemie

,

39, 121 Three hundred and fifty-six references grouped by subj ects,without comment .

26 . Heber : Physikal ische Chemie der Zelle und Gewebe . WilhelmEngelmann , Leipzig, 191 1 .

27 Ridea l and Taylor Catalysis in Theory and Pra ctice . The

AUTHORS’INDEX

ALEX ANDER,

101 , 1 15

ALSBERG,1 18

APPLEYARD, 74

ASHLEY, 105

BA ILEY,1 12

BANCROFT,19

,25, 33, 34,

107,108

,1 15

BARTEL,8

BASKERV ILLE,33

BECHOLD ,27

, 91 , 1 15

VAN BEMMELEN,105

BENSON, 59B I GELow , 8

BINGHAM,67

BLEININGER,105

BOSWORTH,1 18

BRAY,1 10

,1 1 1

BRED I G,1 8

BRENZ I NGER,40

BRIDGMAN,25

BRIGGS,57

, 70

BROWN, WM . 7 , 8

BURTON, 24

CAMERON,64

,104

CH ILD,57

CLAYTON,27

CLOW Es,56

,62

CUSHMAN,104

CUY,15

JOHNSON,T . B .

,1 12

KENRICK,1,59

KING,102

KOBER,3

KRECKE,14

KRUYT AND VAN DER SPEK,24

FARMER,8

FINK,70

FISCHER,M . H 3 34, 35, 38, 39, 45,

56, 58

FISCHER,M CLAUGHLIN AND HOOKER,

120

FISCHER AND HERTz,21

FRAZER,1 10

,1 1 1

FREMY,15

FREUNDLICH, 24, 72, 73

HARDY,22

,1 13

HARKINS, 49, 60HATSCHEK, 22, 67, 91, 92, 93, 1 15HILLYER

,69

HOLMES,H . N .

,5,34

,47

,57

,64

, 91

2, 70

LARSON,1 1 1

LAMB,75, 1 10, 1 1 1

LAMB,CHANEY ANDWILSON, 75

LANGMUIR,75

LEA,CA REY

,29

,30

LIESEGANG, 95

LINDER AND PICTON,24

124 AUTHORS ’ INDEX

LOCHTE,BAILEY AND W . A . NOYES, R IDEAL AND TAYLOR

,1 1 1

1 12 RUSSELL,106

LOEB,46

LOONEY, 7

LUPPO-CRAMER, 30

MARCK,15

MATTHEWS,E . B .

,105

MATTHEWS,J . H .,

2

M CBA IN,39

BAOORE,104

NEIDLE, 9, 1 1

NEWMAN,62

NICHOLAS,25

,34

NAGEL,21

NOYES,W . A .,

1 12THOMAS AND GARARD

, 72

ODEN,121 UPSON

,45

OESPER, 59

OSTWALD,W0 ” 4, 9, 13, 25, 67, 72

VAN KLOOSTER, 23VAN SLYKE , 74

PAAL,1 1 1

PARSONS,L . W . ,

7,54

,55

,62

, 87

88 , 89

PATTEN,70

PATTEN AND GALLAGHER, 105PATrEN AND WAGGAMAN, 69PATRICK

,77, 87

PAUL I,46

PEAN DE ST . G ILLES , 14PELIVET-JOLI VET

,107

PETERS, 40

PICKERING,41

, 56, 58

PRINGSHE IM , 92 Z ECHMEI STER,42

PROCTOR, 1 17 ZSIGMONDY, 12, 13, 17, 26, 28, 34

SAHLROHM,72

SCHOEP, 8 , 1 15

SHEPPARD,S . E .

,12

S IMMONS,108

SKITA,1 1 1

SMITH,C . R .,

46

SOUTHCOMBE,1 13

SPEAR,108

SPRING,15

STOCKS,47

SVEDBERG,22

VVALPOLE,8

WASHBURN, 4, 20WATTS, 105VON WE IMARN, 35

WEISER,72

WEISER AND NICHOLAS,25

WILLIAMS,42

WI LLSTKTTER, 42, 1 1 1

WILSON,J . A .,

1 16, 1 17

WILSON,R . E ., 7, 54, 55

126 SUBJECT INDEX

Di-benzoyl cystine gel,40

Diffus ion, 5, 1 1Dispersion methods

,18

Donnan ’ s pipette,49, 61

Drop spread, 49Dyeing

,107

Emulsifier,Hatschek

’s,57

Emuls ions, 56chroma tic

,64

idea l film for, 60O il—in-Wa tel‘, 58 Ha rdy ’s rule

,22

pharma ceutical , 59 Hopca lite,1 10

Pickering ’s, 59 Humus

,103

tran spa rent, 63 Hydroph ile, 33

theories,57

,60 Hydroxides

,14

types,how to recognize, 63

water-in-oil, 58 , 62 Ice cream 29Emulsifying a gent, cellulose n itra te , Indica tors

,in soap solutions

,37

eggg

as 59Intermittent shaking, 57I 1

gela tin as, 57soe ectrI c pomt, 22

soap as,56

Emulsoids,32

Jelly, 33

Enzyme action, 102

Fa ts,58

Fehling ’s test, 3Ferric a rsena te, 21jellies

,47

Ferric hydroxide,14

,20

,21

gel,88

,89

Fibrin,pure

,1 18

Flota tion , 1 14Flowmeter

, 8 1, 82, 83, 87

Foam,stabilization of, 55

Fractiona l precipita tion, 25Froth concentration of a dye

,59 M anganese dioxide, 15

Fullers ’ earth , a ctivation of, 89 M astic, 2, 24, 27

in adsorption filtration , 71 Mayonna ise , 59water of constitution in, 89, 90 M ercuric ch loride, basic, 99

iodide,bands

,95

Gel,33 oxide , 3

structure, 37 sulph ide, 16

Gels,rea ction in, 91 Mercury on iron gauze, 1 15

Gelation , 29, 47 Molybdenum blue, 14capacity of soaps, 37, 38

Gelatin,imbibition of

,1 16 Neph elometry, 3

Gelatinous precipitates,33

Germ,theory of lubrication

,1 13

Glues,1 18

Go ld,bands and crystals, 98

by forma ldehyde,12

by tannin,13

by pyroca tech in,13

number,28

Grea ses,lubrica ting

,63

Gum arabic, 19

La cta lbumin,30

Lead iodide crystals, 93

tree, 93

Liesegang ’ s rings,95

Lloyd ’ s reagent,71

Lubrica tion,1 13

germ th eory of,1 13

mechanism of,1 13

theories of,1 13, 1 14

Lyoph ile,33

Lyoph obe,33

SUBJECT INDEX

Oedema and nephritis, 45Oiliness

,1 13

,1 14

Osmose, anoma lous , 8

Osmotic pressure,1 17

Oxides,14

Pa triotic tube,1 1

Pectin jelly, 39

Peptiza tion,18

Photometric methods,1 18

Pla stic flow,67

Powders,adsorption by, 75

coa rse and fine,70

Preferentia l adsorption, 19Problems

,19

,55

Protective colloids,27

Protein swelling,45

Prussian blue,4,20

Pyroxylin membranes, 7

Rea ctions in gels,th eory of

, 93

Recovery of adsorbed ga ses, 86 ,Reduction

,12

Rhythmic banding,95

Rosin,2

Rubber,108

as an emulsifying agent, 1 10as a solvent

,109 Tungstic a cid

,17

elonga tion of,108 Tynda ll cone

,2

re t t'

f,109

50 180 11

1

1

6;Ion 0

Ultra clay, 104

sm iling of 109Ultrafiltration,

1 15,1 16

ta ckiness O’

f 108Ultramicroscope, 101

Schul ze ’s law ,22 .

Selenium,30

Silicic a cid, 92

j elly,34

gel, 76

a ctiva tion of,76

properties of,76

gels of basic reactionSilver

,29

by tannin,13

Kohlschiitter ’s, 13

bromide, 27

127

Silver ha lides, 19, 20iodide , 19

Springs ’ soap cleaning experiment, 68

Soaps,35

Soaps and proteins,35

, 38 , 67

Soap curd,39

Soap-oil gels,39

with a lcohols,36, 37

Soils and clays,103

adsorption Of wa ter vapor by,105

effect of va ria tions on humidityupon

,106

Solid a lcohol,33

Solva ted collo ids,32

,47

Sta lagmometer,49

Stannic a cid,17

Surfa ce and solubil ity, 1

Sulfides,16

Sulfur, 14Surface films on soap solutions

, 54

Surfa ce increase, 3tension

,48

appa ra tus,52

Suspensions,1

Suspensoids,32

Syneresis, 35

Vibrating gels, 34Viscos ity

, 32, 65

of an emulsion, 66of gela tin , 66of benzopurpurin

,66

of soap , 66Viscous flow,

67

Viscometers, 65, 66, 67

Wa ter glass, 92

Wa ter-holding power,36

Wa ter rings,71

von Weimarn’

s law, 4

Laboratory Manual Colloid Chemistry - Forgotten Books

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