(navigation image)
Home American Libraries | Canadian Libraries | Universal Library | Community Texts | Project Gutenberg | Children's Library | Biodiversity Heritage Library | Additional Collections
Search: Advanced Search
Anonymous User (login or join us)
Upload
See other formats

Full text of "Soluble silicates in industry"

UNIVERSITY 
OF FLORIDA 
LIBRARY 




SOLUBLE SILICATES 
IN INDUSTRY 



BY 



JAMES G. VAIL 

CHEMICAL DIRECTOR 
PHILADELPHIA QUARTZ COMPANY 



^UliLll 



American Chemical Society 
Monograph Series 



* •- v m m 

• * • .* • * # 



BOOK DEPARTMENT 
The CHEMICAL CATALOG COMPANY, Inc. 

419 FOURTH AVENUE, AT 29th STREET, NEW YORK, U. S. A. 

1928 



v 9.4) 



M/29s 



Copyright, 1928, by 
The CHEMICAL CATALOG COMPANY, Inc. 



All rights reserved 



1 



, ■ • \ < ' « . c' 

• • * • * 



CI 



Printed in the United States of America by 

J. J. LITTLE AND IVES COMPANY, NEW YORK 






GENERAL INTRODUCTION 

American Chemical Society Series of 
Scientific and Technologic Monographs 

By arrangement with the Interallied Conference of Pure and 
Applied Chemistry, which met in London and Brussels in July 
1919, the American Chemical Society was to undertake the pro- 
duction and publication of Scientific and Technologic Mono- 
graphs on chemical subjects. At the same time it was agreed 
that the National Research Council, in cooperation with the 
American Chemical Society and the American Physical Society 5 
should undertake the production and publication of Critical 
Tables of Chemical and Physical Constants. The American 
Chemical Society and the National Research Council mutually 
agreed to care for these two fields of chemical development, 
The American Chemical Society named as Trustees, to make 
the necessary arrangements for the publication of the mono- 
graphs, Charles L. Parsons, Secretary of the American Chemical 
Society, Washington, D. C; John E. Teeple, Treasurer of the 
American Chemical Society, New York City; and Professor 
Gellert Alleman of Swarthmore College. The Trustees have 
arranged for the publication of the American Chemical Society 
series of (a) Scientific and (b) Technologic Monographs by the 
Chemical Catalog Company of New York City. 

The Council, acting through the Committee on National Policy 
of the American Chemical Society, appointed the editors, named 
at the close of this introduction, to have charge of securing 
authors, and of considering critically the manuscripts prepared, 
The editors of each series will endeavor to select topics which 
are of current interest and authors who are recognized as author- 
ities in their respective fields. The list of monographs thus far 
secured appears in the publisher's own announcement elsewhere 
in this volume. 

3 



^W 



4 GENERAL INTRODUCTION 

The development of knowledge in all branches of science, and 
especially in chemistry, has been so rapid during the last fifty 
years and the fields covered by this development have been so 
varied that it is difficult for any individual to keep in touch with 
the progress in branches of science outside his own specialty. 
In spite of the facilities for the examination of the literature 
given by Chemical Abstracts and such compendia as Beilstein's 
Handbuch der Organischen Chemie, Richter's Lcxikon,Ostwald's 
Lehrbuch der Allgemeinen Chemie, Abegg's and Gmelin-Kraut's 
Handbuch der Anorganischen Chemie and the English and 
French Dictionaries of Chemistry, it often takes a great deal 
of time to coordinate the knowledge available upon a single topic. 
Consequently when men who have spent years in the study of 
important subjects are willing to coordinate their knowledge 
and present it in concise, readable form, they perform a service 
of the highest value to their fellow chemists. 

It was with a clear recognition of the usefulness of reviews of 
this character that a Committee of the American Chemical 
Society recommended the publication of the two series of mono- 
graphs under the auspices of the Society. 

Two rather distinct purposes are to be served by these mono- 
graphs. The first purpose, whose fulfilment will probably render 
to chemists in general the most important service, is to present 
the knowledge available upon the chosen topic in a readable 
form, intelligible to those whose activities may be along a wholly 
different line. Many chemists fail to realize how closely their 
investigations may be connected with other work which on the 
surface appears far afield from their own. These monographs 
will enable such men to form closer contact with the work of 
chemists in other lines of research. The second purpose is to 
promote research in the branch of science covered by the mono- 
graph, by furnishing a well digested survey of the progress 
already made in that field and by pointing out directions in 
which investigation needs to be extended. To facilitate the 
attainment of this purpose, it is intended to include extended 
references to the literature, which will enable anyone interested 
to follow up the subject in more detail. If the literature is so 
voluminous that a complete bibliography is impracticable, a 
critical selection will be made of those papers which are most 
important. 



GENERAL INTRODUCTION 5 

The publication of these books marks a distinct departure in 
the policy of the American Chemical Society inasmuch as it is 
a serious attempt to found an American chemical literature with- 
out primary regard to commercial considerations. The success 
of the venture will depend in large part upon the measure of 
cooperation which can be secured in the preparation of books 
dealing adequately with topics of general interest; it is earnestly 
hoped, therefore, that every member of the various organizations 
in the chemical and allied industries will recognize the impor- 
tance of the enterprise and take sufficient interest to justify it. 



AMERICAN CHEMICAL SOCIETY 



BOARD OF EDITORS 



Scientific Series: — 

William A. Noyes, Editor, 
Gilbert N. Lewis, 
Lafayette B. Mendel, 
Arthur A. Noyes, 
Julius Stieglitz. 



Technologic Series: — 

Harrison E. Howe, Editor, 
Walter A. Schmidt, 
F. A. Lidbury, 
Arthur D. Little, 
Fred C. Zeisberg, 
John Johnston, 
R. E. W t ilson, 

E. R. Weidlein, 
C. E. K Mees, 

F. W. Willard. 



Digitized by the Internet Archive 

in 2010 with funding from 

Lyrasis Members and Sloan Foundation 



http://www.archive.org/details/solublesilicatesOOvail 



Acknowledgment. 

A life which is rich in friendship and association with interesting, 
helpful people is so much a product of those contacts that acknowl- 
edgment of their influence in any piece of work can be neither complete 
nor adequate. Such is the present case. The author has a sense of 
indebtedness to many people who by inspiration, instruction, or counsel 
have contributed to his effort. He wishes to acknowledge and thank 
them cordially, though he mentions but a few. 

Specifically his thanks are due to his colleagues of the Board of 
Directors of the Philadelphia Quartz Company for the release of in- 
formation of a sort often regarded as confidential and for an attitude 
of sympathy and understanding not always found among those who 
guide industrial enterprises; to Dr. William Stericker for consultation, 
criticism, and bibliographical help throughout the work ; to Laura Jane 
Lee, who checked manifold references, typed the manuscript, read the 
proofs, and in general supplemented his limited stock of time and 
patience; to very many co-workers and friends who by suggestion, 
advice, and encouragement have led him to believe the work was needed. 
In the hope that each may be justified in his faith this book is offered 
to those who share with us the desire to know more of soluble silicates. 



Table of Contents. 



Chapter 1. — Introduction 11 

Historical Development — 'Beginnings of Soluble Silicates — Industrial 
Uses — Manufacture — Literature of the Silicates — Nomenclature — Present 
Importance. 

Chapter 2. — The Constitution of Silicate Solutions 17 

Natural Occurrence of Colloidal Silica — Dispersion in Water — Utiliza- 
tion of Silica by Certain Organisms — Behavior of Silica Sols — Develop- 
ment of Colloidal Properties — Tendency Toward Gelation — Transition 
from Sol to Gel — Crystallization — Structure of Silica Gels — Constitu- 
tion of Solutions of Sodium Silicates — Electrical Evidence — Effects 
Due to Number of Particles — Chemical Evidence— Structure of Systems 
with Relatively Low Water Content — Adsorption of Sodium Ions on 
Silica Particles. 

Chapter 3. — Definite Soluble Silicates 58 

Sodium Silicates — Formation of Hydrous Forms of Metasilicate — Trans- 
formations of Hydrates — Preparation of Anhydrous Metasilicate and Di- 
silicate — Anhydrous Systems — Potassium Silicates — Lithium Silicates — 
Rubidium Silicates. 

Chapter 4. — Reactions 72 

Precipitation — Compounds Causing Precipitation — Presence of Products 
of Hydrolysis — Reactions of Metallic Salts — Fractional Precipitation by 
Alcohol — Ammonia — Gelation — Electrolytes — Reaction with Coloring 
Materials and Various Solid Compounds. 

Chapter 5. — Preparation 88 

Wet Methods — Infusorial Earth — Insoluble Silicates — Sodium Sulfide — 
Adsorbent Carbon from Rice Hulls — Electrolysis— Sodium Hydroxide 
and Silicon Carbide — Sodium Chloride — Dry Methods — Sodium Nitrate 
— Sodium Hydroxide — Sodium Sulfate and Carbon — Fusion of Car- 
bonates with Silica — Formation of Crystalline Metasilicate — Indication 
of Orthosilicate — Disilicate — Fusion of Soda Ash and Silica — Dissolving 
— Character of the Solution — Apparatus for Dissolving. 

Chapter 6. — Commercial Forms and Properties 108 

Classification — Raw Materials — Anhydrous Solids — Neutral Glass — Al- 
kaline Glass — Glass Made from Sulfate — Properties — Hydrous Solids — 
Absorption of Moisture by Glass — Hydration — Dehydration — Preferred 
Methods of Solution — Properties — Hydrates of Sodium Metasilicate — 
Solutions — Range of Ratios — Clarity — Properties — Methods of Analysis 
— Glass — Determination of Sodium Oxide — Determination of Silica — De- 
termination of Water — Composition — Containers — Transportation and 
Storage — Pumps. 

9 



10 TABLE OF CONTENTS 

PAGE 

Chapter 7. — Silicate Cements 165 

Definition of Cements and Adhesives — Classification of Silicate Cements 
— Cements which Set Primarily by Loss of Moisture — General Prop- 
erties — Fillers — Abrasives — Briquets — Modification of Properties — 
Accelerated Setting — Acid-Proof Cements — Temperature Relations — 
Kaolin Cements — Casting Metals — Molded Articles — Miscellaneous Ce- 
ments — Cements which Set by Chemical Reaction — Lime Mortars — 
Characteristics — Addition of Acids and Salts Which React Quickly — 
Calcium Carbonate — Special Cements — Bituminous Materials — Mixtures 
Containing Portland Cement — Metallic Cements — 'Saturation with Sili- 
cate Solutions. 

Chapter 8. — Adhesives 210 

Definition and General Behavior — Silicate Adhesives Unmodified by 
Other Materials — Glass — Mica — Asbestos Paper — Wood — Vulcanized 
Fiber — Fiber Board — Corrugated Paper — Laminated Board — Miscella- 
neous Uses — Adhesive Mixtures — Mixtures with Insoluble Inorganic 
Powders — Silicate-Carbohydrate Mixtures — Silicate-Casein Mixtures — 
Blood Adhesives — Glue-Silicate Mixtures — Other Materials Compatible 
with Silicate Solutions — Testing Adhesives — General References. 

Chapter 9. — Sizes and Coatings 252 

The Nature of Silicate Films — Uses of Silicate Films without Pigment 
— Coating Paper — Barrel Testing and Sizing — Fire-proofing — Miscella- 
neous Uses for Silicate Films— Coatings on Metal — Silicate Paints — 
Nature of Paint Systems — Suitable Pigments — Silicate Vehicles — Light 
Diffusion — Coatings on Wood — Miscellaneous Uses — Dry Paint Mix- 
tures — Patent Literature — Analysis — Paper Sizing — Silicate Sizing — 
Manipulation of Silicate in the Mill — Combinations with Soluble Sili- 
cates — Advantages of Silicate Sizing — Textile Processes — Silk Weight- 
ing — Dyeing and Printing — Sizing — Mercerizing — Degumming Silk. 

Chapter 10. — Deflocculation and Detergency 300 

Characteristics of Soluble Silicates Which Affect Their Detergent Ac- 
tion — Deflocculation — Wetting Power — Emulsification — Lathering — Lu- 
brication — Solution — Soap-Sparing Action of Silicate Solutions — Effects 
on Fabrics — Silicates in Detergent Practice — Silicates Alone — Silicates 
in Conjunction with Other Materials — Silicates and Soaps — Analysis 
of Detergents Containing Soluble Silicates — Testing Detergency. 

Chapter 11. — Gelatinous Films and Gels 370 

Conditions Necessary for Gel Formation — Gelatinous Films — Formation 
by Cataphoresis — Prevention of Corrosion — Boiler Compounds — Elec- 
trolytic Baths — Galvanized Iron — Egg Preserving — Gels — Conditions 
Necessary for Formation — Gels Formed by the Action of Salts of Heavy 
Metals — Drying and Rehydration — Adsorption — Base for Catalysts — 
Base-Exchanging Gels. 

Chapter 12. — Additional Uses 405 

Purifying Water — Precipitation of Silicate Solution by Sodium Com- 
pounds — Treatment of Greensand by Silicate Solutions — Miscellaneous 
Uses — Purifying Sugar Solutions — Physiological Effects of Silicate Solu- 
tions — Therapeutic Uses — Accidental Doses. 



SOLUBLE SILICATES IN INDUSTRY 

Chapter I. 
Introduction. 

Historical Development. 

Pliny the Elder x began his great book, "Naturalis Historia", with the 
statement that he had assembled 20,000 facts. At least as many facts 
pertinent to the uses of soluble silicates in industry are known, for so 
widely have their applications been extended in the past two decades 
that there are few manufacturing plants which are not using, somewhere, 
at least one of the many grades. 

The mere assembly of facts is insufficient; there must be an effort 
to correlate them and to understand the reactions and properties which 
underlie each use separately and groups of uses collectively. The data 
with which to do this are in many cases incomplete, but an attempt has 
been made to review the most important literature and to set forth such 
parts of it as have been adjudged reliable and helpful for the purpose 
in hand. This critical selection is essential, for much has been written 
which is of little value in the light of our present knowledge. 

Beginnings of Soluble Silicates. 

Some of Pliny's accounts belong in the category of the doubtful, but 
one of them sets the stage for the beginnings of soluble silicates. The 
story 2 is of sailors who took chunks of natural soda from their cargo 
to support cooking vessels over their fire on a sandy beach. They were 
ignorant of the fact that the glass formed by the interaction of sand 
and soda was soluble in water. This observation was not made until 
many centuries later. 

A manuscript accredited to the alchemist Basil Valentine and sup- 
posed to have been written about 1520, contains the first reference to 

'Pliny, "Natural History," Text of Hardouin, Lemaire's Ed., Vol. 1 (1827), 
p. 16. 

a Pliny, "Natural History," Vol. 36 (1827), p. 65-6. 

1 1 



12 SOLUBLE SILICATES IN INDUSTRY 

soluble silicates as products of the arts. 3 He seems to have known how 
to make a glass which was fluid in the cold by melting a mixture of 
powdered silica and "sal tartari" which, after cooling, gradually became 
liquid on exposure to the air. It was said to be thick and oily, capable 
of being dried out by warming, and suitable for artificially petrifying 
wood or making building stone. The work, indeed the existence, of 
Basil Valentine is shrouded in mystery — he may be a creation of the 
imagination of a writer of later date; but whatever the merits of this 
account may be, we have reliable records beginning in the year 1640. 
In that year Van Helmont 4 was aware that the combination of silica 
with an excess of alkali will become liquid in damp places and that it 
is possible to precipitate silica equal in weight to the original amount 
by treatment of the solution with acids. Eight years later Glauber 5 
named the liquid "oleum silicium" and showed that solutions of various 
metallic salts caused the precipitation of compounds of silicic acid and 
the metal. These were proposed as specifics for the treatment of gall- 
stones. The results were not encouraging and the discovery was 
forgotten. Records show that Georg Bauer, often referred to as 
Agricola, knew of the existence of a silicate of potash. 6 In 1783 Guyton 
de Morveau melted quartz and sodium carbonate together; the fusion 
resulted in a transparent glass that could be dissolved in water. 7 

Industrial Uses. 

The real beginning of industrial uses for soluble silicates was due 
to the work of Johann Nepomuk von Fuchs. 8 He rediscovered them 
by accident in 1818 in the course of experiments undertaken for the 
purpose of purifying silicic acid. He dissolved silica in caustic potash, 
observed the glass-like properties of the solution, and named it water- 
glass. After investigating its property of hardening when spread upon 
surfaces, he was able to show how it could be employed as a coating 
of glass for a multitude of different uses. Some of these have survived 
until the present time — others were based on insufficient knowledge 
and have been forgotten. Von Fuchs proposed soluble silicates as glues, 
cements and mortars, fireproof paints, hardening agents for natural 
and artificial stone, and as a binder for colors used in fresco painting. 

3 l Z. Oesterr. Ingenieurer, 14, 229 (1862). 
4 Zwick, Hermann, "Das Wasserglas," 1877, p. 4. 

5 Glauber, "Furnis novis philosophicis," 1648. 

6 Agricola, "De Re Metallica," trans, by Herbert Clark Hoover and Lou 
Henry Hoover, 1912. 

7 Buffon, "Die naturgeschichte der minerale," trans, by Schaltenbrand, 2 
(1783-5). Chem, Ztg., 19, 117-118 (1895). 

8 von Fuchs, Johann Nepomuk, Poly. J., 17, 465-481 (1825). 



INTRODUCTION 13 

Ffe also suggested their use in the laundry, both in the process of 
washing directly and as a constituent of the soap ; in the textile indus- 
tries, for sizing and for reagents in dyeing ; and as a flux for soldering 
and welding. He even suggested silicates for fertilizer material. 
Though potassium silicates are doubtless effective, the justification of 
their use on economic grounds is open to question until they can be 
produced more cheaply. 

The failure of early efforts to produce a uniform product allowed 
some processes to fall into disuse which are now well served by silicates 
made under close control. Fluctuations in quality and the over-enthusi- 
astic claims of von Fuchs account for many disappointments. Public 
interest which was keen in 1820 had subsided to a very low ebb in 
1867 when W. Gossage & Sons of Widnes, England, exhibited a soap 9 
which was said to contain thirty per cent of a 20° Baume solution of 
sodium silicate. It became very popular and was made at the rate of 
60 tons a week. In Vienna, a silicate coconut oil soap containing eight 
per cent silica as silicate was made at this time by A. C. Diedecks 
Sohn. 10 

In France silicate solutions became popular for making rigid surgical 
bandages. During the year of 1873, this use consumed 2223 kilograms. 

Manufacture. 

The manufacture of soluble silicates in this country dates back to 
1864 when it was introduced by the Philadelphia Quartz Company. A 
closing of the commerce in pine products between northern manufac- 
turers and southern harvesters, brought on by the war between the 
States, had forced soap into the class of a luxury because of the high 
cost of the rosin used in its production. It was an outgrowth of this lack 
that soluble silicates were first manufactured here. They were used as 
substitutes for rosin. 

Other uses developed steadily, though until the opening of the present 
century the increase of tonnage was very slow. Mostly, the new uses 
were based on the old suggestions ; but as interest increased, fresh ideas 
evolved and developments are perhaps more actively in progress now 
than at any former time. 

Literature of the Silicates. 

There are comparatively few general treatises on waterglass although 
it is referred to in practically every work on general chemistry. Von 

9 Oesterr. Ausstelhtngsber., 5, 438 (1867). 
10 Zwick, Hermann, "Das Wasserglas," 1877, p. 10. 



14 SOLUBLE SILICATES IN INDUSTRY 

Fuchs published his researches in 1825. A forty-six page pamphlet 
by Zwick 11 in 1877 gives a good statement of the available knowledge 
of soluble silicates in Germany at that time and Kratzer 12 in 1887 pub- 
lished a book which, even in revised editions of 1907 and 1922, is much 
out of date. A book by Bernhard 13 was published in 1893; Dralle 
devoted a section of his work on glass making to soluble silicates (1911) 
and Mayer 14 published a useful but brief treatise in 1925. The rest 
of the literature is scattered as journal articles and incidental treat- 
ments in books on other subjects or works of reference. The Carnegie 
Library of Pittsburgh 15 published in 1922 a valuable bibliography, but 
a daily contact with problems related to soluble silicates emphasizes the 
fact that there is much known which has never been published and 
critical treatment from the point of view of American industry is 
lacking. 

Nomenclature. 

The nomenclature of silicates throughout the literature is various. 
The word silicate of soda is so deeply intrenched in commercial usage 
that it seemed best not to set it entirely aside. In writing formulas, the 
practice is here adopted of using the symbols for the two oxides with a 
period between them when it is intended to indicate a definite compound. 
A comma has been used between the two oxide symbols when the pur- 
pose of the formula is merely to indicate the ratio in which oxides are 
present. Sodium disilicate will thus be represented as Na 2 0.2Si0 2 , 
while a system of the same ultimate composition in which the state of 
chemical combination is not known will be represented as Na 2 0, 2Si0 2 . 

Present Importance. 

The present scope of the industry in the United States 16 may be 
gauged by the following statistics taken from a report by the Bureau 
of the Census. The weights are based on 40° Baume liquid which con- 
tains about 38 per cent total solids. The result is approximate only as 

11 Zwick, op. cit. 

"Kratzer, Hermann, "Wasserglas und Infusorienerde," Hartleben's "chemisch- 
technische Bibliothek," 1907. 

13 Bernhard, L., "Das Wasserglas," 1893. 

14 Mayer, Hermann, "Das Wasserglas," Sammlung Vieweg, No. 79, Friedr. 
Vieweg & Sohn Akt.-ges. Braunschweig, 1925. 

"Carnegie Library of Pittsburgh, "Waterglass, A Bibliography," compiled by 
Morris Schrero, 1922. 

"Chenu Met. Eng., 34, 585 (1927). 



INTRODUCTION 15 

no allowance is made for varying ratio between silica and soda, and 
some variation in water content. 

1925 1923 

Establishments 22 21 

Production 494,000 tons (2000 lbs.) 418,849 

Consumed by maker 100,000 87,849 

For sale 394,000 331,000 

Value $5,715,026 $5,066,719 

Per ton $14.48 $20.95 

The 1927 production may be roundly estimated at 500,000 tons. 
The other principal producing countries are England, Germany, 
France, Holland, Belgium, Switzerland, Italy and Greece, with rela- 
tively minor output in Mexico and Japan. Statistics are not available 
but a rough idea may be had by estimating production outside the United 
States in 1927 at 150,000 metric tons 40° Baume solution. The neces- 
sity of establishing large units for economical production and the 
restriction of markets by freight costs which draw a line around each 
producing unit have led to a capacity far in excess of the 1927 market, 
not only as a whole but in each local consuming center. This is a world 
* situation and would probably take care of a growth of 50 per cent. 

From the point of view of industry, the soluble silicates are those of 
sodium and potassium although all the alkali metals form silicates which 
dissolve in water, and even ammonia affects the solubility of silica. 
Because of their lower cost, the sodium compounds are used in amounts 
compared with which those of potassium silicates are insignificant. 
There are, however, a few cases where the distinctive advantages of 
potassium silicates give them a place. The following pages will there- 
fore treat principally of sodium silicates and refer to the others pri- 
marily for the purpose of analogy and suggestion. 

Silicates of soda provide a favorite theme for the patentee. In par- 
ticular, that type of inventor who produces compositions of matter 
without competent knowledge of the materials he uses, seems to find 
much of interest in the colloidal and fire-resisting properties of the com- 
mercial grades. Their low cost is doubtless an added attraction. 
Numerous patent citations will be found in the following pages, but 
it should be understood that no attempt has been made to treat this 
literature exhaustively nor to mention all of the hundreds of patents 
which have been examined but are regarded as unimportant. 

Among persons interested in silicates of soda are found those whose 
primary outlook is based on the consideration of scientific data while 
there are others, perhaps a more numerous class, who think of silicates 



16 SOLUBLE SILICATES IN INDUSTRY 

first from a practical standpoint. To the latter, the author would sug- 
gest that they proceed next to Chapter VI, returning to Chapters II, III, 
IV and V later or as the data they contain may be needed for reference 
purposes. 



Chapter II. 
The Constitution of Silicate Solutions. 

Natural Occurrence of Colloidal Silica. 

Industrial silicate solutions are systems in which colloidal silica plays 
an important role. To attempt to interpret their behavior without taking 
this into account is to miss the meaning of some of the most important 
phenomena. 

Dispersion in Water. 

Silica is so abundant and so slightly affected by long contact with 
water that we easily forget it is most omnipresent in a highly dispersed 
condition. All natural waters contain silica. Silica constitutes, accord- 
ing to Clarke, 1 nearly 60 per cent of the lithosphere, 2 so that contact 
between water and silica is inevitable and dispersion into particles of 
colloidal size takes place in every spring or stream. High concentra- 
tions are not reached in this way, but from these dilute natural systems 
crystalline quartz and many silicious rocks have been laid down. 

The first waters that condensed upon the surface of the earth must 
have flowed over igneous rocks and contained as one of their principal 
solid constituents, silica colloidally dispersed. Clarke 3 says that silicious 
deposits are formed by all waters containing silica but are commonly 
so small as to be inconspicuous. It may be here remarked that a thin 
gelatinous film of silica is always inconspicuous until dehydrated. 
Bastian, 4 speculating upon the origin of life, has been able to produce, 
under the influence of sunlight, cell-like structures from dilute solutions 
containing silica. 5 Under these conditions the silica tends to aggregate 
and yield structures so like living cells as to make this author believe 
that it was on this wise that life began on the earth. 

Hydrous deposits of silica occur in nature as opal, and massive quan- 

1 Bull. U. S. Geol. Sur., 770, 20, 26-34 (1924). 

2 Vail, James G., /. Soc. Chew, hid., 44, 214T-219T (1925). 

3 Clarke, loc. cit. 
'Nature, 92, 579 (1914). 

5 Moore, Benjamin, and W. G. Evans, Proc. Roy. Soc, ser. B, 89, 17 (1915). 

17 



18 SOLUBLE SILICATES IN INDUSTRY 

tities of silica gel were found in the course of excavating the Simplon 
Tunnel. 6 

Utilization of Silica by Certain Organisms. 

Certain it is that many of the simpler forms of life use silica as an 
essential of their structure, building it into their framework in the 
most intricate and beautiful forms. Such are the diatoms, 7 whose 
remains constitute vast deposits of nearly pure silica. The great surface 
of diatomaceous earth makes it valuable for thermal insulation and 
other processes such as filtration where its structure distinguishes it 
from other forms of silica. Higher organisms, among them the horse- 
tail rushes (equisetum) and certain cereal plants, notably rice, build 
large amounts of silica into their structures. The former has enough 
to make it useful as an abrasive for cleaning metal ware. The seed 
hulls of rice contain about 35 per cent of silica. 8 Charred rice chaifF 
after extracting with caustic soda is used to make absorbent carbon 9 
and this process has been proposed as a source of commercial silicate 
of soda as a by-product. 10 The ability of plants to disperse and coagu- 
late silica has not been fully investigated. Acheson showed that tannic 
acid or other vegetable extractive matter was useful for dispersion. 
Diatoms are able to disperse flocculent silicious precipitates. 11 ' 12 The 
action of algae on volcanic waters, 13 running as in the case of the Opal 
Spring in Yellowstone National Park up to 700 parts per million, ac- 
counts for deposits of silicious sinter characteristic of various geyser 
beds. Further evidence of this sort of action has been reported by 
Gesell 14 from experience in a paper mill. He was able to produce a 
particularly tinny sheet of paper owing to the presence in the water of 
organisms which had the power of accumulating silica. 

Baylis, 15 in his work dealing with the problems of municipal water 
works, also calls attention to the ability of algae to utilize silica from 
the water. It seems fair to assume that the action of organisms which 

8 Spezia, G., Atti accad. Set. Torino, 34, 705 (1899). 

7 Richter, Oswald, Aus Dem PHanzen physiologischen Inst, der K.K. Deutschen 
Universitdt in Prag., No. 118, 22 (1911). 

8 Blardone, George, U. S. Pat. 1,293,008 (Feb. 4, 1919). 

9 McKee, R. H., and P. M. Horton, Chem. Met. Eng., 32, 14 (1925). 

10 Puttaert, Jean Frangois and Francis J. Puttaert, U. S. Pat. 1,588,335 (June 
8, 1926). 

11 Acheson, Edward G., Trans. Am. Ceram. Soc, 6, 31-46 (1904). 

13 Richter, loc. cit. 

"Weed, W. H., Am. J. Set., 3rd ser., 37, 351 (1889). 

14 Paper, 33, No. 23, 5-6 (1924). 

15 Baylis, John R., personal communication ; /. Am. Water Works Assoc., 9, 
712 (1922). 



THE CONSTITUTION OF SILICATE SOLUTIONS 19 

use silica has to do with accelerating or suppressing the tendency of 
the silica particles to become massed together and that this may take 
place in very dilute solutions. This power is especially remarkable in 
view of the difficulty of completely removing silica from dilute solution 
by precipitation or even repeated evaporation with acids, as in the or- 
dinary course of analysis. 

Behavior of Silica Sols. 

Development of Colloidal Properties. 

Silica freshly liberated by adding hydrochloric acid to a dilute solu- 
tion of alkali metal silicate exists in a very fine state of dispersion. 
It will diffuse through an animal, collodion, or parchment paper mem- 
brane sufficiently fine in texture to retain colloidal silver. 16 It causes 
a depression of the freezing point of water 17 and an electrical conduc- 
tivity which confirms the idea that the particle dimensions are more 
nearly like those of true solutions than like colloids. Mylius and 
Groschuff found a lowering in the freezing point of 0.118°. They 
observed only a slight decrease in the conductivity — 0.4 per cent 
(14088-14032). 

Egg albumen causes no precipitation at first, but changes soon take 
place. A silica sol which has aged, although it may remain liquid and 
appear superficially unchanged, will be retained by the membranes 
through which it previously passed ; it no longer gives a measurable 
depression of the freezing point of water, and its conductivity has fallen 
practically to zero. 18 ' 19 

Tendency toward Gelation. 

If now the liquid sol be concentrated under reduced pressure, it be- 
comes increasingly unstable and finally undergoes a rather sudden 
change in which the viscosity rises abruptly and the entire mass sets 
to a solid gel. 20 Silica gels containing three hundred molecules- of water 
for each molecule of silica set to a firm texture, and any sol containing 
this amount of water or less tends to form a gel including the whole 
of the liquid. 21 The rate at which the changes take place depends upon 
concentration, purity, temperature, time, and degree of agitation. A 

10 Zsigmondy, Richard, and R. Heyer, Z. anorg. Chem., 68, 169-187 (1910). 

11 Mylius, F., and E. Groschuff, Ber., 39, 121, 124 (1906). 
18 Sabanejeff, /. Russ. Phys. Chem. Soc, 21, 515 (1889). 
19 Bruni and Pappada, Gazs. Chim. Ital., 31 (1), 244 (1901). 
20 Graham, Thomas, Phil. Trans., 151, 205 (1861). 

a Holmes, Harry N., "Colloid Symposium Monograph," Vol. 1 (1923), p. 25. 



20 SOLUBLE SILICATES IN INDUSTRY 

sol containing 1 per cent of silica may, under favorable circumstances, 
remain fluid for a year, but the higher concentrations are exceedingly 
unstable. It may be regarded as a rare accident if a pure sol containing 
10 per cent of silica is obtained. 22 Such sols are so unstable that they 
gel very easily. Shaking of the containing vessel may be sufficient to 
cause the transition from liquid to solid. Graham, 23 whose classical 
studies laid the foundations of colloid chemistry, showed that the gels 
formed from silica sols developed with increasing speed, the greater 
the concentration. 

Sols of substantially identical character can be prepared only by 
minute attention to the composition and concentration of silicate solu- 
tions, to strength of the acid and all the conditions of dialysis. 24 

Zsigmondy 25 was able to prepare sols of much greater purity than 
Graham and to follow their increasing instability by measuring osmotic 
pressure, which declined steadily with advancing age of the sol. 

Ormandy 26 says that a silicic acid solution made by the electro-osmose 
process has, at the moment of its preparation, a molecular weight which 
corresponds to the formula H 2 Si0 3 and that the molecular weight in- 
creases steadily with time until with a 10 per cent solution, after about 
six weeks, the molecular weight is of the order of 60,000 to 80,000 and 
separation takes place. The conductivity of such solutions, kept in 
paraffin wax-lined vessels, affords such a close index of the change that 
the age of the solutions can be estimated within a few hours. 27 

Electrolytes may precipitate or stabilize the sols and these tendencies 
affect the time of gelation of sols which contain electrolytes. 28 ' 29 ' 30 

If we assume that these phenomena are the result of a tendency on 
the part of very small particles of colloidal silica to gather together 
into clusters or masses until finally they become large enough and 
sufficiently immobile to produce first a viscous liquid and then a solid 
gel structure, we shall have a concept which, though it does not offer 
a complete explanation, at least fits in with a large number of observed 
facts and helps to correlate them. 

22 Zsigmondy, Richard, "Kolloidchemie," Leipzig : Otto Spamer, 1912, p. 145. 

23 Fro. Roy. Soc, 13, 336 (1864). 

2 ; Grundmann, W., Kolloid Z., 36, 328-331 (1925). 

25 Zsigmondy, R., "Kolloidchemie," p. 149. 

28 Ormandy, W. R., "The Physics and Chemistry of Colloids and Their Bear- 
ing on Industrial Questions," Report of Joint Discussion of Faraday Society 
and the Physical Society of London, 1920 (Oct. 25), p. 143. 

27 Searle, A. B., "Third Colloid Report of the British Assoc, for the Advance- 
ment of Science," 1925, p. 123. 

28 Zsigmondy and Heyer, loc. cit. 

20 Werner, /. Am. Pharm. Assoc, 9, 501 (1920). 
30 Krozer, Kolloid Z., 30, 18 (1922). 



THE CONSTITUTION OF SILICATE SOLUTIONS 21 

Transition from Sol to Gel. 

Zsigmondy stated that silica sols always tend to aggregate and form 
gels, but limited it to sols that had been well purified and were not too 
dilute. It has been found, however, that a large number of reactions 
of soluble silicates encountered in industry may be at least partly ex- 
plained on the assumption that colloidal silica tends always to form 
larger particles and finally to produce a gel structure. 31 ' 32 ' 33 ' 34 ' 35 ' 3G 




Fig. 1. — Growth of Silica Crystals on Rounded Grains of Sand. 
(Courtesy C. L. Dake) 

Crystallization. 

Crystallization may take place from the same solutions which under 
other conditions form gels. Dake, 37 in his work on the St. Peter sand- 
stone, has found small rounded sand grains upon which crystal faces 

^Schwarz and Stowener, Kolloidchem. Beihefte, 19, 171 (1924). 

32 Schwarz and Leide, Ber., 53, 1509, 1680 (1920). 

^Schwarz and Leondard, Kolloid Z., 28, 77 (1921). 

34 Zsigmondy and Spear, "Chemistry of Colloids," 1917, p. 137. 

35 Grundmann, Kolloidchem. Beihefte, 18, 197 (1923). 

3G Bachman, Z. anorg. Chem., 100, 1 (1917). 

37 School of Mines and Met., U. of Missouri, Tech. Scr. Bull., 6, No. 1 (1921). 



22 SOLUBLE SILICATES IN INDUSTRY 

-have grown. The grains have evidently been worn round by long con- 
tinued attrition with the formation of colloidal silica from which, under 
other conditions, definite crystals could be developed. 38 Quartz crystals 
are built up very slowly from dilute sols. This is what we should expect, 
for crystals are arrangements of particles of atomic dimensions and 
silica sols contain these in a free condition for a short time only. 
Further, though the method of X-ray interference does not give any evi- 
dence of crystal structure in fresh silica gels, it is found in gels which 
have aged. 39 The particles of the fresh gel structure are then capable of 
rearrangement, a fact which we know also from the phenomenon of 
syneresis, in which the gel contracts and squeezes out some of the 
liquid phase. 

Structure of Silica Gels. 

Natural gels are familiar as opal. The rhythmic bands of agate 
resembling closely the rings formed by silica gels, in the experiments of 
Liesegang, 40 point strongly to the genesis of agates as gels. The en- 
during character of these minerals suggests that when it has once been 
formed, the gel structure of silica is not easily dispersed. 41 ' 42> 43 Agate 
must have remained for long periods of geologic time under water, 
becoming progressively harder until the point has finally been reached 
at which no definite gel structure can be detected. The work of 
Zsigmondy, 44 Patrick, 45 and others, has established the structure of 
silica gels as a system of pores in a solid phase. The silica particles, 
which have coalesced until their size became sufficient to permit adjacent 
particles to touch and form one unified mass, will of necessity have 
comparatively great spaces between them filled with the liquid phase 
from which the particles separated. The dimensions of these pores can 
be established only by their behavior, for they are ultramicroscopic. 
The amount of surface which can be exposed when such sols are dried 
is almost incredible. As we shall later return to the subject of gels, 
it will suffice, for the moment, to recall their very high capacity to 
adsorb vapors from gases and various colloid materials from organic 
liquids, as for instance, sulfur compounds in mineral oils. 

^Spezia, G. J., Atti Accad. Torino, 34, 705 (1899); /. Chem. Soc, 76, 300 
(1899); 78, 595 (1900). 

^Scherrer, P., Nachr. Ges. Wiss. Gottingen, 96, 100 (1918). 

40 Liesegang, R. E., Z. anorg. Chem., 48, 364 (1906). 

41 Holmes, Harry N., /. Am. Chem. Soc, 40, 1187-95 (1906). 
43 Zsigmondy, op. cit., p. 166. 

"Centr. Mineral. Geol., 593-597 (1910) ; 497-507 (1911). 

"Anorg. Chem., 71, 356 (1911). 

45 Patrick, W. A., and John McGavack, /. Am. Chem. Soc., 42, 947 (1920). 



THE CONSTITUTION OF SILICATE SOLUTIONS 23 

Constitution of Solutions of Sodium Silicates. 

Electrical Evidence. 

Charges on Silica Particles. The ability of silica to ads0rb ions 
has an important bearing upon the behavior at concentrations above 
those contemplated by Zsigmondy in his statement of the tendency of 
the particles to coalesce because the adsorbed material may, and fre- 
quently does, influence the rate at which such coalescence takes place, 
or in some cases inhibits it entirely. The colloidal particles of silica 
are, in general, negatively charged. 46 The electrolysis of an alkaline 
silicate solution is accompanied by migration of the silica particles 
toward the anode, and this condition persists except in solutions which 
have been made strongly acid. 47 The negative charge is steadily reduced 
by adding HC1 and may be reversed without precipitation. Gordon 48 
has shown the hydrogen-ion concentration at which the charge is re- 
versed and has pointed out that this may be due to a dissociation of 
silica which acts like an acid radical until the hydrogen-ion concentration 
is raised to a point where this phenomenon is suppressed. 49 

Table 1. Effect of pH on the Electrical Charge on Silica Gel. 



pH Values 


Charge 
on Gel 


Rate of Travel 

of Water in 

Mm. per Sec. 


E.m.f 


6.526 
4.717 
3.567 
1.217 


Negative 
Negative 
Negative 
Positive 


6.3 
3.1 
2.4 
1.4 


116 
120 
120 
119 



Electrometric Titration of Silicic Acid. Electrometric titration 
curves are characteristic of dibasic acids suggesting the formula H 2 Si0 3 
with salts NaHSi0 3 and Na 2 Si0 3 . 50 This acid has been studied by 
dialysis and taking into account the portion which does not diffuse it is 
probably a much stronger acid than has been realized. 

Multi-Charged Colloidal Micelles. If the colloidal silica particles 
are negatively charged and they continually tend to coalesce into larger 
particles without a change in the charge, it is convenient to assume the 
existence of charged colloidal micelles which McBain postulated in 
order to explain abnormally high conductivity of soap solutions. Nega- 
tively charged colloidal silica particles would tend to adsorb upon their 

40 Zsigmondy, R., op. cit., p. 147. 

47 Stericker, Wm., Doctor's Thesis, University of Pittsburgh, 1922, p. 6. 

48 L6senbeck, Kolloidchem. Beihefte, 16, 27 (1922). 

49 Gordon, Neil S., "Colloid Symposium Monograph," 2, 119-121 (1924). 

w Harman, /. Phys. Chem., 31, 616-625 (1927). 



24 



SOLUBLE SILICATES IN INDUSTRY 



surfaces positively charged ions which may be present in solution. We 
may think of the more silicious sodium silicate solutions as containing 
much of their sodium content attached in this way to colloidal silica 
particles. 

Electrical Conductivity. The work of Kohlrausch 51 on the con- 
ductivity of silicate solutions was the first to show evidence of a con- 
stitution in which colloidal silica exists along with sodium silicates which 
may be characterized as chemical individuals. He studied solutions 
of sodium metasilicate, Na 2 Si0 3 , and systems with more silica up to 
Na 2 0, 3.4Si0 2 and found that the former conducted the current better 
in very dilute solutions than an equivalent concentration of any of the 
numerous salts he investigated. With rising concentration the conduc- 
tivity fell off rapidly and concentrated solutions were found to be 
among the worst conductors. The metasilicate used was a crystalline 
commercial product with nine molecules of water and dissolved to a 
clear solution without residue. Its conductivity at high dilutions was 
30 to 40 per cent better than sodium chloride. At 0.75 mol per liter 
the two salts were nearly equal, and in concentrated solutions the meta- 
silicate was not more than one-third as good. 

Table 2. Conductivity of Sodium Metasilicate. 





Conductivity of 




Conductivity 


Mols Na 2 Si0 3 


Solution 


Temperature 


of Water 


per Liter 


Hg = l 


Coefficient 


for Dilution 


0.0001 


0.1363 X 10" 8 


0.0273 


0.011 


0.0005 


0.6853 " 


0.0249 


0.013 


0.0010 


1.359 


0.0232 


0.014 


0.0045 


5.74 




0.011 


0.0225 


27.73 





0.01 


0.0450 


53.11 


0.0216 


• • • • 


0.1004 


108.3 


.... 


.... 


0.2008 


198.3 


0.0225 


• • * • 


1. 


670. 







1.2650 


763.9 


0.0244 


• * • • 


2.5290 


1028. 


0.0273 


.... 


3.7930 


1031. 


0.0316 


• • • • 


4.5000 


963.9 


0.0347 


.... 


6.4 


655. 


0.0465 


.... 



Long boiling of a strong solution of the metasilicate with silica yielded 
a solution containing 3.4 mols Si0 2 per mol Na 2 0. This was at all 
dilutions an inferior conductor as compared with equivalent sodium 
chloride, though at concentration 0.0001 mol Na per liter it was 
nearly as good. As much more silica was present, the mobility was less 
than in the metasilicate solution. The conductivity fell off precipitously 

P1 Z. phys. Chem., 12 s 7?3-79\ (1893). 



THE CONSTITUTION OF SILICATE SOLUTIONS 25 

as the concentration rose, and at 0.01 mol per liter and above it was 
the worst conductor of all the salts investigated. 

Table 3. Conductivity of Na>0,3.4Si02. 



Mols 
Na 2 0, 3.4Si0 2 


Conducti 


vity of 


Temperature 


per Liter 


Solution (1) Hg = 


Coefficient 


0.000157 


0.1527 


X 10" s 


0.0297 


0.000788 


0.605 


u 


0.0302 


0.00788 


4.863 


a 


0.0263 


0.0788 


38.86 


u 


0.0258 


0.788 


203.7 


<< 


0.0288 


1.576 


279.4 


(i 


0.0310 


3.152 


289.2 


a 


0.0369 


3.693 


265.7 


u 


0.0406 



The conductivity of both solutions reached a maximum before satura- 
tion ; in the case of Na 2 Si0 3 , 1055 X 10~ 8 at 3.2 mols per liter concen- 
tration or 17 per cent; and the Na 2 0, 3.4Si0 2 , 300 X 10" 8 at 2.5 mols 




C * c e *? f~ra /"/' o fi 

Fig. 2. — Conductivity and Concentration. 



Na or 27 per cent. Kohlrausch also found an abnormal temperature 
coefficient of conductivity at all concentrations of the 1 : 3.4 ratio silicate. 
He expressed the opinion that this might be due to the breaking down 
of the silicate with increase of temperature. The metasilicate showed 



26 



SOLUBLE SILICATES IN INDUSTRY 



no extraordinary change of conductivity with temperature except at 
extreme dilution. Greater freedom of movement of the relatively large 
aggregates of silica at higher temperatures might also account for this. 

In order to throw light on the condition of the excess of silica over 
that required to form Na 2 Si0 3 in the more silicious silicates, mixtures 
were made in two series, the first beginning with NaOH and receiving 
1 : 3.4 silicate and the second beginning with 1 : 3.4 silicate to which 
NaOH solutions were added. Conductivity was measured on these after 



V 














, 


Temp eratvre 













s 



Fig. 3. — Effect of Increasing Silica en the Conductivity of Silicate Solutions. 

they had come h'to equilibrium. In the first. senes the conductivity de- 
creased rapidly until the ratio Na 2 0, 2Si0 2 was reached Values for the 
higher <rajtios were only, slightly smaller. Conversely, the second series 
showed no real change until Na 2 0, 25i0 2 was reached, then the conduc- 
tivity rose rapidly. It is to be noted that there was no bend in either 
series corresponding to the ratio of Na 2 Si0 3 , the definite substance 
from which the study began. The change of behavior corresponded to 
Na 2 Si 2 5 and the curve broke sharply at this point. The temperature 
coefficient which increased from to 2 did not change from 2 to the 
higher ratios. 

Freshly diluted solutions showed higher conductivity than those 
which had stood. The time required to reach equilibrium when mix- 
tures of silicate with sodium hydroxide or of two silicates of different 
ratio were made, depended on the order of mixture and the composition 



THE CONSTITUTION OF SILICATE SOLUTIONS 27 
Table 4. Conductivity ivith Changing Ratio. 



Si0 2 per 


Cone. Na 






Temp. 


k lol Na 2 


Mols per Liter 


Conductivity 


Coefficient 





0.00955 


1820 


X 10~ 8 




0.209 


0.00956 


1685 


u 




0.419 


0.00958 


1330 


H 




0.632 


0.00961 


1420 


(( 




0.829 


0.00964 


1290 


tt 




1.035 


0.00966 


1156 


<« 




1.237 


0.00969 


1031 


<( 




1.44 


0.00972 


930 


K 




2.05 


0.00980 


667 


U 




2.53 


0.00987 


634 


« 




3.41 


0.01000 


614 


(( 


0.0263 


3.02 


0.00994 


627 


(( 




2.53 


0.00988 


628 


« 


0.0265 


2.04 


0.00981 


629 


U 


0.0274 


1.54 


0.00975 


868 


« 


0.0243 


1.00 


0.00968 


1183 


tt 


0.0218 


0.497 


0.00961 


1503 


tt 


0.0204 





0.00955 


1826 


tt 


0.0197 



of the reacting solutions. Also the time which had transpired since the 
concentrated silicate solution was diluted had a marked influence. If 
the mixture contained less than two molecules of silica for each sodium 
(Na 2 0) it came into equilibrium quickly. Its conductivity was the 
average of the conductivities of its components. 

The following table shows the increase in conductivity readings above 
equilibrium after various time intervals from the mixing of 1 : 3.4 sili- 
cate which had stood three days since dilution to 0.01 mol Na per liter. 
with a sodium hydroxide solution to bring the ratio to 1 : 1.84. 

Table 5. Time Required to Obtain Equilibrium. 





Conductivity Above 




Conductivity Above 


Jinutes 


Equilibrium 


Minutes 


Equilibrium 





24.6 


100 


6.9 


0.5 ... . 


24.5 


120 

160 


49 


1 


24.2 


2.5 


5 


22.9 


180 


1.8 


10 


21.8 


200 


1.3 


20 


20.0 


250 


0.9 


40 


16.4 


300 


0.7 


60 


12.9 


500 


0.3 


80 


9.7 







Potassium silicate with potassium hydroxide showed similar behavior, 
the initial conductivity being in- some cases as much as 16 per cent above 
the equilibrium figure. 

Kahlenberg and Lincoln 52 determined the conductivities of solutions 
made by adding sodium hydroxide solution to silica sols. They found 

63 /. Phys. Chem., 2, 77-90 (1898). 



28 SOLUBLE SILICATES IN INDUSTRY 

Table 6. Conductivity of Silicate Solutions Prepared from Sodium Hydroxide 

and Silica Sol. 

Equivalent Conductivity at 25° C. 



V 


N 


NaOH 


Na 2 Si0 3 


NaHSiOa 


Na 2 0, 5SiO 


8 


0.125 


194.7 


105.3 


72.4 




16 


.0625 


197.4 


112.0 


78.8 




32 


.03125 


199.0 


117.8 


84.9 


73.6 


64 


.01563 


199.1 


115.0 


90.1 


79.9 


128 


.00781 


199.0 


119.5 


103.7 


87.3 


256 


.00391 


196.3 


95.7* 


114.2 


93.1 


512 


.00195 


188.9 


91.8* 


133.1 


101.1 



1024 .00098 181.8 104.8* 148.5 113.3 

v = volume in liters containing 1 gram molecule. 
N = volume normality, i.e., gram molecules per liter of solution. 

* Kahlenberg and Lincoln doubted these results because they were lower than 
those for NaHSi0 3 . 

that the freezing points of solutions of sodium metasilicate made in this 
manner did not differ greatly from those made from the metasilicate 
prepared by fusion and concluded from this that solutions made in 
the two ways were identical. From later work it seems highly im- 
probable that this conclusion can be applied to solutions containing two 
or more equivalents of silica to one of sodium oxide and even the 
metasilicate solutions would probably show slight but distinct differ- 
ences, as they did in freezing point determinations. The results 
obtained by Kahlenberg and Lincoln are given in Table 6. Hantzsch 53 
also made some determinations, but they do not agree with any other 
results and are probably incorrect. 







Table 7. Equivalent 


Conductivity 














T = 


= 25°C. 
















Ratio Na 2 0: 


SiO a 








Nv 


NaOH 


2: 1 


1:1 


1: 1* 


1:1.5 


1:2 


1:3 


1:4 


2.0 


142.0 


57.32 


57.25 


57.50 


32.09 


25.80 


20.46 


16.17 


1.0 


172.5 


85.57 


81.25 


81.20 


50.23 


36.10 


31.42 


23.24 


0.5 


200.0 


107.80 


96.80 


96.5 


66.75 


49.05 


45.41 


33.14 


0.2 


209.0 


136.90 


112.70 


113.0 


86.20 


62.59 


57.33 


48.25 


0.1 


214.5 


157.5 


130.80 


130.0 


99.20 


72.70 


66.48 


57.80 


0.05 


220.0 


175.5 


143.8 


142.6 


107.04 


78.00 


75.63 


65.80 


0.02 


225.5 


190.1 


152.7 


151.8 


114.20 


84.00 


81.75 


75.06 


0.01 


227.5 


193.0 


155.0 


156.0 


118.10 


89.50 


85.16 


81.50 


0.005 


228.0 


194.2 


158.0 


159.0 


120.14 


93.20 


89.90 


86.04 


0.0 






160.0 


.... 


121.00 


95.00 


91.00 


88.00 


*Fig 


ures taker 


l from 


Kohlrausch. 












Rrmt 


valent rnn 


dnrtivit 


X (1000 + X) 

v = — . 











— '"■> Afw P 

Where X = specific conductivity. 

X = no. grams solid in 1000 gms. water. 
Nw = weight normality, i.e., gram molecules of solute per 1000 gms. 
of water. 
P = density of the solution. 

53 Z. anorg. them., 30, 289-324 (1902). 



THE CONSTITUTION OF SILICATE SOLUTIONS 29 

Harman 54 confirmed and extended the work on conductivity and cal- 
culated equivalent conductivities. 

Plotting these against concentration, he points out the following : 

"(1) Ratio 1: 1, i.e., sodium metasilicate, Na 2 Si0 3 , has a very high 
conductivity in dilute solution. 

"(2) Ratio 2: 1 gives practically the same values as 1 : 1 at concen- 
trations 1-2 N w . This is very remarkable. 




10 



COAICENTRAT/OA/ A/a/ 



3 1.0 1.5 

Fig. 4. — Equivalent Conductivity. 



2.0 



"(3) All the other ratios are quite fair conductors in dilute solution, 
but show an abnormally low conductivity in concentrated solution, 
especially the higher ratios 1 : 3 and 1 : 4." 

Plotting equivalent conductivity against ratio, a sharp break in the 
curves seems to indicate the presence of Na 2 0*2Si0 2 in solution and 
similar deviations suggest but do not prove that 2Na 2 OSi0 2 and 
Na 2 Si0 3 are also present in the more concentrated solutions. 

Kohlrausch and the other earlier investigators had concluded that 
the high conductivity in dilute solutions was due to hydrolysis. This 
seemed a reasonable basis on which to explain the abnormally high 
values for dilute solutions of metasilicate. In these solutions the salt 



/. Phys. Chem., 29, 1155-1168 (1925), 



30 



SOLUBLE SILICATES IN INDUSTRY 



was supposed to be almost completely converted into sodium hydroxide 
and "silicic acid". 

Later work, especially after methods of measuring the hydroxyl ion 
concentration had been developed, indicated the hydrolysis was not so 
great as had been assumed. Harman 55 found that when this hypothesis 
was tested on a quantitative basis, it was inadequate. "Hydrolysis into 
NaOH and colloidal silicic acid cannot account for this high conduc- 



V) 



/So \ 








/oo 








so 









fit /-z 

flat** of M*j0 /• ^4 



/ 3 



Fig. 5. — Variation of Conductivity with Ratio. 



tivity, not even with ratios relatively rich in NaOH, nor in dilute 
solution where hydrolysis is greatest, and with ratios rich in silica, 
where hydrolysis is practically negligible, it is apparent that the ex- 
planation that the conductivity is due to hydrolysis is totally inadequate." 
This does not mean that hydrolysis is not a factor nor that the 
hydroxyl ions formed do not carry a portion of the current in solutions 
containing less than two equivalents of Na 2 0. But, "In ratios 1 : 2, 1 : 3, 
and 1 : 4 where the hydroxyl-ion concentration is very low, even in dilute 
solution, the fair conductivity of dilute solutions points to a high degree 
of ionization and a fairly mobile silicate ion, while in concentrated 

65 /. Phys. Chem., 32, 44 (1928). Summary article. 



THE CONSTITUTION OF SILICATE SOLUTIONS 31 

solution there may be either very little ionization or there may be com- 
plex or colloid formation." 5G 

Kohlrausch pointed out that if the conductivity of the metasilicate 
were to be explained by dissociation into 2Na and Si0 3 ions, it would 
necessitate the assumption that the mobility of the latter exceeds that 
of the CI ion by 70 per cent, which seemed improbable. If, however, 
we assume partial hydrolysis of the metasilicate, the mobility of the 
silicate ion would not be as high. Harman calculated. from measure- 
ments of the freezing points and concentrations of sodium and hydroxyl 
ions the mobility of the silicate ions. Assigning values of 45 and 180 
to the sodium and hydroxyl ions respectively he obtained these results : 

Table 8. 

Ratio Mobility of Silicate Ion 

Na 2 : Si0 2 in Dilute Solution 

1:1 60 

1:2 35 

1:3 43 

1:4 41 

The idea of a multi-charged micelle put forward by McBain 57 in 
connection with soap solutions might offer a more satisfactory explana- 
tion. He had pointed out that sodium silicate solutions are also "col- 
loidal electrolytes". This theory would explain the observed changes. 
Thus, when the silicate solution was highly dilute, the many charges 
upon the colloidal aggregates would make for high conductivity. As 
concentration increased the coalescence of the multi-charged micelles 
would proceed and their mobility would decrease. 

Transport Numbers. Harman undertook some transport number 
experiments which he hoped "would produce some evidence as to 
whether the silica existed as colloid, simple ions, aggregates of simple 
ions carrying a sum total of their separate charges (i.e., ionic micelles), 
or as complex ions". 58 He obtained the following values by analyses 
of the liquids in anode, cathode, and intermediate chambers. 

"Considering first the ratio 1:1, i.e., sodium metasilicate, it is seen 
that the mean of the six values of n Na is 0.31, of n S i03, 0.16, and 
n H 0.53. The proportion of the current carried by the silicate ions is 
very small, being only about one-half that carried by the sodium ions, 
while over one-half the total current is carried by the hydroxyl ions. 
This latter result was to be expected, since e.m.f. measurements show 

56 Harman, /. Phys. Chem., 29, 1162-3 (1925). 

"McBain and Salmon, /. Am. Chem. Soc, 42, 426-60 (1920). 

68 /. Phys. Chem., 30, 359-368 (1926). 



No. of 
Expt. 


Ratio 


Approx. 


1 
2 
3 


1:1 
1:1 
1:1 


2.36 

1.0 

0.10 


4 
5 
6 


1:2 
1:2 
1:2 


1.0 
0.5 
0.1 


7 
8 


1:3 
1:3 


1.0 
0.5 


9 
10 


1:4 
1:4 


1.0 
0.1 





By Difference 




tlOH = 1 


llsios* 


' (riNa "T nsi03) 


0.17 


.56 


.13 


.51 


.18 


.51 


.16 


.53 


.88 




.70 


% # 




.87 






.82 






1.35 






1.42 


t . 




1.38 






2.32 






2.44 






2.38 


. , 





32 SOLUBLE SILICATES IN INDUSTRY 

Table 9. Transport Numbers. 



llNa 

0.27 

.36 

.31 
Mean .31 

.42 

.35 

.45 
Mean .41 

.40 

.45 
Mean .43 

.53 

.44 
Mean .48 

* These values as calculated disregard the possibility of the existence of 
HSi0 3 ions or of more complex ions containing more than one mol of Si0 2 , 
e.g. Si0 3 .2Si0 2 . 

that 10 to 30 per cent of the silicate is hydrolyzed according to the con- 
centration, and the hydroxyl ion moves four times as fast as the sodium 
ion. In caustic soda n Na is 0.2, and n H is 0.8; therefore the present 
result, where n H is not even double n Na , shows that the concentration 
of the hydroxyl ions is not nearly equivalent to that of the sodium 
ions. 

"The T.N. of sodium metasilicate shows no evidence whatever of 
any complex silicate ions or of micelle formation. If the silica is col- 
loidal with OH ions adsorbed, such a high mobility as 70 would not be 
expected, as hitherto measurements have shown that such colloidal 
particles have a mobility approaching that of the slowest moving ions. 

"When we look at the results obtained with ratio 1:2, 1:3, and 1 : 4, 
we at once notice the very high transport numbers of the silicate anions. 
They are for ratios 1 : 3 and 1 : 4, much greater than unity. The average 
value for ratio 1:2 is 0.88, for ratio 1:3, 1.44, and for ratio 1:4, 
2.38, while the T.N. of the sodium remains much the same, about 
0.45 in each case. 

"Further, the T.N. for the silicate ion is approximately twice that of 
the sodium ion in ratio 1 : 2, three times in ratio 1 : 3, and four times in 
ratio 1 : 4. This high T.N. for the silicate ion at once points to the fact 
that the anion cannot possibly be the simple ion Si0 3 "~, nor in fact 
should we expect it to be." 

He concludes that : 

"Ratio 1: 1 evidently ionizes to Na + , OH~ and Si0 3 ~~ ions; n Si o 3 is 
small, n H, found by difference, is large. 



THE CONSTITUTION OF SILICATE SOLUTIONS 33 

"In ratios 1:2, 1:3, and 1 : 4, the T.N. of the silicate ion is high, and 
the silicate anion contains more than l(Si0 2 ) per divalent charge; 
the average number of mols Si0 2 per divalent charge being equal to the 
ratio. 

'The mobility of the Si0 3 ion in ratio 1 : 1 is about 70. In ratios 
1:2, 1:3, and 1 : 4, it is approximately equal to that of the sodium ion, 
thus agreeing with mobilities calculated from conductivity experiments. 

"In ratios 1:2, 1:3, and 1 : 4, the silicate anion is not the simple 
Si0 3 ~" ion, but is either an aggregation of simple silicate ions with or 
without colloidal silica, or a definite complex silicate ion." 

Although the constitution of the anions is still an open question, this 
work proved that the silicate ions in the ratios of 1 : 2 and above did 
carry the current, in spite of the earlier investigators' assumption that 
they could not. 

Hydrogen-Ion Concentration. Therefore, the discrepancy which 
was apparently raised by Bogue's electrometric determinations of the 
hydrogen-ion concentration has been explained. Bogue 59 worked with 
sodium metasilicate and a series of commercial silicate of soda solutions 
of higher silica ratio up to approximately Na 2 0, 4Si0 2 . His results are 
given in Table 10. 

Table 10. Values Obtained for Each Silicate at Various Dilutions. 





Silicate No. 1. 


Na 2 0, 3.97Si0 2 




Volume Con- 








taining 1 Gr. 






Hydrolysis 


Molecule 


pH 


OH X 10 -4 


Per Cent 


3.3 


11.01 


10.2 


0.20 


10 


10.80 


6.4 


0.38 


20 


10.77 


6.0 


0.68 


50 


10.61 


4.13 


1.11 


100 


10.48 


3.00 


1.58 




Silicate No. 2. 


Na 2 0, 3.48Si0 2 




3.3 


11.08 


12.1 


0.24 


10 


10.90 


8.2 


0.49 


20 


10.82 


6.6 


0.75 


50 


10.67 


4.76 


1.28 


100 


10.52 


3.36 


1.77 




Silicate No. 3. 


Na 2 0, 2.93Si0 2 




3.3 


11.23 


17.6 


0.35 


10 


11.08 


12.0 


0.71 


20 


10.92 


8.4 


0.95 


50 


10.77 


5.95 


1.60 


100 


10.57 


3.72 


1.96 



Bogue, R. H., /. Am. Chem. Soc, 32, 2575-2582 (1920), 



34 



SOLUBLE SILICATES IN INDUSTRY 



Table 10. Values Obtained for Each Silicate at Various Dilutions — {Continued) 



Volume Con- 
taining 1 Gr. 
Molecule 

3.3 

10 

20 

50 

100 



3.3 

10 

20 

50 

100 



3.3 

10 

20 

50 

100 



3.3 

10 

20 

50 

100 



Silicate No. 4. Na 2 0, 2.48Si0 2 



pH 

11.36 
11.16 
11.02 
10.84 
10.69 

Silicate No. 5. 

11.74 
11.50 
11.25 
10.93 
10.77 

Silicate No. 6. 

12.18 
11.95 
11.63 
11.42 
11.24 

Silicate No. 7. 

12.69 
12.43 
12.21 
11.93 
11.73 



OH X 10 _1 

23.4 

14.5 

10.8 
6.95 
4.94 

Na 2 0,2.11Si0 2 

54.8 
32.0 
18.0 

8.8 

6.0 

Na 2 0, 1.63Si0 2 

155.0 
90.0 
53.5 
26.8 
17.6 

Na 2 0, l.HSi0 2 

504.0 
275.0 
162.0 

85.0 

54.0 



Hydrolysis 
Per Cent 

0.46 
0.85 
1.23 
1.87 
2.60 



1.08 
1.88 
2.04 
2.37 
3.15 



3.05 
5.29 
6.08 
7.21 
9.27 



9.92 
16.18 
18.40 
22.81 
28.43 



Three assumptions were made, namely, (1) that if no hydrolytic 
dissociation had occurred, the hydroxyl-ion concentration would be the 
same as that of water at the same temperature, (2) that if hydrolytic 
dissociation had proceeded to completion, the hydroxyl-ion concentra- 
tion would be the same as that of an equivalent solution of sodium 
hydroxide, (3) that the hydroxyl-ion concentration is a straight-line 
function of the degree of hydrolysis. 

Although his work confirmed the findings of the earlier investigators 
that the hydrolysis is most nearly complete in the metasilicate and that 
the degree of hydrolysis is less as the relative amount of silica is in- 
creased, the amount of hydroxide formed was very much less than had 
been thought previously. At a dilution of 100 liters per gram molecule 
the metasilicate was only 28.43 per cent hydrolyzed, less than a third 
as much as had been assumed. The degree of hydrolysis in the more 
silicious solutions at this concentration varied from 9.27 to 1.58 per cent. 

Stericker 60 recalculated Bogue's results to show the amounts of 

"Chem. & Met. Eng., 25, 61 (1921). 



THE CONSTITUTION OF SILICATE SOLUTIONS 35 

silicate of each type in contrast with the amount of sodium hydroxide 
present in each 100 cc. of solution, as follows : 



Table 11. 


Concentration of Sod 


lum Hydroxic 
at 30 C. 


\e in Sc 


dium Silicate 


Solution 




Na 2 0, l.HSi0 2 
Silicate NaOH 


Na 2 0, 1.63Si0 2 
Silicate NaOH 


Na 2 0,2.11Si0 2 
Silicate NaOH 


0.33 molar 
0.10 molar 
0.05 molar 
0.01 molar 


3.70 0.1205 
1.22 0.0647 
0.61 0.0369 
0.122 0.0115 


4.605 
1.52 
0.76 
0.152 


0.0364 
0.0212 
0.0122 
0.0038 


5.51 
1.82 
0.91 
0.182 


0.0239 
0.0082 
0.0041 
0.0013 




Na 2 0, 2.48Si0 2 
Silicate NaOH 


Na 2 0, 2.93SiO* 
Silicate NaOH 


0.33 molar 
0.10 molar 
0.05 molar 
0.01 molar 


6.42 
2.12 
1.06 
0.212 


0.0056 
0.0034 
0.0024 
0.0011 




7.34 
2.42 
1.21 
0.242 


0.0042 
0.0029 
0.0019 
0.0008 




Na 2 0, 3.48Si0 2 
Silicate NaOH 


Na 2 0, 3.97Si0 2 
Silicate NaOH 


0.33 molar 
0.10 molar 
0.05 molar 
0.01 molar 


8.245 
2.72 
1.36 
0.272 


0.0029 
0.0020 
0.0015 
0.0007 




9.15 
3.02 
1.51 
0.302 


0.0024 
0.0015 
0.0014 
0.0007 



Silicate = grams of silicate of the given formula per 100 cc. of solution. 
NaOH = grams of NaOH per 100 cc. of solution. 

It will be noted that these figures are approximate percentages. 

Thompson 61 conducted studies at higher concentrations than Bogue. 
He set out to find by physical measurements differences between highly 
concentrated sodium silicate solutions which, though of substantially 
the same chemical composition, behaved differently in industrial 
processes. He measured hydrogen-ion concentrations and freezing point 
depressions,* and developed a theory of the constitution of sodium 
silicate solutions. Six samples formed the basis of his work. 

Table 12. Analysis of Commercial "Alkaline" Silicates. 



A 

29.01 
8.94 



B 



Si0 2 

Na 2 

R 2 3 

C0 2 

S0 3 

CI 

H 2 61.56 

Sp. gr 1.415 



1.690 



c 


D 


E 


F 


35.6 


34.78 


37.44 


1.725 


16.55 


17.83 


17.08 




.67 


.20 


.15 




.... 


.94 


1.21 




.12 


.54 


.39 




.19 


.20 


.22 




46.8 


45.62 


43.35 






1.707 



1.707 



1.700 



1.725 



All of these, with the exception of A, closely approximated the 

composition Na 2 0, 2Si0 2 . Table 13 shows the pH values which he 

61 Thompson, Lincoln, Master's Thesis, Worcenter Polytech. Inst. 1923. 
* Cf. pages 40-44, 61-63. 



36 



SOLUBLE SILICATES IN INDUSTRY 



found. It should be noted that a normality of 1.632 corresponds to 
21.5 grams solids in 100 cc. of solution in the case of the 1:3.3 
ratio silicate. Likewise, the normality of 3.65 for the 1:2 ratio 
means 34.6 grams solids in 100 cc. of solution. Thompson found 
higher pH values in three freshly diluted solutions than in the same 
after standing. The effect of freezing the silicates solidly for an hour 
was also studied but was not found to influence the pH value after 
standing a few hours. 

When Thompson plotted Bogue's values with the pH figures as or- 
dinates and the Na 2 0,Si0 2 ratios as abscissae, he found, as Kohlrausch 
had for conductivity, a sharp break in the curve at Na 2 0, 2Si0 2 . From 
this he postulated that sodium silicate solutions of less sodium content 
than is indicated by the ratio Na s O, 2Si0 3 are composed of Na 2 Si 2 5 
and free silicic acid while those of more sodium than the ratio indicates 
contain free sodium hydroxide and sodium disilicate. It is not unlikely 
that either sodium metasilicate or sodium disilicate may be present in 
concentrated silicate solutions. But the hydroxyl-ion concentrations 
prove that the relation is not as simple as that suggested by Thompson. 





Table 13. 


Thompson's Hydri 


igen Electron 


? Measi 


irements. 




Silicate A 


Silicate E 


Silicate C 




Silicate D 


Na 2 0, 3.3Si0 2 


Na 2 0, 2.25Si0 2 


Na 2 0,2.21Si0 2 


Na 2 O,2.01SiO 2 


Volume 




Volume 




Volume 




Volume 




Normality pH 


Normality 


pH 


Normality 


pH 


Normality 


pH 


1.632 


11.42 


3.378 


12.18 


3,286 


12.16 


3.652 


12.49 


.816 


11.36 


3.116 


12.13 


2.592 


12.09 


2.781 


12.37 


.680 


11.20 


1.689 


12.08 


1.325 


12.07 


2.739 


12.35 


.204 


10.70 


1.631 


12.03 


1.296 


12.00 


2.642 


12.33 


.157 


10.59 


.845 


11.96 


.8258 


11.91 


2.191 


12.28 


.119 


10.53 


.769 


11.90 


.6628 


11.83 


1.684 


12.26 


.107 


10.50 


.576 


11.83 


.648 


11.81 


1.321 


12.20 


.0669 


10.48 


.432 


11.70 


.5456 


11.80 


.9169 


12.11 


.0487 


10.38 


.216 


11.57 


.334 


11.76 


.8419 


12.06 


.0297 


10.23 


.0576 


11.05 


.2498 


11.54 


.6604 


11.96 


.0201 


10.05 


.0288 


10.73 


.167 


11.49 


.2292 


11.76 


.0101 


9.80 


* .0144 


10.40 


.136 

.0627 

.03404 


11.35 
11.04 
10.95 


.05733 


11.10 




Silicate B 






Silicate F 






Approx. Na 2 0, 2Si0 2 




Approx. N"; 


i 2 0, 2Si0 2 




Volume 






Volume 






Normality 


pH 




Normality 


pH 






3.2 


12.40 




3.1 




12.03 






1.6 


12.23 




1.55 




11.90 






.8 


12.10 




.7* 


1 


11.70 





Harman 62 extended this investigation of hydroxyl-ion concentra- 
tions and calculated hydrolysis as shown in the following table : 
63 /. Phys. Chem,, 30, 1100-1111 (1926). 



THE CONSTITUTION OF SILICATE SOLUTIONS 37 



Table 14. Electrometric Measurements of Hydrolysis. 













Per Cent 


Per Cent 










Hydrolysis 


Hydrolysis 












Calc. from 


Calc. from 












NaOH 


Exptly. 












Which 


Found 




E.m.f. 








Gives Expt 


• (OH) 


ATw 


corrected 


pH 


(H) 
Ratio 2:1. 


(OH') 


(OH) 


Ion Alone 


2.0 


1.483 


13.48 


0.33 X 10 _u 


0.29 


17.5 


14.5 


1.0 


1.0334 


13.23 


0.59 


0.165 


19.0 


16.5 


0.398 


1.059 


12.93 


0.12 X 10" 12 


0.0804 


22.6 


20.2 


0.159 


0.9981 


12.63 


0.235 


0.0424 


28.3 


26.6 


0.0398 


0.9697 


12.12 


0.77 


0.01297 


32.6 


32.6 


0.0159 


0.9455 


11.74 


0.18 X 10" u 
Ratio 1:1. 


0.0056 


36.0 


35.0 


2.435 


1.0490 


13.49 


0.325 X 10 -13 


0.295 


14.8 


12.1 


1.133 


1.0328 


13.22 


0.600 


0.163 


16.3 


14.3 


0.547 


1.0181 


12.97 


0.11 X lO" 13 


0.0896 


18.7 


16.3 


0.204 


0.9956 


12.59 


0.255 


0.0388 


20.0 


19.0 


0.1 


0.9798 


12.32 


0.48 


0.0207 


21.8 


20.7 


0.05 


0.9628 


12.04 


0.91 


0.011 


22.6 


22.0 


0.02 


0.9406 


11.67 


0.215 X HT U 


0.00465 


23.25 


23.25 


0.01 


0.9274 


11.44 


0.36 
Ratio 1:1.5. 


0.00278 


27.8 


27.8 


2.0 


1.0046 


12.74 


0.18 X 10" 12 


0.054 


3.0 


2.7 


1.0 


1.0040 


12.73 


0.185 


0.0532 


5.9 


5.3 


0.5 


0.9915 


12.52 


0.30 


0.0329 


7.0 


6.6 


0.2 


0.9724 


12.20 


0.63 


0.0158 


8.25 


7.9 


0.1 


0.9574 


11.95 


0.115 X 10 -11 


0.00868 


8.7 


8.9 


0.05 


0.9424 


11.69 


0.205 


0.00488 


9.7 


7.7 


0.02 


0.9218 


11.34 


0.46 


0.0022 


11.0 


11.0 


0.01 


0.9064 


11.08 


0.83 
Ratio 1:2. 


0.0012 


12.0 


12.0 


2.450 


0.9720 


12.19 


0.645 X 10"" 


0.0152 


0.65 


0.62 


1.110 


0.9677 


12.12 


0.76 


0.013 


0.21 


1.01 


1.0 


0.9678 


12.12 


0.76 


0.013 


1.35 


1.3 


0.5 


0.9584 


11.96 


0.11 X 10 -11 


0.0091 


1.88 


1.8 


0.204 


0.9424 


11.69 


0.205 


0.00486 


2.38 


2.4 


0.1 


0.9290 


11.46 


0.35 


0.00285 


2.85 


2.8 


0.05 


0.9180 


11.28 


0.53 


0.0019 


3.8 


3.8 


0.021 


0.9034 


11.03 


0.935 


0.00107 


5.1 


5.1 


0.011 


0.8924 


10.84 


0.14 X 10" 10 
Ratio 1:3. 


0.000714 


6.5 


6.5 


2.0 


0.9196 


11.31 


0.49 X lO - " 


0.00202 


0.101 


0.101 


1.0 


0.9190 


11.29 


0.515 


0.00192 


0.192 


0.192 


0.5 


0.9170 


11.27 


0.55 


0.00180 


0.36 


0.36 


0.2 


0.9060 


11.07 


0.85 


0.00117 


0.57 


0.57 


0.1 


0.8954 


10.89 


0.13 X 10 -10 


0.00768 


0.77 


0.77 


0.05 


0.8854 


10.73 


0.185 


0.00054 


1.10 


1.10 


0.02 


0.8651 


10.38 


0.42 


0.00024 


1.20 


1.20 


0.01 


0.8324 


9.83 


0.14 X 10 -8 


0.000069 


1.38 


1.38 



38 SOLUBLE SILICATES IN INDUSTRY 

Table 14. Electrometric Measurements of Hydrolysis — {Continued). 

Per Cent Per Cent 











Hydrolysis 


Hydrolysis 










C 


ale. from 

NaOH 

Which 


Calc. from 

Exptly. 

Found 




E.m.f. 






Gives Expt 


• (OH) 


N„ 


corrected 


pH 


(H) 
Ratio 1 : 4. 


(OH') 


(OH) 


Ion Alone 


2.0 


0.8904 


10.81 


0.155 X 10 -10 


0.000638 


0.032 


0.032 


1.0 


0.8934 


10.86 


0.14 


0.000709 


0.071 


0.071 


0.5 


0.8916 


10.84 


0.14 


0.000711 


0.14 


0.14 


0.2 


0.8921 


10.84 


0.14 


0.000712 


0.35 


0.35 


0.1 


0.8869 


1075 


0.175 


0.00057 


0.57 


0.57 


0.05 


0.8818 


10.67 


0.215 


0.000464 


0.93 


0.93 


0.02 


0.8675 


10.42 


0.38 


0.00026 


1.30 


1.30 


0.01 


0.8534 


10.18 


0.66 


0.00015 


1.50 


1.50 



These figures are not directly comparable with those obtained by 
Bogue and Thompson because they are based on weight normality while 
the others are on the basis of volume. In addition, Harman made a 
correction for the liquid potential difference which Bogue did not apply. 
In spite of these differences, the results, shown graphically below, are 
in general agreement with those of Bogue. 




A .8 \Z 

CONCENTRATION N„ 

Fig. 6. — Percentage Hydrolysis against Concentration. 

Therefore Harman concluded that : 

"None of these silicates are largely hydrolyzed. At 0.01 iV w , Na 2 Si0 3 
is only 27.8 per cent hydrolyzed, while ratios 1 : 3 and 1 : 4 at the same 
concentration show only 1.5 per cent hydrolysis. 



THE CONSTITUTION OF SILICATE SOLUTIONS 39 

"In concentrated solution the percentage hydrolysis is very low. 

"It appears probable that much of the silica is present as simple and 
complex silicate ions (and ionic micelles). This also accounts for the 
good conductivity and the high transport numbers." 

These results further emphasize the misleading character of some of 
the methods which have been proposed for the determination of free 




RAT/O 



I:? 14 

Fig. 7. — Percentage Hydrolysis against Ratio. 



alkali in commercial silicate solutions. The assumption that some defi- 
nite compound such as Na 2 Si 4 9 is waterglass, and that alkali found by 
analysis in excess of that required to satisfy this or some other arbi- 
trarily chosen formula, is present as sodium hydroxide is particularly 
misleading. 

Special Effects in Concentrated Solutions. It must also be re- 
membered that even if dilute solutions are highly hydrolyzed, it does 
not follow that the same is true of concentrated solutions. The work 
thus far cited shows plainly that the hydrolysis is less as the concen- 
tration rises. Equilibrium is attained slowly in concentrated solutions 
and rearrangements result from such simple processes as dilution or 



40 SOLUBLE SILICATES IN INDUSTRY 

changing the temperature. A flocculent precipitate has been observed 
to form at the interface when water is poured over a concentrated 
viscous solution of Na 2 0, 2Si0 2 . Attempts to titrate concentrated solu- 
tions result in the separation of gels and their behavior toward indi- 
cators which may be adsorbed on the colloid particles further complicates 
studies directed to throw light on their constitution. 

Effects Due to Number of Particles. 

Freezing Points. Bogue pointed out the possibility that colloidal 
silica might be able to adsorb hydroxyl ions or otherwise interfere with 
their effect. Thus the electrometric method for determining hydrogen- 
ion concentration shows the actual alkalinity of one phase rather than 
of the whole system. If this were the case the hydroxyl ion adsorption 
would have to be great, especially with higher silica ratios. Therefore, 
the osmotic activity would be very small. On the other hand, if the 
activity is large, it will indicate the concentrations found by means of 
the hydrogen electrode are correct. 

The first work of interest in this connection is that of Kahlenberg 
and Lincoln. 63 Their observations covered the silicates of sodium, 
potassium, lithium, rubidium, and caesium, and included measurements 
of freezing point depressions at high dilutions. 

Table 15. Freezing Point Depression. 





Freezing Pt. 


Calc. 


Mol. Wt. 


Prep'd by 


Calc. 


V 


Depression 


Mol. Wt. 


NaOH 


Fusion 


Mol. Wt, 


8 


0.695 


41.3 


27 






12 


0.498 


38.4 


26.2 






16 


0.385 


37.3 


24.4 






24 


0.280 


34.2 


23.9 






32 


0.210 


34.9 


22.4 


0.200 


36.5 


48 


0.150 


31.9 


20.9 


0.140 


34.8 


64 


0.110 


32.6 


21.4 


0.108 


33.8 


96 


.... 






0.077 


31.6 



V = concentration expressed as liters containing 1 mol of solid Na 3 Si0 3 , mol. 
wt. 121.58. 

Their method of preparation was to mix sols of silicic acid prepared 
by dialysis, according to Graham, 64 with hydroxides of the alkali metals. 
They showed that in the case of sodium metasilicate this procedure 
yielded a solution with a freezing point depression not greatly but 
appreciably different from the metasilicate produced by fusing silica 

63 Kahlenberg and Lincoln, /. Phys. Chem., 2, 77-90 (1898). 
61 Graham, Phil. Trans., 151, 205 (1861). 



THE CONSTITUTION OF SILICATE SOLUTIONS 41 

with the alkaline carbonate. The differences would probably be much 
greater with the more silicious silicates, which Kohlrausch showed 
reached a condition of equilibrium very slowly. Comparison of these 
solutions by the conductivity method showed them alike but still leaves 
a question about the more concentrated and more silicious silicate 
solutions. 

Kahlenberg and Lincoln studied also the ratios Na 2 0, 2Si0 2 and 
Na 2 0, 5Si0 2 . Expressing the former as NaHSi0 3 , mol. wt. 100.1, they 
found the following : 

Table 16. Freezing Point Depression. 



Observed Free 


zing 


Calc'd. 


NaOH 


V Point Lowering 


Mol. Wt. 


Mol. Wt. 


8 0.332 




70.9 


31. 


12 0.263 




59.7 


26.1 


16 0.202 




58.3 


25.5 


24 0.146 




53.7 


23.5 


32 0.110 




53.5 


23.4 


d for Na 2 Si 5 0ii = mol. wt. 


361.34 






32 0.178 




119.9 


27. 


48 0.139 




102.4 


23.1 


64 0.104 




100.3 


22.6 


96 0.089 




79.9 


18. 


128 0.059 




90.4 


20.4 



V = volume in liters in which one gram-molecule of the salt expressed by 
the formula is contained. Third column — molecular weights calculated on the 
supposition that the salt when in solution has the composition indicated by the 
formula. 

These figures do indicate high osmotic activities, which Kahlenberg 
and Lincoln attributed to the formation of sodium hydroxide by the 
hydrolysis of the silicates. This explanation agreed with the facts that 
were then known (1898), but not with those found by the hydrogen 
electrode and transport number experiments.* Another explanation 
would be that silicate ions are formed, which would be in accord with 
all the facts so far presented. 

Thompson determined freezing points of three of the silicates with 
which he worked.f The lowering of freezing points is summarized 
in the curve. 

The freezing point lowering was somewhat greater for a freshly 
diluted solution than for one that had reached equilibrium, which was 
accomplished after a few hours but not fully studied. 

* Cf. pages 31-39. 
f Cf . pages 42, 44. 



42 



SOLUBLE SILICATES IN INDUSTRY 



Table 17. Thompson's Freezing Point Results. 



Silicate D 


Silicate C 


Silicate E 


Na 2 O,2.01SiO 2 


Na 2 0,2.21Si0 2 


Na 2 0,2.25Si0 2 




r reezing 




Freezing 




Freezing 




Point 




Point 




Point 


Normality 


Lowering 


Normality 


Lowering 


Normality 


Lowering 


3.37 


3.31 


2.652 


2.59 


3.227 


2.93 


2.781 


2.74 


2.592 


2.59 


3.08 


2.82 


2.642 


2.67 


1.39 


1.56 


1.614 


1.63 


1.684 


1.80 


1.325 


1.52 


1.54 


1.63 


1.668 


1.79 


1.296 


1.56 


1.076 


1.245 


0.842 


1.15 


0.60 


1.00 


0.807 


1.07 


0.695 


1.03 


0.6628 


1.03 


0.779 


1.04 


0.66 


1.06 


0.653 


0.99 


0.769 


1.04 


0.421 


0.75 


0.30 


0.66 


0.385 


0.68 






J* 

V 

















t 


So ** 








cf* 




freezing Point Ltweni^ 
„ (a ■ C Silicate 


t 



/* 2f/ 3N 

Normality in Terms of /** 0M 



ah 



Fig. 8. — Thompson's Freezing Point Results. 



THE CONSTITUTION OF SILICATE SOLUTIONS 43 



Harman G5 studied freezing point depressions much more thoroughly 
with the following results : 



Table 18. Freezing Point Measurements. 



A* 



Molal lowering at infinite 
dilution for ideal substance 



Wt. 




Observed 


Molecular 


% - 


mX 1.858 


>rmality 


Molality 


Lowering 


Depression 
A 




Kahlenberg 
and 


N„ 


m 


A 


m 
Ratio 1 : 1 


Harman 


Loomis Lincoln 


2.435 


1.217 


4.290 


3.525 


1.89 


• • • 


1.062 


0.531 


2.160 


4.067 


2.18 


2.i 


0.204 


0.102 


0.548 


5.370 


2.88 


2.8 2.9 


0.100 


0.050 


0.291 


5.820 


3.13 


3.1 3.4 


0.05 


0.025 


0.155 


6.600 


3.55 


3.4 3.7 


0.02 


0.010 


0.070 


7.00 


3.75 


3.5 3.7 


0.01 


0.005 


0.036 


7.20 
Ratio 2 : 1 


3.87 




0.796 


0.398 


2.225 


5.59 


3.0 




0.398 


0.199 


1.195 


5.97 


3.2 




0.159 


0.079 


0.495 


6.26 


3.35 




0.0796 


0.0398 


0.3002 


7.54 


4.0 




0.0398 


0.0199 


0.170 


8.45 


4.5 




0.0159 


0.0079 


0.080 


10.12 
Ratio 1:2 


5.4 




2.450 


1.225 


2.140 


1.747 


0.94 




1.100 


0.550 


1.215 


2.209 


1.94 




0.500 


0.250 


0.770 


3.080 


1.65 




0.204 


0.102 


0.415 


4.068 


2.19 




0.100 


0.050 


0.255 


5.100 


2.74 




0.050 


0.025 


0.140 


5.600 


3.01 




0.020 


0.010 


0.060 


6.000 


3.22 




0.010 


0.005 


0.033 


6.600 
Ratio 1 : 3 


3.55 




2.00 


1.00 


1.465 


1.465 


0.772 




1.00 


0.50 


0.985 


1.970 


1.06 




0.50 


0.25 


0.680 


2.720 


1.46 




0.20 


0.1 


0.405 


4.050 


2.17 




0.10 


0.05 


0.220 


4.400 


2.36 




0.05 


0.025 


0.130 


5.200 


2.73 




0.02 


0.01 


0.055 


5.500 


2.96 




0.01 


0.005 


0.030 


6.000 
Ratio 1 : 4 


3.22 




2.00 


1.00 


1.050 


1.050 


0.565 




1.00 


0.50 


0.795 


1.590 


0.855 




0.50 


0.25 


0.540 


2.160 


1.16 




0.20 


0.10 


0.340 


3.400 


1.83 




0.10 


0.05 


0.215 


4.300 


2.31 




0.05 


0.025 


0.125 


5.000 


2.69 




0.02 


0.01 


0.055 


5.500 


2.96 




0.01 


0.005 


0.028 


5.600 


3.01 






* A = 


Molecular depression 





J. Phys. Chem., 31, 355-373 (1927), 



44 



SOLUBLE SILICATES IN INDUSTRY 



4M-S38 




«S ' 



Fig. 9. — Molecular Depression of Freezing Point against Concentration. 

Vapor Pressures. Lowering of the vapor pressure of water by 
silicate solutions of ratios 1 : 1 and 1 : 2 was also studied by Harman. 66 

Table 19. Vapor Pressures at 25° C. 



iVw 


Mean Exptl. 
Lowering 


Calc'd Lower- 
ing if No 
Dissociation 

Ratio 1 : 1 


Exptl. Lower 

ing — Calc'd 

Lowering 


2.427 
1.062 
0.41 
0.102 


1.06 mm. 
0.55 
0.29 
0.08 


0.5096 mm. 
0.2230 
0.08610 
0.02142 

Ratio 1:2 


2.08 
2.46 
3.36 
3.73 


2.0 
1.0 
0.5 
0.2 
0.1 


0.45 mm. 

0.31 

0.20 

0.10 

0.055 


0.42 mm. 

0.21 

0.105 

0.042 

0.021 


1.08 
1.49 
1.90 
2.38 
2.61 



Bennett 67 extended the work on vapor pressures by means of the dew 
point method. 



69 J. Phys. Chem., 30, 917-924 (1926). 
91 1. Phys. Chem., 31, 890-896 (1927). 



THE CONSTITUTION OF SILICATE SOLUTIONS 45 



10 



Degression of F.Pr. /_£_ ) 



or 




Ratio 



2:1 in n a, i : a j : 4 

Fig. 10. — Molecular Depression against Ratio. 

Table 20. Dew Point Lozverings in Degrees Centigrade. 
NaOH Ratio Na 2 to Si0 2 in Silicates 



M 1 




1:0.5 


1 : 0.87 


1:1 


1:1.4 


1:2 


1:3.2 


1 : 3.95 


1.5 


2.40 


1.74 




1.35 


1.06 


0.75 


0.48 


0.41 


1.0 


1.51 


1.19 


0.88 


0.92 


0.74 


0.56 


0.35 


0.29 


0.5 


0.75 


0.60 


0.46 


0.46 


0.37 


0.30 


0.19 


0.15 


0.3 


0.45 


0.37 


0.28 


0.28 


0.22 


0.19 


0.12 


0.10 


0.2 


0.29 


0.25 


0.19 


0.19 


0.14 


0.13 


0.08 


0.07 



1 = gram mols of Na 2 per 1000 grams of water 



Boiling Points. Cann, 68 Cheek, and Gilmore 69 worked on boiling 
point determinations of solutions of sodium silicate and found a direct 
relationship between the soda and silica content and the elevation of 
the boiling point. 

68 Cann, Jessie Y., and Dorothy L. Cheek, Ind. Eng. Chem., 17, 312 (1925). 
60 Cann, Jessie Y., and Gilmore, /. Phys. Chem., 32, 72 (1928). 



46 



SOLUBLE SILICATES IN INDUSTRY 




Fig. 11. — Boiling Point Elevations. 



Table 21. Boiling Point Elevation of Silicate Solutions. 



Na 2 0, 


1.68Si0 2 


Na 2 0, 2.06SiO 2 




Boiling 




Boiling 


Per Cent 


Point 


Per Cent 


Point 


Soda 


Elevation 


Soda 


Elevation 


Content 


at 760 Mm. 


Content 


at 760 Mm 


0.556 


0.086 


0.316 


0.1276 


0.685 


0.124 


0.316 


0.1243 


0.708 


0.025 


0.421 


0.1567 


0.823 


0.160 


0.946 


0.2463 


0.897 


0.073 


0.947 


0.2453 


0.933 


0.137 


1.136 


0.2723 


1.046 


0.141 


1.170* 


0.2531 


1.100 


0.189 


1.933 


0.3936 


1.204 


0.258 


1.888 


0.3819 


1.900 


0.345 


4.874 


0.7334 


3.010 


0.495 


7.486 


1.0578 


4.039 


0.678 


7.508f 


1.0721 


5.490 


0.835 


9.516$ 


1.3617 


6.650 


0.991 


9.540 


1.3480 


8.390 


1.269 






9.752 


1.475 







Na 3 0,2.55Si0 2 
Boiling 
Per Cent Point 

Soda Elevation 

Content at 760 Mm. 



0.476 
0.849 
1.074 
1.463 
7.359 
8.054 
8.293 



0.097 
0.177 
0.199 
0.236 
0.897 
0.854 
0.961 



* Uneven pumping in silicate apparatus due to insufficient heat. 

f Uneven pumping in water apparatus. 

$ Uneven pumping in silicate apparatus probably due to viscosity of solution. 



THE CONSTITUTION OF SILICATE SOLUTIONS 47 
Table 21. Boiling Point Elevation of Silicate Solutions — (Continued) . 



Na 2 0, 


2.96Si0 2 


Na 2 0, 


3.25 SjO. 


Na 2 ( 


3, 3.87SiO. 




Boiling 




Boiling 




Boiling 


Per Cent 


Point 


Per Cent 


Point 


Per Cent 


Point 


Soda 


Elevation 


Soda 


Elevation 


Soda 


Elevation 


Content 


at 760 Mm. 


Content 


at 760 Mm. 


Content 


at 760 Mm 


0.109 


0.0639 


0.307§ 


0.0707 


0.143 


0.1013 


0.223 


0.0993 


0.309§ 


0.0627 


0.143 


0.0937 


0.495 


0.1230 


0.611§ 


0.1071 


0.498 


0.1490 


0.809 


0.1743 


0.637§ 


0.1207 


0.497ff 


0.1629 


1.241 


0.2272 


1.122 


0.1960 


0.762 


0.1986 


1.253 


0.2246 


1.122 


0.1902 


0.778 


0.1932 


2.472 


0.3625 


2.433 


0.3027 


1.512 


0.2828 


2.466 


0.3550 


2.455 


0.3051 


1.495 


0.2834 


3.550 


0.4529 


3.55311 


0.4122 


2.571 


0.3664 


3.502 


0.4579 


3.55311 


0.3905 


2.572 


0.3730 


4.511 


0.5361 


4.78311 


0.5082 


3.479 


0.4223 


4.416 


0.5434 


4.70611 


0.5183 


4.577 


0.5067 


5.942 


0.6856 


5.46711 


0.5970 






5.982 


0.6865 










7.456 


0.8394 










8.638 


0.9659 











§ Per cent by volume. 

|| Large amount of frothing occurred. 

II Used new apparatus for water which did not pump well. 




o-a 



3 



o4 of o 6 „ o-t 

nolo 1 1 ty *.e. <*N„. 



oq 



Fig. 12. — Activity Coefficient against Concentration. 



Activity Coefficients. Calculation of activity coefficients from his 
vapor pressure and freezing point depressions led Harman to the fol- 
lowing conclusions : 

"From the results it appears that ratio 1 : 1 is the salt Na 2 Si0 3 under- 
going both hydrolytic and ionic dissociation giving rise to Na + , OH" 



48 



SOLUBLE SILICATES IN INDUSTRY 



and Si0 3 "" ions and H 2 Si0 3 , most of the latter being crystalloidal. 
Na 2 Si0 3 is practically completely dissociated in dilute solution, but only 
27.8 per cent hydrolytically. Ratio 1 : 2 is the definite salt NaHSi0 3 , 
behaving like Na 2 Si0 3 and giving rise to Na + , OH - and HSi0 3 " ions 



10 r 




Activity Coefficient against Ratio. 



and H 2 Si0 3 . There is 0.60 per cent dissociation at concentration 
0.005 m but only 0.05 per cent hydrolytic dissociation. The results from 
ratios 1 : 3 and 1 : 4 are not in accord with the view that these ratios are 
definite salts but agree well with the existence of complex aggregates in 
concentrated solution and of ionic micelles of the composition (m Si0 3 
wSi0 2 aq.) m ~ where m + n/m = ratio ; the following equilibrium also 
existing : 

Si0 3 ~~ + (Colloid Si0 2 aq.) (mSiOs.n Si0 2 aq) m " 
(Colloid Si0 2 aq.) crystalloid H 2 Si0 3 2H + Si(V"." 

Activity coefficients calculated from vapor pressure and dew point 
measurements by Bennett are in close agreement with the foregoing. 



THE CONSTITUTION OF SILICATE SOLUTIONS 49 



Harman and Bennett 7d both used v = 4 in the equation 

A 



7=1 



v\m 



in order to get comparable and reasonable results for all ratios of Na 2 

to Si0 2 in the range covered. Randall and Cann 71 point out that 

"their (Harman's and Bennett's) calculations tacitly assume for the 

reaction 

Na 2 Si0 3 (Aq.) + H 2 (1) = 2Na + + OH" + HSiCV (4) 

K = 1, in accordance with the conventions adopted by Lewis and Ran- 
dall in developing the basic equations used. In other words, the 



S 



^ 



1.0 






< 



-1.0 



M» 



Na 2 Si03 

* Bennett, D. P. L, 61.5° (1:0.5) 
^Bennett, D.P. L., 61.5° (l:0.8fl 
a Bennett, D.P. L, 61.5° (1:0 

* Bennett, D.P. L,61.5°(l:1.4) 




n Cann & Cheek, B.P. (1:1.68) 

» Harman, F.P. (1:0.5) 

o Harman, F.P. (1:1) _ 

® Harman, V. P.(l:l) 

v Kahlenberg& Lincoln, F.P. (1:1) 

x Loomis, F.P. (1:1) 







1 



1'2 



Square Root of Molality, m 
Fig. 14. — Activity Function of Sodium Metasilicate. 

activity of the sodium silicate is made equal to the geometric product of 

the activities of the ions on the right of Equation 4." Randall and Cann 

used "v = 3 for ratios of 1 : 1 of Na 2 to Si0 2 and v = 2 for ratios of 

1:2 to 1:5. In the latter case, the molality was taken equal to the 

number of gram atoms of sodium ion constituent. These assumptions 

correspond to K = 1 for the reactions : 

Na 2 Si0 3 (aq.) = 2Na + + SiCV" (5) 

NaHSiOa (aq.) = Na + + HSiCV. (6) 

70 Lewis and Randall, "Thermodynamics," Equation 2, 1923, p. 342. 
"Randall, Merle, and Jessie Y. Cann, /. Am. Chem. Soc, 50, 347 (1928). 



Na 2 Si0 3 


Na 2 0, 2Si0 2 


0.501 


0.464 


0.408 


0.347 


0.322 


0.246 


0.232 


0.131 


0.182 


0.076 


0.141 


0.043 




0.027 



50 SOLUBLE SILICATES IN INDUSTRY 

It has been impossible to eliminate the effect of hydrolysis, but in the 
concentrated solutions, this effect cannot be large, and the method of 
extrapolation here used eliminates to a large extent the effect in the 
more dilute solutions." The results of these calculations are given in 
Figure 14 and the values for the activity coefficients in Table 22. 

Table 22. Activity Coefficients of Sodium Silicate Solutions (0-100° C). 

Molality 
0.05 
0.10 
0.20 
0.50 
1.00 
2.00 
4.00 

The low values obtained for the more silicious silicates are explained 
on "the assumption of the existence of micelles, which are not entirely 
dissociated except in very dilute solutions." The assumption may be 
made that the size and number of micelles is less in solutions containing 
relatively less silica. The charge of the micelle will then be greater, 
the greater the silica content of the negative constituent. 

"In a very real sense, the assumption that the ions existing in acid 
silicate solutions are Si 2 5 "" or some hydrated multiple thereof, may be 
considered as the first stage in the formation of a micelle, for undoubt- 
edly the negative constituent consists of many different sorts of mi- 
celles all in equilibrium (more or less rapid) with each other. But, as 
we do not have a method of picking out the concentrations of the 
individual species of micelles, we may as well take HSiCV just as we 
do in the case of water, when we choose H 2 as the species to repre- 
sent this substance. 

"All the micelles referred to have been considered to be ionic mi- 
celles. McBain and Salmon 72 postulate both ionic and neutral micelles. 
. . . There has been no suggestion of the separate existence of neu- 
tral micelles in the silicate solutions." 

Sodium-Ion Activity. Harman 73 determined the sodium-ion activ- 
ity by means of a sodium amalgam electrode. The results are given 
in Figure 15. 

"The values for the activity coefficient of Na 2 Si0 3 show that in con- 
centrated solution as much as 40 per cent of the total sodium exists 
in active ionic state, while in dilute solution practically all the sodium 

72 /. Am. Chem. Soc, 42, 426 (1920). 
73 /. Phys. Chem., 30, 917-924 (1926). 



THE CONSTITUTION OF SILICATE SOLUTIONS 51 

exists so. The coefficient for ratio 1 : 1 passes through a minimum at 
concentration 0.2 N w , while none of the other ratios exhibit such a 
minimum. It is not unusual to find this minimum for strong electro- 
lytes in concentrated solution. 




.2466 1.0 

Fig. 15. — Sodium-Ion Activity against Concentration. 

"In ratio 1 : 3 and 1 : 4, the values are very low in concentrated so- 
lution and even in dilute solution are still comparatively low, indicat- 
ing that all the sodium in solution does not exist as sodium ion, or if 
so, the silica present has considerably affected and reduced its 
activity." 

Diffusion Through Membranes. Additional support for the fore- 
going evidence of the presence of silicate ions was obtained by Ganguly 74 
and by Harman 75 from diffusion experiments using collodion and parch- 
ment membranes. 

The relative instability of collodion films in silicate solutions ren- 
ders results with membranes of this material open to serious question. 
Both found that equilibrium was reached in about a week. 

"All ratios at all concentrations gave evidence of diffusion of sili- 

74 Ganguly, /. Phys. Chem., 31, 407-416 (1927). 
"' Harman, op. cit., 623-625. 



52 SOLUBLE SILICATES IN INDUSTRY 

cate ions both with the collodion membrane and with parchment paper. 
. . . With ratios of 1 : 1 and 1 : 2 equal distribution of both sodium 
and silica was found to have taken place with a 0.3 N w solution." 

Here certainly is definite proof of the crystalloid nature of sili- 
cates of these ratios in dilute solution. Harman found "about 2/3 of 
the silica in 0.3 N w 1 : 4 and about 1/3 in 1.0 N/ w H 2 SiO s was crystal- 
loidal." He points out that investigators of silicic acid should take 
cognizance of this fact and not prepare their material by dialysis. 

Ganguly worked with the ratios above 1 : 2. 

Table 23. Analyses After Equilibrium with Parchment Paper. • 





Silicate Compartment 


Water Compartment 








Si0 2 Gms. 


Na 2 Gms. 


Si0 2 Gms. Na 2 Gms. 






Molar 


per 100 


per 100 


per 100 per 100 


Difference 


Ratio 


cc. 


cc. 


cc. cc. 


Si0 2 


Na 2 


4.2 


1.8930 


0.399 


1.107 0.335 


0.786 


0.064 


3.95 


1.8024 


0.4238 


1.1908 0.3648 


0.6116 


0.059 


3.8 


1.6996 


0.4308 


1.2942 0.3806 


0.4054 


0.0502 


3.3 


1.6308 


0.4802 


1.3664 0.4548 


0.2644 


0.0254 


3.0 


1.5254 


0.5192 


1.4734 0.5090 


0.052 


0.0102 


2.5 


1.5372 


0.6236 


1.4752 0.6140 


0.062 


0.0096 


2.0 


1.5074 


0.766 


1.4918 0.7748 


0.0156 


—0.0088 


Table 24. At 


lalyses After 


Equilibrium with Collodi 


on Memb. 


ranes. 


Molar 


Silicate Compartment 


Water Compartment 






Ratio 


Si0 2 Gms. 


Na 2 Gms. 


Si0 2 Gms. Na 2 Gms. 






Si0 2 


per 100 


per 100 


per 100 per 100 


Difference 


Na 2 


cc. 


cc. 


cc. cc. 


Si0 2 


Na 2 


4.2 


1.1094 


0.2062 


0.3968 0.1624 


0.7126 


0.0438 


3.95 


1.0478 


0.2172 


0.4608 0.1748 


0.5870 


0.0424 


3.8 


0.9298 


0.2246 


0.5776 0.1834 


0.3522 


0.0412 


3.3 


0.8788 


0.2524 


0.6294 0.2176 


0.2494 


0.0348 


3.0 


0.7736 


0.2640 


0.7332 0.2524 


0.0404 


0.0116 


2.5 


0.7722 


0.3178 


0.7338 0.3022 


0.0384 


0.0156 


2.0 


0.7568 


0.3852 


0.7496 0.3896 


0.0072 


—0.0044 



"The distribution was greatly dependent on the original molar ra- 
tios of the solutions. Solutions up to the molar ratio 1 : 3 showed very 
little variations in concentrations during diffusion, showing thereby 
that the quantity of non-diffusible matter in those solutions was com- 
paratively small. 

"The quantity of non-diffusible matters increased very rapidly after 
the ratio 1 : 3. This result is quite in line with the previous measure- 
ments on the light-scattering of the silicate solutions, 76 and shows be- 
yond doubt that after the ratio 1 : 3, the quantities of colloidal matter 

"Ganguly, /. Phys. Chem., 30, 706 (1926). 



THE CONSTITUTION OF SILICATE SOLUTIONS 53 



in the silicate solutions increase at a very rapid rate. . . . Measure- 
ments of pH of the solutions after equilibrium showed that hydrolysis 
does not take any prominent part 
during these distribution processes/' 
The osmotic pressures also indicated 
an increase of colloidal matter with 
ratio. 



^ 6 






u 



3 






Chemical Evidence. 

Colorimetric Reaction with 
Crystalloidal Silica. A colori- 
metric test for crystalloidal silica 
was used by Harman 7? to give still 
further evidence of silicate ions. 
This test depends upon the forma- 
tion of a greenish yellow silico- 
molybdate. 78 Though less convinc- 
ing than the transport measurements 
it is interesting to note that this test 
seems to show that in dilute solutions 
most of the silica is crystalloidal but 
with rising concentration, first in the 
higher ratios, the colloidal content is 

increased. The color produced by a given normality of the ratio in 
question was matched with a solution of ratio 1 :1 whose normality was 
determined. From these figures the ratio of crystalloidal silica in the two 
solutions was determined as shown in the third, sixth, and last columns 
of the following table: 



/ 




Fig. 16. 



3 



If 



a 



-Molar Ratio. 



Table 25. Colorimetric Test. 





Normality 
















Na 2 


Std. 


Crys. 


sil. in 2 : 1 


Std. 


1:3 




Std. 


1:4 


2: 1 


1: 1 


Crys. 


sil. in 1 : 1 


1:1 


1: 1 


1:4 


1: 1 


1: 1 


0.0005 


0.00025 


0.5 


0.0005 


0.0015 


3.9 


0.0005 


0.002 


4.0 


0.001 


0.0005 


0.5 


0.001 


0.0025 


2.8 


0.001 


0.004 


4.0 


0.002 


0.001 


0.5 


0.003 


0.009 


3.0 


0.003 


0.010 


3.3 


0.003 


0.0015 


0.5 


0.005 


0.014 


2.8 


0.005 


0.016 


32 


0.004 


0.002 


0.5 


0.007 


0.018 


2.6 


0.007 


0.022 


3.1 



"It is seen that in very dilute solution, 0.0005N, ratio 1 : 4, contains 
as much crystalloidal silica as 0.002N, 1:1, the normalities in accord- 

77 /. Phys. Chem., 31, 622-623 (1927). 

"Dienert and Waldenbulcke, Compt. rend., 176, 1478 (1923) : Bull. Soc Chim 
33, 1131-1140 (1923). 



54 



SOLUBLE SILICATES IN INDUSTRY 



ance with the practice adopted in this investigation being expressed in 
terms of the sodium content. In other words, practically all the silica 
in ratio 1 : 4 exists in the crystalloidal state at a dilution of 0.005N, 
or more correctly, ratio 1 : 4 contains 4 times as much crystalloidal 
silica as ratio 1 : 1 at this dilution. 

"Similarly at this dilution, all the silica in ratios 2 : 1 and 1 : 3 exists 
in the crystalloidal state. 

"As the solution gets more concentrated we see that ratio 1:4 no 
longer contains 4 times as much crystalloidal silica as ratio 1:1, indi- 
cating that in the more concentrated solutions some of the silica in 
ratio 1 : 3, and still more in ratio 1 : 4, passes into the colloidal state. 

"Hence in extremely dilute solutions of these ratios practically all 
the silica exists in the crystalloidal state, but with increasing concen- 
tration increasing amounts of colloidal silica are manifested." 

Electrometric Titrations. Stericker 79 titrated sodium silicate so- 
lutions electrometrically and found breaks at points suggesting the 



90 



70 



f, 3 . m fi 



Sod/urn 



metric Tttrm 
•S/Z/catt So* 



?Vof? 



of 
Jvf/ on 



50 



2C 30 40 

Cubic Cent/meters of ffce/ 

Fig. 17. 



so 



presence of NaoSi 2 5 and Na 3 Si0 3 . Harman 80 also made titrations 
of this kind on entirely different solutions and came to similar con- 
clusions. 

79 Stericker, Wm, Doctor's Thesis, University of Pittsburgh (1922). 
8 V. Phys. Chem., 31, 616-622 (1927). 



THE CONSTITUTION OF SILICATE SOLUTIONS 55 

Conclusions. All the results indicate that solutions of the sodium 
silicates contain much less colloidal material than has commonly been 
believed. Simple and complex silicate ions are present ; they remove the 
discrepancy between the earlier views of complete hydrolysis and hy- 
drogen-ion measurements. Although the exact nature of the silicate 
solutions has not been completely explained, a substantial advance has 
been made in the last few years. 

Harman 81 has given the following- summation of our present knowl- 
edge of these solutions. 

"Silica exists in solutions of these ratios not wholly colloidal as 
heretofore supposed, but wholly or partly as crystalloidal silica de- 
pending upon the ratio Na 2 : Si0 2 , and upon the concentration. This 
crystalloidal silica exists in equilibrium with silicate ions, or elec- 
trically charged aggregates, of silicate ions and silica, i.e., ionic mi- 
celles, or pure colloidal aggregates, as the case may be, depending upon 
the ratio and concentration. 

"In aqueous solution at 25 °C. two and only two salts, viz., Na 2 Si0 3 , 
i.e., ratio 1:1, and NaHSiO s , i.e., ratio 1:2, appear to exist as such, 
the behavior and nature of which are now elucidated. 

"Ratios other than 1 : 1 and 1:2 are not definite salts but are 
typical examples of colloidal electrolytes. 

"The fundamental nature of silica in solution appears to depend 
upon the existence, at least in the range here investigated, of only one 
acid, metasilicic acid, in which the equilibrium between the crystal- 
loidal and the colloidal constituents depends upon the concentration, 
the crystalloidal content at ordinary concentrations being much greater 
and the acid, therefore, much stronger, than generally supposed." 

Structure of Systems With Relatively Low Water Content. 

Exchange Properties. When sodium has been adsorbed on col- 
loidal silica, it reduces but does not entirely destroy the tendency of 
the particles to coalesce. Silicate solutions in which the ratio of silica 
to sodium is above 4.2 are unstable. They tend to gel on standing, 
and solutions of much lower ratio are easily thrown out of equilibrium 
by the removal of part of the alkaline content by neutralization, by 
dialysis, or by electrolysis. A gel made by the partial neutralization 
of a sodium silicate solution will undergo exchange reactions in which 
the adsorbed sodium is replaced by adsorbed calcium from any soluble 
calcium salt. Sodium may be replaced by treating the calcium gel with 

81 /. Phys. Chem,, 32, 44 (1928). 



56 SOLUBLE SILICATES IN INDUSTRY 

a solution of a soluble sodium salt of sufficient concentration to reverse 
the equilibrium. Wheaton's formation of a gel for water softening 82 
is based on this principle. 

Effect of Age on Viscosity. There is a tradition that indus- 
trial silicate solutions tend to increase in viscosity with age. This is 
always observed on long standing of silicates having ratios of 3Si0 2 , 
Na 2 or more, when stored in glass bottles or even when hermetically 
sealed in a glass tube. Storage of five years' duration in iron bombs 
showed that adhesive silicates do not change in viscosity within the limits 
of measurements made with the Stormer viscometer during such a 
period. The familiar thickening must be attributed to loss of moisture 
or to a reaction with the containing vessel which reduces the protective 
action of the adsorbed sodium on the silica particles. 

Structure in Concentrated Solutions. With the increase of alkali 
metal the concentrated solutions depart from the physical character- 
istics of gels, which are quite evident in solutions of the composition 
Na 2 0, 3Si0 2 and those with larger amounts of silica. Such solutions 
may be concentrated to a point where they appear to be solids. Under 
sudden stress, they break with a conchoidal fracture. They show 
elastic properties, for though they can easily be molded in the hand, 
they will bounce like a rubber ball, but if allowed to stand, they will 
flow under the slightest pressure. Determinations of their stress-flow 
curves show that these pass to the zero point ; they are viscous liquids 
and not, like suspensions of clay, which remain immovable up to a 
critical stress, plastic solids. 83 What, then, is the explanation of the 
bouncing ball of concentrated silicate? Until a better explanation is 
forthcoming, the idea that colloidal silica has begun to form a gel 
structure which it is unable to complete due to the viscous character 
of the liquid phase, seems to satisfy the requirements. Then we 
might have a liquid free to move in the interspaces of the loosely 
formed gel which, continually tending to reconstruct itself, would push 
it back toward its original position and yet not be strong enough to 
resist the tendency to flow under very slight pressure, operating through 
a considerable period of time. 

Adsorption of Sodium Ions on Silica Particles. 

Experimental evidence tending to show the adsorption of sodium 
ions on silica particles has been obtained in a large number of cases. 

82 Brit. Pat. 142,974 (1920). 

83 Bingham and Jacques, Chem. & Met. Eng., 28, 727 (1923). 



THE CONSTITUTION OF SILICATE SOLUTIONS 57 

Jordis, 84 working on the precipitation of ferric chloride by sodium 
silicate, obtained precipitates of strong alkaline reaction and supernatant 
liquors which were strongly acid although the amounts of sodium and 
chlorine in the solutions mixed were in a stoichiometrical relation. The 
sodium was so firmly attached to the colloidal particles of silica that 
it was actually removed from solution. A rather extended experience 
with precipitates from silicate solutions, as, for instance, the precipi- 
tate formed with aluminum sulfate in sizing paper with sodium sili- 
cate, justifies the statement that these precipitates always carry alkali 
with them out of solution in a form which requires prolonged wash- 
ing for its removal. Some recent studies on a steam boiler operating 
on a closed circuit with high-grade distilled water showed a steady 
decline of both sodium and silica content after the addition of sodium 
silicate put into the system to control corrosion. 85 

In all cases where silica is separated from an alkaline solution either 
as an amorphous precipitate or gel, some of the base is carried with 
it. This takes place under such widely differing circumstances as the 
separation of films from dilute solutions and the precipitate of silica 
and stannic phosphate adsorbed on silk fibers in the process of 
weighting. 

Although colloidal silica is present in all silicate solutions of indus- 
trial importance, its behavior does not alone account for all their prop- 
erties. The bouncing ball of concentrated silicate solution contains 
in addition to its incipient structure a fluid phase in the interspaces. 
We have here to do not only with colloidal systems but with salt solu- 
tions the exact nature of which remains to be explored. 

84 Z. angew. Chem., 19, 1697-1702 (1906). 

85 Hecht, Max, personal communication. 



Chapter III. 
Definite Soluble Silicates. 

Sodium Silicates. 

The composition of soluble silicates is not bounded by the limits 
implied by the formulas of definite compounds which may be separated 
and studied. In dilute solutions the silica and base may be present 
in any proportions. These solutions have characteristics which dis- 
tinguish them from those of all other alkaline salts. From some of 
them definite crystalline bodies may be obtained, while others remain 
viscous and glue-like and yield no compounds which can be separated 
as crystals or otherwise identified as chemical individuals. Each ratio 
yields, however, a set of reproducible properties of widely varied char- 
acter as we progress from one end of the series to the other. The 
compounds which may exist in solution, as well as the nature of the 
silica or alkali above the amounts thus accounted for, are matters of 
consequence if we would understand the behavior of silicate solutions 
in industry. 

Formation of Hydrous Forms of Metasilicate. 

If a solution containing equi-molecular proportions of Na 2 and Si0 2 
be concentrated to a water content of 50 per cent and allowed to stand 
at ordinary temperatures, crystalline sodium metasilicate will be formed. 
This salt was first reported by Fritzsche, 1 who described two hydrates, 
Na 2 Si0 3 . 6H 2 in monoclinic crystals, and Na 2 Si0 3 . 9H 2 in rhombic. 
Subsequent workers reported crystalline sodium metasilicates with 
five, 2 seven, 3 ten, 4 and twelve 5 and 6 molecules of water but it is probable 
that these were mixtures of other hydrates, more or less decomposed. 

1 Fritzsche, Poggendorfs Ann. der Physik und Chem., 131, N.S. 43, 135-138 
(1838). 

2 Peterson, Theodor, Bcr., 5, 409 (1872); also /. pr. Chem., N.F.S., 397 
(1892). 

3 Yorke, Phil. Trans. Roy. Soc, 147, 533 (1857). 
4 Mylius, F. and F. Foerster, Ber., 22, pt. 1, 1092 (1888). 

6 Weber. See Gmelin-Kraut, "Handbuch der anorgischen Chemie," 7 Auflage, 
Bd. 3, Abt. 1, pp. 222-223 and 229-234 (1909). 
6 Jordis, Z. anorg. Chem., 56, 305 (1907). 

58 



DEFINITE SOLUBLE SILICATES 



59 



Vesterberg 7 prepared the ennehydrate Na 2 Si0 3 . 9H 2 by crystal- 
lizing from solutions containing alcohol and also reported the exist- 
ence of a compound with 6H 2 from observations of the dehydra- 
tion of the salt with 9H 2 over concentrated sulfuric acid and 
rehydrating over sodium hydroxide at specific gravity 1.26. Dehydra- 
tion of 9H 2 over 50 per cent potassium hydroxide led him to believe 




Fig. 18. — Sodium Metasilicate. 
Na 2 Si0 3 .4H 2 



there is a hydrate with 3H 2 but later workers have not confirmed 
this. 

In an effort to produce a silicate analogous to NaHC0 3 , Jordis s ob- 
tained after long standing of the solution a crystalline mass which 
proved to be Na 2 SiO s . Finally the hexahydrate crystallized from a 
very alkaline solution. 

The most complete studies of sodium metasilicates are those of Erden- 
brecher, 9 who began his work at Erlangen under Jordis. He applied 
physico-chemical methods to determine what definite hydrates are 

7 Vesterberg, K. A., Proc. 8th Int. Congress of Exp. Chcm., 8, 235 (1912). 

8 Jordis, E., Chem. Ztg., 38, 922 (1914). 

9 Erdenbrecher, A., Chcm. Ztg., 39, 583 (1915); Mikrokosmos, 15, 55-60 
(1921) ; Z. anorg. allgem. Chem., 124, 339-354 (1922). 



60 



SOLUBLE SILICATES IN INDUSTRY 




Fig. 19. — Sodium Metasilicate. 
Na 2 Si0 3 .6H 2 




Fig. 20. — Sodium Metasilicate. 
Na 2 Si0 3 .9H 2 



DEFINITE SOLUBLE SILICATES 



61 



formed and then prepared and studied the crystalline forms containing 
four, six, and nine molecules of water. 

With an apparatus like that shown in the cut the temperature of a 
water bath during heating and cooling was observed with one ther- 
mometer and the readings were plotted in comparison with those of a 




Fig. 21.— Erdenbrecher's Apparatus for Studying the Hydrates of Sodium 

Metasilicate. 

thermometer immersed in the metasilicate in the test tube. As crystal- 
lization took place or crystals dissolved, alterations in the rate of 
thermal change in the silicate indicated the points at which definite 
hydrates formed and melted. Manipulation was difficult because the 
silicate crystals tended to set to a solid mass, but it was found that 
the addition of paraffin oil would keep them in a mushy condition so 
that they could be stirred with a thermometer, without invalidating 
the results. 



62 



SOLUBLE SILICATES IN INDUSTRY 



The method was tested with sodium carbonate and sulfate and found 
to give results in accord with the known characteristics of these salts ; 
the breaks in the time-temperature curves corresponded to the melting 
points of the crystal hydrates. With Na 2 Si0 3 , the manipulation was 




Fig. 22. — Cooling Curves of Sodium Metasilicate. 
Na 2 Si0 3 .6H 2 



further complicated by the tendency to undercool without crystal forma- 
tion and to crystallize so slowly that the temperature differences could 
not be observed. The solutions were seeded with metasilicate crystals 
and a technic was developed which showed the correct melting points 
of the three hydrates illustrated. 



DEFINITE SOLUBLE SILICATES 



63 



Na 2 Si0 3 . 9H 2 melts at 47°, crystals rhombic. 
Na 2 SiO ; . . 6H 2 melts at 62.5°, crystals monoclinic. 
Na 2 Si0 3 . 4H 2 melts about 85°, crystals hexagonal. 

Studies of the vapor pressure of sodium metasilicate with 57.4, 58.6, 
60.5, and more than 60.5 per cent water, showed a change at 37.2°C. 



€0 



56 



8 



«i 46 



£ 44 



« 



40 



3b 























































< 












h 












1 










_L 


1 









77/ 



t* 



M/n u fes 



JO 



Fig. 23. — Cooling Curves of Sodium Metasilicate. 
Na 2 Si0 3 .9H 2 

which is thought to be the melting point of Na 2 Si0 3 . 14H 2 0, but this 
salt has not been isolated. 

The ennehydrate is the most easily prepared. Commercial metasili- 
cate was found to contain 10H 2 O, probably due to the presence of a 
mixture of hydrates more or less decomposed or to incomplete sepa- 



64 



SOLUBLE SILICATES IN INDUSTRY 



ration of crystals and mother liquor. If 30 grams of the crude sub- 
stance and 6 to 9 grams of sodium hydroxide were dissolved in 30 cc. 
of water, Na 2 Si0 3 .9H 2 crystallized in beautiful long rhombic plates. 
With the sodium hydroxide increased to 18 grams the hexahydrate in 
well defined crystals was obtained while with 26 grams of sodium 
hydroxide on long cooling the product was Na 2 Si0 3 .4H 2 0. 

Transformations of Hydrates. 

By altering the amount of water or of sodium hydroxide in the 
mother liquor, a series of transformations from one crystal form to 




Fig. 24. — Sodium Metasilicate. Transformation of 4 into 6 Hydrate. 

another was secured. These were carried out under the microscope 
and photographed. The hydrate with six molecules of water in the 
appropriate mother liquor was covered with a cover glass but this 
was not cemented to the slide. The mother liquor absorbed water 
from the air at the exposed edges of the glass and the Na 2 Si0 3 .6H 2 
crystals were dissolved while Na 2 Si0 3 .9H 2 crystals formed. The 
change from Na 2 Si0 3 .4H 2 to Na 2 Si0 3 .6H 2 was similarly observed. 
By putting Na 2 Si0 3 .9H 2 into a mother liquor of Na 2 Si0 3 .6H 2 0, the 
former was slowly dissolved as the latter formed. 

A series of cooling curves on mixtures 6 or 9 hydrates with water, 
plotting time against temperature, showed distinct changes in direction 
at 47° and 62.5°. At 37.2° the melting point of the probable hydrate 



DEFINITE SOLUBLE SILICATES 



65 




Fig. 25. — Sodium 'Metasilicate. Transformation of 6 into 9 Hydrate. 




Fig. 26. — Sodium Metasilicate. Transformation of 9 into 6 Hydrate. 



66 SOLUBLE SILICATES IN INDUSTRY 

with 14 mols of water is indicated. The series was investigated up 
to 18 mols water. 

Preparation of Anhydrous Metasilicate and Disilicate. 

Anhydrous crystalline sodium metasilicate, Na 2 Si0 3 , and sodium disili- 
cate, Na 2 Si 2 5 , have been prepared by Morey 10 from systems at 
high temperatures and pressures in the presence of water. The former 
is formed above 400° when glass of the ratio Na 2 0,Si0 2 is heated 
with water. The crystals are rapidly decomposed by water. The disili- 
cate is crystallized from a glass of the same composition as the meta- 
silicate heated at 300° with an amount of water insufficient to give 
complete solution. The disilicate is much less soluble than the meta- 
silicate and can be purified by leaching with water. Long exposure to 
cold water causes decomposition with a residue of hydrous silica. 

An investigation of the system Na 2 — Si0 2 — H 2 at 25 °C. was 
undertaken by Harman, 11 who stirred his mixtures at constant tem- 
peratures from 8 to 14 days and then analyzed the liquid and solid 
portions separately. This was difficult in the cases where there was 
little water in the system on account of great viscosity and where 
silica was above ratio 1:3 on account of the appearance of gel-like 
characteristics. 





Table 26. 


Analyses 


of Solutions and Residues. 






Solution 






Residue 




Na 2 


Si0 2 


H 2 


Na 2 


SiO a 


H 2 


9.37 


8.74 


81.89 


10.51 


9.94 


79.55 


9.45 


2.22 


88.33 


12.48 


6.75 


80.77 


13.70 


1.19 


85.11 


14.50 


3.46 


82.04 


24.48 


1.34 


74.18 


24.02 


5.48 


70.50 


27.52 


1.84 


70.64 


27.25 


7.52 


65.23 


29.58 


1.90 


68.51 


29.74 


5.04 


65.22 


33.02 


2.92 


64.06 


31.96 


7.57 


60.47 


35.54 


2.94 


61.52 


35.70 


10.06 


54.24 


36.39 


0.49 


63.12 


36.75 


7.75 


55.50 


44.78 


0.85 


54.37 


45.31 


5.82 


48.87 


14.11 


19.65 


66.25 


16.20 


20.26 


65.54 


19.32 


31.33 


49.35 


20.18 


27.71 


52.11 


16.57 


31.30 


52.23 


17.72 


35.44 


46.84 


10.53 


28.80 


60.67 


11.19 


29.95 


58.86 


36.75 


11.65 


51.60 
Theoretic 


36.07 
:ally Calculated. 


14.90 


49.03 


21.80 


21.21 


56.99 


Na 2 Si0 3 


.9H 2 




26.93 


26.18 


46.89 


Na 2 SiO s 


.6H 2 




37.06 


36.04 


26.89 


Na 2 Si0 3 


.2.5H 2 




50.69 


49.31 


• • • • 


Na 2 Si0 3 






17.99 


34.98 


47.00 


Na 2 0.2Si0 2 .9H 2 




53.45 


.... 


46.55 


NaOH.: 


IH 2 





Morey, G. W., /. Am. Chem. Soc., 36, 215 (1914). 
/. Phys. Chem., 31, 511-518 (1927). 



DEFINITE SOLUBLE SILICATES 



67 



He confirmed the existence of Na 2 Si0 3 .6H 2 and Na 2 Si0 3 .9H 2 — ■ 
the hexa- and ennehydrates of sodium metasilicate and concluded that 
the only other hydrate stable at 25°C. contains 2.5 molecules of water; 
and he plotted the areas in which they constitute the stable phase. As 
a hydrate with 2.5 molecules of water has not been isolated and as 
Erdenbrecher appears to give conclusive evidence of a definite hydrate 

HxO 

Z^ TnaTfe theoretical positions 
Of 

A. Ne«S;0 3 .<l H»0. 

B. Na^S.0 3 . 6 H z 

C. Na z SiO z 2 5H<Q 

D. WOjSi'Oj. 

E. Na.fi. -2S.O^. qhfi. 



Ternary Systen 

Na*0 - $.C\ - H x 0. 



N'^Q 




Na.0H.l4ty 



Fig. 27.— Ternary System. Na 2 = SiQ 2 = H 2 0. 



with less water than Na 2 Si0 3 .6H 2 0, which he believed to be 
Na 2 Si0 3 .4H 2 0, the conclusion that only the three hydrates can exist 
at 25° must be received with reservations. 

An area was found, before experimental difficulties concluded the 
study, in which the disilicate Na 2 0,2Si0 2 .9H 2 was indicated. This 
has never been isolated at ordinary temperatures though there are 
many evidences of its existence. 

Anhydrous Systems. 

Sodium metasilicate, Na 2 Si0 3 , and sodium disilicate, Na 2 Si 2 5 , have 
been crystallized from anhydrous fusions by Niggli 12 and Morey. 13 

"Niggli, Paul, Z. anorg. Chem., 84, 229-272 (1913). 

13 Morey, G. W., /. Am. Chem. Soc, 36, No. 2, 215 (1914). 



6S SOLUBLE SILICATES IN INDUSTRY 

Schwarz and Menner 13a claim to have produced another definite crys- 
talline compound, Na 2 0. 3Si0 2 from a glass of that composition, which 
on long heating became crystalline. Their evidence is inconclusive. 
Morey and Bowen 14 found that the optical properties of metasilicate 
and disilicate were very nearly alike, differences being shown only 
by very exact measurement of their optical constants. They both have 
positive elongation and low refractive indices, and are apparently ortho- 
rhombic. Table 27. The melting point of the metasilicate is in close 
agreement with that found by Jaeger. 15 

Na 2 Si0 3 — 1088°, Jaeger 
1086°, Morey 
Na 2 Si 2 5 — 874°, Jaeger and Morey 

Table 27. Optical Constants of Sodium Metasilicate and Sodium Disilicate. 

(Morey and Bowen) 

Na 2 Si0 3 Na 2 Sb0 3 

Crystallization Orthorhombic Orthorhombic 

Habit Needles Plates and needles 

Cleavage Prismatic in zone of y Pinacoidal 

y /3 and y a 

Optic axial angle 2V very large 2V = 50° to 55° 

Optical Character Negative Negative 

f y 1.528 ± .002 1.518 ± .002 

Refractive indices -{ (3 1.520 ± .002 1.514 ± .002 

a 1.513 ± .002 1.504 ± .002 

Potassium Silicates. 

Morey and Fenner also determined the melting points of K 2 SiO s and 
K 2 Si 2 5 . Potassium silicates, owing to their great deliquescence, were 
not prepared in crystalline form until Morey, 16 in an investigation de- 
signed to throw light on the equilibria existing in rock magma, studied 
the system K 2 Si0 3 — Si0 2 — H a O at temperatures from 200° to 1000° C. 
Glasses of known composition were made by fusing potassium carbo- 
nate or potassium hydroxide with silica. These were heated with 
silica and water in a bomb so made that no vapor could escape. The 
desired temperature was maintained in an electric resistance furnace 
until equilibrium was established and then by cooling rapidly a series 
of hydrous solids was produced which showed the equilibrium which 

13a Schwarz and Menner, Ber., 57B, 1477-1481 (1924). 

"Morey, G. W., and N. L. Bowen, /. Phys. Chem., 28, No. 11, 1167-1179 
(1924); Ber., 57B, 1477 (1924); 58B, 73 (1925). 

15 Jaeger, F. M., /. Wash. Acad. Sci., 1, 49-52 (1911) ; Abst. in /. Chem. Soc., 
100A, 2981-2982; C. A., 5, 3770. 

"Morey, G. W., /. Am. Chem. Soc, 39, 1173-1229 (1917). Cf. Pukall, W., 
Ber., 49, 397-436 (1916). 



DEFINITE SOLUBLE SILICATES 



69 



had existed at the higher temperature. Microscopical examination of 
the quenched products made it possible to fix the amounts of the glasses 
of each composition which would remain dissolved at the temperature 
in question. The crystalline products were identified by means of 
their optical constants and their composition fixed by study of the 
isothermal saturation curves and checked where possible by the analysis 



K,SiO, 




Fig. 28. — The System Potassium Metasilicate, Silica, Water. Diagram showing the 
boundary curves. The compound stable in contact with liquid in each field is 
shown by the large letters ; the point representing the composition of the com- 
pound, by the small letters. Arrows show the direction of falling temperature. 
The broken line is the isotherm at 200°. 



of pure compounds or by the method of residues. Six potassium sili- 
cates were thus identified. 

KHSi 2 5 — decomposed by H 2 below 420°. As observed under the 
microscope the action is so slow that it appears to be practically unat- 
tacked by H 2 0. 

K 2 Si 2 5 — melts at 1041° and is not decomposed by H 2 0. The crys- 
tals break up irregularly in water under the microscope showing char- 
acteristic shred-like forms as they go into solution. 

K 2 Si 2 5 .H 2 — rapidly decomposed by water at ordinary tempera- 
tures. Crystals dissolve completely. 



70 SOLUBLE SILICATES IN INDUSTRY 

K 2 Si0 3 — melts at about 966°. It is very hygroscopic and crystals 
dissolve rapidly and uniformly. 

K 2 Si0 3 .^2H 2 — completely soluble in water. 

K 2 Si0 3 .H 2 — decomposed by H 2 at temperatures below 200°. It 
breaks down at 370° into K 2 Si0 3 .^H 2 and vapor. Crystals dissolve 
completely in water. 

Lithium Silicates. 

Solutions of lithium silicate have been studied by Ordway 17 but 
he did not succeed in isolating any definite compounds. He precipitated 
sodium silicate solutions with solutions of lithium chloride and ob- 
tained a cake composed of a mixture of sodium and lithium silicates. 
This was dissolved in water and the process repeated with increase 
of Li 2 in the cake. Finally a solution was obtained containing 
2(Li 2 0,4Si0 2 ), Na 2 0,4Si0 2 . A solution containing 8.5 per cent 
Li 2 Si0 3 and a slight excess of LiOH was prepared by the action of 
LiOH on hydrous silica. This could not be concentrated above 11 
per cent. 18 Four definite lithium silicates have been prepared by fusion 
but none of them dissolves without decomposition. A difficultly soluble 
lithium metasilicate monohydrate is described by Vesterberg 19 as pre- 
cipitated by heating to 80° solutions made from hydrous silica and twice 
the theoretical amount oi 2 N LiOH at ordinary temperatures. Solu- 
tions containing 3.4 mols Si0 2 for each Li 2 were made with 2 N LiOH 
and hydrous silica. Carter 20 in attempting to prepare solutions of 
lithium metasilicate, found that a clear glass of the composition Li 2 0, 
2Si0 2 could be prepared from the carbonate by fusion with silica at 
1300° and dissolved with some decomposition to a solution containing 
6 per cent Li 2 0, 3.2Si0 2 but not entirely free from carbonate. The 
melts corresponding to the metasilicate cooled to crystalline masses 
which decomposed with the separation of hydrous silica but could not 
be brought into solution. The system Li 2 Si0 3 -Si0 2 was worked out 
by Jaeger and van Klooster. 

Rubidium Silicates. 

Rubidium metasilicate does not crystallize under ordinary conditions. 21 
A solution of rubidium hydroxide containing 21 per cent Rb 2 readily 

17 Ordway, J. M., Am. I. Sci., 174, 4th Ser., 473-478 (1907). 

18 Le Chatelier, "La Silice et les Silicates," 1914, p. 400-401 ; Jaeger and H. S. 
van Klooster, Proc. Acad. Sci. Amsterdam, 16, 857-880 (1914). 

19 Vesterberg, K. A., Medd. K. Velenskapakod, Nobel Inst., 5, No. 30, 1-9 
(1919). 

20 From the unpublished records of the Philadelphia Quartz Company (1917). 

21 Ordway, loc. cit. 



DEFINITE SOLUBLE SILICATES 71 

dissolved enough silica in hydrous condition to give Rb 2 Si0 3 but yielded 
a thick viscous liquid at 83 per cent solid content. This when diluted 
took up enough silica to form disilicate, but no crystallization took 
place. Precipitation by alcohol gave compounds of higher Si0 2 con- 
tent up to Rb 2 0, 4Si0 2 , which was freely soluble in water. 



Chapter IV. 
Reactions. 

Precipitation. 

Compounds Causing Precipitation. 

So many substances react with and precipitate silicate solutions that 
it is almost safe to assume that a clear viscous solution of any alkaline 
silicate contains nothing but silica, alkalies, and water. At least from 
the point of view of the analyst, it is possible to eliminate so many 
classes of compounds that examination is relatively simple. Yet, be- 
cause the commercial solutions are viscous and partake of the nature 
of colloids, it is possible for trifling quantities of the most various 
substances to be present. 

Mineral Acids and Acid Salts. The substances which may be 
mixed with silicate solutions without reaction are few in comparison 
with those which react. All strong mineral acids are able to bind 
alkali metal and liberate silica which remains as a sol or separates in 
gel form according to the amount of water or electrolytes present and 
to the temperature, time, and other factors. Even carbon dioxide and 
hydrogen sulfide are absorbed when conducted into silicate solutions, 
and when the concentration is sufficient may cause precipitation. Acid 
salts, such as bicarbonates, bichromates, and bisulfates of the alkali 
metals, produce similar results. 1 

Other Salts and the Halogens. All soluble compounds of metals 
which form insoluble silicates, i.e., all except the alkali metals, also 
react with silicate solutions. In this category are included the zincates, 
aluminates, and plumbates of the alkali metals but not their chromates 
or permanganates. Fluorine, chlorine, and bromine react but iodine 
is much less active. Ammonium salts in concentrated solution will 
precipitate soluble silicates with the liberation of ammonia. This reac- 
tion is used to render silicate of soda insoluble as a binder for deco- 
rative colors on glass. Cold ammonium hydroxide, sp. gr. 0.921, will 
precipitate Na 2 0,3Si0 2 at sp. gr. 1.392. 2 

1 Basset, L. P., Fr. Pat. 410,038 (March 4, 1909). 

2 Fluckiger, F. A., Buchner's ncues Repertorium fur Pharmacie, 19, 260 
(1870) ; American Chemist, 2, 64 (1871). 

72 



REACTIONS 73 

Certain Organic Compounds. Commercial sugar, dextrin, glu- 
cose, glycerin, and gum arabic (after it is freed from naturally occur- 
ring soluble salts) are miscible with silicate of soda solutions of 
commerce. Phenol, chloral hydrate, tannic acid and most organic 
compounds which readily react with alkalies cause precipitation with 
concentrated silicates. 

Alcohols. Ethanol and methanol produce precipitates from con- 
centrated silicate solutions. These are mostly soluble in water and 
are to be regarded as dehydration products. Von Fuchs 3 proposed 
this reaction as a distinction between silicates of soda and potash, as 
the latter is more difficult to precipitate, but since both may be precipi- 
tated from strong solutions the test has very little value. 

Presence of Products of Hydrolysis. 

Few of these reactions have been carefully investigated ; but it is 
safe to make the general statement that, as we are dealing with col- 
loidal material, the character of the products of reaction will vary in 
every case with changing conditions. The assumption that even defi- 
nite silicates such as sodium metasilicate will react quantitatively with 
metallic salts of definite composition in solution to form definite in- 
soluble silicates will lead to serious error. Attempts to prepare me- 
tallic silicates in the wet way would never be expected to lead to simple, 
definite products but always to a mixture in which one or more sili- 
cates are associated to a greater or less degree with hydroxides, complex 
silicates, and silica. 4 

The simple equation : 

Me"X 2 + Me'SiOs = Me"Si0 3 + 2Me'X 

never represents the observations of experimental work. The products 
of reaction are not the simple ones which might be expected if hy- 
drolysis were complete and the metallic salts should cause the separa- 
tion of the corresponding hydroxide and silicic acid. Equilibrium is 
attained but slowly, changes in some cases taking place over a period 
of years. 

It does not follow that because the bases are present in equivalent 
amounts a neutral product will be obtained or that because the reaction 
product is an insoluble substance it will not remain dispersed as a sol 
in the aqueous reaction medium or that the phenomena observed at 
one temperature can be forecast from those at another. 

3 Dingler's polvtech. J., 142, 365-392 (1857). 

4 Jordis and Hennis, /. prakt. Chem., 77, 226 (1908). 



74 SOLUBLE SILICATES IN INDUSTRY 

Reactions of Metallic Salts. 

This being so, it follows that experimental work, to be of value, 
must be carried out under the most precise control of all variables 
which have an influence. Jordis and his collaborators have followed 
a few of these reactions with great thoroughness and care. In the 
effort to use only solutions of known composition, sodium metasili- 
cate was selected, and its reactions with solutions of cupric sulfate, fer- 
rous sulfate, and ferric chloride investigated. 5 

Copper. The metasilicate of copper occurs in nature with one and 
two molecules of water in definite crystal form as dioptase and chryso- 
colla respectively. The former was prepared by Becquerel, 6 who placed 
cupric nitrate and potassium silicate on opposite sides of a permeable 
membrane. The diffusion which brought the two solutions together 
was slow, permitting the formation of crystals but at the same time 
holding back colloidal constituents of the solutions which would have 
interfered with the definite character of the result. 

Jordis and Hennis 7 mixed 0.1 molar solutions of sodium metasili- 
cate and copper sulfate in equal amounts quickly and with agitation 

under varying conditions. 

Total Per Cent 

of Silica Found 

in Filtrate 

Copper solution poured into silicate 3.53 

Silicate poured into copper solution 4.75 

At boiling temperature 4.03 

When the amount of silicate solution was doubled the filtrate con- 
tained 43.8 per cent of the total silica. The first three experiments 
show that the reaction is not a simple exchange of molecular equiva- 
lents as silica remained in solution while all the copper was precipi- 
tated, and further evidence of complicated relations lies in the fact 
that when the amount of silicate was doubled the additional silica thus 

Table 28. Results of Precipitation. 

Mols CuO Per Cent of the Original 
per Mol Si0 2 Silica in the Filtrate 

3 31 87 

2.24 1440 (33.1 CuO %) 
1.12 1.24 

1.00 3.88 

0.56 26.37 

0.50 41.91 av.gjgg 

5 Hennis, W., Dissertation, Erlangen, 1906. 

'Jahresber. der Chem. (1868), 87-90; Compt. rend., 67, 1081 (1868). 

7 Jordis and Hennis, /. prakt. Chem., 185, 238-266 (1908). 



REACTIONS 75 

introduced did not all appear in the nitrate, which showed but 43.8 per 
cent compared with an expected 54 per cent. 

Equal measures of N CuS0 4 and N silicate of soda of composition 
Na 2 0,2Si0 2 , gave 4.47 per cent of the total silica in the nitrate. When 
the ratio of volumes was 1 : 0.983, the silica was reduced to 3.24 per 
cent. The precipitates, at first amorphous, developed microscopic green 
crystals on standing. Evidence of the presence of a copper silicate 
in the precipitate rather than a mixture of copper hydroxide and silica 
was the color of the precipitates on boiling. Copper hydroxide becomes 
black on boiling but the precipitates of blue copper silicate under like 
treatment did not go beyond a green. The color is not changed to 
black if mixtures of gelatinous silica and copper hydroxide are rubbed 
together and then boiled. 

Iron. Ferrous silicates in various minerals and slags are blue green 
to green in color and relatively stable. Precipitated ferrous silicate 
mixtures are, however, very easily oxidized to a yellow color in acid 
solutions and become grayish in alkaline solutions. The stability of 
the minerals containing ferrous iron may be in part accounted for by 
the presence of basic constituents. 

Tenth-molar solutions of ferrous salts with equal volume of 0.1 molar 
sodium metasilicate gave iron-free nitrates containing an average of 1.8 
per cent of the silica, and excess of either constituent, as in the case of 
copper, increased the silica in the solution. The silicate precipitates 
did not become black like ferrous hydroxide on boiling in the mother 
liquor. Tenth-molar ferric chloride which was made acid with hydro- 
chloric acid and neutralized with sodium hydroxide, then mixed with 
equivalent 0.1 molar sodium metasilicate, gave a variety of precipitates 
under varying conditions of heating, mixing, and standing. All the 
filtrates had an acid reaction. A few typical analyses of unwashed 
ferric precipitates are given in the table below. 

Table 29. Composition of Precipitates (Unzvashed). 

Si0 2 Fe 2 3 Na 2 CI H 2 

39.35 45.48 2.80 1.3 11.37 

33.45 42.95 4.68 ... 19.03 

29.91 41.36 3.57 ... 25.29 

26.39 18.53 15.74 10.37 (33.51) 

It is obvious that no definite substance, but a mixture, is thrown 
out of these solutions. If methyl orange or phenolphthalein be added 
to the silicate solution during the precipitation of a gelatinous precipi- 
tate the color is largely carried out of the solution with the precipi- 
tate and shows the alkaline color in spite of the presence of an acid 



76 SOLUBLE SILICATES IN INDUSTRY 

supernatant liquor. Adsorption of sodium ions on the silicious precipi- 
tate probably accounts for this. Large additional amounts of caustic 
alkali must be added to bring about an alkaline reaction whether or 
not the clear solution and the precipitate are separated by filtration. 
On standing, the alkalinity vanishes and only after several additions 
does the solution remain alkaline. If all the alkali is added at once, 
a smaller amount is required to neutralize than when it is added a little 
at a time or slowly. 8 After the ferric chloride solutions had been 
carefully adjusted to the composition FeCl 3 and a similarly standard- 
ized sodium metasilicate was used and filtered promptly the clear 
filtrate contained all the ions of the original solutions but none of 
them in stoichiometric relations. If the clear filtrate is boiled precipi- 
tation occurs. The addition of an electrolyte, such as Na 2 S0 4 , will 
also cause precipitation. If the original precipitate and supernatant 
liquor are allowed to remain long in contact both are changed and 
eventually the acidity will disappear. 

2Na:lSi0 2 and 0.66 Fe : 2C1 were mixed. No precipitate formed 
at first but in about 7 minutes it began to separate as a gelatinous pre- 
cipitate and the filtrate showed the analysis given below, after the time 

stated. 

Table 30. Progress of Precipitation (Mols). 

Na Si0 2 Fe CI 

After 13 min 2.55 1 3.86 0.95 

23 min 8.08 1 .78 7.70 

83 min 10.80 1 .23 9.43 

5 hrs 13 1 .54 12.50 

24 hrs 19.15 1 .50 19.50 

5 days 21.2 1 .60 23.50 

At first, silica is precipitated with much chlorine and goes into so- 
lution. As time goes on, silica and iron are further precipitated and 
sodium and chlorine approach molecular relations. 

The character of precipitation when ferric chloride solution is 
added to silicate solution is different from that yielded by the reverse 
procedure. An excess of either component reduces the amount of pre- 
cipitation when the two solutions are poured quickly together. When 
iron solution is added in small portions to silicate solutions precipita- 
tion occurs at once but half of the silicate solution can be added to the 
iron solution without causing turbidity. The liquid only becomes pro- 
gressively darker. 

Experiments made with a 40° Baume commercial silicate of soda solu- 
tion (probably about Na 2 0,3Si0 2 ) and ferric chloride led Liesegang 9 

8 Jordis and Lincke, Z. angew. Chem., 21, 11, 1982-1986 (1908). 
9 /. prakt. Chem., 88, 358 (1913). 



REACTIONS 77 

to the belief that only ferric hydroxide and hydrous silica were pre- 
cipitated and the attempt to work with pure compounds had led to 
more complicated phenomena. A solution of ferric chloride flowed 
over the viscous silicate increased in volume and gradually formed a 
gelatinous film even between the glass and the silicate, finally completely 
enveloping the latter. This translucent film was streaked with ferric 
hydroxide, which could be partly removed by a jet of water and almost 
completely with dilute acid. A similar firm silicious membrane was 
formed when 15 per cent hydrochloric acid was poured over the 40° 
silicate, the acid diffusing into the silicate solution, although acid of 2 
per cent strength yielded a soft gelatinous mass. An interesting varia- 
tion of the film or membrane that forms when concentrated colloidal 
silicates come in contact with relatively strong solutions of ferric chlo- 
ride or other metallic salts is known as the "silicate garden." * Crystals 
of ferric chloride dropped into a viscous silicate solution will be 
promptly surrounded by a membrane through which an aqueous liquid 
diffuses under osmotic pressure. 

Aluminum. The reactions between sodium metasilicate and alu- 
minum sulfate and chloride were studied by Gottwald. 10 The com- 
positions of the solutions were precisely adjusted to correspond with 
the formulas but the flocculent precipitates always contained sodium 
along with aluminum silicate. Both silica and aluminum compounds 
remained in the filtrate, although the amount of aluminum was very 
small after standing. The reaction did not cause noticeable tempera- 
ture changes. The precipitate was first weakly acid to litmus and 
then neutral. When precipitates were formed in the presence of CI 
ions, they were more easily separated by filtration or by settling than 
in the presence of S0 4 ions. 

Sodium in the filtrates was nearly equivalent to the anion but in re- 
lation to the silica it was much greater in the chloride series than when 
the aluminum was present as sulfate. The average molecular rela- 
tions in the precipitates are shown in the following tables : 

Table 31. Precipitates from Equivalent Amounts of Sodium Metasilicate and 

Aluminum Sulfate. 
(Concentrations between 1 and 2 per cent.) 

Mols Mols Mols Mols 

Time SiO a Al SO* Na 

1 hr 1.0 0.8720 0.0469 

1 " 25 min 1.0 0.7633 0.0358 0.1899 

4 " 1.0 0.7205 0.0124 0.3695 

8 days 1.0 0.6786 0.0665 0.2770 

14 " 1.0 0.6421 0.0940 0.4120 

* Cf . pages 79-80. 

10 Gottwald, Dissertation, Erlangen, 1913; Neues Jahrbuch Min. Gcol., 11, 51-53 
(1915). 



78 SOLUBLE SILICATES IN INDUSTRY 

Table 32. Sodium Metasilicate and Aluminum Chloride. 

Mols Mols Mols Mols 

Time Si0 2 Al S0 4 Na 

45 min 1.0 0.9341 0.1078 0.1352 

48 " 1.0 0.8328 0.0927 0.2015 

3 hr. 45 min 1.0 0.9849 0.0764 0.1359 

1 day 1.0 0.9072 0.0650 0.1376 

8 days 1.0 0.7526 0.0627 0.1210 

10 " 1.0 0.6735 0.1179 0.1753 

14 " 1.0 0.7280 0.0733 0.1195 

4 months 1.0 0.6813 0.0656 0.1954 

An attempt to determine whether aluminous precipitates from high 
ratio silicates contain free silica was made by Carter, 11 who found them 



-*IO' 



CALCIUM. 




o.3 



10 20 30 40 SO 

Cc. Sodium S/l/c^te. 



60 



Fig. 29. — Electrometric Study of Precipitation of Silicate Solution Na 2 0, 2.16Si0 2 

with Metallic Salts (Britton). 

completely soluble in a hot solution of sodium hydrogen sulfate which 
did not dissolve a freshly made precipitate of silica. 

Electrometric titrations of a solution of Na 2 0, 2.16Si0 2 with hydro- 
chloric acid, alkaline earth hydroxides and various metallic salts have 

11 Unpublished records of Philadelphia Quartz Company. 



REACTIONS 79 

been made by Britton. 12 When all the alkaline earth metals had been 
precipitated more silica was found in the precipitate than that which 
had been held by an amount of sodium equivalent to the alkaline earth 
metal. The conditions of his experiments were as follows : Na 2 0, 
2.16Si0 2 in a solution 0.102 normal with respect to its sodium content 
was used for hydrogen electrode titrations of 100 cc. portions of salt 
solutions of the strengths indicated in the following table. The tem- 
perature was 18° C. and the time at which a precipitate first appeared 
was noted. The pH values of the silicate precipitations were com- 
pared with the known data for hydroxide precipitation. 

Table 33. Electromctric Titrations with a Solution of Nch,2.i6Si02. 

Precipitation Began at Hydroxide 

Solution Titrated cc. of Sodium Precipitation 

pH Silicate atpH 

0.01 M — ZrCl 4 3.98 35.0 1.86 

0.01 M — ThCh 3.50 30.0 3.50 

0.0067 M — A1 2 (S0 4 ) 3 4.04 5.0 4.14 

0.02 M — BeS0 4 5.31 20.0 5.69 

0.02 M — ZnS0 4 5.25 1.0 5.20 

0.02 M — MnCU 7.35 1.0 8.41 

0.02 M — MgS0 4 9.50 1.0 10.49 

0.02 M — CaCl 2 10.07 3.0 

In this connection see also the work of Oka and Noda, 13 Joseph and 
Oakley, 14 and Hagg. 15 

Silicate Garden 

The familiar experiment known as the "silicate garden" 16 is an 
example of reaction at a higher concentration. The substances which 
appear as flocculent precipitates when much water is present have a 
firm texture when strong solutions react. Crystals of easily soluble 
salts of the heavy metals when dropped into suitable silicate solutions 
begin to dissolve, and reacting, are soon encased in a film of gel-like 
character. Water from the silicate solution diffuses through the per- 
meable membrane to dissolve more of the salt. The osmotic pressure 
soon becomes sufficient to deform or burst the cell wall. Thus new 
surfaces of salt solution are exposed which continue the process and 
form long tendrils or fungoid growths. The speed with which this 
curious reaction takes place varies with the concentration and rela- 

13 /. Chem. Soc, 127, 2814 (1925). 

13 Oka and Noda, /. Sci. Agri. Soc. (Japan), 258, 287 (1924). 

"Joseph and Oakley, /. Chem. Soc, 127, 2814 (1925). 

15 Hagg, Z. anorg. Chem., 155, 20 (1926). 

"Krug, George C, U. S. Pat. 1,584,779 (May 18, 1926). 



80 



SOLUBLE SILICATES IN INDUSTRY 



tive alkalinity of the silicate, being more rapid and yielding more fragile 
formations in dilute solutions and developing more rapidly in solutions 
of higher alkalinity when the concentration is the same. Many soluble 
salts yield growths of more or less characteristic form. 




Fig. 30. — Silicate Garden. 

The layer with which the crystal is surrounded is at first liquid, but 
the sol goes over into the rigid gel condition in a longer or shorter time, 
according to circumstances. Quincke 17 worked with solutions of the 
composition 2Na 2 0,3Si0 2 and found the setting time to be as follows : 

0.3 to 0.5 second with FeCl 3 and NiCh 
15 to 20 seconds with MnCh 
1 to 30 seconds with CuS0 4 
120 seconds with CuCl 2 

The gel formed at the interface between silicate and hydrochloric 
acid may, under favorable circumstances, remain liquid for months. 
During the liquid phase, bubbles are formed due to surface tension. 
These solidify before equilibrium is established and as the liquid pene- 
trates under osmotic pressure, the shape of the walls is distorted in 
curves or broken according to their texture at the moment. This gives 
rise to the most various forms. The cell walls or tubular filaments 
give up water (syneresis) on solidifying and become opaque so that 
a varicolored garden such as can be made from copper, nickel, cobalt, 
iron, manganese, and uranium salts, increases in beauty for some days 
after the filaments have ceased to grow. One of the best ways to 
exhibit this reaction is to make a cell of glass about four inches square 
and place in it layers of silicate solution of varying concentration, thus 
"Quincke, G., Ann. Physik., 312, ser. 4, v. 7, 631.82 (1902). 



REACTIONS 81 

changing the growths as they pass from one level to another. Sili- 
cates of the composition Na 2 0,2Si0 2 at specific gravities 1.090, 1.045, 
and 1.015, are a convenient series. The diffusion of the silicates is 
so slow that if carefully prepared, they will remain in separate layers 
for a long time. 

A good example of the importance of describing the chemical com- 
position of any silicate used in experimental work is afforded by the 
work of Ross, ls who reported that uranium nitrate and acetate would 
not grow in a silicate solution of the sort used for preserving eggs. 
This is very indefinite but from the relatively meager growths secured, 
it seems likely that the composition approached Na 2 0,4Si0 2 . Uranium 
salts will produce fungoid forms of brilliant yellow color and great 
beauty in a silicate of the composition Na 2 0,2Si0 2 . 19 

Fractional Precipitation by Alcohol. 

Fractional precipitation of silicate solutions with ethanol, methanol, 
or acetone, was found by Ordway 20 to be a useful means of eliminat- 
ing, at least partially, other compounds which might be present. A 
10 per cent silicate of soda solution is mixed with a tenth its volume 
of 95 per cent alcohol and the precipitate rejected. Two volumes of 
alcohol added to the filtrate cause a voluminous white opaque precipi- 
tate which, when well drained, contains about 50 per cent water. A 
mass of this precipitate allowed to stand will flatten out and become 
increasingly translucent. The first precipitation carries down most 
of the alumina, lime, magnesia, or heavy metal compounds which may 
have been in the original silicate, but iron cannot be entirely removed 
in this way. The alcoholic supernatant liquor contains most of the 
sodium chloride or sulfate from the silicate solution. The precipitate 
can be dissolved in four parts of water and the operation repeated. 
Ignition of silicates precipitated from alcohol, even after they appear 
quite dry, is accompanied with a blackening not only indicative of 
the incomplete removal of organic matter but suggesting that there 
may be a reaction between the silicate and alcohol. This has not been 
investigated. 

Alcoholic precipitates of silicates of soda more alkaline than Na 2 0, 
1.7Si0 2 are generally liquid but as the' relative amount of silica in- 
creases, the masses are progressively firmer, though even the hardest 
retain the ability to flow slowly at ordinary temperatures. This is 

18 Proc. Row Soc. N. S. Wales, 44, 583-592 (1910). 
19 Dollfus, Robert, Compt. rend., 143, 1148-1149 (1906). 
20 Am. J. Sri., 83, ser. 11, v. 33, 27-36 (1862). 



82 SOLUBLE SILICATES IN INDUSTRY 

characteristic of all silicate solutions which, like those precipitated by 
alcohol, contain about 50 per cent of water. 

The more dilute the silicate solution in which a precipitation is in- 
duced by alcohol, the greater will be the difference between the com- 
position of the separated material and the original solution. The more 
water present, the greater will be the Na 2 in the supernatant liquid 
and correspondingly the more silicious the precipitate. Ordway ob- 
tained precipitates as silicious as Na 2 0, 4.78Si0 2 , but his statement 
that they were insoluble must not be taken as final because he boiled 
them with an excess of water and we now know that the favorable 
condition for bringing such materials into solution is to treat them 
first with very little water or even to allow them to absorb water from 
an atmosphere of steam. 

Ammonia. 

Ammonia yields soluble precipitates from silicate of soda solutions. 
As with alcohol, the precipitate tends to have a higher silica ratio 
than the solution and this tendency increases with increasing water. 
The following examples are from Ordway. 21 Forty cc. of ammonium 
hydroxide of specific gravity 0.900 mixed with 50 grams of a 29 per cent 
solution of Na 2 0, 3.66Si0 2 yielded a precipitate containing 43 per cent 
of Na 2 0, 3.4Si0 2 . The same amount of ammonia added to 50 grams 
of a 21 per cent solution of Na 2 0, 3.8Si0 2 , gave a ratio of Na 2 0,4Si0 2 
in the precipitate. 

Gelation. 

Any reaction for the precipitation of a soluble silicate can be made 
to yield a gel provided it is possible to mix thoroughly the reacting 
substances at an appropriate concentration before a separation takes 
place. The gel, including the whole solution, may form in neutral, 
strongly acid, or strongly alkaline solutions and at concentrations from 
one to twenty-five per cent or perhaps even higher. The density of 
the gel even after it has been slowly dried and completely dehydrated 
will depend on the density of the original solution in which it formed. 
The porosity of the gel structure appears to be related also to the time 
consumed in passing from the sol to the gel condition. 

Crystals and Rhythmic Banding. 

Not only acids and alkalies, but many salts, may be present during 
the process of silica or silicate gel formation and as the gel is easily 
21 Am. I. Set., 24, ser. 4, 473-478 (1907). 



REACTIONS S3 

permeable it offers a convenient means for bringing two reacting solu- 
tions together so gradually that crystals are formed of much greater 
size and beauty than result from mixing the solutions directly. Thus, 
Holmes 22 prepared lead iodide, metallic gold, etc., and Liesegang 23 
produced examples of rhythmic banding very like the patterns which 
are so familiar in agates. 

Relation Between Colloidal Silicates and Cell Structure. 

Metastable dilute silicate solutions have been shown to yield cell- 
like structures closely suggestive of the forms of animate organisms. 
Thus Moore and Evans 24 following the suggestions of Bastian, 25 who 
reported spontaneous growth of living cells, were able to produce 
growths of diverse form in solutions from which all organic matter 
had been excluded with extreme precautions. Silicate of soda of specific 
gravity 1.44 (presumably Na 2 0,3Si0 2 ) was used and solutions pre- 
pared with ferric nitrate. In one case, 10 cc. of a 1 per cent solution 
of ferric nitrate was treated with 4 cc. of a 1 per cent solution of the 
silicate and shaken well, and after standing, a membranous precipitate 
formed. One to two per cent sols, stable for 3 weeks, yielded micro- 
structures of fibrous character. 

In another case a solution containing 0.03 per cent ferric nitrate 
and about 0.2 per cent silicate, which was clear yellow and yielded a 
slight deposit on boiling for ten minutes, produced a variety of mi- 
croscopic plant-like growths when left in sealed tubes for several 
weeks. Additions of ammonium phosphate and sodium carbonate varied 
the forms somewhat, but did not bring them nearer to the character 
of living organisms. 26 

Herrera 27 carried the study further and concluded that colloidal sili- 
cates yield structures most like natural forms when produced from 
reaction-mixtures of very low concentration, when contact between 
precipitating agents is made slowly and when the viscosity of the 
reacting solutions is great. 

The problem of the spontaneous generation of life is a fascinating 
field of research and quite unsolved, though it must be remarked that 
the many repetitions of his experiments by Bastian, and the care with 

28 Holmes, H. N., /. Am. Chem. Soc, 40, 1187-1195 (1918). 

33 Liesegang, Raphael Ed., Z. anorg. Chem., 48, 364 (1906) ; Z. phvsik. Chem., 
59, 444 (1907). 

34 Moore and Evans, Proc. Roy. Soc. (London), ser. B. 89, 17-27 (1915). 
23 Bastian, Nature, 92, 579 (1914) ; Proc. Row Soc. Med., 8, 55-68 (1915). 
""Onslow, H., Nature, 98, 489-490 (\9\7) ;' Proc. Roy. Soc. (London), 90B, 

266-269 (1918). 

27 /. Lab. Clin. Med., 4, 479-483 (1919). 



84 



SOLUBLE SILICATES IN INDUSTRY 



which they were executed, point strongly toward the view that the 
cells which started the long chain of evolution were probably produced 
in silicate solutions comparable to those with which Bastian worked. 

Electrolytes. 

The action of electrolytes which are not decomposed by the silicate 
solutions presents a series of interesting phenomena. Fluckiger 28 re- 
cords that when equal parts of a certain silicate of soda of 1.392 specific 
gravity and a solution of sodium nitrate in twice its weight of water 
were mixed there was no precipitation, but that on heating to 54° he 
obtained an almost complete gel which redissolved on cooling. Larger 

















4.Z 














i 














t 










iSfretiyth of Bnn 


e Ref*"** * 












fortovs S il'tate 


r.scult, of 

fel.flons »' 39.B' 8i 




























1 






o 

* — ^c 


O 












o 








<*• 






°fV 


/» ~" 






$ 















Concentr+f -•* «f Brine 



Fig. 31. 

amounts of sodium nitrate retarded and finally prevented this redis- 
solving. He also notes that potassium bromide is miscible in the cold 
but causes precipitation on heating. Saturated solutions of sodium 
sulfate added to concentrated silicious sodium silicates cause precipi- 
tates which dissolve on dilution. 

Malcolmson 29 and Stericker 30 have studied the action of sodium 
chloride solutions when mixed with relatively concentrated silicates of 
soda. It was first found that by the use of brines of appropriate 
strength, the volume of adhesive silicate of soda solutions could be 
extended more than 20 per cent without reducing the viscosity. A 16 
per cent brine will cause a gelatinous precipitate in a concentrated 
silicate solution of composition Na 2 0, 3.5SiO z , but this may be dis- 

28 Chem. Zentr., 41, ser. B 1, 639 (1870). 

29 Malcolmson, J. D., Ind. Eng. Chem., 12, 174 (1920). 

30 Stericker, unpublished report of Mellon Institute of Ind. Research. 



REACTIONS 85 

persed by stirring, after which the solution is thicker than before and 
remains so permanently. Mylius 31 found that sodium chloride would 
not precipitate silica from solutions less alkaline than NavO,2Si0 2 , 
but an effort to relate the amount of sodium chloride required to re- 
store the viscosity of the more silicious silicates to their silica content 
did not succeed. It was found that the addition of brine changed the 
hydrogen-ion concentration of the silicate which passed through a mini- 
mum when the original viscosity was restored. The formation of 
adsorption compounds may account for this. Dehydration may have 
a part in this phenomenon but does not account for all the variations 
in pH value. 

Other electrolytes may be manipulated to bring about similar changes 
but they have not been studied. 

Reaction with Coloring Materials. 

Many dyestuffs which are soluble in alkaline solutions are so com- 
pletely salted out of strong silicate solutions as to be useless for color- 
ing them. A few of the most soluble are available,' among them, rho- 
damine, fluorescein, and various eosin colors. Alkaline tannates are 
effective coloring agents for silicate solutions. Any silicate of soda 
solution sufficiently dilute to be fluid will draw a rich coffee brown 
color from a red oak barrel and such extracts as cutch, made strongly 
alkaline with sodium hydroxide, serve the same purpose. A good 
blue may be made by adding glycerin to a copper salt and making 
it strongly alkaline with caustic soda before adding to the silicate. 
Yellow solutions are best made with chromates. 

Reaction with Various Solid Compounds. 

There remain to be mentioned the reactions which take place be- 
tween silicate solutions and various solid substances which have a tech- 
nical importance in the manufacture of various cements, which will 
receive separate consideration in a later chapter. 

Dilute hot solutions of Na 2 0,2Si0 2 or more alkaline silicates react 
vigorously on zinc and aluminum. The hydrogen liberated is some- 
times sufficient to burst a galvanized drum which has been, in error, 
filled with silicate ; but at ordinary temperatures and commercial con- 
centrations the action is so slow as to be practically negligible. Zinc 
or aluminum powders, on account of their greater surfaces, yield appre- 
ciable amounts of gas. The more silica relative to Na 2 the less is 

31 Sprechsaal, 41, 140-142 (1908). 



86 SOLUBLE SILICATES IN INDUSTRY 

the reaction. This is partly due to the tendency of high ratio silicates 
to form films on metal surfaces such as those which prevent the solu- 
tions of lead by marsh waters containing very small amounts of soluble 
silicates. 

Calcium Carbonate. 

The desire to harden calcareous building stone and works of art 
which had weathered, led early investigators to consider the reaction 
between soluble silicates and calcium carbonate. Liebig and von Fuchs 32 
believed that addition compounds were formed and rejected the assump- 
tion of Kuhlmann 33 that calcium silicates result at ordinary tempera- 
tures from contact of silicate solution and chalk or limestone. Ordway, 
Kobel, and Lemberg assert that this occurs only at elevated tempera- 
tures. An investigation by Kallauner 34 with a silicate containing : 



Na 2 


8.40 


Si0 2 


27.96 


Fe 2 3 + A1 2 3 


.09 



developed the fact that a mixture with calcium carbonate exposed to 
the air developed a skin on the surface very like that which formed on 
the silicate without such admixture ; furthermore the mixture below 
the top crust remained soft for a long time — there was no evidence that 
anything but drying was taking place. 35 

In closed vessels in atmospheres saturated with water vapor and free 
from carbon dioxide the slight skin which formed at first disappeared 
on standing, a clear demonstration that the set was not due to reaction 
between the silicate solution and the calcium carbonate. Controls of 
the silicate solution alone behaved in the same way. The mixture which 
set in free air absorbed C0 2 . Extraction with water at ordinary tem- 
perature showed less Na 2 0, not accounted for as Na 2 C0 3 , than was 
present in the solid mixture and the amount was still less when the 
extraction was done with boiling water, which would seem to indicate 
a reaction tending to produce calcium silicate, but in the conditions 
recited the amount was very small. 

The point which has so many times been overlooked is important 
in this case. It makes a difference what sodium silicate is chosen. 
Calcium carbonate does not appreciably react with solutions of Na 2 0, 
4Si0 2 at atmospheric temperatures. Suspensions of the most reactive 

32 Liebig' s Ann. Chem., 105, 121 (1858). 

33 Liebig's Ann. Chem., 41, 220 (1842). 

84 Gmelin-Kraut, 3, 1, 247 (1908). 

35 Kallauner, O., Chem, Ztg., 33, 1174-1175 (1909). 



REACTIONS 87 

forms of CaC0 3 may be kept in closed vessels for days without thick- 
ening, but Na 2 0,2Si0 2 when mixed in like manner begins to show 
changes in a few hours, and mixtures may be so chosen that after stand- 
ing for two weeks in a closed container they will resist disintegration 
by water. 30 Such a mixture is 

8 parts of water 
10 parts of Na a O, 2Si0 2 59.1° Baume, specific gravity 1.688 
25 parts of CaCOs 

Mixtures with dolomite, which behaves much like calcium carbonate, 
were made by von Fuchs. 37 At elevated temperatures insoluble masses 
are easily made from silicates of various ratios, but the conditions of 
the reactions have not been fully explored. Barium and strontium car- 
bonates also have similar properties. 

Other Materials. 

Calcium phosphate, silica, and calcined clays were all found to pro- 
duce firm masses with silicate solutions. After these had been ex- 
posed to the air for some time a soluble efflorescence appeared on the 
surface, which even in the case of silicates containing more potassium 
than sodium, proved to be pure sodium carbonate. One of the few 
cases in which silicates of potash are preferable to silicates of soda is 
where efflorescence is to be avoided. 

Zinc oxide reacts most rapidly with silicates of high silica ratio but 
reacts with highly concentrated Na 2 0,2Si0 2 at 200° to 300° C. Litharge, 
calcium oxide, magnesium carbonate, and Portland cement are useful 
for making silicate cements which react differently as concentration and 
ratio are varied. Asbestos reacts with silicate solutions which ap- 
proach the composition of the metasilicate so that it is often quite im- 
possible to determine by analysis of a plastic cement what silicate solu- 
tion was used in its manufacture. 

36 From unpublished data of Philadelphia Quartz Company. 

37 Dingier' 's polytech. /., 142, 365-392, 427-444 (1856). 



Chapter V. 
Preparation. 

Wet Methods. 

The reactions which give rise to soluble silicates are conveniently 
grouped as wet and dry methods. x\ll the hydroxides of the alkali 
metals stabilize silica sols and exert a solvent action on the hydrous 
forms of silica. Anhydrous silica such as quartz reacts much more 
slowly but when finely pulverized is comparatively easily dissolved by 
hot solutions of the hydroxides of potassium and sodium. 

Infusorial Earth. 

The great surface presented by infusorial earth makes it the most 
convenient source of silica for solution in alkaline hydroxides. Experi- 
ments reported in 1857 by von Liebig 1 introduced the wet method. The 
earth was first calcined to free it from organic matter which would 
otherwise discolor the silicate solution, and then stirred in small quan- 
tities into boiling solutions of caustic alkali and dissolved. 2 An alter- 
native method consists in mixing the sodium or potassium hydroxide 
solution into a stiff paste with the infusorial earth and keeping it hot, 
but below 100°C, while the reaction takes place. The end of the re- 
action could be observed in either case by a partial clearing of the 
mixture which could then be diluted for the separation of a precipitate, 
consisting of silica and bases which form insoluble silicates, arising 
from impurities in the earth. Liebig added lime water to facilitate this 
process but it is now known that this ,is not necessary. He cautioned, 
however, against the use of milk of lime, which reacts at once with the 
silicate and displaces sodium. The impurities are usually in a flocculent 
condition but can be separated by decantation if the concentration be 
not above 1.25 specific gravity. A cycle consisting of a wash with fresh 
water, which is decanted and returned to the process when twice re- 
peated, removes most of the soluble silicate, but the residue always 

Buchner's neues Repertorium fiir Pharmacic, 6, 64-67 ; Chew.. Zentr., 28, 
286-287 (1857). 

3 Thomas, C, Brit. Pat 2756 (October 13, 1862). 



PREPARATION 89 

contains a large percentage of silica. A typical residue of this sort 
would contain 80 per cent silica and 20 per cent as the sum of calcium, 
magnesium, iron, and aluminum oxides and such other bases as may 
have been present in the earth. 

The silicate solutions may now be brought to the condition of stiff 
jellies by evaporation at atmospheric or reduced pressure. This reaction 
can be carried as far as the ratio Na 2 0, 2.75 Si0 2 at 100° C, i.e., in open 
vessels. Liebig causticized 7,415 parts crude sodium carbonate with 
lime and evaporated to 1.5 specific gravity. Then 120 parts of infusorial 
earth were stirred into the boiling liquor, which yielded 240 to 245 parts 
of a jelly with 52.3 to 53.5 per cent water. Two analyses of such 
solutions showed the following : 

Silica, Si0 2 72.9 74.39 

Sodium oxide, Na 2 27.1 24.65 

Mol ratio 2.76 3.09 

It will be noted that the variation in ratio is considerable. This is diffi- 
cult to regulate in the wet process. Silicate of potash prepared in 
similar fashion could be concentrated to a lower water content — about 
41.5 per cent. The composition on the dry basis was the following: 

Silica, Si0 2 64.1 68.98 

Potassium oxide, K 2 35.9 32.07 

Mol ratio 2.66 3.35 

The state of division of the silica, as well as the water it contains, 
affects the rate at which it is dissolved and the extent to which the 
reaction may be carried in a given time. For example, calcined in- 
fusorial earth will yield a silicate of composition Na 2 0,3Si0 2 when 
digested 3 to 4 hours with 1.2 specific gravity caustic soda solution at 
3 atmospheres pressure, but flint broken into pieces of about one cubic 
centimeter required 6 to 8 hours in 1.25 to 1.3 specific gravity caustic 
soda at A l / 2 to 6 atmospheres pressure to give a ratio Na 2 0,2Si0 2 . 

Insoluble Silicates. 

The presence of impurities in the silica increases the time required 
to attain high silica ratios as well as the difficulty of obtaining clear 
solutions. Gaize, a rock which occurs in France, proved unsuitable 3 
because of 7.6 per cent of oxides of aluminum, calcium, and iron. The 
silica was 84.5 per cent and water 6.6 per cent. Boiling of the calcined 
rock with a sodium hydroxide solution of 1.25 specific gravity yielded 
a dry silicate containing 68.7 per cent SiQ 2 and 31.3 Na 2 — a molecu- 

3 Scheurer-Kestner, A., Compt. rend., 72, 767-769 (1871). 



90 SOLUBLE SILICATES IN INDUSTRY 

lar ratio of Na 2 0, 2.12Si0 2 . Longer boiling brought the composition 
to 67.98 per cent SiO. and 24 Na 2 0, i.e., Na 2 0, 2.74Si0 2 . An effort 
to bring the ratio to a higher figure by the use of pressure was not 
successful. Somewhat better results might have been secured by the 
use of the rock without calcining, as hydrous silica dissolves more 
easily than dehydrated. Heating magnesium-bearing mineral with 
sodium hydroxide has also been proposed. 4 Sodium carbonate and 
sodium sulfate have been used with barium silicate. 5 

Hydrous forms of silica, such as freshly formed silica gel or by- 
product silica from the decomposition of SiF 4 by water, may, when 
washed nearly free of electrolytes, be dissolved in silicate of soda solu- 
tions of ratio Na 2 0, 3.3Si0 2 at 100°C. until the ratio exceeds Na 2 0, 
4Si0 2 . 6 ' 7 

In order to obtain clear silicate solutions by the wet process, Capi- 
taine 8 considers it best to so choose the amount of silica that it can 
be completely dissolved and to allow the liquor to settle hot at 1.18 
specific gravity or less. At higher concentrations or with an excess of 
silica the solutions are turbid and hard to purify. 

Sodium Sulfide. 

The process of Crispo and Mols 9 is designed to produce sodium 
metasilicate from silicates of high ratio by adding sodium sulfide and 
treating with steam which induces a reaction with the liberation of 
hydrogen sulfide. This has not attained any industrial importance. 
The Jaubert or Silicol process is designed to produce hydrogen but 
yields silicate of soda as a by-product. 10 ' iX It depends on the reaction 
between ferrosilicon, manganosilicon, or silico spiegel with concen- 
trated sodium hydroxide. Silicon itself would be the most convenient, 
but the alloys are used for reasons of economy. The temperatures are 
60° to 80° C. and the silicon-bearing alloys are used in the form of 
turnings in order to give maximum surface. The reaction may be 
written in the following manner : 

2NaOH + Si + H 2 = Na 2 O.Si0 2 + 2H 2 . 

4 Peacock, Samuel, U. S. Pat. 1,231,423 (June 26, 1917). 
5 Deguide, Camille, U. S. Pat. 1,463,037 (July 24, 1923). 
"Phillips, John Francis, Brit. Pat. 163,877 (June 2, 1921). 

7 Phillips, John Francis, and Edward J. Rose, U. S. Pat. 1,357,183 (October 
26, 1920). 

8 Capitaine, Dingier 's polytcch. /., 222, 363-366 (1876) ; abst. in Bull. soc. chim., 
32 [2], 27, 476-477 (1877) ; Chem. News, 36, 82 (1877). 

9 Brit. Pat. 6,057 (March 22, 1901). 

10 Engineering, 107, 103 (1919). 

"Raney, Murray, U. S. Pat. 1,563,587 (Dec. 1, 1925). 



PREPARATION 91 

A war time plant using this process was erected by the British Ad- 
miralty but the cost was high. Though no data are given for the 
compositions of the silicate solutions obtained, the process was operated 
to produce hydrogen and would almost inevitably yield a varying alkali- 
silica ratio and a solution of inferior color. 12 

Adsorbent Carbon from Rice Hulls. 

The manufacture of adsorbent carbon from rice hulls is a variation 
of the wet process for soluble silicates. 13 ' 14 The rice hulls, which con- 
tain about 35 per cent silica, are first charred and then extracted with 
sodium hydroxide solutions. This yields a very porous structure, useful 
in decolorizing sugar solutions and as a gas adsorbent, but again the 
resulting silicate is of variable composition and usually more or less 
discolored with colloidal carbon and organic impurities. 

Electrolysis. 

The most silicious silicate solutions may be made by electrolysis of 
some of the sodium into a mercury cathode using a cell of the same sort 
as those in which caustic soda is made from salt by the Kastner process. 
This method is able to reduce the alkalinity of any silicate so- 
lution, but Kroger 15 found it difficult to avoid the separation of 
gels as the loss of sodium rendered the silica less stable. The con- 
ditions of a manufacturing operation were worked out by Codd 16 and 
others, 17 ' 18 > 19 ' 20 ' 21 as a result of which a solution of Na 2 0, 3.3Si0 2 
which is easily prepared may be converted to Na 2 0, 4.2Si0 2 which is 
difficult to make by other methods. Solutions of still higher ratio could 
be made but are too unstable to be used for the many purposes where 
a silicate of lower alkalinity would otherwise be desirable. 

Modification of silicious silicates by the addition of sodium hydroxide 
and heating to hasten equilibrium has been practiced. It yields solu- 
tions of properties similar to those made by other wet methods. 

"Caven, /. Soc. Chcm. hid., 37, 63T-67T (1918). 
13 Blardone, George, U. S. Pat. 1,293,008 (February 4, 1919). 
"Puttaert, Jean Francois, U. S. Pat. 1,588,335 (June 8, 1926). 
15 Kroger, Kolloid Z., 30, 16-18 (1922). 

18 Codd, William Laurence, Brit. Pat. 206,572 (1923); U. S. Pat. 1,557,491 
(Oct. 13, 1925); U. S. Pat. 1,562,940 (Nov. 24, 1925). 

17 Electro-Osmose Ges., Ger. Pat. 283,886 (1913). 
M Praetorius, M., and K. Wolf, Fr. Pat. 612,486. 

19 Collins, N., U. S. Pat. 1,562,946. 

20 Silica Gel Corporation, Aust. Pat. 100,191. 

21 Lottermoser, Kolloid Z., 30, 346 (1922). 



92 SOLUBLE SILICATES IN INDUSTRY 

Sodium Hydroxide and Silicon Carbide. 

Sodium hydroxide reacts in the wet way with silicon carbide, accord- 
ing to the equation : 22 

4NaOH + SiC + 2H 2 = Na 2 Si0 3 + Na 2 CO s + 4H 2 . 

This reaction may take place at 50° C. when a 50 per cent solution of 
Na 2 0,2Si0 2 is mixed with abrasive grains of silicon carbide. 23 ' 24 

Sodium Chloride. 

Because of the economies which might result from a reaction be- 
tween silica and common salt, many workers have experimented and 
suggested ways to bring it about. 25 Salt melts at 815°C. and boils 
at 1490° C. When silica is put into molten salt in a crucible no notice- 
able reaction takes place. Most of the salt can be distilled out of the dry 
mixture unchanged. If steam is introduced, some decomposition takes 
place and hydrochloric acid is set free. Gay Lussac and Thenard pro- 
posed this in 1809 as a step in the manufacture of soda. 26, 27 ' 28 ' 29, 30, 31 

In the ceramic industry this reaction is of interest in connection with 
the formation of salt glazes. This led to a study by Clews and 
Thompson. 32 The method chosen was to heat mixtures of approxi- 
mately equal parts of finely divided silica and sodium chloride in silica 
tubes through which a gas stream of known composition and volume 
was passed. The extent of the reactions was determined by collecting 
the HC1 and Cl 2 produced as follows : 

(a) 4x NaCl + y Si0 2 + x 2 = 2xNa,0,ySiO a + 2xCl 2 

(b) 2x NaCl + y SiO, + x H 2 = xNa 2 0,ySi0 2 + 2xHCl 

(c) 4HC1 + 2 = 2H 2 + 2C1 2 

Reaction (a) took place in dry air. In moist air all three reactions 
occurred. There was no reaction in dry nitrogen and reaction (b)" 
was obtained in moist nitrogen. The residues from the tubes never 
showed an amount of alkali equal to that calculated from the CI and 

22 Treadwell, "Analytische Chemie," 1919-21, Eel. 5, vol. 2. 

"Baillio, Gervais, U. S. Pat. 1,178,205 (Apr. 4, 1916). 

24 Vail, James G., Abrasive hid., 2, No. 6, 393-394 (1921). 

25 Natho, Ernst, Ger. Pat. 257,826 (Mar. 17, 1913). 

28 Blanc and Bazille, Brit. Pat. 8386 (1840). 

27 Fritzsche, Wagner's Jahresbericht, 4, p. 118 (1858). 

^Gossage, Brit. Pat. 2050 (1862). 

^Ungerer, Dingier s polytech. I., 197, p. 343 (1870). 

30 Williams, Brit. Pat. 5406 (1881). 

31 Sanderval, Compt. rend., 116, 641 (1893). 

32 /. Chem. Soc, 121, 1442-1448 (1922). 



PREPARATION 



93 



HC1 but this may have been due to imperfect methods of solution or 
an inappropriate indicator. The rate of gas now, temperature, and 
moisture present affected the extent of reaction which begins at 575° to 
640° C. and rises sharply just above 1000°. 

Table 34. Effect of Temperature on the Reaction of NaCl with SiO*. 



Tubes 


19-20 mm. dia. 


Tubes 


9-10 


mm. dia. 


Rate of 


flow, 


112 


cc./hr. 


Rate of 


flow, 


88 cc./hr. 


Temp. 




Cc. 0.017V HC1 


Temp. 


Cc.O.OUVHCl 


1045 






41.7 


1045 




30.2 


1010 






29.5 


1000 




16.5 


930 






25.1 


947 




16.4 


880 






15.6 


900 




14.3 


827 






10.2 


828 




9.1 


784 






6.2 


753 




8.3 


725 






5.1 


640* 




8.0 


675* 






3.7 


569 




6.7 


575 






3.3 









* Lowest temperature at which solid residue was alkaline. 

The reaction starts somewhere around 575° -640° C. but is still feeble 
at higher temperatures. Just above 1000° C. there is a marked increase 
in the yields. Acid obtained at the lowest temperatures may have been 
retained in the mixture when it was dried at 120° C. 

The table given below shows the results obtained by heating 1 gram of 
mixture for 6 hours in tubes 9-10 mm. in diameter with 88 cc. of air 
per hour. Air saturated with moisture at room temperature gave far 
better results than dry air. 

Table 35. Comparison of Reaction in Dry and Moist Air. 





Cc. 


0.01A7 HC1 






Cc 


. 0.01 JV HC1 




Temp. 




Dry Air 


Moist Air 


Temp. 




Dry Air 


Moist Air 


1045 




30.2 


100.9 


753 




8.3 


12.3 


1000 




16.5 


70.1 


708 






10.0 


947 




16.4 


45.9 


640 




8.0 


8.5 


900 




14.3 


31.3 


569 




6.7 


7.8 


828 




9.1 


27.3 











The maximum yield was from a mixture heated for 36 hours to 1000° C. 
in moist nitrogen. It corresponded to 18.74 per cent decomposition of 
the salt. A study of the reaction at higher temperatures and in an 
atmosphere of water vapor would be interesting as both of these appear 
from the data obtained to make for increased yields. 

Kersten 33 claims to bring about a quantitative reaction between a 
highly silicious silicate and salt by blowing steam into a molten bath 
and forming sodium metasilicate and hydrochloric acid. 

33 U. S. Pat. 1,533,009 (April 7, 1925). 



94 SOLUBLE SILICATES IN INDUSTRY 

Dry Methods. 

Dry methods for the preparation of soluble silicates are limited to 
materials of greater purity than wet methods. The latter yield solu- 
tions directly which may more or less readily be separated from in- 
soluble impurities. But a fused silicate of soda or potash to be of 
service must be put into solution, which in the case of the more silicious 
varieties, is at best a matter of some difficulty and in the presence of 
more than 5 per cent alkaline earth or heavy metals becomes practically 
impossible. 

Sodium Nitrate. 

It has been proposed to fuse silica with sodium nitrate and recover 
the liberated oxides of nitrogen but the reaction is not complete under 
any easily obtained conditions and the melt attacks refractory materials 
with such vigor that the process is not used. 34 ' 35 ' 36 ' 3T 

Sodium Hydroxide. 

Sodium hydroxide can be used to make the silicate in the dry way. 
This reaction begins at lower temperatures than the other dry methods 
but has no industrial significance. 

Sodium Sulfate and Carbon. 

One of the first reactions used for the manufacture of silicates of 
soda on a commercial scale is that between sodium sulfate, carbon, and 
silica. 38 ' 39 ' 40 ' 41 It appears never to have been thoroughly investigated 
although it has been extensively used. A batch designed to produce a 
glass of the composition Na 2 0, 3.25Si0 2 reacts at 1100°C. The surface 
becomes pasty 42 and is broken by characteristic eruptions or candles 
of burning gas which burn for a little while and subside. The use of 
the correct amount of carbon either as coal, sawdust, charcoal, petroleum 
coke, or other convenient form is important. If too much is used, a 
dark amber colored glass containing sulfides and colloidal carbon will 
result. A deficiency will leave Na 2 S0 4 in the glass, an alternative which 

3i Wagner's lahresbericht, 11,250 (1865). 
35 Brit. Pat. 2026 (1866). 
39 Brit. Pat. 2866 (1870). 

37 Brit. Pat. 2489 (1896) and 22397 (1897). 

38 Buchner, Bayer, "Kunst Gewerbebl.," 1856, p. 645 ; Wagner's lahrcsbericht, 
2, 92 (1856). 

^Fuchs, Johann Nepomuk von, Poly. L, 17, 465-481 (1825). 
"Peacock, Samuel, U. S. Pat. 1,425,048 (Aug. 8, 1922). 
"Deckert, R., Chem, Ztg., 72, 535 (July, 1926). 
^Caven, R. M., /. Soc. Chem, hid., 37, 63T-67T (1918). 



PREPARATION 95 

is usually accepted in practice. The fundamental reaction is assumed 
by Scheurer-Kestner 4;1 to be 2Na 2 S0 4 + C = 2Na 2 + 2SO a + C< ),. 
It is said that as much as twice the amount of carbon stated in the 
formula can be used without yielding sulfides in the final product. 
Maetz, 44 however, recommends 75 parts of Na 2 S0 4 and 8 of coal to 
100 of Si0 2 and a fusion temperature of 1500°C. This is a little less 
C than the formula and corresponds closely with the experience of the 
author. Scheurer-Kestner found that carbon monoxide was always 
present to the extent of about % of the gas evolved and was also con- 
vinced that sulfur in the vapor phase is also set free, to account for 
which he suggests 3Na 2 S0 4 + 6Si0 2 + 5C = 3S + 4C0 2 + CO + 
3(Na 2 0,2Si0 2 ). (Six atoms of oxygen which would yield 3S0 2 are 
omitted from the right side of the equation.) His suggestion that S0 3 
is liberated, then breaks down into S0 2 + O which reacts with C to 
form C0 2 , CO -f- S, does not seem tenable in view of the fact that 
there is no reaction between Na 2 S0 4 and Si0 2 in the absence of a re- 
ducing agent. Some soda is lost by volatilizing, probably as Na 2 S. 

The attack of this fusion on refractory materials is very severe. The 
purest available form of carbon should be used, as bases introduced by 
the ash of coal reduce the solubility of the silicate of soda glass. The 
disposal of large quantities of sulfur dioxide has been urged as a serious 
problem; but the rate of the reaction is such that in most localities, a 
high stack is sufficient to disperse the gas at dilutions which are not 
harmful to adjacent vegetation. The manufacture of a glass of accurate 
composition by the sulfate process is difficult and in this country is not 
used for grades in which a high degree of purity or accuracy of com- 
position is important. 

Fusion of Carbonates with Silica. 

Fusion of sodium and potassium carbonates with silica is the most 
important means of preparing alkali metal silicates. 45 In the first place, 
the raw materials are available in a high state of purity; secondly, they 
react at temperatures compatible with economical furnace operation ; 
and thirdly, the process lends itself to accurate technical control and 
it yields neither offensive nor troublesome by-products. 

The first study of this series of reactions was undertaken for the 
purpose of establishing the atomic weight of silicon. The assumption 
that the amount of carbon dioxide evolved was equivalent to the silica 

"Compt. rend., 114, 117-120 (1892). 

44 Maetz, O., Chem. Ztg., 42, 569-570, 582-583 (1918). 

45 Weber, G., and J. Davidsohn, Scifensiedcr Ztg., No. 29, 775 (1908). 



96 SOLUBLE SILICATES IN INDUSTRY 

present led to the false conclusion that silica was possessed of different 
molecular weights in different melts. 40 ' 47 The temperatures were not 
accurately controlled, but it was found that equal quantities of silica 
displaced varying amounts of carbon dioxide from sodium, potassium, 
and lithium carbonates. Scheerer 48 found that higher temperatures 
caused a larger evolution of C0 2 from both sodium and potassium 
carbonates with the same amount of silica and also that as the amount 
of silica increased the C0 2 released per mol SiOo was reduced. The 
speed of the decomposition was investigated by Mallard, 49 who found 
that for each temperature the evolution of C0 2 approached a limit, and 
Ebell 50 showed with successive additions of silica to molten potassium 
carbonate at medium red heat a series of declining values of C0 2 dis- 
placed per mol of Si0 2 added. 

These observations lead to the view that in melts of alkali carbonates 
with silica conditions of equilibrium obtain which vary with changing 
temperature, time, and composition and which cannot be expressed by 
an equation which fixes the relation between Si0 2 and C0 2 . 

Wittorf 51 showed this to be the case because a melt that had come 
to constant weight at a given temperature above the melting point 
would, if placed in an atmosphere of C0 2 , take up some of the gas 
which would be again released when, at the original temperature, air 
was substituted for the atmosphere of C0 2 . The conditions of the 
experiment were not sufficiently exact to make the results entirely 
conclusive but the following systems were found to behave as though 
equilibria existed. In all except the one case cited the equilibrium was 
approached from one direction only, that is by loss of C0 2 . 

In the course of this work it was also discovered that the losses of 
molten carbonate in a covered crucible were negligible though they 
might be serious in a brisk stream of C0 2 . 

The reactions of potassium, sodium, and lithium carbonates with 
silica were studied by Niggli 52 with great care and better experimental 
facilities than had been available to previous workers. He chose, how- 
ever, a limited set of conditions and worked between 898° and 1000° 
in C0 2 at a pressure of 1 atmosphere. He showed that the equilibria 
may be approached from either direction and that definite alkali silicates 
are formed. Under his conditions the amount of C0 2 displaced per mol 

4a Yorke, Phil. Mag., 14, 476 (1857). 

47 H. Rose, Gilbert's Ann. Phys., 73, 84 (1823). 

48 Scheerer, T, Ann. Chcm. Pharm., 116, 149 (1860). 

49 Ann. Chim. Phys., 28, 105 (1873). 

50 Ebell, Paul, Dingier s polytech. /.. 228, ser. 5, 160 (1878). 

51 Wittorf, N. M. von, Z. anorg. Chem., 39, 187 (1904). 

52 Niggli, P., Z. anorg. Chem.. 84, 229-272 (1913). 



PREPARATION 97 



o 



. • • '. '. ! 

■M 

1-. c o 

03 1) C lOOOO^OLO 

CLi >i'- | +j CM 00 00 CM CM 

^3 <£ oor^r^oooooo 

to m 
• <u 

av«N c o 
EPhQ E 000000 

/" °< 000000ON0000 

t"" 1 am 

O o\os 

•J CM CM i-h ■* O' O 

P4 



£"2 o 



CO 



„0 *>» On CM On CM en 

C O^ OOO r-H OO 



u 



pD «0 VO Tf 00 t-j t^ vo 

w ,j? vd 10 vd 10 i-i K 



< ii 



"3-t^coTi- 



(j 3 tnCO^CMCMCOCMCM- 



^ 






CO 

w 
m 

< 



-t-> 




£ 






a 


w 




OJOfONO'-* 


O 
U 




00KNrHqO\ 


O 




10 r>I vd cm' lo ^ 

1— 1 r-H CO 


c 








Tf 


.2 


O 






Os 


-4-> 


d 




CM 


t— 1 rf .— i O 


t/J 


.« 








O 

o, 


fid 


3 


i—t 


HHHi-l 



u 


0^ 


OS 


00 ^cm r^ 




*8 




NO 


i-if^CM CM 






O 


o^'oo 






u 

J-l « 












CM 


On On r>. On 






CO 


cqvqN^r 






t< 


t< MD cm' 00 






10 


NO-^t^r^ 




<u 


+-» 








id 


£ 


t^ 


VOrHOrH 







O "* "<*■ On 






>. 


00 


KfOtOls 




.2 C/} ,u 


CM 


CO CM CM'-' 




i-i 


£ 








Ph =, 




1— 1 


10 CO O 




O 




i— 1 


O On 00 no 




u 




1 — 1 


lo On co co 
CM 



1.1 io69Q 



+ ++++ 

CM iH^-iHiH 



98 



SOLUBLE SILICATES IN INDUSTRY 



Table 37. Effect of Alkali-Silica Ratio on COi Remaining in Melt at 1 Aim. 

Pressure and 898° and 956° C. 



Mol Ratio 
K 2 : Si0 2 



KoO— Si0 2 — C0 2 (Pressure 1 Atmosphere C0 2 ) 

898° 956° 

Mol Per Cent in Melt Mol Per Cent in Melt 

K 2 Si0 2 C0 2 K 2 Q Si0 2 C0 2 



0.113 
0.122 
0.187 
0.248 
0.312 
0.470 
0.565 
0.594 
0.957 
0.998 
1.111 
1.476 
2 



*k*'O s 



49.6 
49.6 
49.2 
49.0 
48.4 
47.5 
46.8 
46.6 
43.7 
43.2 
42.3 

33.3 



5.6 
6.1 
9.2 
12.1 
15.1 
22.3 
26.4 
27.7 
41.7 
43.0 
47.0 

667 



44.8 
44.3 
41.6 
38.9 
36.5 
30.2 
26.8 
257 
14.6 
13.8 
107 

0.6 



49.5 

49.6 
48.2 
47.6 
47.5 
44.6 
44.1 
43.3 
39.0 
33.3 



9.3 

15.2 
21.5 
26.9 
28.1 
42.6 
44.0 
48.0 
57.6 
66.7 



41.2 

35.8 

29.3 

25.5 

24.4 

12.8 

11.9 

87 

3.4 

0.0 




Fig. 32. — Isotherms in the System K 2 C0 3 , K 2 SiOa, K 2 Si 2 O s . 



of Si0 2 is greater the less the concentration of Si0 2 in the melt, but in 
no case did the C0 2 liberated from K 2 C0 3 by silica reach a figure as 
high as the molecular equivalent. In a fusion of K 2 0,2Si0 2 only half 
this amount is set free at 1000°. Higher temperatures and lower partial 
pressures of C0 2 would increase the amount of C0 2 expelled. 



PREPARATION 99 

Potassium carbonate melts at 891° and forms with 2Si0 2 a crystal- 
line mass of KoSio0 5 with a melting point of 1015° ± 10°. The melt- 
ing point of K 2 Si0 3 could not be determined because it could not be 
prepared free from carbonate and disilicate and melts of the compo- 
sition K 2 Si0 3 heated to higher temperatures always gave vitreous rather 
than crystalline masses. The proportions of carbonate, metasilicate and 
disilicate which remain in equilibrium at three temperatures investi- 
gated are best shown in the diagram (Fig. 32). 

Small amounts of C0 2 were found in melts of K 2 C0 3 with equivalent 
or more SiOo after a half hour at 1400° to 1500° in a gas furnace. 
Melting times employed in the manufacture of commercial silicates are 
much longer than this and the residual C0 2 , if any is present, is so 
little as to escape the ordinary means of detection. 

Although Niggli confirmed the findings of previous workers that 
the losses of both sodium and potassium carbonates were, under his 
conditions in a closed vessel with greater partial pressure of carbon 
dioxide, negligibly small, a slight decomposition does, however, take 
place when soda ash is heated in the air. In Niggli's experiments it 
amounted to less than one per cent but was slightly greater in the case 
of sodium carbonate than potassium carbonate. Lithium carbonate 
undergoes much more serious losses. 

Formation of Crystalline Metasilicate. 

Sodium carbonate melts at 853° and a mixture containing 50 mol 
per cent Si0 2 gave up all its C0 2 at 1000° yielding a crystalline meta- 

Table 38. Expulsion of Carbon Dioxide by Silica at 898° and 956° 

(Niggli). 

Na 2 — SiOo— C0 2 (Pressure 1 Atmosphere CO.) 

Molecular 898° 956° 

Ratio Mol Per Cent in Melt Mol Per Cent in Melt 

Na 2 : Si0 2 Na 3 Si0 2 C0 2 Na 2 Si0 2 C0 2 

1:0.085 51.7 3.9 44.4 

1:0.098 51.4 4.4 44.2 51.9 4.4 43.7 

1:0.112 51.4 5.8 42.8 51.9 5.9 42.2 

1:0.140 51.4 7.2 41.4 

1:0.143 51.3 7.4 41.3 52.1 7.6 40.3 

1:0.191 51.7 9.9 38.4 



1 : 0.287 
1 : 0.302 
1 : 0.344 
1:0.353 
1 : 0.428 
1 : 0.495 



53.3 15.7 31.0 

53.2 16.1 30.7 

53.6 18.6 27.8 

53.7 19.3 27.0 
54.2 23.9 21.9 
54.5 27.2 18.3 



1 : 1 50.0 50.0 0.0 50.0 50.0 0.0 



100 SOLUBLE SILICATES IN INDUSTRY 

silicate with a melting point of 1018° as determined by Niggli. Jaeger 53 
had earlier determined the melting point as 1088°, which figure has been 
confirmed by Morey. 

Indication of Orthosilicate. 

When the melts contained more Na 2 than the metasilicate the equi- 
librium relations indicated an orthosilicate, formed according to the 

equation : 

Na 2 C0 3 + Na 2 Si0 3 z± Na 4 SiC>4 + CO a 

in which lSi0 2 displaces 2C0 2 . 

Disilicate. 

When more silica than that needed to produce the metasilicate was 
introduced, the result was always a mixture of metasilicate and quartz. 

/Va,C0 3 




Fig. 33. — Isotherms in the System Na 2 C0 3 , NatSiCX, Na 2 Si0 3 . 

Wallace 54 is of the opinion that there is no higher silicate than the 
metasilicate in fusions but that silica in excess of this is taken up as a 

63 Jaeger, /. Wash. Acad. Sci., 1, 49-52 (1911) ; /. Chem. Soc, 100, II, 981-982 
(1911). 

"Wallace, R. C, Z. anorg. Chem., 63, 1-48 (1909). 



PREPARATION 



101 



solid solution. All the soluble silicate fusions made for industrial use 
have higher silica than this, up to four mols Si0 2 for each mol Na 2 0. 
They are not crystalline but vitreous. It has been shown, however, 
that the disilicate prepared hydrothermally by Morey may exist also in 
anhydrous fusions. 

A careful study of the system Na 2 Si0 3 — Si0 2 by Morey and 
Bowen 55 shows no evidence of silica in solid solution. 

Inaccuracies in previous work on this system are in part due to failure 
to recognize the danger of loss of Na 2 from the melt at high tempera- 
tures which, though almost negligible after the silicate has been formed, 
may be serious as long as some of the Na 2 is present as carbonate. 
Mixtures prepared from quartz and pure sodium carbonate were held 
at definite temperatures until equilibrium was reached and then 
quenched, usually in mercury. The small amounts used could then be 
examined optically. This permitted the accurate determination of the 
points at which the system in equilibrium was all liquid and when it 
first contained a solid phase. Thus the following table was established. 50 







Table 39. 


Determination of L 


iquids. 




Desig- 


Anal) 


'■sis 


Mol % 


Mol % 


Melting 


Solid 


nation 


Na 2 


Si0 2 


Na 2 Si0 3 


SiO. 


Point 


Phase 


21S4A 


50.40 


49.44 


99.23 


0.77 


1086.5 


Na 2 Si0 3 


2330A 


45.88 


54.03 


82.32 


17.68 


1031.0 


Na 2 Si0 3 


2 142 A 


44.92 


54.93 


79.27 


20.73 


1001. 


Na 2 Si0 3 


2115A 


39.55 




63.42 


36.58 


863. 


Na 2 Si0 3 


25 12 A 


37.83 




60.85 


39.15 


847. 


Na 2 Si 2 5 


2144A 


37.59 


62.29 


58.48 


41.52 


859. 


Na 2 Si 2 5 


2510A 


35.90 





54.29 


45.71 


871. 


Na 2 Si 2 5 


2518A 


34.04 




50.03 


49.97 


873.5 


Na 2 Si 2 5 


2414A 


33.99 




49.91 


50.09 


873.0 


Na 2 Si 2 3 


2034A 


33.26 




48.44 


51.69 


872.5 


Na 2 Si 2 5 


2411A 


32.83 


67.25 


47.32 


52.68 


868. 


NaaSiaO., 


2530A 


29.20 




39.97 


60.03 


831. 


Na 2 Si 2 5 


2530B 


27.32 




36.44 


63.56 


802. 


Na 2 Si 2 5 


2530C 


25.78 




33.27 


66.73 


830. 


High quartz 


2520A 


24.81 




31.99 


68.01 


841. 


High quartz 


2429A 


19.54 




23.55 


76.45 


1145. 


Tridymite 


2429B 


11.67 


• • • . 


12.51 


87.49 


1457. 


Tridymite 


2431A 


4.07 


.... 


5.12 


94.88 


1596. 


Cristobalite 



The liquidus and the areas in which the various solid phases exist are 
shown in Figure 38, page 1 12. ; , i \ . 

Melts near the cqtnpositipi.' of sodium mctacilicat^ crystallize easily 
so that, while glasses^ of this composition can be .prepared in small 
amounts by quenching, large batches would certainly crystallize. 

"/. Phys, Chem., 28, 1167- -179 -'1924}., c 

68 Morey and Bowen, /. Phys. Chem., 28, 1167-1179 (1924). 




Fig. 34. — Drawing Molten Silicate of Soda Directly into Rotary Dissolver. 




Fig. 35.— Drawing Molten Silicate of Soda on to Chain to Make Solid Glass-Like 

Cakes for Shipment. 



102 



PREPARATION 103 

Sodium disilicate is readily crystallized by heating for a few hours 
at the appropriate temperature, though melts of this composition remain 
as glasses in the ordinary course of manufacture. All the higher ratios 
which can be regarded as soluble are normally glasses, though Morey 
has obtained crystalline mixtures of Na 2 Si 2 5 and Si0 2 from all of 
them. 

Fusion of Soda Ash and Silica. 

On an industrial scale, soluble silicates are made by melting soda ash 
and silica or salt cake (Na 2 S0 4 ), carbon, and silica in furnaces built 
of clay refractories. As in the glass industry, the open hearth regenera- 
tive type of furnace is most widely used, 57 although satisfactory results 
are also obtained from reverberatory furnaces in which coal is burned 
on a grate and from furnaces heated with mineral oil. The tempera- 
tures in vogue range from 1300°-1500°C., sufficient to drive out sodium 
chloride which is always present in the raw materials. In soda ash 
produced by the ammonia process, the amount is usually very small, 
but some of the natural sodas may contain 5 or 6 per cent. This, except 
from the point of view of loss, is not objectionable because it is com- 
pletely expelled with the furnace gases. In the regenerative system 
in which the gas is cooled to temperatures below the condensation point 
of sodium chloride there is a tendency for this salt to accumulate, but 
it is found after the furnace has been shut down, as sodium sulfate, 
the sulfur in the fuel having been sufficient to produce enough sulfuric 
acid to decompose the condensed chloride. 

It has been proposed to prepare soluble silicates in arc furnaces and 
this is entirely possible, the question being one of cost of units of heat 
supplied by electricity as compared with those supplied by coal, petro- 
leum or gas. The problem of refractories, however, becomes very 
serious at higher temperatures for the melt contains so much silica that 
it readily attacks any basic refractory, and the equilibrium between silica 
and soda is such that highly silicious refractories fail almost equally 
rapidly. It would therefore appear that future developments, if they 
involve high temperatures, will also have to take into account the neces- 
sity of enclosing the fusion in a mass which is little reactive because 
it is cooled, and the economic aspect of this is likely to be discouraging. 

There is, however, a great deal of room for the development of clay 
refractories less susceptible to solution in silicate glasses than those at 
present available. Water cooling is resorted to in a great many silicate 

57 Stanton, William H., U. S. Pat. 1,425,551 (Aug. 15, 1922) ; U. S. Pat. 
1,352,700 (Sept. 14, 1920). 



104 SOLUBLE SILICATES IN INDUSTRY 

furnaces but unless the cooling water is needed in the process the loss 
of heat involved is unsatisfactorily large. 

The silicate furnace differs from the glass furnace in that it is not 
essential for it to deliver an absolutely homogeneous product. Fine 
striations in the glass representing slight variations in composition seem 
to increase rather than retard the rate of solution. 

Dissolving. 
Character of the Solution. 

Sodium metasilicate dissolves in water easily and completely. Silica 
and soda appear to go into solution at the same rates, perhaps because 
the whole is dissolved so rapidly. At least in a practical way one may 
expect a solution of the same relative composition as the solid from 
which it was made. Equipment like that used for dissolving other 
soluble salts by simple stirring or lixiviation is sufficient. 

When fused sodium silicate glasses containing three or more mols 
of Si0 2 for each Na 2 are brought into contact with water, the phe- 
nomena are those of decomposition. Sodium goes into solution more 
rapidly than silica and leaves a silicious film on the surface from which 
it came. When a powdered anhydrous silicate of soda of the compo- 
sition Na 2 0,3Si0 2 is stirred in tenfold or larger quantity of water, 
the soda-silica ratio in the solution which is first formed is always in 
excess of the ratio existing in the glass. If the water is now replaced, 
the tendency is to increase the silicious layer on the surface of the glass 
particles and further solution is impeded. This is partly due to hy- 
drolysis ; at least the conditions which suppress hydrolysis reduce the 
difference between the composition of solution and solid. Solution at 
boiling temperature proceeds more uniformly than in the cold and small 
amounts of water are more effective than large. 

There is no point at which a solution of Na 2 0,3Si0 2 may be said to 
be saturated, as homogeneous systems of the solid and water may exist 
in all proportions at ordinary temperatures. A lump of the glass which 
has been exposed to an atmosphere of steam will, if broken across, 
exhibit a sharply defined outer layer which, though it retains the ap- 
pearance of glass, has lost its original hardness and becomes more 
resilient. This outer layer contains water and may easily be dissolved 
in hot water though the portion which has not been hydrated is 
brought into solution very slowly and incompletely by similar treat- 
ment. 

Morey 58 has pointed out that these solutions are very different from 

68 /. Soc. Glass Tech., 6, 21 (1922). 



PREPARATION 



105 



the systems in which definite equilibria between true solutions and 
crystalline phases exist, and has called attention to the fact that silicate 
of potash appearing as a viscous liquid at ordinary temperatures may 
be prepared which would not be stable as a true solution below 450° 
to 500°. Silica must, from this point of view, be regarded as present 
in a colloidal condition but this does not explain the mechanism of its 




Fig. 36. — Stationary Dissolver Installation. 



behavior. Whether the solution of silicates of soda and potash, like 
that of a high grade animal glue, necessarily goes on in two stages, the 
first of which is hydration and the second dispersion, has not been 
proven, but some hydration can be brought about and leads to the most 
satisfactory solutions. Industrial methods for bringing such materials 
into solution must provide conditions which suppress hydrolysis and 
favor hydration. Glasses of the composition of the disilicate or mix- 
tures of metasilicate and disilicate dissolve without decomposition. 



106 



SOLUBLE SILICATES IN INDUSTRY 



Apparatus for Dissolving. 

The apparatus used for solution of soluble silicates 59 is of two gen- 
eral types. Horizontal rotary digesters operating at atmospheric or 
higher pressures revolve slowly so that the material to be dissolved lies 
in a mass at the bottom. Most of the solution takes place in this mass 
where, the solid being in excess, there is little tendency to decomposition 
and the solution, as formed, is diluted by the contact of the slowly 




Fig. 37. — Stationary Dissolver Installation. 



moving mass with supernatant liquor. It has been proposed to speed 
this reaction by grinding. Spensley and Battersby 60 introduced flints 
into a rotary dissolving drum, but these do not increase hydration except 
as they increase the surface by grinding, and hence their value is slight. 
Similar conditions are secured in stationary dissolvers by packing 
the entire chamber with a relatively coarse glass and covering it with 
water. The circulation in this case must be sufficient to prevent the 
heavy solution which forms at first from accumulating in the bottom 

59 Taylor, E. A., U. S. Pat. 1,467,342 (Sept. 11, 1923). 

60 Spensley and Battersby, U. S. Pat. 1,176,613 (March 21, 1916). 



PREPARATION 107 

of the vessel. If this takes place the operation is very hard to control. 
In either type of dissolver the solution must he removed hefore it he- 
comes too viscous. Otherwise solution proceeds to a point where the 
whole liquid will form with the glass a mass hard enough to require 
a quarryman's tools for its removal and elastic enough to expel, with 
sufficient violence to be dangerous, a cold chisel driven into it with a 
sledge. 61 

Some dissolvers are charged by drawing the molten glass directly 
into water, and others with larger pieces which have been cooled in the 
air ; but in all cases they must provide sufficient circulation to permit the 
operator to test the solution with a hydrometer and discharge it at the 
right time, but not enough to promote decomposition by hydrolytic 
action. In every case an excess of solid is used; that is, the dissolver 
is loaded with a larger amount of glass than can be dissolved at one 
charge. 

61 Stanton, William H., and James G. Vail, U. S. Pat. 1,138,595 (May 4, 1915). 



Chapter VI. 
Commercial Forms and Properties. 

Classification. 

Probably no product of chemical industry comes upon the market in 
a greater variety of forms than the soluble silicates. As the ratio of 
alkali to base is not limited by any stoichiometric boundaries, the number 
of different products is limited only by the precision with which we 
choose to define them. As a practical matter the limits are set by the 
metasilicate, Na 2 Si0 3 on the side of maximum alkalinity, and the highest 
silica is found in a sodium silicate solution having the composition 
Na 2 0, 4.2Si0 2 , although still higher ratios can be secured in more dilute 
solutions should they be required. 

Three groups of products are found : first, anhydrous silicates as 
glasses or powders formed by fusion processes ; second, hydrous solids 
formed by hydration of glasses or evaporation of solutions ; and third, 
the solutions, among which there are greater differences than is gen- 
erally known. 

Raw Materials. 

Glasses which are to be put into solution must obviously be as free 
as possible from bases which form insoluble silicates. The degree of 
purity achieved depends upon the raw materials used and upon their 
action on the refractory materials of the furnace. When the carbonate 
fusion is employed, excellent raw materials are available as may be seen 
from the following typical analyses of washed Ottawa sand and Solvay 
process soda ash. The analysis of Ottawa sand is the average of 
determinations made on twenty samples. 

Table 40. Analysis of Washed Ottawa Sand. 

Per Cent 

Si0 2 99.14 

A1 2 3 0.29 

Fe 2 3 0.07 

CaO 0.28 

MgO 0.09 

Ti0 2 0.01 

Ignited Loss 0.14 

108 



COMMERCIAL FORMS AND PROPERTIES 109 

Table 41. Analysis of 58 Per Cent Light Soda Ash. 

Per Cent 

Na 2 C0 3 99.20 

NaHC0 3 None 

NaCl 0.42 

Na 2 S0 4 0.016 

Si0 2 0.003 

Fe 2 3 0.0011 

A1 2 3 0.0041 

CaCO. 0.025 

MgCOa 0.006 

NH S None 

H 2 0.32 

Total 99.99 

Na 2 58.02 

Insoluble 0.014 

These are mixed and charged directly into a furnace at a temperature 
of about 1450° C. In the early stages of melting, most of the sodium 
chloride is lost as a vapor which condenses in the cooler parts of the 
regenerating system and is finally converted into sodium sulfate by 
contact with sulfur-bearing products of combustion. The specific 
gravity of fused soda ash is 2.43-2.51 and that of ordinary glass sand 
is 2.66. Reaction begins at once and copious volumes of carbon dioxide 
are liberated, so that there is comparatively little tendency of soda and 
sand to separate; but for practical reasons it is necessary to choose a 
sand of sufficient grain size to prevent too rapid reaction and to make 
batches which allow the escape of gas. Sodium carbonate melts sharply 
at 849° C. to a thin liquid and this results in local differences of compo- 
sition which have a bearing on the behavior of the soluble glass. 
Products of different ratio differ in viscosity and are not easily mixed 
to perfect uniformity. Even small pieces of silicate glasses usually 
show striae and lines of greater and less solubility due to local varia- 
tions of ratio, for these variations of composition behave like the bubble 
in a lump of glass which can be drawn out into capillary dimensions. 
They form long threads in the mass as it is drawn from the furnace. 
The arts of the glassmaker are of course available to secure a uniform 
mixture, but the advantage is not commensurate with the cost. 

A trifling loss of carbonate occurs due to decomposition by heat 
before reaction with the silica : but this is very small indeed, and after 
reaction with silica there is no loss from volatilization of Na 2 with 
the times and temperatures employed. Some loss of carbonate as dust 
is unavoidable but careful practice can reduce this to a very low point. 



110 SOLUBLE SILICATES IN INDUSTRY 

Anhydrous Solids. 

Two types only of sodium silicate glasses are well established com- 
mercially, the so-called "neutral glass" and "alkaline glass" which has 
the composition of the disilicate. 

Neutral Glass. 

The molten glass in the furnace immediately begins to attack the 
clay refractories of which it is made. Glasses more viscous than the 
soluble silicates are formed on the surface of the brick. They are also 
heavier and tend to accumulate at the bottom of the melt, but some are 
unavoidably mixed in and thus we have added to the impurities from 
the raw materials small amounts of alumina and iron and traces of 
alkaline earth metals. A typical composition of a silicate from the 
foregoing materials would then be : 

Table 42. Neutral Glass. 

Na 2 0, 3.265Si0 2 

Per Cent 

Na 2 23.24 

Si0 2 75.89 

Fe 2 3 0.043 

A1 2 3 0.195 

CaO * 0.069 

MgO 0.069 

Ti0 2 less than 0.01 

100.006 

Such a glass is a clear, pale green solid of satisfactory commercial 
solubility though it must not be understood that it dissolves like sugar. 
Glasses which approximate the composition Na 2 0, 3.3SiO- 2 are known 
in the trade as "neutral glass". With the rise of impurities the solu- 
bility declines, or at least the time required to produce a uniform 
colloidal solution increases. It is, however, practical to deal with a 
neutral glass containing something more than one per cent of impurities. 
Alkaline earth metals are more objectionable than alumina. One-half 
per cent of calcium oxide and magnesium oxide is the maximum 
tolerable, while something more than one per cent aluminum oxide is 
permissible in a glass for making adhesive solutions. Not all sources 
of sand supply are equal in quality to the St. Peter sandstone which 
crops out in Illinois and Missouri, and the attack on refractories varies 
according to the composition and method of manufacture. The follow- 
ing analysis of "neutral glass" gives an idea of the degree of purity 
which is ordinarily found. 



COMMERCIAL FORMS AND PROPERTIES 111 

Table 43. Neutral Glass. 

Per Cent 

Na-,0 23.61 

Si0 2 75.31 

A1 2 3 0.38 

Fe 2 Op 0.10 

CaO 0.40 

MgO 0.20 

Alkaline Glass. 

This usually appears as a yellowish glass with its iron in the ferric 

condition, although it is sometimes green. Both neutral and alkaline 

glass may be made yellow by carbon. A typical analysis of "alkaline 

glass" follows : 

Table 44. Alkaline Glass. 

Na 2 0, 2.06SiO 2 

Per Cent 

Na 2 33.10 

Si0 2 66.27 

Fe 2 O s 0.036 

A1 2 3 0.199 

CaO 0.098 

MgO 0.071 

Ti0 2 Trace 

Ignited loss 0.16 

99.93 
Glass Made from Sulfate. 

Glasses produced by the sulfate process are never equal in quality 
to the carbonate glasses. Sodium sulfate dissolves to about 1 per cent 
in the glass and can always be found in the solutions. Sodium sulfide 
formed by the action of some form of carbon on the sulfate is subject 
to serious loss by volatilization at the temperatures necessary to produce 
the silicate, and it attacks the refractories of the furnace with much 
more vigor than the carbonate batch. The composition is, therefore, 
difficult to control. Sulfate glasses are most successfully made in con- 
tinuous furnaces permitting a slow reaction. All sulfides must be 
oxidized in the final glass or the solutions will be black from sulfides 
of iron. Sulfate glasses are usually ultramarine blue, irregular from 
one batch to the next and unsatisfactory for the more refined uses of 
the solution. 

Properties. 

Melting Temperatures. Morey x has investigated the melting tem- 
peratures of the system Na 2 SiO s — Si0 2 . The soluble glasses, like the 
1 Morey, G. W., and N. L. Bowen, /. Phys. Chcm., 28, No. 11, 1167 (1924). 



112 



SOLUBLE SILICATES IN INDUSTRY 



more familiar insoluble varieties, soften gradually with rising tempera- 
ture. The crystalline metasilicate shows a sharply defined melting point 
at 1088° C, but glasses containing more silica simply become more and 
more fluid with no sharp transition. Morey found, however, that there 
is for each composition a temperature below which a solid phase will 
separate if the temperature be maintained until equilibrium is reached. 




NtffS/Oj 



MOL P£RC£NT 
Fig. 38. 



S/O2 



He found that Na 2 Si0 3 remained the primary phase until the mix- 
ture containing 39.15 per cent Si0 2 was reached, when the disilicate, 
Na 2 0,2Si0 2 , appeared as the primary phase. The eutectic, located by 
extrapolation of the metasilicate and disilicate curves, gave a tempera- 
ture of 840° C. and composition 37.5 mol per cent Si0 2 . 

The melting point curve of sodium disilicate is unusually flat, espe- 
cially on the side toward Na 2 Si0 3 , 4.3 per cent excess of the latter, low- 
ering the melting point only 2.5 degrees. When an excess of Si0 2 is 
added, there is a more rapid lowering of the melting point, until the 
disilicate-quartz eutectic is reached. The mixture with 63.56 per cent 
Si0 2 melts at 802.7° C. and the primary phase is Na 2 0,2Si0 2 ; the mix- 
ture containing 66.73 per cent Si0 2 melts at 827° C. and high-tempera- 
ture quartz is the primary phase. Both the preparations gave a eutectic 
temperature of 793 ± °C. Since the eutectic temperature is known, 



COMMERCIAL FORMS AND PROPERTIES 113 

extrapolation of the two melting point curves becomes a more reliable 
method of locating the eutectic composition, which is estimated as 35 mol 
per cent Na 2 Si0 3 , 65 per cent Si0 2 , or 26.5 per cent Na 2 0, 73.5 per 
cent Si0 2 . 

Morey found that the addition of Na 2 to silica produces a rapid 
lowering of the melting point, and that, unlike the oxides studied by 
Greig, 2 it shows no limited miscibility. The addition of 4.07 per cent 
Na 2 0, giving a mixture containing 5.12 per cent Na 2 Si0 3 and 94.88 
per cent SiOo, lowers the melting point from 1710° C, the melting point 
of cristobalite, to 1598°C, with cristobalite as solid phase. 

His results are interesting in comparison with similar data from 
Jaeger and van Klooster, 3 in their study of the lithium system, and 
from Morey and Fenner 4 on the potassium system. The metasilicates 
of the three show perfect regularity in the relation of melting point 
to atomic weight — the melting point decreasing with increased atomic 
weight, while the disilicates show no such relation. 

Metasilicates Disilicates 

Li 2 Si0 3 1201° LhSioOs 1032° (incongruent) 

Na 2 Si0 3 1088° Na 2 Si 2 5 875° 

K 2 Si0 3 976° K 2 Si 2 5 1041° 

Morey calls attention to the fact that, although there is no regularity 
of melting points of the disilicates, there is a striking periodicity when 
the shape of the disilicate liquidus is taken into consideration. Thus, 
the liquidus for K 2 Si 2 5 rises to a well-defined maximum; the meta- 
silicate-disilicate and the disilicate-quartz eutectics for potassium are 
both at lower temperatures than the corresponding sodium eutectics, 
though the potassium disilicate melts 157 degrees higher. The sodium 
disilicate liquidus was found to be unusually flat, showing a difference 
of only 35 degrees between the temperature of the metasilicate-disilicate 
eutectic and the melting point of Na 2 0.2Si0 2 . And the liquidus of 
lithium disilicate is even flatter; the disilicate-trydymite eutectic being 
at 1029° C, while the temperature of decomposition of the disilicate 
into metasilicate and liquid is 1032° C, only 3 degrees higher. The 
increasing amount of flattening, in the disilicate curves, he ascribes to 
an increase in the amount of dissociation of the disilicate in the liquid 
phase. This dissociation is comparatively small in the case of potassium, 
is quite large for sodium, and is so great in the case of lithium that this 
compound is able to exist only when in contact with liquids containing 

2 Greig, J. W., Am. J. Scl, 13 (Feb. 1927). 

3 Jaeger and van Klooster, Proc. Acad. Sci. Amsterdam, 16, 857-880 (1914). 
4 Morey and Fenner, /. Am. Chem. Soc, 39, 1173-1229 (1917). 



114 



SOLUBLE SILICATES IN INDUSTRY 



an excess of Si0 2 . There is, in the dissociation of these three alkali 
silicates, a progressive increase in dissociation at the melting tem- 
perature with decreasing atomic weight. 

Thermal Expansion. The coefficient of thermal expansion 5 for 
silicate of ratio 1:2= 13.46 X 10 6 , for Na.O, 3.3SiO, 2 glass = 9.17 X 
10~ 6 . The electrical conductivity is similar to that of glass so long as 
water is not present. Even in concentrated solutions the resistance is 
very high.* 

Refractive Indices and Specific Gravity. The refractive indices 
of sodium silicate glasses have been investigated by Tillotson, 6 and are 
given below. 

Table 45. Refractive Indices of Sodium Silicate Glasses. 

Silica, Refractive 

Per Cent by Vol. Index 

100.00 (1.464) 

85.50 (1.4865)* 

80.55 1.4950 

78.00 1.5000 

76.75 1.5000 

70.70 1.5110 

63.80 1.5137 

54.20 1.5200 

* Extrapolated. 

Peddle 7 gives the following refractive index and specific gravity 



figures. 












Table 46. Composition. 






Per Cent 


] 


Per Cent 


Per Cent 


Melt 


Si0 2 




Na 2 


Ab0 3 +Fe,0 3 


A 


83.00 




16.58 


0.42 


B 


76.64 




22.98 


0.38 


C 


71.20 




28.44 


0.36 


D 


66.46 




33.21 


0.33 


E 


62.32 




37.37 


0.31 


F 


58.68 




41.03 


0.29 


G 


55.42 




44.30 


0.28 


H 


52.52 




47.22 


0.26 


K 


49.91 




49.84 


0.25 




Table 47. Refractive Index. 






Refractive 






Refractive 


Melt 


Index 


Melt 




Index 


A 


1.4851 


F . 




1.5118 


B 


1.4952 


G . 




1.5139 


C 


1.5015 


H . 




1.5155 


D 


1.5056 


K . 




1.5168 


E 


1.5090 









5 English and Turner, /. Soc. Glass Tech., 5, 121-123 (1921), 
* Cf. pp. 24-31. 

"Tillotson, E. W., /. Am. Ceram. Soc, 1, 76-93 (1918). 
7 Peddle, C. J., /. Soc. Glass Tech., 4, 5-17 (1920). 



COMMERCIAL FORMS AND PROPERTIES 115 

Table 48. Specific Gravity. 

Specific Specific 

Melt Gravity Melt Gravity 

A 2.353 F 2.535 

B 2.413 G 2.544 

C 2.457 H 2.555 

D 2.495 K 2.560 

E 2.521 

Solubility. The solubility of glasses containing more than two 
mols of silica, although it may proceed to the complete liquefaction 
of the solid, is nevertheless a problem in decomposition. If a "neutral 
glass" (Na 2 0, 3.3Si0 2 ) be powdered to pass 100 mesh screen and ex- 
posed to ten times its weight of water for 12 hours, the ratio of Na 2 
to Si0 2 in solution will be more alkaline than the metasilicate. A 
silicious layer forms on the surface of the particles which interferes 
with further solution. It is practically impossible to dissolve neutral 
glass completely even by stirring it in a large amount of hot water. A 
glass of the composition of the disilicate, on the other hand, dissolves 
with much less tendency to separate, as will appear from the following 
table. 

Table 49. Solubility of Sodium Silicates. 

Ratio in 

Solution Heated to 

After 12 20 Parts Boiling 

Mol Ratio Hrs. at Hot H 2 with 20 Heated at 90° with 20 Parts H,0 

Na 2 0:Si0 2 20° C. in 10 Poured Parts 

in Glass Parts H 2 through H 2 10 Min. 20 Min. 40 Min. 

1:2.056 1:1.91 1:1.95 1:2.08 

1:3.341 1:0.42 1:0.99 1:1.87 1:2.78 1:2.81 1:3.12 

1:3.868 1:0.84 1:0.82 1:0.60 1:0.61 1:2.29 1:2.34 

Although decomposition of this type is the rule in commercial soluble 
glasses at atmospheric pressures, true solubilities may be found at higher 
temperatures and corresponding pressures. 

Morey found that glass of the composition sodium disilicate-quartz 
eutectic not only showed the lowest melting temperature, but in the 
range investigated, the greatest solubility. Thus Na 2 0, 2.8Si0 2 with 
13.1 per cent of water was completely liquid at 500° C. At such tem- 
peratures crystalline phases separate promptly in sharp contrast to their 
behavior at atmospheric temperatures. Proceeding to lower tempera- 
tures it was found that at 200° C. the reactions proceeded quickly with 
the formation of the same crystalline phases as at the melting-point 
curve, namely, sodium metasilicate, sodium disilicate and quartz. Other 
crystalline compounds appear at 60°-80°C. but have not been studied 



116 



SOLUBLE SILICATES IN INDUSTRY 



in detail. The 125°C. isotherm shown in the chart gives some new light 
on solubility of sodium silicates. 8 

"Sodium metasilicate is the solid phase from D or IT to E, at which 
point sodium disilicate appears. Since, when sodium metasilicate is 
dissolved in water and the solution evaporated sodium metasilicate 



NLO 




tojfi-tS,-^ 



Fig. 39. — Solubility of Sodium Silicates in Water at 125° C. (Morey). 



separates, as is shown by saturation curve of sodium metasilicate, HE, 
being cut by the tie-line H 2 0-Na 2 . Si0 2 , it follows that sodium meta- 
silicate is not decomposed by water. This is in marked contrast to 
potassium metasilicate, which I showed to be stable in contact with 
water only above 185°C. Below 185°C, potassium metasilicate is de- 
composed by water with formation of potassium disilicate. This 
difference is in the opposite direction from what one would expect from 
the fact that potassium is a much stronger base than sodium. 

"The solubility of sodium disilicate is not greatly different from that 
of sodium metasilicate, and it too is stable in contact with water. This 

8 Morey, George W., personal communication (Dec. 1927). 



COMMERCIAL FORMS AND PROPERTIES 117 

is different from potassium, potassium disilicate being decomposed by 
water below 240° C. 

"This isotherm, though not complete, has brought out some interest- 
ing facts. The outstanding fact is the great solubility of the sodium 
silicates in water. Both the metasilicate and the disilicate are to be 
classed among the most soluble of substances, and ordinary waterglass 
solutions are not as far from being stable as has commonly been sup- 
posed. The second fact, following from the first, is the unusually 
small increase in solubility with temperature found in these silicates. 
The direct comparison between 125 °C. and 500° C. is not possible as 
yet, but it is evident that the amount of water required to dissolve a 
given amount of silicate is not greatly different at the two temperatures. 
This has an important bearing on the constitution of these solutions 
and the reaction taking place between the silicates and water. The 
third important fact that has been found is that the solubility, or the 
percentage of water in the saturated solution, is not greatly affected 
by the Na 2 : Si0 2 ratio in the solution, being about the same at the 
18 : 1 ratio as at the 1 : 2 ratio. This is surprising, and its explanation 
will doubtless throw light on the constitution of these solutions. It is 
evident that our preconceived conceptions in regard to sodium silicate 
solutions require complete revision." 

Hydrous Solids. 

Absorption of Moisture by Glass. 

Neutral glass in lump form is little altered on exposure to the air for 
short periods. A month of damp weather is sufficient to cause the 
brilliant luster of the original surface to become clouded with a film of 
sodium carbonate. If the surface be increased by pulverizing the glass, 
it absorbs moisture more rapidly and sticks together into a rock-like 
mass. A glass of 1 to 4 ratio may remain brilliant for a year in the 
climate of Philadelphia, but the "alkaline glass" is quickly clouded. 
The carbonating action does not, however, extend much below the 
surface, and a wash with cold water is sufficient to free glass which 
has become coated till it appears opaque from carbonate and to permit 
the preparation of a nearly pure silicate solution. 

All the powders produced by grinding the furnace product must be 
stored in air-tight containers. Attempts to keep them in wooden 
barrels, paper cartons, or cloth sacks have all failed even when these 
were protected by layers of asphalt or rubber. The powders ultimately 
set up as hard as stone with the absorption of about 5 per cent of water. 



118 SOLUBLE SILICATES IN INDUSTRY 

Hydration. 

Mechanism. The process of solution of these glasses seems to be 
the entering of water into the glass, at first in amounts so small that 
its glass-like character is maintained, and then increasing until fluid 
solutions are formed. This is clearly indicated by the experiment of 
placing a large lump of neutral glass into a chamber where it can be 
exposed to steam under pressure. At the temperature of 158.5°C, 
corresponding to 100 pounds steam pressure, an exposure of 15 minutes 
is sufficient to hydrate a layer about 2 mm. thick. If the piece be 
broken and an attempt made to scratch it with a steel point, a sharp 
line of demarcation between the hydrated outside portion and harder 
unaltered glass can be found, though there is no visible difference and 
the hydrated part, which may contain 15 per cent of water, is hard 
enough to cut the hand. Morey was able to make potassium silicate 
glasses with 8 to 25 per cent of water. These hydrated glasses are 
much more easily dissolved than anhydrous ones. 9 They flow at 
elevated temperatures, which are higher as the amounts of water de- 
crease. 

Hydration with Water. The difference between the dehydration 
and hydration methods is nicely shown by Schneider, 10 who pointed out 
that in the case of dehydration, water was removed from the existing 
liquid to form the solid waterglass, while the hydration method involves 
an addition of water to the powdered furnace glass, sufficient to render 
the solid material readily soluble in water. There have been various 
suggestions and theories concerning the amount of water to be added, 
the manner of its application, and the proper temperature required for 
subsequent heating. 11 Caven 12 emphasized as particularly important the 
amount of water to be used and the temperature of heating the mixture. 
He recommended that 2 to 3 parts by weight of water be used to 8 
parts of the ground furnace glass (50 mesh) and the mixture be heated 
at 70°- 100° C. The result was a vitreous material containing from 20 
to 25 per cent moisture. Although none of the low temperature hydra- 
tion methods recommended yield a solid waterglass which is completely 
soluble, Caven's process gives the most satisfactory product. 

Hydration with Steam. Paterson 13 proposes to make a readily 

9 Henkel & Cie., Brit. Pat. 215,328 (May 14, 1925). 

10 Schneider, Louis, Address before Am. Chem. Soc, Ind. Section at Rochester 
(1921). 

11 Spensley, Jacob Wm, and John W. Battersby, U. S. Pat. 1,176,613 (Mar. 
21, 1916). 

13 Caven, R. M., /. Soc. Chem. Ind., 37, 63T (1918). 
"Paterson, E. A., U. S. Pat. 1,119,720 (Dec. 1, 1914). 



COMMERCIAL FORMS AND PROPERTIES 119 

soluble silicate of high silica ratio by exposing powdered glass of the 
requisite composition to the action of steam. 14 This process yields a 
soluble product but the mass flows and adheres tenaciously to the trays, 
making it inconvenient and costly. Making a solution under pressure 
of such concentration that it would solidify when released through a 
nozzle was proposed by Justice. 15 The solution must be released from 
the container at exactly the right concentration because the glass is 
dissolving rapidly and if left too long the entire charge will solidify, 
while if released too soon it will not become solid on blowing from the 
pressure vessel. 

Dehydration. 

Intumescence. The most satisfactory methods of making hydrous 
solid silicates 16 are based on drying solutions. Evaporation in trays 
vields lumps suitable for making the intumescent silicate of Arthur. 17 - 18 
When the water content of a silicate, Na 2 0, 3.3Si0 2 , is reduced to 20 
per cent and it is broken into hard granules, these will, if suddenly 
heated to temperatures well above 100° C. (300°C. to 400° C. has been 
used in practice) first soften on the surface and then rapidly lose water 
as steam which blows bubbles in the concentrated hot liquid. The films 
soon lose enough water to become solid at the prevailing temperature 
and this process goes on until the whole is a mass of solid bubbles of 
30 to 100 times the volume of the original particles. This intumescent 
silicate may easily be made by dropping the hydrous granules upon a 
hot stove and moving them about by any convenient means or by heat- 
ing them in a wire mesh container such as is used for corn popping. 
The softening point of such an expanded material may be raised to 
about 525°C, by using a silicate of composition Na 2 0, 3.8Si0 2 . The 
thermal conductivity of this material between 25° and 300° C. is 0.00012 
calory per degree centigrade per second compared with 1.01 for metallic 
silver. Arsem 19 obtained silica in the same form by treating the in- 
tumescent silicate with hydrochloric acid, washing and drying. 

Vacuum and Atmospheric Drum Dryers. Hydrous solid silicates 
have been made on vacuum and atmospheric drum dryers heated by 
steam or other suitable means. A rotating drum is coated with a film 
of solution which is dried to the required degree in less than a full 

"Gossage, William, & Sons, Ger. Pat. 210,885 (June 14, 1909). 

"Justice, Brit. Pat. 23,391 (Oct. 23, 1911). 

16 See, for example, Rouse, Thomas, U. S. Pat. 1,109,704 (Sept. 8, 1914). 

"Arthur, Walter, U. S. Pat. 1,041,565 (Oct. 15, 1912). 

18 Arsem, William C, U. S. Pat. 1,270.093 (Tune 18, 1918). 

10 Arsem, William C, U. S. Pat. 1,077,950 (Nov. 4, 1913). 



120 



SOLUBLE SILICATES IN INDUSTRY 



revolution and scraped off with a knife. 20 The silicate is hard enough 
to wear the knife rapidly, making continuous attention necessary. 
Ratio 1: 3.3 breaks up immediately into separate pieces, while 1 : 2 tends 
to come off in large sheets which are brittle only after cooling. The 
product of the drum dryer exposes a large surface and its irregular 
form is such that each particle rests on points rather than flat surfaces 
and so, if dried to a point where there is no danger of flowing at the 
temperatures encountered, it gives less trouble from sticking than forms 
which pack with smaller interspaces. 21 ' 22 ' 23 

Spray Drying. Edgerton 24 atomizes a silicate solution into a cur- 
rent of warm air and obtains a fine powder, each particle of which is 




Fig. 40. — Particles of Silicate Dried by Atomizing (Magnification Approximately 

250). 



a more or less perfect sphere. It remains loose when kept in air-tight 
vessels and is easily made with uniform physical and chemical properties. 
This method also lends itself readily to the preparation of hydrous solids 
of various ratios. 25 

Other Methods. Other hydrous silicates have been proposed by 
Dickerson, 26 who causes drops of solution to pass through an atmosphere 
hot enough to cause intumescence on the surface only, and by Schnei- 

20 Dunham, Andrew A., U. S. Pat. 1,373,224 (Mar. 29, 1921). 
^Lihme, I. P., U. S. Pat. 1,403,556 (Jan. 17, 1922). 
23 Goetschius, D. M., Chem. Age, 30, No. 3, 103 (1922). 
^Paterson, U. S. Pat. 1,119,720 (Dec. 1, 1914); 1,111,918 (Sept. 29, 1914). 
Edgerton, L. B., U. S. Pat. 1,198,203 (Sept. 12, 1916); 1,194,827 (Aug. 15, 



1916), 



Clayton, William, and H. W. Richards, Brit. Pat. 203,749 (Sept. 18, 1923). 
Dickerson, Walter H. ? U p 3, Pat. 1,517,891 (Dec. 2, 1924). 



COMMERCIAL FORMS AND PROPERTIES 



121 



der, 27 who mixed powdered caustic soda (NaOH) with hydrous silica 
containing 1 to 4 per cent of water. He also used sodium metasilicate 
crystals and hydrous silica gel, drying the mass to 17.8 per cent water. 
Vail and Carter 28 added sodium sulfate, an efflorescent salt, to reduce 
the tendency of the particles to stick together. 

Preferred Methods of Solution. 

The hydrous silicates, like'the glasses, dissolve best when treated with 
relatively small amounts of water. The same effect is obtained if the 
silicate be put into a cotton sack and suspended in water. The solu- 
tion escapes from the sack as formed and mixes with the water, while 
the residue of solid remains in contact with relatively small amounts 
of water. A test in which 33 grams of powder were stirred in 100 cc. 
of water for 15 minutes gave the following undissolved residues. 

1. 2. 3. 4. 

Na 2 0,3.3Si0 2 Na 2 0,2S.i0 2 Na 2 0,3.3Si0 2 Na 2 0, 2Si0 2 

At 100°C Anhydrous Anhydrous 17.5% H 2 17.5% H 2 

At 100° C 23% 1% 0.2% 0% 

At 20°C 93% 44% 36.0% 1.6% 

The effect of varying amounts of water on sample 3 of the above 
series was determined by stirring the amounts given into 100 cc. of 
water, bringing to a boil and determining the residue. 

Gm. in 100 cc. Undissolved 

3 16.4% 

6.3 3.6 

12.6 3 

25.2 2 

50 1 

In cold water the results were : 

Residue Residue 

After Stirring After Stirring 

Gm. in 100 cc. 30 Minutes 60 Minutes 

6.3 : 31% 17% 

12.6 20 12 

25.2 12 5 



Properties. 

Density and Stability. Schneider studied the hydration and drying 
of certain silicate solutions and came to the conclusion that hydrous 
solids of maximum density are the most stable. They would be ex- 

27 Schneider, Louis, U. S. Pat 1,493,708 (May 13, 1924). 

28 Vail, James G., and John Carter, U. S. Pat. 1,139,741 (May 18, 1915). 



122 



SOLUBLE SILICATES IN INDUSTRY 



% 




Mo/ ff a ffo /*% OiS/Ojf/;*. ez 
fcO - 2S-.6Z, 



1 1 me in Hours 

Fig. 41. — Dehydration of Hydrous Silicate at 100° Centigrade (Average of 5 and 

10 Grams). 









206 "C 


gro'C 




JOt>t 




















S 




I7S*C 












K 
















t; 














vS 


fso'c J 








Mel ftar/o N« 
A7esA 


t 5,0 i '/:£6Z 












20-40 










M>o- 


/4-.S% 





T„ 



Fig. 42.— Dehydration of Solid Hydrous Silicate at Different Temperatures. 



pected to be least subject to atmospheric influence because they expose 
the least surface. 

Effect of Humidity. Schneider carried out a series of experiments 
designed to show the percentage moisture loss or gain of various solid 
waterglasses of molecular ratio 1 : 2.97, at different humidities. At the 
low humidities, that is, at or 25 per cent relative humidity, the glasses 
containing the smaller percentages of water exhibited a slight tendency 
to take on water, while those of higher water content lost moisture 
rapidly. At relative humidities of 62 and 86 per cent, all of the water- 










4 U9 2 J9 d 



o 
co 



o 

CO 

O T3 
•O '5 



.23 psj 

o 

£# 

.2 ~ 

a <-> 

Slo 
< 













V 



co 



o 

CO 



o "S 

V 

>, > 

_c ■ ~ 
a 

u > — 



'O 



o a 



< 



Pj7 »'*{S-/Ofy /"?? - / *'/-/ 



123 




J"* J "d 




'.'6>J JO SSOJ *S/tjS-?Ofij/ -{"^J "* 9 d 



124 



COMMERCIAL FORMS AND PROPERTIES 



125 



glasses gained a considerable amount of water. Schneider points out 
that the rate of hydration or dehydration at different humidities is de- 
pendent upon the components and the percentage of these components 



in the waterglass. 



Hydrates of Sodium Metasilicate. 

Sodium metasilicate is the only commercial form * which dissolves 
quickly and completely in a large excess of cold water. The com- 




Time 



Hi 



/n flours 



Fig. 47.— Dehydration of Sodium Metasilicate Crystals, Na 2 Si03.9H 2 0, at 

Different Temperatures. 

mercial product until recently contained above 50 pe,r cent of water and 
was a mixture of hydrates. Four analyses indicate between 8 and 10 

* See Chapter III. 



126 



SOLUBLE SILICATES IN INDUSTRY 



mols of water. Schneider gives data on dehydration of the ennehydrate 
at various temperatures. 

Sodium metasilicate must be kept in tight containers, as it absorbs 




Fig. 48. — Sodium Metasilicate at Varying Relative Humidities. 

or loses moisture at atmospheric temperature according to humidity. 
The most recent and the most stable commercial sodium metasilicate 
contains close to 6 molecules of water and is able to withstand tem- 
peratures up to 40° C. without caking. 



Solutions. 



Range of Ratios. 



The sodium silicates which appear commercially in solution range 
from Na 2 0, 1.5SiO, 2 to Na 2 0, 4.2SiOo. The minimum viscosity for a 



COMMERCIAL FORMS AND PROPERTIES 127 

given solid content is found near the composition of the disilicate. Thus 
the liquid of this ratio is capable of the highest concentration, although 
the ratio 1 : 1.5 is regularly sold at 70° Baume and it is not convenient 
to carry any silicate above this point. All the solutions within this 
range have more or less glue-like characteristics. Unlike the glasses, 
there are grades in use representative of the whole scale of gradations 
from maximum silica to maximum alkali. The limit is set in the first 
instance because of the low solubility and hence low concentration, 
and in the second by the fact that highly concentrated solutions con- 
taining more Na 2 will, under some conditions, show hardening due to 
separation of metasilicate. 

Clarity. 

The solutions made from glass are always more or less opalescent. 
The amount of suspended matter is usually very small and may be 
removed by a sufficiently fine filter. This is a simple matter with 
or without filter aids if the solution be sufficiently dilute. Clear con- 
centrated solutions can then be prepared by evaporation or by the 
method of flocculation 29 of the suspended matter at a higher concentra- 
tion and settling. Filtration of silicate solutions sufficiently concentrated 
to have a syrupy consistency is either very slow or unsatisfactory in 
that a flocculent precipitate gathers in the filtrate on standing and mars 
the brilliant clarity of the fresh solution. On this account it is usual 
to filter silicate solutions below 20° Baume and concentrate them to the 
desired degree by evaporation either in open vessels or under reduced 
pressure. The small increase in boiling point renders evaporation under 
atmospheric pressure less wasteful than would be the case with crystal- 
loid compounds which require much higher temperatures for concentra- 
tion. Solutions not required to be brilliantly clear are almost always 
brought to the requisite concentration by a saturation process. 

Properties. 

Specific Gravity. Baume Hydrometers. The Baume hydrometer 
is the universal measure of silicate concentrations in the United States 
and in continental Europe. The Twaddell scale is used in England. The 
Baume scale being an arbitrary one, several variations have come into 

20 Vail, James G., and John Carter, U. S. Pat. 1,132.640 (March 23, 1915). 



128 



SOLUBLE SILICATES IN INDUSTRY 



use. That sanctioned by the U. S. Bureau of Standards for liquids 
heavier than water bears the following relation to specific gravity : 



Sp. gr. = 



145 




Fig. 49.— 
B a u m e 
Hydrome- 
ter. 



'Baume = 145 



(145— °Baume) 
145 



sp. gr. 



Hydrometer Errors. It should be pointed out that 
hydrometers used in viscous silicate solutions are more 
liable to error than those used in most salt solutions. If any 
of the liquid gets on the stem above the point at which it 
comes to rest it may dry and depress the reading by 
weighting the instrument and yet escape notice because it 
is transparent. For the same reason hydrometers are not 
always well cleaned after use. They should be washed with 
clean water until no alkali is detected by taste — a homely 
but effective test. Silicate hydrometers are often kept under 
water when not in use. This is effective from the point of 
view of preventing the accumulation of silicate on the 
glass, but instruments used in this way should be fre- 
quently checked as they tend to lose weight and give heavy 
readings due to the solvent action of alkaline waters on the 
glass. Heavy hydrometers with short ranges are most satis- 
factory because they come to rest more quickly in syrupy 
solutions. Care is required to prevent the formation of a 
surface skin on the solution which may prevent the 
hydrometer from sinking to its proper level. It is some- 
times permissible to place two or three drops of water on 
the surface of the sample shortly before the hydrometer 
comes to rest in cases where the sample is not to be further 
examined. Viscosity readings would be worthless after 
adding even the most trifling amounts of water. 

Relation to Composition. The total solids in a silicate 
solution are not indicated by the hydrometer reading unless 
the ratio of alkali to silica is known, as will appear from 
the following data from Stericker, which have been 
checked by other workers and shown to be reliable. 



COMMERCIAL FORMS AND PROPERTIES 129 



Table 50. 


Total Solids vs. 


Intuitu' for I 


'arious Ratios — ( 


[Continued) . 


Per Cent 


Per Cent 








Na 2 


SiC> 2 


Total Solids 


Baume Specific Gravity 








Na 2 0, 


3.9Si0 2 


6.79 


25.75 


32.54 


34.0 


1.3063 


6.62 


25.11 


31.73 


33.7 


1.3028 


3.95 


14.98 


18.93 


20.6 


1.1656 


3.51 


13.31 


16.82 


18.2 


1.1435 


2.99 


11.34 


14.33 


15.6 


1.1206 


2.48 


9.41 


11.89 


13.0 


1.0985 


1.99 


7.55 


9.54 


10.5 


1.0781 


1.50 


5.69 


7.19 


8.0 


1.0584 


.99 


3.75 


4.74 


5.5 


1.0394 


.49 


1.86 


2.35 


2.7 

Na 2 0, 


1.0190 
3.36Si0 2 


9.12 


29.76 


38.88 


420 


1.4078 


9.00 


29.37 


38.37 


40.7 


1.3902 


8.50 


27.74 


36.24 


39.1 


1.3692 


8.04 


26.24 


34.28 


37.4 


1.3476 


7.47 


24.38 


31.85 


34.9 


1.3170 


6.88 


22.46 


29.34 


32.0 


1.2832 


6.49 


21.18 


27.67 


30.4 


1.2653 


5.97 


19.49 


25.46 


28.1 


1.2404 


5.08 


16.58 


21.66 


23.5 


1.1934 


4.03 


13.15 


17.18 


18.9 


1.1137 


3.03 


9.89 


12.92 


14.8 


1.1499 


2.06 


6.72 


8.78 


9.9 


1.0733 


,.55 


1.80 


2.35 


2.6 

Na 2 0, 


1.0183 
2.44Si0 2 


11.98 


28.39 


40.37 


45.2 


1.4529 


11.40 


27.00 


38.40 


43.1 


1.4230 


10.82 


25.64 


36.46 


41.2 


1.3969 


10.20 


24.17 


34.37 


39.8 


1.3783 


9.25 


21.92 


31.17 


35.7 


1.3266 


8.29 


19.64 


27.93 


32.3 

Na 2 : 


1.2866 
,2.40SiO 2 


4.99 


11.66 


16.65 


20.0 


1.1600 


3.02 


7.06 


10.08 


12.4 


1.0935 


1.03 


2.41 


3.44 


4.4 


1.0313 


.52 


1.21 


1.73 


2.1 


1.0147 








Na 2 0, 2.06SiO 2 


18.42 


36.84 


55.26 


58.8 


1.6821 


17.20 


34.40 


51.60 


55.6 


1.6219 


12.89 


25.78 


38.67 


44.5 


1.4428 


12.43 


24.86 


37.29 


42.8 


1.4188 


12.01 


24.02 


36.03 


41.6 


1.4023 


11.55 


23.10 


34.65 


40.3 


1.3849 


11.12 


22.24 


33.36 


38.8 


1.3653 


10.53 


21.06 


31.59 


37.0 


1.3426 


9.38 


18.76 


28.14 


33.7 


1.3028 


8.43 


16.86 


25.29 


30.5 


1.2664 


6.06 


12.12 


18.18 


22.0 


1.1789 


4.50 


9.0 


13.50 


17.0 


1.1328 


2.99 


5.98 


8.97 


11.1 


1.0829 



130 



SOLUBLE SILICATES IN INDUSTRY 



Table 50. Total Solids vs. Bauine for Various Ratios — (Continued) 



er Cent 


Per Cent 










Na 2 


Si0 2 


Total Solids 


Baume 


Specific Gravity 








Na 2 0, 1.69SiO, 


13.93 


22.94 


36.87 


44.4 




1.4414 


13.00 


21.40 


34.40 


41.7 




1.4037 


12.04 


19.82 


31.86 


39.2 




1.3705 


10.14 


16.70 


26.84 


33.2 




1.2970 


6.02 


9.91 


15.93 


20.4 




1.1673 


4.04 


6.65 


10.69 


14.0 




1.1069 


1.90 


3.13 


5.03 


8.0 




1.0584 


.64 


1.05 


1.69 


2.3 




1.0161 



By plotting on a sufficiently large scale it is possible to deduce by 
extrapolation the silica content of any commercial silicate solution of 
which alkali content and gravity are known. As these are much more 
easily determined than silica, such a chart is a great convenience for 
quick estimation of ratio where the greatest accuracy is not required. 




% #*tO 



Fig. 50. — Variation of Specific Gravity with Per Cent NaaO. 



COMMERCIAL FORMS AND PROPERTIES 



131 




10 20 30 40 



so 



Fig. 51. — Variation of Specific Gravity with Total Solids. 



Another convenient method of plotting these data is to consider the 
dilutions by weight and by volume of commercial solutions at their 
standard concentrations. 



132 



SOLUBLE SILICATES IN INDUSTRY 




20 4o so ao 

Per Ce»/ f Standard Grade "> 0//vfed Si'/fcrnf* 

Fig. 52. — Dilution of Standard Grades by Weight. 




20 40 60 SO 

Per Cent »f .Standard Grade ~//t Oj/uted S/ticate 

Fig. 53. — Dilution of Standard Grades by Volume. 



too 



COMMERCIAL FORMS AND PROPERTIES 



133 



Main 30 has shown the effect on density of increasing silica at constant 
Na 2 content for weight normality of sodium 1 and 3 and observed 
that above ratio 1 : 4 the density declines as silica is increased. 







Table 51. Dens 


'ty- 


Ratio 


Si0 2 : NdiO. 






Molecular 














Ratio 


Cone. Density 


Conc. 


Density 


Cone. 


Density 


Si0 2 : Na 2 


Nw 


P 


N„- 


P 


Nw 


P 


NaOH 


1.0 


1.040 


2.0 


1.080 


3.0 


1.116 


1:2 


" 


1.052 




' 


1.101 


a 


1.150 


1: 1 


u 


1.062 




i 


1.123 


it 




2: 1 


a 


1.075 




i 


1.147 


a 


1.217 


2.5 : 1 


a 


1.085 




< 


1.168 


it 


1.247 


3.0: 1 


a 


1.099 




< 


1.190 


a 


1.274 


3.3: 1 


a 


1.105 




< 


1.195 


tt 


1.276 


3.8: 1 


a 


1.111 




< 


1.208 


a 


1.296 


3.95 : 1 


n 


1.113 




< 


1.207 


it 


1.295 


4.2: 1 


a 


1.109 




< 


1.205 


it 





Specific gravity of sodium silicate solutions is not directly propor- 
tional to concentration but at high concentrations the density is greater 
than would be expected from projecting the parts of the curves repre- 
senting dilute solutions. This may be due to the beginnings of struc- 
tural arrangement of colloidal silica in these highly viscous liquids as 
suggested in Chapter II. 

Variation with Temperature. The variation of specific gravity with 
temperature has not been fully investigated, but as the most viscous 
solutions must be tested hot it is a matter of importance. The more 
concentrated the solution the smaller is its coefficient of expansion, as 
indicated by the following table. 



Table 52. Baume Changes with Temperature 



Water 



Temp. 

5 

10 
20 
30 
40 
50 
60 
70 
80 
90 
100 



'C. 



Degrees 
Baume 

. . .01 

. .00 

. . .03 

. . .36 

. . .63 

. . 1.13 

.. 1.75 

. . 2.41 

. . 3.29 

. . 4.20 

. . 5.20 

. . 6.29 



Na 2 0, 3.34Si0 2 , dil. 

Temp. °C. 



20 

90 

100 



to 20° Baume 
Degrees 
Baume 

20.7 

20.0 

16.3 

15.4 



Main, V. R., /. Phys. Chem., 30, 541 (1926). 



134 



SOLUBLE SILICATES IN INDUSTRY 



Table 52. Baume Changes 

Na 2 0, 3.34Si0 2 , 41° Baume 

Degrees 
Temp. °C. Baume 
0.0 42.0 


with Temperature — ( Continued) . 

Na 2 0,2.61Si0 2 , 42° Baume 

Degrees 
Temp. °C. Baume 
30 00 42.30 


4.4 41.7 


39.50 42.00 


10.0 41.5 


43.00 41.80 


15.5 41.2 


48.50 41.60 


21.1 41.0 


54.00 41.40 


26.6 40.8 


60.00 41.20 


32.2 40.6 


65.50 40.90 


37.7 40.4 


71.00 40.60 


43.3 40.1 


76.50 40.40 


48.8 39.9 


82.00 40.20 


55.5 39.7 


86.50 40.00 


60.0 39.4 


92.00 39.60 


65.5 39.2 




71.1 39.0 




76.6 38.7 




82.2 38.5 




87.7 38.3 




93.5 38.0 




100.0 37.8 




Na-,0, 2.47Si0 2 , 52° Baume 
52.06 


Na.0, 2.06SiO 2 , 50°Baume 
34 00 49.60 


10 51.82 


41.00 49.40 


20 51.40 


44 80 49.20 


50 50.30 


50.00 49.00 


80 49.23 


55 00 48.80 


90 48.83 


60.20 48.60 




65.50 48.40 




70 00 48.20 




75.00 47.70 




81 00 47.30 




86 50 47.20 




93.00 47.20 


Na 2 0, 2.06SiO 2 , dil. to approx. 

40° Baume 
17 39 1 


Na 2 0, 2.06SiO 2 , 59.1°Baume 
35 00 59.80 


21 39 


45 00 59.20 


30 38 5 


50.50 59.00 


40 38 5 


55.50 58.80 


50 . 38 


61.50 58.60 


60 37 6 


67.00 58.40 


70 37 2 


71.50 58.20 


80 . 36 9 


77.00 58.00 


90 . 37 


85.00 57.80 




88.50 57.60 

91.00 57.40 




95.50 57.30 



COMMERCIAL FORMS AND PROPERTIES 13.5 

Refractive Index. Stericker undertook measurements of the re- 
fractive indices of silicate solutions in an effort to gain a knowledge 
of their constitution. This property can be measured with a high de- 




2 3 

Afc/s S/Og per Mo/ fa 2 



Fig. 54.— Variation of Refractive Index with Ratio at Constant Na 2 Content. 



gree of accuracy and is a very useful means of detecting changes of 
chemical composition and arrangement. Like the conductivity data 
of Kohlrausch this property suggests a marked change of composition 
at ratio 1 : 2 as shown graphically in Figure 54. 



136 SOLUBLE SILICATES IN INDUSTRY 

Tables of refractive index measurements are as follows : 

Table 53. Refractive Index Measurements. 

Refractive 
Na 2 Si0 2 H 2 0* Index 







Na 2 0, 3.9Si0 2 




7.01% 


26.599 


66.40% 


1.3855 


6.91 


26.21 


66.88 


1.3844 


6.79 


25.75 


67.46 


1.3840 


6.62 


25.11 


68.27 


1.3814 


6.47 


24.54 


68.99 


1.3807 


6.40 


24.28 


69.32 


1.3800 


6.30 


23.89 


69.81 


1.3793 


6.06 


22.99 


70.95 


1.3774 


5.79 


21.96 


72.25 


1.3735 


5.49 


20.82 


73.69 


1.3718 


4.64 


17.60 


77.76 


1.3666 


3.95 


14.98 


81.07 


1.3614 


3.51 


13.31 


83.18 


1.3570 


2.99 


11.34 


85.67 


1.3538 


2.48 


9.41 


88.11 


1.3501 


1.99 


7.55 


90.46 


1.3466 


1.50 


5.69 


92.80 


1.3430 


.99 


3.75 


95.26 


1.3400 


.49 


1.86 


97.65 
Na 2 0, 3.36Si0 2 


1.3367 


9.12 


29.76 


61.12 


1.3997 


8.50 


27.74 


63.76 


1.3944 


8.04 


26.24 


65.72 


1.3905 


7.47 


24.38 


68.15 


1.3860 


6.88 


22.46 


70.66 


1.3809 


6.49 


21.18 


72.33 


1.3777 


5.97 


19.49 


74.54 


1.3733 


5.08 


16.58 


78.34 


1.3671 


4.03 


13.15 


82.82 


1.3609 


3.03 


9.89 


87.08 


1.3529 


2.06 


6.72 


91.22 


1.3470 


1.03 


3.36 


95.61 


1.3403 


.55 


1.80 


97.65 
Na 2 0, 2.44Si0 2 


1.3368 


13.88 ' 


32.89 


53.23 


1.4247 


13.36 


31.65 


54.99 


1.4219 


12.93 


30.64 


56.43 


1.4176 


12.42 


29.43 


58.15 


1.4142 


11.98 


28.39 


60.63 


1.4100 


11.40 


27.00 


61.60 


1.4059 


10.82 


25.64 


63.54 


1.4009 


10.20 


24.17 


65.63 


1.3948 


9.25 


21.92 


68.83 


1.3883 


8.29 


19.64 


72.07 


1.3823 


7.04 


16.68 


76.28 
Na 2 0, 2.40SiO 2 


1.3734 


4.99 


11.66 


83.35 


1.3610 


3.02 


7.06 


89.92 


1.3495 


1.03 


2.41 


96.56 


1.3388 


.52 


1.21 


98.27 


1.3359 



COMMERCIAL FORMS AND PROPERTIES 137 

Table 53. Refractive Index Measurements {Continued). 

Refractive 
Na 2 Si0 2 H 2 0* Index 





Na 2 O,.2.06SiO 2 




14.80% 


29.60% 


55.60% 


1.4222 


13.30 


26.60 


60.10 


1.4122 


12.89 


25.78 


61.33 


1.4090 


12.43 


24.86 


62.71 


1.4043 


12.01 


24.02 


63.97 


1.4016 


11.55 


23.10 


65.40 


1.3984 


11.12 


22.24 


66.64 


1.3972 


10.53 


21.06 


68.41 


1.3916 


9.38 


18.76 


71.86 


1.3850 


8.43 


16.86 


74.71 


1.3787 


7.66 


15.32 


77.02 


1.3740 


6.06 


12.12 


81.82 


1.3651 


4.50 


9.00 


86.50 


1.3570 


2.99 


5.98 


91.03 


1.3484 


1.48 


2.96 


95.56 


1.3399 




Na 2 0, 


1.69Si0 2 




19.18 


31.58 


49.24 


1.4473 


18.03 


29.69 


52.28 


1.4390 


17.14 


28.23 


54.63 


1.4337 


16.10 


26.51 


57.39 


1.4264 


15.60 


25.69 


58.71 


1.4235 


15.00 


24.70 


60.30 


1.4188 


14.46 


23.81 


61.73 


1.4157 


13.93 


22.94 


63.13 


1.4127 


13.00 


21.40 


65.60 


1.4077 


12.04 


19.82 


68.14 


1.4010 


10.14 


16.70 


73.16 


1.3886 


8.10 


13.34 


78.56 


1.3770 


6.02 


9.91 


84.07 


1.3651 


4.04 


6.65 


89.31 


1.3550 


1.90 


3.13 


94.97 


1.3425 


.64 


1.05 


98.31 


1.3358 



* These figures have been obtained by difference. Small amounts of impuri- 
ties, occurring as calcium, magnesium, and aluminum have been disregarded. 

The graph showing the relation between refractive index and total 
solids shows plainly that this property can be used as a measure of 
concentration only when the ratio between alkali and silica is known, 
but it is a convenient, quick, and accurate method of control for solu- 
tions which differ only in water content. 

Freezing. The difficulty of manipulating silicate solutions at high 
concentrations has resulted in a paucity of exact information on the 
freezing of silicate solutions but as their behavior at low temperatures 
is a matter of industrial importance some general observations must 
be set down. It has been pointed out that water and silicate may be 
present in all proportions. When the amount of water is so small 
that the system appears as a solid it remains clear at temperatures below 
the freezing point of water. It behaves like a supercooled liquid and 



138 SOLUBLE SILICATES IN INDUSTRY 

only becomes more brittle and glass-like. Dilute solutions, on the other 
hand, may be frozen.* They become opaque due to separation of ice 
crystals. These tend to float to the surface of any considerable body 
of solution in course of freezing or melting and cause a corresponding 
concentration at the bottom. This is very troublesome in solutions de- 
signed for uses in which exact control of concentration or viscosity 
is important. The degree of concentration at which crystals of water 
separate, i.e., the liquidus of these three-component systems, has not 
been studied in detail but it may be said that a 1 : 3.3 solution of 38 
per cent total solids will freeze at about 28° F. (— 2.22° C), and sepa- 
rate, while a 54 per cent solution of 1 : 2 remains clear far below 0°F. 

Frozen silicate solutions after warming and complete mixture, which 
is sometimes mechanically difficult on account of the gummy nature 
of the concentrated portion, show the same physical character as before. 
No case has come to the author's attention where adhesive properties 
were altered but this does not justify the statement that no disturbance 
of equilibrium takes place. A few instances of change of water re- 
sistance of silicate cements apparently attributable to freezing of sili- 
cate have been observed even in cases where the concentration was 
such that no separation could occur. 

Boiling. Here again the absence of much scientific data is due to 
experimental difficulties but some general observations are necessary 
to an understanding of silicates in industry. 

In the first place, the colloidal character of the concentrated solutions 
makes it possible to boil them at temperatures much below those re- 
quired for crystalline compounds. 31 ' 32 For instance, a solution of 63 
per cent total solids, ratio 1 : 1.5, may be boiled in an open vessel at 
about 105 °C. The more silicious solutions, 1 : 3 and above, are trou- 
blesome to boil, due to the separation of a partly dehydrated coating 
on the heating surface. This difficulty is negligible when working 
under moderately reduced pressure. 

The stability of silicate solutions on boiling has to do with critical 
concentrations 33 above which no separation of flocculent silica takes 
place or even which permit the re-solution of flocculent material al- 
ready separated. Failure to maintain sufficient concentrations in dis- 
solving and evaporating equipment often gives rise to troublesome 
deposits. The floe when dehydrated forms a white amorphous mass 
very difficult to remove. The writer has seen evaporator tubes and 

* Cf . pp. 40-44. 

^Cann, Jessie Y., and Dorothy L. Cheek, Ind. Eng. Chem., 17, 312 (1925). 
^Cann, Jessie Y., and K. E. Gilmore, /. Phys. Chem., 32, No. 1, 72 (1928). 
33 Codd, Lawrence Wm, Brit. Pat. 206,572 (Nov. 5, 1923). 



COMMERCIAL FORMS AND PROPERTIES 139 

pipe lines almost closed in this way. Stability is also a matter of 
importance when the solutions are used at high dilutions as in the textile 
industry, where the separation of a little floe may cause goods to dye 
unevenly. Carter has found that solutions prepared in different ways 
with the same composition vary widely in stability on dilution and 
heating. It is frequently found that a solution will remain clear at 
two concentrations as at 5° and 20° Baume and will flocculate at inter- 
mediate points. Much remains to be learned in this realm. For pur- 
poses of control, an idea of stability may be gained by partly neutralizing 
a diluted silicate, heating and measuring turbidity under closely de- 
fined procedure. 

Viscosity. Industrially speaking, viscosity is the most important 
property of silicate solutions. Beginning at the viscosity of water all 
silicate solutions above the ratio Na 2 0, 1.5Si0 2 may be concentrated 
till they become too viscous to flow at ordinary atmospheric tempera- 
tures. The same is true at higher temperatures but the concentrations 
are higher. Although silicates of like viscosity may differ widely in 
other respects they all, except the metasilicate which crystallizes, may 
be brought to any viscosity within the range indicated. The curves 
on which viscosity changes are graphically shown give no clear evidence 
of the constitution of the solutions except that the more silicious ones 
indicate the presence of increased amounts of colloidal matter and an 
approach to the phenomenon of gelation. 

Range. In order to visualize the flowing characteristics of silicates 
of various viscosities here given in centipoises it will be convenient 
to consider the approximate values of some other substances, more 
or less familiar, on the same scale at 20° C. 

Table 54. Comparative Viscosities. 

Centipoises 

Water 1.0050 

Glycerin 80 per cent 55.34 

Winter medium oil 163. 

Glycerin 90 per cent 207.6 

Castor oil 9.86 

Heavy cylinder oil "600 W" 3,581. 

Pure corn syrup 15,586. 

Viscometers. Devices for measuring viscosity are many, but only 
a few are adapted to deal successfully with very viscous sticky liquids. 
Bingham 34 has pointed out that all the silicate solutions encountered 
industrially are viscous liquids and not plastic solids — that is, their 
stress flow curves pass to zero — they flow, however slight the force 

34 Bingham and Jacques, Chem. & Met. Eng., 23, 727 (1923). 



140 SOLUBLE SILICATES IN INDUSTRY 

applied to them, though often this can be detected only after consider- 
able lapse of time. 

The only method which has been found satisfactory for the most 
viscous silicates is that which depends upon the rate at which a steel 
ball drops through a column of silicate. 35 By a somewhat involved 
calculation the data thus obtained can be expressed in terms of abso- 
lute viscosity. The instrument consists of a graduated glass tube, 29 
cm. long and 2.5 cm. in diameter. It is conveniently held vertically 
in a wider tube which serves as a thermostat. The liquid, the viscosity 
of which is to be determined, is placed in the graduated tube, the tem- 
perature of the thermostat adjusted to 20° C, and the liquid allowed 
to stand until its temperature is precisely 20° C. This accurate adjust- 
ment of the temperature is important since small variations in the tem- 
perature cause large differences in viscosity. A steel square 1/16 inch 
in diameter is allowed to fall through the liquid and its velocity obtained 
by noting the time in seconds required for it to fall through a section 
15 cm. long ending 5 cm. above the bottom. The density of the solution 
is determined either by the specific gravity bottle or by a hydrometer, 
and the viscosity in C.G.S. units obtained by substituting in the formula. 

„_ 2 far\a~ft) 



V 

I = acceleration due to gravity 981 cm. per sec. 2 
r = radius of sphere 

a = density of sphere 

ft = density of liquid 

V = uniform velocity in cm. per sec. 

For adhesive silicates the time required for the ball to pass through 
a column of convenient length is too short to be easily measured with 
sufficient accuracy. Means must in any case be provided to avoid side 
or end effects by using a sufficiently wide tube, inserting the ball in 
the center of the surface and measuring its rate of travel through a 
section suitably removed from both ends. 

Flow-out viscometers are suitable only for approximate shop meas- 
urements where large samples and large apertures can be used. Instru- 
ments like the Redwood, Engler, and Saybolt used in work with oils 
become clogged and unreliable due to the formation of a film or skin 
upon the surface of the silicate in the cup and, especially at higher 
temperatures, on the surface of the stream leaving the viscometer. 

This film has a minimum effect on the instruments which depend 

35 Gibson, William H., and Jacobs, Laura M., /. Chan. Soc, 117, 472 (1920). 



COMMERCIAL FORMS AND PROPERTIES 



141 




Fig. 55. — Stormer Viscometer. 

on the resistance of the silicate solution to the rotation of a cylinder 
immersed in it. The viscometers of MacMichael, Doolittle, and 



TEST CUP 



CYLINDER 




Fig. 56. — Stormer Viscometer. 



Stormer are of this type. The last, on account of simplicity and con- 
venience, has been used for the following work. It depends on the 



142 



SOLUBLE SILICATES IN INDUSTRY 



retarding action of the "silicate on the rotation of a hollow cylinder 
actuated hy a falljng weight. Duplicate readings are easily made on 
the latest form of this instrument if the temperature is maintained 
constant. The cord is wound up on the drum and a reading in seconds 
of the time in which the cylinder makes a hundred revolutions is taken. 



2O0 








] 


iSO 

s 

< /OO 



Jo 






3 




\ 






< 


^ i 

< 

» 


i 








i 










• 




S A 





I 2 3**6 7 3 9 iO // /2 /S /4 is 

% Na e O 

Fig. 57. — Variation of Absolute Viscosity with Na 2 0. 

The weight is adjustable, permitting the instrument to be calibrated to 
give readings on thick or thin liquids in a convenient time. Viscosity 
is expressed in the number of seconds required for the cylinder to 
make 100 revolutions. It has the additional advantage of yielding 
values which within the range of adhesive silicates bear a straight- 
line relation to viscosities expressed in absolute units. As an illus- 
tration, using our form of instrument and our calibration, V = 



COMMERCIAL FORMS AND PROPERTIES 



143 



5.25 t — 33, between 15 and 40 Stormer seconds, and above 40 Stormer 
seconds, V = 3.11 1 + 36 (t = time in seconds). 36 

Relation to Composition. Viscosity of silicate solutions varies with 
concentration, with ratio, and with temperature 



The following meas- 



zoo 



/Sd 






to 



JdO 



J& 















1 




• 






> 
si 


1 





















/o 



20 



so 



% s,o 2 

Fig. 58. — Variation of Viscosity with Si0 2 . 

urements 37 ' 38 were made on commercial solutions and may vary some- 
what from perfectly pure ones. 

The difficulty of making close checks with different samples, par- 
ticularly in the steep part of the curves, is considerable on account of 

M Higgins, E. R, and E. C. Pitman, Ind. Eng. Chem,, 12, 587-591 (1920) ; C.A.. 
14, 2262. 

^Stericker, Wm, Doctor's Thesis, Mellon Inst, Pittsburgh, Pa. (1922). 

38 Dedrick, Charles H., Unpublished report of Philadelphia Quartz Company. 



144 



SOLUBLE SILICATES IN INDUSTRY 



the large influence of small variations in composition. For example, 
silicate solutions take up C0 2 from the air and as far as viscosity is 
concerned the conversion of Na a O to NaXO. in a silicate solution is 





Table 55. Vis 


Na 2 


Si0 2 ' 
Na 2 0, 3.9SiQ 2 


Centipoises 


7.01% 


26.59% 


7026.0 


6.91 


26.2] 


1545.0 


6.79 


25.75 


375.0 


6.62 


25.11 


147.7 


6.47 


24.54 


101.9 


6.40 


24.28 


67.9 


6.30 


23.89 


55.2 


6.06 


22.99 


35.5 


5.79 


21.96 


26.7 


5.49 


20.82 


20.6 


4.64 


17.60 


14.4 


3.95 


14.98 


12.3 


3.51 


13.31 


10.3 


2.99 


11.34 


8.7 


2.48 


9.41 


8.2 


1.99 


7.55 


8.2 


1.50 


5.69 


5.1 


.99 


3.75 


4.1 


.49 


1.86 
Na 2 0, 3.36Si0 2 


3.1 


9.12 


29.76 


454.0 


9.00 


29.37 


278.3 


8.68 


28.33 


186.8 


8.50 


27.74 


147.1 


8.26 


26.96 


89.1 


8.04 


26.24 


65.2 


7.75 


25.30 


42.2 


7.47 


24.38 


35.0 


6.88 


22.46 


23.6 


6.49 


21.18 


21.1 


5.97 


19.49 


18.0 


5.08 


16.58 


12.9 


4.03 


13.15 


10.3 


3.03 


9.89 


7.8 


2.06 


6.72 


6.8 


1.03 


3.36 


5.7 


.55 


1.80 
Na.O, 2.44Si0 2 


3.1 


13.88 


32.89 


1376.0 


13.36 


31.65 


659.9 


12.93 


30.64 


321.8 


12.42 


29.43 


197.4 


11.98 


28.39 


144.5 


11.40 


27.00 


82.4 


10.82 


25.64 


48.4 


10.20 


24.17 


30.3 


9.25 


21.92 


21.6 


88.29 


19.64 


17.0 


7.04 


16.68 


12.3 



Viscositv Measurements. 



Na 2 


Si0 2 Centipoises 




Na 2 0, 2.40SiO 2 




4.99% 


11.66% 


6.7 


3.02 


7.06 


5.1 


1.03 


2.41 


3.6 


.52 


1.21 
Na 2 0, 2.06SiO 2 


1.5 


18.42 


36.84 


87080.0 


17.20 


34.40 


6115.0 


15.77 


31.54 


835.0 


14.80 


29.60 


341.0 


13.30 


26.60 


119.0 


12.89 


25.78 


81.4 


12.43 


24.86 


62.5 


12.01 


24.02 


49.0 


11.55 


23.10 


38.0 


11.12 


22.24 


32.4 


10.53 


21.06 


25.7 


9.38 


18.76 


21.6 


8.43 


16.86 


17.0 


7.66 


15.32 


15.4 


6.06 


12.12 


12.4 


4.50 


9.00 


9.8 


2.99 


5.98 


6.2 


1.48 


2.96 
Na 2 0, 1.69SiO a 


4.1 


19.78 


32.58 


22900.0 


19.18 


31.58 


8496.0 


18.03 


29.69 


1697.0 


17.14 


28.23 


633.0 


16.10 


26.51 


290.0 


15.60 


25.69 


210.5 


15.00 


24.70 


148.7 


14.46 


23.81 


101.4 


13.93 


22.94 


72.6 


13.00 


21.40 


41.6 


12.04 


19.82 


29.0 


10.14 


16.70 


18.0 


8.10 


13.34 


12.4 


6.02 


9.91 


7.2 


4.04 


6.65 


5.6 


1.90 


3.13 


1.5 


.64 


1.05 


.9? 




£* °> •>• £ 
, 3l_ _<*• ? *j 





JOjgggj n 7 Dt 




O^KK 










1 o.« l 3ffo 1 eKJ' 










l O|S06'f o 


*b W 














In i 












h In 

lU 

ifi III 

c>i | 












Z 


$ V 


1 


8 




o 
o 


o 
© 










to 

+-> 

o 







H 


c 




■4-1 







O 


I** 




O 
> 




^ 


<L> 






3 


n 


£ 


O 



V 



■S 



V * *^7 */ '</- / *"c -? j-/>< 



< 



> 



a 

i— i 



H5 



146 



SOLUBLE SILICATES IN INDUSTRY 



equivalent to removing it. At a point where 0.1 per cent Na 2 ac- 
counts for the difference between a syrup and a jelly it is easy to see 
how small changes become important. 




mperature ~ Degrees FaAc 

Fig. 61. — Variation of Viscosity with Temperature. 

A large number of viscosity measurements were made by Main, 39 
whose results are not fully satisfying because of the large differences 
found in working with different instruments. He points out, as Ster- 

38 Main, V. R., /. Phys. Chem., 30, 553-561 (1926). 



COMMERCIAL FORMS AND PROPERTIES 



147 



icker 40 had done, that the curves show the properties characteristic 
of lyophile sols and that the slope of the viscosity curve at a given 
concentration is dependent upon the Na 2 : SiOo ratio and is greater for 
the more silicious solutions. He worked with efflux type viscometers 
using capillary tubes, the Ostwald, in which the liquid flows through 
the tube under its own hydrostatic pressure, and the Ubbelohde vis- 




?0 V? % V 40 

TEMPERA TU/?E 

Fig. 62. — Effect of Temperature on Viscosity. 



cometer, in which the liquid is forced through the capillary under a 
variable pressure of gas. Neither of these instruments lends itself to 
the study of high viscosities encountered in commercial silicates ; they 
both have high drainage errors, and the values obtained are kinematic 
rather than absolute. His conclusions must therefore be considered 
as applying relatively to the range between the viscosity of water 
and that of the thinnest silicate which could be used for adhesive pur- 
poses. The maximum specific gravity investigated was under 1.3. 
Within this range it appears that the effect of temperature on viscosity 

40 Bogue, Robert H., "Theory and Application of Colloidal Behavior," New 
York: McGraw-Hill Book Co., Chap. XXIV, by Wm. Stericker, 1924, p. 563. 



148 



SOLUBLE SILICATES IN INDUSTRY 



is a straight line function, the slope of the line being dependent on the 
ratio as shown in Figure 62. 

A series of curves in which viscosity is plotted against concentra- 
tion in terms of weight normality of sodium oxide does not differ in 
type from those obtained at higher concentrations. 

When the viscosity is plotted against ratio the minimum found by 




12 5 4 

COMCENTRAT/ON A/„ 



Fig. 63. — Results with Ostwald Viscometer. 



Stericker 41 and confirmed by Dedrick 42 at higher concentrations was 
not shown. 

The sharp rise of the curves to the left of the minimum does not 
affect adhesive silicates, for solutions in this range are too alkaline to 
be often chosen for such use. The shape of the curves, however, sug- 
gests that the disilicate at high concentrations has less internal resistance 
than either metasilicate or silicates with considerable amounts of col- 
loidal silica. 

41 Stericker, loc. cit. 

42 Dedrick, Unpublished records of the Philadelphia Quartz Company. 



COMMERCIAL FORMS AND PROPERTIES 



149 




Z 5 

RAT/O 5iO?:Na?0 

Fig. 64. — Ostwald Viscometer. 



k 

I 

8 








^iTo o -©j^*© /^^ 



/?at/o 5/0 2 :/Vc7 Z 



Fig. 65. — Change of Viscosity with Ratio. 



150 



SOLUBLE SILICATES IN INDUSTRY 



Table 56. Changes in Viscosity with Changes in Temperature. 



Temp. °C. Centipoises 

Na 2 0, 1.58Si0 2 

10 v 307606 

15 130986 

20 61147 

25 29519 

30 14624 

35 9391 

40 5607 

45 3900 

50.5 2331 

53.3 2158 

60.6 1255 

66.7 945 

74.4 627 

80.5 518 

Na 2 0, 3.25Si0 2 . °Baume 39.7 

1.7 509 

4.4 384 

7.2 331 

10.0 287 

12.8 242 

15.6 216 

18.3 192 

20.0 176 

21.1 174 

23.9 167 

26.7 142 

29.4 129 

32.2 116 

35.0 105 

37.8 92 



Na 2 0, 3.86Si0 2 

10.0 

12.8 

15.6 

18.3 

20.0 

21.1 

23.9 

26.7 

29.0 

32.2 

35.0 

37.8 



'Baume 33.8 

798 

400 

255 

187 

165 

161 

119 

98 

83 

72 

61 

51 



Na 2 0, 3.86Si0 2 

12.8 

15.6 

18.3 

20.0 

21.1 

23.9 

26.7 

29.0 

32.2 

35.0 

37.8 



'Baume 34.4 

2076 

798 

425 

322 

263 

198 

163 

138 

109 

101 

80 



Temp. °C. Centipoises 

Na 2 0, 2Si0 2 

20.0 56016 

21.1 37456 

23.9 29803 

26.7 18696 

29.4 14342 

32.2 10765 

35.0 8122 

37.8 6225 

40.6 4779 

43.3 3830 

46.1 3115 

48.9 2493 

51.7 1902 

54.4 1591 

57.2 1441 

Na 2 0, 3.25Si0 2 . °Baume 40.3 

1.7 758 

4.4 565 

7.2 440 

10.0 449 

12.8 311 

15.6 268 

1S.3 230 

20.0 216 

21.1 210 

23.9 182 

26.7 173 

29.4 167 

32.2 132 

35.0 129 

37.8 109 

Na.O, 3.86Si0 2 . °Baume 34.6 



12.8. 
15.6. 
18.3. 
20.0. 
26.7. 
29.0. 
32.2. 
35.0. 
37.8. 



922 
479 
290 
231 
132 
121 
110 
96 
83 



COMMERCIAL FORMS AND PROPERTIES 



151 



Temp. °C. Centipoises 

Na 2 0, 3.25Si0 2 . °Baume 41 

4.4 857 

7.2 677 

10.0 434 

12.8 423 

15.6 397 

18.3 353 

20.0 331 

21.1 314 

23.9 269 

26.7 237 

29.4 216 

32.2 190 

35.0 176 

37.8 165 



/20 



90 






60 



JO 



70* 



Temp. °C. Centipoises 

Na 2 0, 3.25Si0 2 . °Baume 41.3 

4.4 1280 

7.2 1052 

10.0 789 

12.8 681 

15.6 542 

18.3 468 

20.0 430 

21.1 390 

23.9 343 

26.7 298 

29.4 269 

32.2 235 

35.0 210 

37.8 191 












































//0° ISO' 



/90° 



Fig. 66. 



-Changes in Viscosity of 60° Silicate Due to Heating under 70 Pounds. 
Pressure for Three Hours. 



Changes Due to Heating. Viscosity is perhaps the most sensitive 
index of changes in equilibrium between the components of a soluble 
silicate in water. Carter 43 investigated the effect of heating 1 : 1.87 ratio 

43 Unpublished records of the Philadelphia Quartz Company. 



152 



SOLUBLE SILICATES IN INDUSTRY 



solutions at temperatures above the boiling point of water and found 
that the change of viscosity with temperature was altered by this 
means. 

Table 57. Changes in Viscosity of Silicate of 1:1.87 Ratio After Heating for 3 

Hours at 70 Lbs. 





Centipoises 


Centipoises 


Degrees C. 


Before Heating 


After Heating 


87.7-82.2 


222.6 


228.8 


76.6-71.1 


398.1 


393.7 


65.5 


850.8 


782.4 


54.4 


2052.0 


1592.8 


46.1 


6567.0 


3545.4 


37.7 


12648.0 


9703.2 



Effect of Salt Brine. Malcolmson 4t found that the viscosity of 
adhesive silicate solutions could be increased by mixing them with 




(PBR CBNT OF Had //V /1PDBD BP/A/JE) 
I 
2.0 



Z4 ?.d 32 3-6 4,o 4.4 



(4PP/ZOX. P£~RC£HT0f A/aCI IN F//VAL SOLUTION) 



Fig. 67. — Effect on Viscosity of Silicate of Soda Produced by Addition of 

Various Brines. 



Ind. Eng. Chem., 12, 174-176 (1920), 



- COMMERCIAL FORMS AND PROPERTIES 153 

sodium chloride brines. Thus a unit of adhesive could be increased 
in volume without loss of viscosity when it would spread over a larger 
area. The adhesive power, rate of drying and other essential qualities 
were not reduced below a point considered safe for making paper 
container board. By using a brine about 66 per cent saturated, the 
volume was increased 21 per cent without violating these conditions, 
but it should be pointed out that this was possible only because the 
adhesive strength of the silicate is so much greater than the paper 
that it can be much reduced and still have a good margin of safety. 

The final viscosity was found to be dependent upon the concentra- 
tion of the added brine, other factors being constant. 

Stericker 45 discusses the probable mechanism of this increase in 
volume as follows : 

"Sodium silicate solutions probably contain sodium, hydroxyl, sili- 
cate ions, undissociated silicates, and colloidal particles which consist 
largely of hydrated silica. Sodium chloride solutions contain sodium 
and chlorine ions and undissociated salt. Both contain, in common 
with all aqueous solutions, very small quantities of hydrogen and 
hydroxyl ions, due to the ionization of the water. 

"When these solutions are mixed, the equilibrium between the vari- 
ous constituents is destroyed. Since at the concentration in question 
none of the salts present are completely dissociated, the solutions will 
be saturated with respect to sodium ions. There will be a tendency to 
repress these ions with the consequent formation of more of the un- 
dissociated salts and sodium hydroxide. The colloidal particles will 



Table 58. Variation in Hydrogen-Ion Concentration of Brine-Treated Silicate 

Solutions. 

NaCl in Relative E.m.f. 

Brine Viscosity in Volts pH 
Original Silicate Na 2 0, 3.32Si0 2 ; 38.9°Baume; Permanent Precipitate Formed. 

Orig. sil. 40.3 .898 9.65 

16.3 28.4 .945 10.45 

17.2 79.8 .944 10.44 

20.4 436. .875 9.25 

Original Silicate Na 2 0, 3.46Si0 2 ; 39.8°Baume. 

Orig. sil. 68.0 .976 10.99 

10.0 16.0 .960 10.71 

13.7 22.4 .954 10.62 

14.8 26.8 .950 10.54 

17.3 47.2 .935 10.28 
21.0 1180. .951 10.56 

45 Stericker, loc. cit. 



154 SOLUBLE SILICATES IN INDUSTRY 

oppose this tendency by attracting the sodium ions to form adsorption 
compounds. The result is an excess of chlorine ions in the solution 
which give rise to more hydrogen ions. But since the concentration 
of hydrogen ions times that of hydroxyl ions is always a constant, 
some of the latter must disappear. Therefore, the hydroxyl ion con- 
centration and the pH value fall until the silica particles are saturated. 
From this point on the change will be to depress the dissociation. At 
the same time the chloride may salt out the colloid, thereby increasing 
the hydroxyl ion concentration. From the results obtained it appears 
that this is what happens." 

Tackiness. Lubricating oil and a sticky silicate solution may 
have internal resistances which make them flow at the same rate but 
there is a vast difference in quality. They may be alike in viscosity 
and yet different in what, for lack of a better term, we may call "tacki- 
ness", the ability to be drawn out into threads when two surfaces with 
a layer of the liquid between them are drawn apart. The silicate solu- 
tions vary all the way from an oily consistency which gives a lubri- 
cating effect to a stickiness which compares with that of sticky fly 
paper. This characteristic is obviously important for adhesives and 
it is easily and with a little experience accurately judged by rubbing 
a small portion of the liquid between thumb and finger and then 
drawing them apart. The stickiness of a silicate solution bears no direct 
relation to its adhesive strength nor yet to its final setting time. 

Efforts to measure this property have been, up to this time, much 
less than satisfying. Mallock 46 considers that this property depends 
upon (1) resistance to change of volume and change of shape, (2) 
volume limits and shear limits, (3) surface tension. It is certain that 
a sticky liquid must have high cohesion and low surface tension. In 
general, sticky liquids easily wet surfaces to which they are applied. 
Looking at it from the angle of the colloidal silica, those liquids which 
have begun to form a structure will be the least tacky. A gel is an 
example of high viscosity and absence of the property under consid- 
eration. 

The time factor must be taken into account in any effort to measure 
tack. Stericker 47 points out that either the instrument used for this 
purpose must be run at constant speed or the speed must be measured. 

The U. S. Bureau of Standards developed an instrument for study- 
ing this property. It consists of a chemical balance from one beam 

"Proc. Roy. Soc. (London), 87, ser. A, 466-478 (1912). 

47 "Annual Summary Report of Philadelphia Quartz Company's Industrial 
Fellowship," Mellon Institute, Pittsburgh, Pa. (1919-1920). 



COMMERCIAL FORMS AND PROPERTIES 155 

of which was suspended a conical bob. A wire loop between beam 
and bob served to prevent jerks and too rapid shearing. Weights ap- 
plied to the opposite pan tended to withdraw the bob and the time 
required for the pointer to pass a certain number of scale divisions 
was measured. 48 Stericker obtained the following results by this 
method : 

Table 59. Attempt to Measure "Tack." 

Time in Seconds with Weight of : 

Material- Centipoises 17.4 g. 17.6 g. 18.0 g. 18.02 g. 

1 Lubricating oil 124.5 Too rapid to read 

2 Na 2 0, 2.1 Si0 2 diluted 124.5 11 .... 

3 Viscous oil 2704.4 21.5 2.1 

4 Na 2 0, 2.1 Si0 2 diluted 2548.9 44.4 11.3 4.5 2.6 

5 Dextrin 137. 69. 

6 Na 2 0,2.1Si0 2 124.5 171. 

7 Na 2 0, 1.24Si0 2 3.8 

8 Na 2 0, 2.84Si0 2 969.0 .... 6.3 1.2 

9 Na 2 0,3.41Si0 2 522.0 .... 1.5 1.0 

10 Na 2 0, 3.47Si0 2 247.5 .... 1.3 0.7 

11 Na 2 0, 3.32Si0 2 167.2 .... 0.6 0.6 

12 Na 2 0, 3.92Si0 2 1723. 

13 Na 2 0, 3.47Si0 2 (control) .. 247.5 .... 0.8 0.7 

14 Na 2 + sodium acetate ... . 281.7 .... 1.0 0.7 

15 Na 2 + urea 261.2 .... 1.0 0.8 

16 Na 2 0, 3.92Si0 2 + 20% H 2 1.4 0.6 0.7 

The difference between a tacky liquid and one of like viscosity which 
is not tacky is brought out in the comparison of 3 and 4 but tackiness 
can be developed only in viscous liquids. Thus the high value of 
number 12 is somewhat misleading for though at the speed of the ex- 
periment Na 2 0, 3.92Si0 2 at the high viscosity appears tacky, yet the 
fact that at higher speeds the threads of this liquid break off short 
while those of Na 2 0, 2.1Si0 2 solutions of the same viscosity do not is 
not shown. It might be by extending the study to faster movement 
of the bob. This method is the best yet devised but must be much 
further studied to be of much use. It gives consistent results in skilful 
hands but would have to be simplified to be of value for controlling 
adhesive silicates. Tackiness decreases as the silica ratio increases and 
it declines with temperature, but the work has not been carried far 
enough to say whether the latter is due to fall of viscosity with rising 
temperature. 

The method proposed by Bonney 49 is more convenient especially 
in mixtures of silicate with inert material but has not been worked out 
for very sticky viscous substances. He plots time against distance 

48 Basseches, J. L., Bur. of Standards, personal communication. 
^Bonney, Robert D., Catalyst, 8, No. 3, 8 (1923). 



136 



SOLUBLE SILICATES IN INDUSTRY 




Thin f/iur/ig enamel 



Thin 



7- f-Zaur/'tty 



Tt,ic/r 



Thick tion-fUw/i 



ft/n/' 



f>Q//jf 



£ S V 

T/me of f~/o*/ - M//ivfei 



J- 



Fig. 68. — Spreading Characteristics of Paints. 

traveled while a large drop of the substance under test flattens out 
on a smooth glass plate. Characteristic forms of curves for tacky 
and "short" adhesives are thus secured. 



Methods of Analysis. 



Glass. 



If the sample be a solid glass, it is most convenient to bring it into 
solution by slow hydration with steam, thus avoiding the uncertainties 
which arise from adding alkali carbonates to make an easily soluble 
fusion. Silica, sodium oxide, and impurities may then be determined 
directly in the same sample and with a great saving of time. Finely 
ground glasses may be weighed out and subjected to open steam until 
they are hydrated sufficiently to dissolve completely in hot water. This 
method is applicable to ratios up to and including Na 2 0, 3.3Si0 2 , a half 
gram sample of which can be hydrated on a water bath in about 2]/ 2 
hours. No water should be put on the silicate ; hydration takes place 
best from the steam direct. A shallow dish such as an inverted porce- 
lain crucible lid supported on a triangle and covered with a round bot- 
tomed glass dish is a suitable arrangement. A small pressure cooker 
or autoclave capable of quickly raising fifteen pounds steam pressure 
will shorten the dissolving time to about an hour. 



Determination of Sodium Oxide. 

When solution is complete, the whole container should be placed 
in about 75 cc. of distilled water, stirred with a glass rod, and one drop 
of standard methyl orange solution added, as soon as the solution is 



COMMERCIAL FORMS AND PROPERTIES 157 

cold. The silicate should he entirely dissolved without leaving any 
grit. If there is grit, it means that the sample has not been ground 
finely enough or that it has not been on the steam bath long enough. 
Titration is carried out with standard hydrochloric acid. 

Sodium oxide is determined, in the liquid grades, by weighing from 
0.5 to 2 grams of the silicate in a small porcelain crucible, covered with 
a watch glass. Care must be taken to avoid any surface skin which 
may have formed on the sample. The silicate and crucible are put 
in a beaker of water, — hot water in the case of the heavy silicate solu- 
tions. When the sample has cooled to room temperature it is titrated 
as above. 

Sodium oxide is best determined by titration with N/5 hydrochloric 
acid and methyl orange, which gives a much sharper end point in 
silicate than in carbonate solutions. Phenolphthalein always gives low 
results. The error is greatest with the solutions of high silica ratio. 
Stericker 50 found the fractional amounts of the total titratable with 
this indicator. 

Table 60. Errors from Titration with Phenolphthalein. 

Mols Si0 2 per Per Cent Total Na 2 Found 

Mol Na 2 with Phenolphthalein 

1.69 95.3 

2.06 92.5 

2.40 93.0 

2.44 91.7 

3.36 87.1 

3.90 85.1 

This may be due to adsorption of sodium oxide on colloidal silica 
or to the formation of acid silicates. The end point is difficult to 
fix and this indicator should not be used. Methyl red and brom-phenol 
blue are satisfactory, but phenol red, attractive on account of its re- 
sistance to hydrogen peroxide, only gives part of the total sodium 
oxide in silicate solutions. 

Determination of Silica. 

The silicate solution is evaporated twice to complete dryness with 
hydrochloric acid and the silica is washed and ignited to constant weight. 
As a check the silica is volatilized with hydrofluoric acid and the resi- 
due weighed. It should be very small. Hillebrand's technic 51 is the 

50 "Annual Summary Report of Philadelphia Quartz Company's Industrial Fel- 
lowship," Mellon Institute, Pittsburgh, Pa. (Sept., 1922). 

^ Hillebrand, "Analysis of Silicate and Carbonate Rocks," U. S. Gcol. Survey, 
Bull. 700 (1919). 



158 SOLUBLE SILICATES IN INDUSTRY 

best for precise analysis in the presence of other silicates than those of 
the alkalies, but the procedure can be somewhat shortened for soluble 
silicates. 

Harman 52 discusses sources of error in determining silica as fol- 
lows : 

"Incomplete removal from solution owing to an insufficient number 
of evaporations to dryness. Two are sufficient in the case of a simple 
silicate such as used here, provided each is a very complete evapora- 
tion to dryness. 

"Failure to remove particles of silica from the evaporating dish. 
This error may be quite large but can easily be avoided by wiping the 
dish with a piece of moist filter paper which is then added to the silica 
to be ignited. 

"Improper ignition. The error here may vitiate the whole experi- 
ment. It is best to begin the ignition with a bunsen flame about the 
size of an ordinary match flame, gradually increasing it so that the 
paper distils as a tar on to the crucible lid and finally disappears. If 
at any time the escaping gases should catch fire, the experiment is quite 
worthless, owing to the fine particles of silica being carried away by 
the draught. Finally ignite in a Meker burner till constant weight is 
obtained — usually half to one hour. The silica residues were always 
snow white. 

"By using these and the usual precautions, duplicate analyses for 
Si0 2 agreed within 0.01 per cent." 

Determination of Water. 

Water may be determined in the solid glass or powders by simple 
ignition to constant weight in a platinum crucible over a Meker or 
equivalent burner. 

Determination of moisture in the liquid grades, however, requires 
considerably more care. Precaution must be taken to prevent the loss 
of silicate. This is best done by carrying out the initial heating below 
the boiling point of water. When most of the water has thus been 
driven off, the temperature is gradually raised. If the temperature 
is increased too rapidly, the silicate will sputter and puff out of the 
container. The last traces of moisture are only removed by ignition. 
Fusion with additional sodium carbonate gives a mass which can be 
more readily removed from a platinum crucible after such a determi- 
nation. 

62 Harman, R. W., /. Phys. Chem., 30, 362 (1926). 



COMMERCIAL FORMS AND PROPERTIES 



159 



Ordway 53 proposed a method which permits more rapid heating 
hy preventing the intumescence. He poured the silicate solution on a 
weighed portion, preferably about two grams, of freshly ignited anhy- 
drous calcium sulfate. 

Composition. 

Although the differences in physical properties of commercial sili- 
cate solutions are very wide, ranging from liquids which are almost 




CUtset 



Fig. 69. — Commercial Silicates in Relation to the System Na 2 0-Si02-H 2 0. 

jellies to liquids comparable in stickiness with the thickest molasses, 
yet if we consider the possible combinations of the three components 
from which these solutions are made they all fall within a compara- 
tively narrow range. 

This point is best brought out in the triaxial diagram. Along the 
base line we may represent anhydrous mixtures of Na 2 and Si0 2 
in any proportion. These are the glasses produced by fusion. The 

53 Am. J. Sci, ser. 2, 33, 27-36 (1862). 



160 



SOLUBLE SILICATES IN INDUSTRY 



points on the line fix the important question of ratio which must be 
grasped in order to apply intelligently any kind of silicate of soda in 
industry. Having fixed a point on the base line, let us take for example 
that representing Na 2 0, 3.3Si0 2 , neutral glass of commerce. We may 
draw a line to the apex of the triangle designated water. Along this 
line will fall all mixtures of this ratio and water. The most familiar 
solution, often referred to as commercial 40°, falls at the point where 
62 per cent water is shown. If we thus locate all the grades which 
are industrially significant, we shall find that they fall within an area 
which includes the lower group of iso-viscosity lines and some points 
representing higher concentrations. It is convenient to transport sili- 
cate solutions at the highest concentrations which are consistent with 
handling them as liquids. All these fall within a comparatively small 
section of the diagram. 

Table 61. Typical Analyses of Commercial Grades. 



■ 


O 
co 

ON 


O 

CO 
1—1 
CO 


O 

CO 


CO 






O 

CO 




CO 


CO 


CM 


CM 




1— 1 




d 


d 


d 


d 




O 


Constituents 


OS 


c3 


03 


OS 






Sodium oxide, Na 2 


6.34 


9.12 


13.80 


18.07 




20.75 


Silica, SiOa 


" 24.47 


29.37 
0.024 


33.33 
0.02 


35.64 
0.03 




34 84 


Iron oxide, Fe 2 3 ... 


0.025 


0.02 


Alumina, AI2O3 .... 


0.092 


0.087 

Trace 

0.059 


0.17 

0.002 

0.02 


0.13 
0.01 
0.03 




017 


Titania, Ti0 2 


0.006 


007 


Lime, CaO 


0.013 


0.04 


Magnesium, MgO . . 


0.044 


0.024 


0.006 


0.02 




0.01 


English Neutral Silicate, 




English Silicate, 






Na 2 0, 3.19Si0 2 , 


39.8°Baume 




Na.0, 3.02SiO 2 , 


45°Baume 




Na 2 


8.76 




Na 2 U 

SiOa 




10.42 

30.62 

0.01 

0.09 

0.05 




Si0 2 


27.21 




Fe 2 O s 


0.006 


Fe-»0 3 






A1 2 3 


0.08 


A1,0 3 






CaO 


0.07 


CaO 






MgO 


.... 0.04 




MgO 




0.06 





The difficulty and expense of preparing easily soluble forms of sili- 
cate, on the one hand, and the technical control necessary to make 
solutions of the required exactness, on the other hand, have resulted 
in the practice of bringing the principal tonnage of soluble silicates on 
the market in solution, and this in turn, has resulted in a tendency 
to locate manufacturing plants in the centers of consumption rather 
than, as in many industries, with primary regard to raw materials, 
water, and fuel. 

The concentration at which any of these solutions can be marketed 



COMMERCIAL FORMS AND PROPERTIES 



161 



depends primarily upon viscosity. The named areas on the triaxial 
diagram indicate in an approximate way the physical character of the 
three components outside the range of commercial products. To make 




Na.O 



Fig. 70. — Iso- Viscosity Curves of Silicate Solutions. 



this relationship clearer iso-viscosity lines have been indicated upon 
an enlarged section of the triaxial diagram, the data being the same 
as those presented during the discussion of viscosity. 



Containers. 
Transportation and Storage. 

Products of fusion in lump form are stored and transported either 
in bulk or in jute sacks. When powdered, they take up enough mois- 
ture from the air to stick together and to a greater or less degree absorb 
C0 2 . They should, therefore, be kept in tight containers, preferably 
of metal. Considerable misapprehension exists about the ability of 
asphalt coatings or even rubber lined sacks to prevent absorption of 
moisture. It is a fact readily verified that containers sufficiently water- 
tight to be used for the transport of dry calcium chloride will not 



162 



SOLUBLE SILICATES IN INDUSTRY 



prevent the powdered forms of silicate of soda from caking. This 
statement does not necessarily hold for mixtures of silicate with other 
substances. Wooden barrels are used for containing silicate powders 
for a short time, but caking invariably takes place on long storage unless 
the surrounding atmosphere is exceptionally dry. Solutions are also 
shipped in wood through which moisture continually evaporates with 
resulting concentration. This is almost negligible for commercial 60° 
Na 2 0,2Si0 2 containing 46 per cent water, but for 40° Na 2 0, 3.3Si0 2 
it is a serious disadvantage, causing a thickening of the liquid to prac- 
tically solid consistency in a few months. A solution, the viscosity of 
which is in the steep part of the viscosity-concentration curve, may 
change its character completely in a short time in wooden packages. 
Test kegs containing 47° Baume adhesive silicate Na 2 0, 3.11Si0 2 and 
placed in a warm room showed the following changes : 

Time Centipoises 

At the start 1280.00 

After 1 day 1317.32 

After 2 days 1404.40 

After 4 days 1591.00 

After 7 days 1902.00 

The changes which may occur in silicate stored in glass bottles are 
illustrated by the picture of two bottles filled with the same silicate 
to approximately the same level at the same time. They were corked 
and sealed with wax, which in one case was broken by accident. The 
composition of the original solution was : ■ 



Si0 2 

Na 2 

AI2O3 

Fe 2 Os 

H.O 



20.78 
5.13 
0.036 
0.007 

74.0 




Fig. 71. — Silicate Samples Stored in 
Glass, Showing Effect of Evaporation 
through Cork. 



At the end of a year the sample 
with the broken seal had evap- 
orated and formed a clear, trans- 
parent solid. The other had kept 
its original volume but was a 
turbid gel which, however, became 
clear on warming to 40° C. and re- 
sumed its turbid appearance gradu- 
ally, beginning some time after it 
had cooled. This cycle could be 
repeated, but gradually the gel was 
disrupted under this treatment by 



COMMERCIAL FORMS AND PROPERTIES 



163 



syneresis. Other samples of the same solution kept in closed iron drums 
were apparently unchanged. Metal drums, tanks, and tank cars arc 
therefore to be preferred. Galvanized metal should not be used because 
during storage it is possible for sufficient reaction between zinc and 
alkali to take place to cause evolution of hydrogen and bursting of 
the package. If a galvanized container partly full of silicate were 
subject to alternating heating and cooling as from day to night water 
might condense upon the walls of the container and flow down, forming 
a him of silicate sufficiently dilute to be reactive. Storage tanks of 
wood, iron, and concrete are in successful use, the last on account of 
convenience and economy in construction are coming increasingly into 
vogue. 




Fig. 72. — Tank Car for Silicate. 

Cans of tin or tin plate are extensively used for silicate solutions 
in small quantities. Na 2 0,3Si0 2 and more silicious silicates at con- 
centrations above 38 per cent leave the metal perfectly bright in most 
cases. Na 2 0,2Si0 2 , sometimes sold for egg preserving, though in the 
judgment of the author, inappropriately so, will usually cause some 
solution of the metal at concentrations below 55 per cent. The crys- 
talline structure of the coating appears as a result of the etching, al- 
though the amount of metal removed is very small and for practical 
purposes negligible. Solutions more alkaline than Na 2 0,2Si0 2 and 
sufficiently dilute to be fluid attack solder and sometimes cause leakage. 



Pumps. 

Adhesive silicate solutions are moved about in quantity through 
ordinary equipment for handling liquids, rotary pumps being used 
on most installations and centrifugal or plunger pumps for larger quan- 



164 



SOLUBLE SILICATES IN INDUSTRY 



tities with no other precaution than to keep stuffing boxes tight by 
saturating with mineral oil and graphite free from saponifiable material 
and, where necessary, applying a water gland or similar stream of 
water to the point at which the shaft emerges from the stuffing box. 
This effectually prevents hardening of silicate and the abrasion which 
would result if it were allowed to dry. Tank cars are emptied either 




Fig. 73. — Centrifugal Pump of a Type Satisfactory for Silicate Solutions. 

by pumping out the liquid or by introducing air at the top to expel it. 
Tank cars used in cold climates must be equipped with heating coils 
to permit thawing solutions which freeze in transit. It has been experi- 
mentally determined that silicate in a tank car can be thawed by build- 
ing a fire under, it but this does not inure to the satisfaction of the 
owner. Wooden cradle blocks and paint are combustible, and even 
metal parts are subject to damage when abused in this way. 



Chapter VII. 
Silicate Cements. 

Industry has frequent need for substances to make joints between 
metals, refractories, fibrous sheets, and all sorts of structural ma- 
terial. In addition to closing joints which would otherwise be im- 
perfect, it is often necessary to improve the service of the principal 
material of construction by means of a coating which will modify the 
surface and fit it for some special type of exposure. 

Cements have been made in a great many ways and thousands of 
formulas are to be found in the literature. Some of them are illogical, 
many are unnecessarily complicated or costly, and others are in suc- 
cessful use as result of custom rather than because a systematic study 
has shown them to be best fitted for their work. 

Soluble silicates are at least mentioned in every compendium of 
formulas for cements. They have found very numerous uses along 
this line, but the general criticism of the literature, that too much is 
left to the imagination of the reader, is warranted ; it is too often 
assumed that he will know which silicate to choose, at what concen- 
tration to use it, and other details which may not occur even to experi- 
enced workers. 

Both the conditions which a cement may be required to meet and 
the character of ingredients are so various that some experimental 
work is inevitable. It is the purpose of this chapter to indicate the 
nature of the variables most likely to be met, and thus to help that 
person who wishes to formulate a mixture for a given use, rather than 
to present a set of recipes for use without experimental preliminaries. 

Cut-and-try methods are still essential because our knowledge of 
the physical and chemical processes on which these mixtures depend 
is not yet sufficiently complete or exact to permit a precise forecast 
of the behavior of any mixture without a basis of experiment. 

Definition of Cements and Adhesives. 

The line between cements and adhesives is not sharply drawn, but 
it is convenient to divide between fluids which are applied as thin 

165 



166 SOLUBLE SILICATES IN INDUSTRY 

films to unite surfaces nearly in contact and the more viscous masses 
which, though they may be sticky and exert adhesive properties, are 
yet expected to occupy more space than adhesives proper. In many 
instances, the primary function of the latter group is to close openings 
or to form one of the elements of a structure such that they must 
be used in thick masses. We shall call them cements. 

Any adhesive liquid may be mixed with inert solid matter, more 
or less finely divided, to form plastic bodies which occupy space or 
serve to resist, in some degree, tensile or compressive stress. Silicates 
of soda have been widely used for diverse purposes in combination 
with many substances which act in the role of fillers. 

Classification of Silicate Cements. 

Cements in which soluble silicates are of use may be divided into 
three groups : 

1. Those which set primarily by loss of moisture from the silicate 
solution. 

2. Those which depend upon a reaction with the silicate to become 
firm. 

3. Those in which silicate is used to modify the properties of other 
cements. 

The materials which are of use as accessories to modify the physical 
character of silicate cements, beyond the variations obtainable by 
using silicate solutions of diverse concentration and ratio, group into 
substances which alter the liquid phase and those which affect the solid 
part of the cement mixture. 

Cements Which Set Primarily by Loss of Moisture. 

General Properties. 

The properties of such mixtures will depend upon the character 
of silicate used, that is, the ratio of base to silica, upon its concentra- 
tion, and upon the kind of filler and its physical state. From the same 
silicate solution with the same filler we may make mixtures as dif- 
ferent as paint and putty. Without changing the concentration of 
the silicate, the state of division of the pigment will alter the plas- 
ticity of the mass and its final strength. Diluting the silicate solution 
enables it to carry more inert mineral matter, and beyond an optimum 
point reduces final strength. Thus a mixture which might dry to a 



SILICATE CEMENTS 



167 



glossy surface with one concentration of silicate would yield a flat 
surface with greater dilution and finally a soft mass easily broken down. 
Assuming an inert pigment, the various ratios of base to silica give 
the whole range between quick-drying substances which seem more 




Fig. 74. — Sulfuric Acid Towers Laid with Silicate Cement. 



like lubricants than anything with bonding strength, to the very sticky 
solutions which thread, like strong solutions of animal glue, and set 
very slowly. 

Endless variants can be introduced by using solid substances capable 
of reaction with the silicates and by adding materials such as oils, 
soaps, glycerin, fibers, et cetera, to modify the character of the final 
mass. A great number of specific formulas have been offered. 1 ' 2 It 

1 Breuer, Carl, "Kitte und Kiebstoffe," Leipzig, 1922, 189-198. 

2 Hacker, Willy, "Handbuch der Kitte und Klebemittel," Meissen, 1920, 
153-156. 



168 



SOLUBLE SILICATES IN INDUSTRY 



is obvious that this process could be continued ad infinitum, but it 
will be of greater service to show some of the characteristics of these 
mixtures and allow specific formulas to take a secondary place. They 




Fig. 75. — Acid Towers Laid with Silicate Cement. 

are easily worked out when the behavior of the raw materials is under- 
stood. 



Fillers. 

Silica as the Filler. The simplest silicate cement is one composed 
of a silicate solution made up to a pasty or putty-like consistency with 



SILICATE CEMENTS 



169 



some form of silica which may be regarded as an inert substance with 
respect to silicate solutions of the composition Na 2 0,3Si0 2 , or those 
containing more silica at ordinary temperatures. 3 A cement of this 
sort is used in the construction of acid-proof masonry. Its character 
may obviously be varied by the ratio of the silicate used, by the amount 
of silicate dissolved in the water, and by the state of subdivision of 
the inert material. The cement is used to lay between bricks of a 




Fig. 76. — Silicate Cement in Acid-Proof Construction. 



dense sort which will be comparatively impermeable to acid. It will 
be mixed immediately before use and it is desirable that it should set 
as promptly as is consistent with long service. These conditions point 
to the selection of a high ratio silicate because we know from the 
viscosity-concentration curves that this type of silicate passes from 
a liquid to a solid condition with the least loss of moisture. Let us 
assume, then, that Na 2 0, 3.9Si0 2 is to be used. This choice would 
not be appropriate if the cement were required to remain soft on long 
storage because the wet mixture hardens too easily. Further, as acid 
resistance is sought, we want to produce a mass which will finally con- 
sist as nearly as possible of pure silica with a minimum of porosity. 
On this account the smallest possible amount of sodium oxide is wanted. 

Having selected the right ratio, the next point is to decide at what 
concentration it should be used. If we mix quartz into a thick gela- 
tinous silicate solution, a comparatively small amount of filler can 
be used, as the mixture would become too dry and thick to work prop- 

3 For example, Winship, William, U. S. Pat. 1,587,057 (June 1, 1926). 



170 



SOLUBLE SILICATES IN INDUSTRY 




Fig. 77. — Silicate Cement in Acid-Proof Construction. 



1 »•-,..„ r 

.!.....,; : - . f ., 

' ■''ft Xa- 


iw-1"/-' f l'l ■ * W- ?r 

to ""■'■■- ■ . .-^ ' 



Fig. 78. — Silicate Cement in an Oil-Fired Acid Concentrator for H 2 S0 4 . 



SILICATE CEMENTS 171 

erly under a trowel or to form a proper bond. Shrinkage will also 
be troublesome. If too much water is present a much larger amount 
of silica can be used, but the silicate will then be spread over too large 
a surface and the air-dry cement will be weak. Experience indicates 
that a specific gravity of 1.30 is about right. 

Effect of Grain Size. Another factor of importance is the 
degree of subdivision of the silica filler. A series of experiments 
in which standard briquets, such as are used for tensile testing 
of Portland cement, showed that air-dried silicate cement containing 
50 parts by weight of silicate solution and 110 parts by weight of 
100 mesh silica average 788 pounds per square inch tensile strength. 
Mixtures of grain sizes were studied in order to make a body of maxi- 
mum density and it was found that by making the filler of equal parts 
by weight of silica passing a screen of 100 meshes to the inch (Tyler 
standard) 4 and a grade between 20 and 40 meshes, the tensile test 
of air-dry briquets rose above 1500 pounds per square inch. By the 
interlocking of sharp angular grains of various sizes a much stronger 
body was produced than that obtainable from either size by itself. 

Although the strength of such cements is obviously dependent upon 
the binding properties of the silicate, it does not follow that the opti- 
mum amount of silicate is the maximum consistent with good working 
properties of the soft mixture, as illustrated by the following experi- 
ment. Crushed silica rock of the following screen analysis was used : 

Mesh Per Cent 

14-20 3.6 

on 28 3.6 

" 35 7.1 

"48 12.5 

"65 16.0 

"100 17.8 

"200 17.8 

through 200 21.6 

100.0 

Silicate of the composition Na 2 0, 3.3Si0 2 at a density of 1.39 gave 

the following results : 

Tensile Strength 

of Briquets 
Dried to Constant 
Parts of Silica Parts of Silicate Wt. at 49° C. 

100 33.1 612 

31.3 556 

29.5 706 

27.8 1472 

26.0 1603 

4 W. S. Tyler Company booklet, Cleveland, Ohio. 



172 



SOLUBLE SILICATES IN INDUSTRY 



Another combination of grain sizes or a different filler might re- 
quire different amounts or concentrations of silicate to give the best 
results, but the illustration will suffice to point out that the proportion- 
ing of ingredients is a matter of prime importance to be worked out 
for each kind and size of inert filler. 

Using a calcined fire clay, the following strengths were obtained 
with the same silicate on various sizes. 

Table 62. Tensile Strength Figures. 
Mesh Tensile Strength 

4- 8 331 

8-10 529 

10-14 558 

14-20 584 

20-28 479 

28-48 492 

48-65 596 

65-100 556 

100-200 495 

through 200 295 



From this it may be seen that with the exception of the coarsest and 
the finest fractions, bodies of similar strength were obtained. The 

Table 63. Tensile Strength Figures. 







Parts Silicate 


Tensile 


Screen Analysis 




Solution 


Strength 


10- 14 


39.1 






14- 20 


1.1 






20- 28 


2.2 






28- 48 


3.9 


33.2 


754 


48- 65 


2.2 






65-100 


8.0 






100-200 


20.4 






through 200 


23.1 






8- 10 


51.1 






10- 14 


1.2 






14- 20 


2.1 






20- 28 


1.5 






28- 48 


.9 


33.5 


923 


48- 65 


10.3 






65-100 


3.6 






100-200 


12.4 






through 200 


16.9 






28- 48 


46.5 






48- 65 


3.5 






65-100 


7.4 


33.1 


1072 


100-200 


13.2 






through 200 


29.4 






28- 48 


48.0 






65-100 


9.3 


37.4 


1154 


100-200 


24.4 






through 200 


18.3 







SILICATE CEMENTS 



173 



effect of mixing the sizes without changing the quality of silicate or 
inert filler is seen from the following, which also indicates the change 
in the amount of the same silicate required to give similar consistency. 

Abrasives. 

Ransome 5 appears to have been the first to devise an artificial stone 
with a sodium silicate binder. Hart made excellent grinding wheels 
by employing silicate as the binder, in place of a linseed oil, which 
was commonly used. 




Fig. 79. — Forming a Silicate Grinding Wheel. 

Wire Web Wheel. In an effort to protect the worker in case of 
breakage while grinding, Hart 6 devised an abrasive wheel containing 
a wire web. This was widely used, and for fifteen years was the best 
grinding wheel on the American market, and saved a great many acci- 
dents before modern protective shields and grinding methods had been 
developed. The silicate made possible a low-temperature bond which 

6 Ransome, Frederick, Brit. Pat. 505 (Feb. 27, 1861); Report of the British 
Association for the Advancement of Science, 42, 248-249 (1872) : /. Soc. Arts, 7, 
593-595 (1859). 

6 Hart, U. S. Pat. 201,778 (March 26, 1878). 



174 



SOLUBLE SILICATES IN INDUSTRY 



allowed the insertion of a strong brass wire in the stone. This process 
is essentially the making of a silicate cement which sets by drying, 
although small amounts of reacting materials are usually added to 
abrasive wheel mixtures. The reactions have not been fully studied 
and are not adequately understood. Pulpstones and refractory masses 
are made from sand or clay and silicate solutions at temperatures of 
incipient fusion. 7 ' 8 




Fig. 80. — Silicate Wheels Ready to Be Baked. 

Method for Making Abrasive Wheels. 9 ' 10 A typical formula for 
making a grinding wheel by the silicate process might call for 100 
pounds of 20 mesh aluminous abrasive grain and 12.5 pounds of a 
finely powdered clay or silica. The binder consists of 12.5 pounds 
of 59.1° (commonly called 60°) Baume silicate of soda, specific gravity 
1.688 and composition Na 2 0,2Si0 2 . This is a very viscous solution, 
about 79.5 poises, and it does not at first appear possible to work 
the ingredients into a uniform condition. A slow moving power mixer 

v See also Barron, W. S. and G. S., Brit. Pat. 123,377 (Feb. 18, 1919). 

"Greenwood, W. W., Paper, 35, No. 17, 12 (1925). 

9 Anon., Abrasive ind., 6, No. 6, 191 (1925). 

10 Iding, Mathew, and Wm. A. Nimtz, U. S. Pat. 1,635,675 (July 12, 1927). 



SILICATE CEMENTS 



175 



is used, the abrasive is put in, and the powdered clay weighed and 
spread out on the weighing vessel. The silicate is then weighed on 
to the powder which prevents it from sticking to the container, and 
silicate and powder are slid together into the mixer. Without some 
such device, it is difficult to weigh with accuracy sufficient to control 
the grade of hardness desired in the wheel. After thorough mixing, 
each abrasive grain is covered with a sticky layer of silicate ; and the 
mass is in condition to be tamped or pressed into molds, a matter re- 
quiring a considerable degree of skill to produce a uniform texture. 




Fig. 81. — Silicate-Bonded Abrasive Wheels. 

A process of air-drying at temperatures below 100°C. follows until 
the mass has set up sufficiently rigid to avoid danger of distortion, 
and the final step is a baking process at 180° to 260° C. until the wheel 
has thoroughly hardened. This is the most convenient method of 
making large grinding wheels and has the advantage that the entire 
operation can be carried through quickly. A 12" X 2" wheel can be 
mixed, dried, baked, and put into service in 12 hours, though longer 
time is needed for large wheels. In any case, the time is much less 
than that needed to form a ceramic bond. 

Wheels for grinding cutlery and for operations requiring a smooth 
finish are generally made with a silicate bond. Many wheels for glass 
cutting are also made by this process. As these wheels are required to 
run wet, the question of adequate water-resistance is important. A small 



176 



SOLUBLE SILICATES IN INDUSTRY 



quantity of zinc oxide is usually added to the mixture for such wheels 
and it probably reacts to form an insoluble zinc silicate, but the amount 
used is less than the equivalent of the Na 2 in the silicate, and a con- 
siderable degree of water-resistance is secured without it. Perhaps 
when clay is used there is some formation of sodium aluminum sili- 
cate, such as analcite and feldspar; but if the subject has been investi- 
gated the results have not been published. 

Tensile Strengths. The tensile strength of abrasive wheel bonds 
goes above 2000 pounds per square inch. Strength and water-resistance 
vary, with conditions which have not been fully explained. A series 




4- 6 

lime in We eks 



Fig. 82. — Tensile Strengths of Briquets. 

of briquets from a mixture made with silicates of identical com- 
position but by different processes of preparation gave, on alternate 
soaking and draining for 12-hour periods, the tensile strengths shown 
in Table 65. Every effort to distinguish the silicates by chemical 
means has thus far failed. The analyses of four samples, designated A, 
B, C, and D, are given below. 



SILICATE CEMENTS 



177 



Table 64. Composition of Briquets. 

ABC 

Per cent A1 2 3 0.22 0.29 0.21 

" " Fe 2 3 0.18 0.18 0.17 

" " CaO None None None 

" " MgO None None None 

" " CI 0.07 0.07 0.09 

" " S0 3 0.02 0.02 0.02 

" " H 2 45.83 45.83 45.31 

" " Si0 2 35.58 35.50 36.29 

" " Na 3 18.08 18.08 18.20 

Table 65. Tensile Strength of Briquets. 

ABC 

Dry 1542 1753 1520 

1st week 1237 2109 1376 

2nd " 1598 2223 

3rd " 822 1938 1696 

4th " 876 1847 767 

5th " 1107 2064 1332 

6th " 955 1368 1136 

7th " 722 1415 1271 

8th " 852 1577 981 

9th " 1378 



D 

0.28 

0.14 

None 

None 

0.09 

Trace 

45.75 

36.92 

17.66 



D 

1926 
2234 
2121 
1874 
1967 
1961 
1969 
2049 
2237 
1950 



Variation from the Above Formula. Attempts to use silicates 
of higher and lower relative alkalinity in this process have had little 
success. Strong wheels which are too soluble can be made with higher 
alkalinities. Silicate of the type Na 2 0, 3.3SiO s , though it gives wheels 
of good strength and grinding properties under conditions of partial 
dehydration, yields a very weak body when all the water is driven off 
unless the temperature is raised to a point where sintering begins, when 
the bond is brittle. 

Urtel lx proposes to make a more water-resistant, though rather 
brittle wheel, from a mixture similar to the one described above, by 
firing to 850° to 1100° C. 12 

The limiting factor in making a hard silicate wheel is the amount 
of silicate which can be introduced. 13 ' 14 The formula given above 
is about the maximum to keep a consistency such that the grains slide 
over each other enough to form a dense body and at the same time 
prevent the liquid from flowing from one part of the body to another 
while the wheel is in process. This situation has been met in some 

11 Urtel, Henry, U. S. Pat. 1,243,783 (Oct. 23, 1917). 

"Tilton, Clarence B., and Milton F. Beecher, U. S. Pat. 1,555,086 (Sept. 29, 
1925). 

"Martin, Harry C, U. S. Pat. 1,310,360 (July 15, 1919). 
"Power, Henry Robert, U. S. Pat. 1,310,292 (July 15, 1919). 



178 SOLUBLE SILICATES IN INDUSTRY 

cases by adding powdered dry silicates which dissolve before the water 
is driven from the wheel. 15 ' 1G 

Solid anhydrous silicate in powdered form, whether the ratio be 
that of the alkaline silicate, as the 1 : 2 ratio is called in the trade, or 
a ratio of 1:3 can be slowly hydrated by keeping the moist molded 
mass warm before drying. 17 Any attempt to make stronger or harder 
wheels by putting in more silicate as a solution is unsatisfactory be- 
cause the mass becomes too fluid, the liquid portion tending to leave 
the upper surfaces and accumulate near the bottom. It is obvious that 
irregularities in the hardness of the grinding stone constitute a fatal 
objection. 

Silicon Carbide. All the aluminous abrasives are easily bound by 
the silicate process, but silicon carbide reacts with some alkaline solu- 
tions with the liberation of hydrogen according to the equation : 
SiC + 4NaOH + 2H 2 = Na 2 Si0 3 + Na 2 C0 3 + 4H 2 . Other reac- 
tions yielding hydrogen take place between caustic alkali and metallic 
aluminum or the element silicon which may be present in carbide abra- 
sives. Soluble silicates in solution produce a reaction which, though 
much less vigorous than the action of caustic alkali, and soon inhibited 
by the deposition of a silicious film, is sufficient to release appreciable 
quantities of hydrogen. This gas liberated at the interface between 
abrasive grain and silicate solution is extremely detrimental to the bond. 
The evolution of gas can be brought under control by use of an oxidiz- 
ing agent in the silicate solution. For this purpose permanganates have 
been found most convenient. 18 ' 19 

Another method which can be used to reduce the evolution of hy- 
drogen consists of giving the abrasive grains a preliminary treatment 
with warm dilute sodium hydroxide or sodium silicate and washing. 
This seems to render the surface less active and allows the silicate to 
wet the grains sufficiently to form a firm bond. 20 It is advantageous 
also for aluminous abrasives. 21 

Briquets. 

Briquetting of fine iron ore, such as pyrite cinder, and carbonaceous 
materials, has been undertaken with the aid of silicate binders. Strong, 

15 Johanson, Pehr, and Clarence B. Tilton, U. S. Pat. 1,555,119 (Sept. 29, 
1925). 

"Keever, Paul, U. S. Pat. 1,548,145 (Aug. 4, 1925). 

17 Henkel & Cie., Ger. Pat. 215,328 (March 27, 1924). 

18 Vail, James G., and John D. Carter, U. S. Pat. 1,139,739 (May 18, 1915). 

19 Vail, James G., Abrasive hid,, 2, 393-394 (1921). 

20 Stowell, Edward R., U. S. Pat. 1,327,448 (Jan. 6, 1920). 

21 Anderson, Harry O., U. S. Pat. 1,400,495 (Dec. 13, 1921). 



SILICATE CEMENTS 179 

hard products can be made with 5 to 10 per cent of 40 per cent solu- 
tions of the more silicious silicates; but the conditions which give 
satisfactory water-resistance together with sufficient economy and the 
desired slagging properties appear not to have been worked out. The 
silicate bond for coal briquets has the advantages of economy, smoke- 
less burning, and holding the form of the briquet in the fire, and is 
worth further study, 22 ' 23 

Modification of Properties. 

It is fairly obvious that any of the cements which depend on the 
drying of the silicate solutions for setting may be modified by sub- 
stances which alter the behavior of the silicate. Thus glycerin, by 
retarding the drying, is sometimes useful. Dextrin in like manner im- 
parts its own characteristics to mixtures. Commercial glucose syrup 
works well in the cold but gels on heating; sugar can be mixed freely 
with silicate solutions and increases slightly their flexibility. Many 
highly hydrolized products, such as the adhesive by-product of the 
manufacture of furfural from corn cobs or that recovered from waste 
sulfite liquors, may find use for special purposes. The latter must be 
neutralized with sodium hydroxide to avoid precipitation of the 
silica. The same is true of most vegetable tanning extracts. Rub- 
ber latex which has been stabilized with ammonia mixes smoothly 
with the silicious silicate solutions and increases resistance to water 
and flexibility. Shellac can be dissolved in silicate to modify the char- 
acter of a cement, and other inert materials can readily be thought of 
which may at times be of use, whether the silicate is to be applied as 
cement, adhesive or protective film. 

Accelerated Setting. 

Treating the exposed cement surfaces with strong sulfuric acid soon 
after the bricks have been placed in position is frequently recom- 
mended, in order to cause immediate setting of silicate cements used in 
acid-proof brick construction. This practice is not consistent with the 
maximum ultimate strength. The acid causes the gelation of the dis- 
solved silica. If this takes place in the presence of much water the 
result is a soft gel which contracts on drying and has little bonding 
power. When drying precedes contact with acid the gel is much 
stronger and shrinks less, though it never equals the tenacity of the 
dried silicate solution. Briquets of the first mentioned series, which 
tested 788 pounds per square inch tensile strength, air-dried, were 

M Taggart, William P., U. S. Pat. 1,396,603 (Nov. 8, 1921). 
"Collins, William Frederick, U. S. Pat. 445,568 (July 27, 1908). 



180 



SOLUBLE SILICATES IN INDUSTRY 



soaked for two days in 60°Baume sulfuric acid, then washed in run- 
ning water until methyl orange showed no further acidity. They were 
then taken out and dried in the air at 49° C. The tensile strength was 
273 pounds. A mass was thus obtained consisting only of silica in 
various states of hydration which had been formed at atmospheric 
temperatures and had a strength equal to a fair 1-2-4 concrete. 



Acid-Proof Cements. 

Glover and Gay-Lussac Towers. The technic of building acid- 
resisting structures with cements of this type involves not only proper 




Fig. 83.- 



-The Effect of Building too Rapidly— Cement Squeezed Out by Load 
Applied before It Was Sufficiently Set. 



mixtures but care in laying them. Walls must not be built at such 
a rate that the cement does not set fast enough to resist the load. The 
illustration of a Gay-Lussac tower wall from which the unset cement 
was squeezed shows the result of too rapid building. Joints should not 



SILICATE CEMENTS 



181 



be thicker than 1/8 inch if possible. Corners should also be braced 
with wooden forms 24 ' 25> 2G until the cement has hardened. The illus- 
trations show construction of this sort which has saved large invest- 
ment for lead in chamber-acid plants. In tower and tunnel concen- 
trators it is good practice to use temperatures above the melting point 
of lead. 

Various clays have been used instead of silica in cements of this 
character ; but so long as they are chemically inert toward the silicate, 
their usefulness depends upon insolubility in the acid and upon their 
fitness to yield a mass of maximum density and mechanical strength. 
Glover and Gay-Lussac towers and even whole chamber systems have 
been built of brick with the aid of this sort of cement and give very 
satisfactory service. 

Tank linings, absorbing towers, linings for lead chamber bottoms, 
equipment for mixing and storing acids, acid house floors and molded 
articles are made with the aid of silicate cements. 27 

Fillers. Other materials which have been recommended for sulfuric 
acid-resisting cements, such as barium sulfate, asbestos, talc, et cetera, 
do not seem to give better results than pure silica. 28 Carter 29 found 
that barium sulfate is somewhat harmful when sulfuric acid is to be 
retained and may lead to prompt failure with nitric or hydrochloric 
acid. Of several mixtures used, he found that containing powdered 
quartz or sand of suitable sizes bound with silicate of ratio 1 : 3.92 
and diluted to 34° Baume to be the most satisfactory.* 

Table 66. Resistance of Silicate Cements to Acids. 



Mixtures 

100 parts powdered silica, 

100 mesh 
50 parts Na 2 0, 3.96Si0 2 



Ground Quartz Rock 

340 parts 20-100 mesh 
220 parts 100 mesh and 
finer 

146 parts Na 2 0, 3.3Si0 2 



Treatment 
Cone. H2SO4 
Dil. H 2 SC>4 
Cone. HC1 
Dil. HC1 
Cone. HNO3 
Dil. HNO3 

Cone. H 2 S0 4 

Dil. H 2 S0 4 
Cone. HC1 
Dil. HC1 
Cone. HNO3 
Dil. HNOs 



Results 
Still hard after 11 months in acid. 



Hard after 5 months. Softened 

on edges. 
Still hard after 11 months. 
Little soft on edges after 5 months. 
Still hard after 11 months. 



'Catalog of Maurice A. Knight, Akron, Ohio, p. 17. 
'Chem. Ztg., 47, 504 (1923) ; C. A., 17, 3083. 

Clark, T. S., hid. Eng. Chem., 15, 227-230 (1923). 
r Windsor-Richards, W. E., Brit. Pat. 153,047 (June 24, 1919) 
'Bassett, Harry P., U. S. Pat. 1,390,327 (Sept. 13, 1921). 
' From the records of the Philadelphia Quartz Company. 

Cf. page 195. 



182 



SOLUBLE SILICATES IN INDUSTRY 



Table 66. Resistance of Silicate Cements to Acids — (Continued), 



Mixtures 

750 parts sand 

(Fox River, 111.) 
250 parts kaolin 
270 parts Na 2 0, 3.3SiQ 2 



500 parts sand 
50 parts BaS0 4 
137 parts Na 2 0, 3.3Si0 2 



500 parts sand 

100 parts talc 

150 parts Na 2 Q, 3.3SiQ 2 



500 parts sand 
50 parts litharge 
185 parts Na 2 0, 3.3Si0 2 

600 parts sand 

200 parts powdered mica 

240 parts Na 2 Q, 3.3Si0 2 



600 parts sand 
200 parts fluorspar 

242 parts Na 2 0, 3.3Si0 2 



600 parts sand 
60 parts blown petroleum 
pitch, asphalt base 



650 parts anhydrous 

Na 2 0, 3.3Si0 2 
230 parts Na 2 Q, 3.3Si0 2 



Treatment 

Cone. H 2 S0 4 

Dil. H 2 S0 4 

Cone. HC1 

Dil. HC1 

Cone. HN0 3 

Dil. HNO3 

Cone. H2SO4 

Dil. H 2 S0 4 

Cone. HC1 

Dil. HC1 

Cone. HN0 3 

Dil. HN0 3 



Cone. 

Dil. 

Cone. 

Dil. 

Cone. 

Dil. 



H 2 SO< 

H 2 S0 4 

HC1 

HC1 

HNO3 

HNO3 



Cone. H 2 S0 4 
Cone. HC1 



Cone. H 2 S0 4 
Dil. H 2 SC»4 
Cone. HC1 

Dil. HC1 
Cone. HNO3 
Dil. HNOs 

Cone. H2SO4 
Dil. H 2 S0 4 

Cone. HC1 
Dil. HC1 

Cone. HNO3 
Dil. HNO3 



Cone. H2SO4 
Dil. H 2 SC>4 
Cone. HC1 
Dil. HC1 
Cone. HNO3 
Dil. HN0 3 

Cone. H 2 S0 4 

Dil. H 2 S0 4 

Cone. HC1 

Dil. HC1 

Cone. HNO3 

Dil. HNO3 



Results 
Much cracked in 2 months. 
Still hard after 11 months. 



Softened on edges in 5 months. 

It (t it H (( U 

Disintegrated after 1 day. 
Softened on edges in 5 months. 
Much softened on edges in 7 days. 
Softened on edges in 5 months. 

Weak and much cracked in 4 days. 
Still hard after 11 months. 

A little softened after 11 months. 
Still hard after 11 months. 
Softened, somewhat, after 1 1 
months. 

Very weak in 1 day. 
Broke up in a few minutes. 



Very weak and cracked in 1 day. 
Much softened in 5 months. 
Much softened on edges in 5 

months. 
Softened in 11 months. 
Much softened on edges in 7 days. 
Softened in 11 months. 

Much softened on edges in 1 day. 
Somewhat softened on edges in 11 

months. 
Much softened on edges in 4 days. 
Much softened on edges in 5 

months. 
Much softened on edges in 7 days. 
Much softened on edges in 5 

months. 

Completely disintegrated in 1 day. 
Softened on edges in 5 months. 
Completely disintegrated in 1 day. 
Softened in 11 months. 
Much weakened in 1 day. 
Softened in 5 months. 

Much disintegrated in 4 days 

Weakened in 5 months. 

Much disintegrated in 1 day. 

Weakened in 5 months. 

Much weakened and broken in 4 

days. 
Weakened in 5 months. 



SILICATE CEMENTS 183 

Temperature Relations. 

High Temperature Cements. Cements which are serviceable at 
higher temperatures than those used for abrasive wheels, but which 
are required to assume a rigid consistency at atmospheric tempera- 
tures, are made from various silicate solutions according to the specific 
properties desired. 30 ' 31 - 32 Cements which set in the air to form a bond 
between glass pieces having a tensile strength of about 1,000 pounds 
per square inch and at the same time capable of withstanding practically 
without deformation a temperature of 1,100° C, may be made from 
chromite and soluble silicate either in liquid form or as hydrous readily 
soluble powder. 33 Clapp 34 adds finely divided ferro silicon. 

Various clay refractories mixed with silicate solutions yield gas- 
tight cements for chemical apparatus, boiler settings, blast furnace 
stoves, coke oven refractories, flues, regenerator casings for open-hearth 
furnaces, and other high-temperature work, 35 ' 36 ' 3r - 38, 39, 40 the efficiency 
of which is improved by making refractory walls impermeable to gases 
either by coating the surfaces of the brick to make a glaze under heat 
or setting them in a cement which will vitrify. 41 Howe 42 determined 
the effect of various additions to a plastic refractory clay of the follow- 
ing composition : 

Table 67. Analysis of Plastic Fire Clay Used. 

Loss on ignition 11.12% 

Silica 56.42 

Alumina 28.46 

Ferric oxide 3.12 

Lime 0.52 

Magnesia 0.44 

Alkalies 0.24 

Fusion point, Cone 30. 

100.32 

30 Willetts, Paul G., U. S. Pat. 1,573,888 (Feb. 23, 1926). 
31 Youngman, Robert H., U. S. Pat. 1,564,394 (Dec. 8, 1925). 
M Youngman, Robert H., Brit. Pat. 250,480 (Oct. 24, 1925); C. A., 21, 1172. 
33 Rochow, William, U. S. Pat. 1,576,550 (March 16, 1926); U. S. Pat. 
1,606,481 (Nov. 9, 1926). 

34 Clapp, Harrv Baker, U. S. Pat. 1,437,584 (Dec. 12, 1922). 

35 For example, Bassett, Harry P., loc. cit. and U. S. Pat. 1,390,328 (Sept. 
13, 1921). 

38 'Meyer, Albert, U. S. Pat. 1,483,468 (Feb. 12, 1924). 
37 Wolcott, E. R., U. S. Pat. 1,617,696 (Feb. 15, 1927). 
38 Reynolds, R. W., U. S. Pat. 1,422,130 (July 11, 1922). 
39 0'Hara, C. M, U. S. Pat. 148,972 (Aug. 9, 1873). 

40 Fulcher, G. S., Can. Pat. 248,315 (March 31, 1925) ; Ceram. Abstracts, 4, 347. 
41 Holley, Earl, U. S. Pat. 235,505 (June 18, 1925). 

42 Howe, Raymond M., "The Necessity for Care in the Preparation and Use 
of Fire Clay Mortar," Refractories Manufacturers Association, 1920. 



184 



SOLUBLE SILICATES IN INDUSTRY 



It is surprising to observe that the effect of sodium silicate is much 
less than other additions tried. Unfortunately, the exact composition 
of the silicate is not available. 






.1! 



30 



25 




^f 3 ^ 



20 



ts 



/a 



\* 






*'"•,' -^-ftf testis 



\ 



\ 



Sl\ 



*"^z;. 



s„/r 



Car6orunJtr*» 



M 



f **Q£~. 



/s 



so 



2f 



30 



3S 



Fig. 



Per Cent tf /ar/ous ftfafer/a/s /WeS fa f/rtcfc/ 

84. — Effect on the Melting Temperatures of Additions to Fire Clay. 



The temperature which any clay will resist is doubtless reduced by 
mixing it with a silicate solution, but if this is done with regard to the 
conditions to be met, many useful cements can be made and built into 
refractory walls which stand temperatures much above the melting 
temperature of the cement by itself. As the silicate penetrates the 
refractory it becomes associated with larger and larger quantities of 
clay so that in practice higher temperatures are resisted than would 
be found by examination of the cements alone. It is probably unwise 
to use silicate cements where refractory bricks are to be used close to 
their melting temperatures, but a great many linings are used where 
the temperature is safely below the limit of the brick and here the ad- 
vantages of the silicate cements are great. 43 ' 44 ' 45 Cements for set- 
ting refractories in iron stoves are chosen rather for their plasticity and 
freedom from shrinkage than in consideration of their melting tem- 
peratures because even those cements which are made with the slow 

43 Societe Generate des Nitrures, Brit. Pat. 1961 (June 20, 1912). 

"Jones, D., and W. Emery, Gas L, 163, 157-159 (1923) ; Gas World, 78, 646. 

"Wakem, F. J, hid. Eng. Chem., 15, 893-894 (1923). 



SILICATE CEMENTS 



185 



setting alkaline silicates are sufficiently refractory to stand the condi- 
tions of a house heating furnace. 

Meloche 46 has elaborated a technic for protecting and repairing re- 
fractory surfaces by coating them with silicate-clay mixtures and caus- 
ing thin layers to vitrify with the aid of a blow torch. 47 

Silicate solutions and clay are used to repair the saggers or earthen 
cases in which pottery is burned. The picture shows pieces of such 
ware which have been broken at other places than the mended joint. 




Fig. 85. — Saggers Repaired with Silicate Cement. 

It may be recognized that the three pieces represent top, side, and bot- 
tom of the sagger. Where the breaks are simple it is cheaper to repair 
them with cement than to grind the broken sagger and make the body 
into new ware which must be burned before use. A satisfactory formula 
for this purpose is 

Na 2 0, 2.5Si0 2 at 45° Baume mixed to the consistency of thick cream 
with kaolin. 

Drying. The temperature at which a silicate cement is to be used 
will affect the choice of the type of silicate. The set which results 
from loss of moisture will reach a maximum and decline before all 
the water has been expelled by rising temperature. Cements made 
from viscous silicates are subject to intumescence or swelling when 
heated suddenly, and even with gradual heating this is likely to occur 

48 U. S. Pat. 1,534,237 (April 21, 1925). 

47 Moldenke, Richard, Chem. & Met. Eng., 29, 231-232 (1923). 



186 



SOLUBLE SILICATES IN INDUSTRY 



at about 500° C. if the body is not sufficiently porous to allow the water 
to escape quietly. After the water has been completely driven off, 
strong bonds may be formed by the sintering of the soluble silicate 
with or without reaction between it and the filler. The different effects 
of ascending temperature on three silicates are indicated, by the chart. 
All tests were made after the briquets had cooled. The most alkaline 



6So 

V 

\SS0 

<u 

V. 

\ 

«•> 
































































/so 
so 























Fig. 



■+O0 too SCO 

Decrees Cent/grade 

-Effect of Rising Temperature on Strength of Briquets Containing 100 

Parts Calcined Fire Clay and 33.3 Parts Silicate Solution. 



of the three ratios examined is used particularly for refractory linings, 
where the practice is to apply a preliminary drying treatment below 
500° C. and to effect the heating above the sintering temperature rapidly 
to form a ceramic bond. This behavior was recognized by Tone, 48 

48 U. S. Pat. 1,042,844 (October 29, 1912). 



SILICATE CEMENTS 



187 



who reported that the maximum strength of the silicate developed be- 
tween 204° and 315°C. He thus produced a lining which was bonded 
by sintered clay at the hottest parts of the furnace and was yet satis- 
factorily strong at the cooler points. Smaller amounts of silicate than 
those used in the preceding experiments may account for a small shift 
in the temperature giving maximum strength. 

Kaolin Cements. 

Spark Plugs. Staley 49 investigated a series of soluble silicate mix- 
tures with silica, aluminum oxide, barium sulfate, and kaolin, raw and 
calcined, for cements to be used in making a gas-tight joint between 
a metallic electrode and a porcelain spark plug body. Only one type 
of silicate solution, Na 2 0, 3.3Si0 2 , was used; but the temperatures se- 



Table 68. Effect of Cements on Electrode Wires. 



' Sodium 
Silicate 

40° 
Baume Water 
Cubic Cubic 
Cement Centi- Centi- Solid 

No. meters meters Grams Kind 

1 5 5 30 Powdered 

silica 



10 



5 
10 



10 



30 

30 

30 

30 
30 

(15 

U 

(15 
\15 



Powdered 
silica 



Barium 
sulfate 



Barium 
sulfate 



Kaolin 

Kaolin 

Kaolin 

Aluminum 

oxide 

Kaolin 

Aluminum 

oxide 



Effect of Heating to 1000° C. 

Oxidation Description 

Very bad Hard, strong, slightly 
porous; part of ma- 
terial had run down 
the wire. 

Very bad Hard, strong, slightly 
porous ; part of ma- 
terial had run down 
the wire. 

Eaten Part of material had 

through melted and run down 
wire, leaving a hard 
blue mass behind. 

Eaten Part of material had 

through melted and run down 
wire, leaving a hard 
blue mass behind. 

None Hard, strong, slightly 

porous. 

None Hard, strong, not po- 

rous. 

Very bad Soft, weak, porous 



Soft, weak, 
very bad. 



porous, 



Bur. Standards Tech. Paper, 155 (1920) 



188 SOLUBLE SILICATES IN INDUSTRY 

lected, 500° and 1000° C, give rise to reactions which do not take place 
at atmospheric temperatures. Pellets of the various cement mixtures 
were dried on a nickel alloy electrode wire and heated in an oxidiz- 
ing atmosphere. The superiority of the raw kaolin mixture as shown 
by the table was evidently due to its ability to wet the surface of the 
wire and then to coat it with a substance which was dense and suffi- 
ciently viscous at all stages of the heating process to remain in place. 

In contrast to the dense viscous coating made with raw kaolin, the 
particles of which are very small, barium sulfate yielded a heterogeneous 
body which liberated sodium sulfate. This coating is thinly fluid at 
1000° C. and oxidation proceeded rapidly. 50 

Silicate and silica afforded poor protection because the mixtures were 
too fluid at the maximum temperature. 

Staley attributed the porosity of cements containing aluminum oxide 
or calcined kaolin to reaction with the silicate in the cold. It would 
have been interesting had the work been extended to other types of 
silicate solutions and to different physical conditions of the filling ma- 
terials. 

Silicate Cements in Case Hardening. Silicate cements applied 
to steel surfaces to keep certain portions soft during case hardening 
were studied by Wood and McMullan. 51 Presumably a silicate similar 
to that used by Staley was employed. These workers found it possible 
to secure better protection with asbestos and sodium silicate or with 
aluminum oxide and sodium silicate than with any mixture involving 
kaolin. The exposures were, of course, different, but it would appear 
that in each case an impermeable viscous layer is needed, and one 
wonders why the kaolin mixture permitted the passage of carbon but 
resisted oxygen, while with aluminum oxide the relation was reversed. 
Many silicate glasses disperse carbon and become highly colored, as 
the glass maker often finds to his sorrow, and the special action of 
the kaolin coating toward carbon may account for its unfitness as a 
protection against case hardening. In this connection it may be worth 
while to note the fact that highly aluminous bricks in a glass furnace 
usually burn to a dark chocolate color, while more silicious types re- 
main light colored when exposed to the same atmosphere. 

Wood concluded that finely ground asbestos and silicate solution (be- 
lieved to be 40°Baume Na 2 0, 3.3Si0 2 ) gave perfect protection at 950° 
and 995 °C. in layers 1 mm. thick when the percentage of silicate was 

^Seger, Herman A., "Collected Writings," 2, Easton, Pa.; Chemical Pub- 
lishing Co., 636. 

"Chem. & Met. Eng., 26, No. 23, 1077 (1922). 



SILICATE CEMENTS 189 

67 or more, and that mixtures with aluminum oxide were also good 
but had to be used in somewhat thicker layers. The removal of these 
adherent hard coatings proved to be a problem. Quenching, a number 
of times if necessary, was satisfactory in most cases. The coatings 
were also broken down and loosened by clipping in molten caustic 
soda or by heating in molten calcium chloride, followed in each case 
by immersion in water. The coatings were not found to prevent de- 
carburizing or absorption of carbon. It may well be that the kaolin 
mixture would be the more useful, as from Staley's work it appears 
to afford better protection against oxygen. There is an excellent 
bibliography attached to Wood's article. Other mixtures have been 
tried by various investigators. 52 ' 53 - 54 

Copper plating is a satisfactory method of locally preventing case 
hardening by carburization and it has been proposed to use finely divided 
copper in a silicate cement. 55 ' 56 The results are not known to be better 
than a suitable silicate mixture with the less costly clays. 

Casting Metals. 

The art of casting metals has frequent use for the binding properties 
of soluble silicates to form molds or to increase the resistance of those 
parts of sand molds most likely to be eroded or deformed by the flowing 
of hot metal. 57 The amount of silicate to mix with molding sand must 
be chosen with regard to the porosity desired, to permit the escape of 
gases, and to its property of not burning out when heated, as organic 
binders do,. Sand molds have also been coated with metals, such as 
chromium, comminuted and mixed with silicate which holds them in 
place until they can alloy with the metal cast into the mold, giving it a 
specially resistant surface. 58 Permanent metal molds for automatic 
casting machines have been made by lining cast iron molds with mix- 
tures of silicates and refractory clays. Meloche prevents the metal 
from sticking to the silicate cement by applying a smoky flame after 
each casting operation. 59 ' G0 

52 Dickens, E. J., Brit. Pat. 185,564 (Sept. 14, 1922). 
53 Bickley, A., U. S. Pat. 1,432,523 (Oct. 17, 1922). 
"Whyte, Samuel, U. S. Pat. 1,366,305 (Jan. 18, 1921). 
65 Gailbourg and Ballay, Rev. Metal., 19, 222-226 (1922). 
59 For example: Whinfrey, Charles G., U. S. Pat. 1,567,632 (Dec. 29, 1925). 
67 Wilhelmy, Odin, U. S. Pat. 1,544,710 (July 7, 1925). 
68 Mitchell, Walter M., U. S. Pat. 1,545,438 (Sept. 24, 1924). 
59 Meloche, D. H., U. S. Pat. 1,453,593 (May 1, 1923); U. S. Pat. 1,506,130 
(Aug. 26, 1924). 

^Udale, Stanley M., U. S. Pat. 1,505,176 (Aug. 19, 1924). 



190 SOLUBLE SILICATES IN INDUSTRY 

Molded Articles. 

Silicate has been mixed with many kinds of fibrous materials to form 
plastic masses. 01 ' G2 ' C3 ' ° 4 ' G5 The process of Lowe for making molded 
articles for heels of shoes and like materials by mixing filaments of oak- 
wood with a silicate solution, pressing into molds and drying, may be 
taken as typical. 66 Fibrous materials with silicate for making molded 
articles require a neat adjustment between concentration and alkalinity 
of the silicate on one hand, and pressure on the other, if dense articles 
which can be quickly formed and will not crack on drying are to result. 
Cotton stalks, sawdust, residual fiber from the process of making 
furfural from corn cobs and many others have been investigated. 67 ' 68 
In molding ceramic materials, silicate is frequently employed as the 
binder. 69 

Miscellaneous Cements. 

For Insulation. Cements of essentially similar composition have 
been used for various insulating purposes, 70 ' 71 ' 72 ' 73, 74 ' 75 such as cover- 
ing the coils of resistance heaters to keep them spaced. Silicate and 
powdered fused aluminum oxide give good results as long as they re- 
main dry. Soapstone and powdered silica have also yielded cements 
useful at low temperatures, 70, though where oxidation is a factor the 
kaolin cement is preferable. If these cements are exposed for extended 
periods to a humid atmosphere, their electrical resistance is reduced but 
can be readily restored by drying. The effect of moisture is somewhat 
reduced by mixing the silicate with an ammoniacal solution of shellac 
or gum solutions. 77 ' 78 ' 79 

61 Haas, Nelson R., U. S. Pat. 1,618,875 (Feb. 22, 1927). 

82 Ritchie, J. A., Brit. Pat. 229,092 (Feb. 15, 1924); Ceram. Abstracts, 8, 331 
(1925). 

63 Wheeler, James A., U. S. Pat. 539,928 (May 28, 1895) ; U. S. Pat. 625,372 
(May 23, 1899). 

"Naylor, Isaac, U. S. Pat. 1,573,734 (Feb. 16, 1926). 

65 Bartlett, Francis A., U. S. Pat. 1,484,370 (Feb. 19, 1924). 

6a Lowe, U. S. Pat. 1,532,908 (April 7, 1925). 

6T Stryker, G. B., and Frank A. Mantel, U. S. Pat. 1,436,061 (Nov. 21, 1922). 

68 Stowell, E. R., U. S. Pat. 1,524,676 (Feb. 3, 1925). 

68 Berry, E. R., U. S. Pat. 1,131,463 (March 9, 1915). 

70 Gerloch, Oscar, U. S. Pat. 1,468,149 (Sept. 18, 1923). 

71 Slepian, Joseph, U. S. Pat. 1,638,888 (Aug. 16, 1927). 

73 Cook, Frank J., U. S. Pat. 1,393,346 (Oct. 11, 1921). 

73 Stowell, E. R., U. S. Pat. 1,382,329 (July 14, 1921). 

74 Covell, Bradford S., U. S. Pat. 1,610,203 (Dec. 7, 1926). 

"Meloche, Daniel PL, U. S. Pat. 1,505,215 (Aug. 19, 1924) ; Brit. Pat. 235,503. 

76 Menuez, Anthony E., U. S. Pat. 438,698 (Feb. 24, 1890). 

77 Barringer, L. E., U. S. Pat. 1,423,985 (July 25, 1922). 

78 Grote, L., U. S. Pat. 789,607 (May 9, 1905). 

79 Norman, J. T., U. S. Pat. 949,493 (Feb. 15, 1910). 



SILICATE CEMENTS 191 

Carbon Arcs. One of the few cases in which a potassium silicate 
performs a service not to be equaled by a suitable adaptation of sodium 
silicate is as a binder for the carbon pencils used as electrodes in arc 
lamps. Not only is the color of the potassium flame preferred, but a 
longer arc and more efficient illumination are secured in this way. The 
carbon, in a finely divided state, is mixed with a silicate solution of the 
approximate composition K 2 0, 3.25Si0 2 , extruded in a pasty condition, 
and baked for drying. 

Other wares such as slate pencils may be made from appropriate 
mineral powders by mixing them to the consistency of dough and 
extruding them through apertures of the desired form. A firm texture 
is usually secured with less than 10 per cent anhydrous weight of 
Na 2 0, 3.3Si0 2 . If slow setting is desired in this type of mixture, 
Na 2 0,2Si0 2 may be chosen. 

Asbestos Cements — Alignum. Wheeler 80 prepared a structural 
material by preparing a stiff dough from short asbestos fiber with or 
without other mineral matter. This was pressed into form and baked at 
200° to 270° C. to form a hard substance, called Alignum, which could 
be used for doors and trim but which could at the same time be worked 
with wood-cutting tools. Na 2 0, 3.3Si0 2 was used and satisfactory fire 
doors were made, though at somewhat greater cost than steel doors, 
which were commercially perfected at a later time. 

Since this behavior of Alignum S1 is analogous to that of other silicate 
cements, data obtained from tests on this material are of value. 82- s: 

Strength tests were made by supporting slabs on knife edges and 
applying a load at the center. The slabs were afterwards hammered 
with a sledge hammer and found to be tough. 

In order to test the fire-resisting quality of Alignum doors, they were 
subjected to the action of a fire of cord wood, maintained at a tem- 
perature of about 930° C. for one hour. During this time the door 
showed no tendency to warp, and prevented perfectly the escape of 
fire or smoke through or around it. Radiation of heat was at all times 
small, the back of the door remaining comparatively cool. The fire 
was extinguished by a stream of water aimed directly at the red-hot 
door. At the end of the test, the Alignum remained intact. It had not 
warped more than J / 2 inch, and that only in one corner. The door was 
practically as good as new. 

80 U. S. Pat. 539,928 (May 28, 1895). 

81 Catalogue of the Alignum Asbestos Lumber Company, New York, 1908, 
p. 20. 

82 Imschenetzky, A., U. S. Pat. 631,719 (Aug. 22, 1899). 
83 Michell, H. C, U. S. Pat. 774,947 (Nov. 15. 1904). 



192 SOLUBLE SILICATES IN INDUSTRY 

Table 69. Strength Tests of Alignum. 

Test No. 1. 

1" X 8" slab. 

Supports 48" apart. 

Load, Deflection, 

Lbs. Inches 

100 

200 125 

300 500 

.0 

350 75 failed by cracking 

Test No. 2. 

2" X 10" slab. 

Supports 46" apart. 

100 

200 

400 032 

500 032 

600 063 

700 063 

800 094 

900 125 

1000 125 

no set 

1100 157 

1200 157 

1300 188 

1400 188 

1500 313 

no set 

1700 313 

1900 313 

2000 313 

no set 

2500 438 

031 permanent set 

3000 688 

3020 Broke 

Tests on dielectric strength and the resistance of Alignum showed 
that although a fairly good insulator when dry, it absorbed moisture 
readily, thus lowering the dielectric strength and resistance and ren- 
dering the material unreliable. Dielectric strength was measured by a 
gradually increasing A.C. potential applied between electrodes ^4 mcn 
in diameter, with rounded edges, with the following result : on ]/\ inch 
samples, five tests showed the break-down voltages to be 900, 1200, 
1300, and 1500 volts, and on a ^ inch sample, two tests gave values of 
1600 and 1650. 

Specific resistance figures (resistance in ohms of a one centimeter 
cube of the material) are given in table on opposite page. 



SILICATE CEMENTS 193 

Table 70. Electrical Resistance of Alignum. 









Sample 


Sample 








J/4" Thick- 


%" Thick 








Specific 


Specific 




Time 


Temp. 


Resistance 


Resistance 


Oct. 


12, 7 :30 A.M. 


20° C. 


7.73 X 10 7 


3.21 X 10 e 






30 


3.16 X 10 7 


1.20 X 10 6 






60 


9.20 X 10 7 








91 


3.07 X 10 8 








112 


1.00 X 10° 


1.74 X 10 6 




11:55 


140 


1.01 X 10 10 


4.23 X 10 7 




2:13 P.M. 


107 


4.77 X 10 10 


1.50 X 10 9 




3:37 


45 


1.38 X HP 


9.70 X 10 u 




5:00 


30 


1.07 X 10 12 


8.21 X 10 10 


Oct. 


13, 10:00 A.M. 


18 


1.48 X 10" 


2.30 X 10 10 


Oct. 


23, 2:00 P.M. 


25 


6.68 X 10 9 


7.91 X 10 8 



The fibrous character of asbestos 84 ' 85, 8G has caused its frequent in- 
sertion in silicate cement formulas, but because the silicate hardens 
around the individual fibers their yielding character is greatly reduced 
and the mixture is more brittle than might be expected. Exception to 
this is found in cases where the spaces between the fibers are not com- 
pletely filled with silicate solution, but such a cement is apt to be weak. 87 
An interesting use of an asbestos-silicate composition is given by 
Benner. 88 

Asbestos is not wholly inert toward silicate solutions. It is notably 
impossible to determine by analysis alone what ratio of silica to soda 
existed in a silicate from which a cement containing asbestos was made. 
This is also the case when any hydrous, easily soluble, form of silica 
is present. 

Cements Which Set by Chemical Reaction. 
Lime Mortars. 

Gilmore 89 experimented with mortars containing lime, sand, and 
soluble silicate, and in spite of vigorous recommendation by Kuhlmann, 
came to the conclusion that the result is an inevitable loss of strength. 
It has, however, been used for cements in which maximum strength 
was not required. 90 

84 Michell, Henry Colbeck, U. S. Pat. 714,947 (Nov. 15, 1904). 
83 Bartlett, Francis A., U. S. Pat. 1,598,636 (Sept. 7, 1926). 
86 Imschenetzky, Alexander, U. S. Pat. 631,719 (Aug. 22, 1899). 
87 Vorlander and Schilling, Ann., 310, 369 (1900). 

88 Benner, R. C, U. S.Pat. 1,495,568 (May 27, 1924). 

89 Gilmore, Q. A., "Limes and Hydraulic Cements," 4th ed., New York • D 
Van Nostrand Co., 1874, p. 287. 

90 Plenty, J., Brit. Pat. 3,458 (March 11, 1886). 



194 



SOLUBLE SILICATES IN INDUSTRY 



Table 71. Effect of Silicate on Adhesive Strength of Lime Mortar. 
The adhesion to hricks cemented together transversely. 



„ r Lime paste 

For mortar of gand 

Lime paste 
For mortar of Sand 

Soluble glass 



3 L ° 93% lbs. 

S7M lbs. 



1.0 

3.0 
.125 



Table 72. Effect of Silicate on Tensile Strength of Lime Mortar. 

Weight in 





















lbs. 


Supported 


ortar 


Composition 


of Mortar, 


in Volumes 




before Breaking 


1 


.... Lime paste 


1.0 


sand 


2.0 


soluble 


glass, 


.11 




40 


2 


' 


i u 


1.0 


" 


2.0 


" 


" 


.11 




54 


3 




I it 


1.0 


(i 


2.0 










77% 


4 




c it 


1.0 


« 


2.0 










67% 


5 




I it 


1.0 


tt 


3.0 










65 


6.. 




« tt 


1.0 


(< 


3.0 


tt 


(i 


.08 




24% 


7 




I « 


1.0 


<( 


3.0 


a 


t( 


.10 




23 


8 




i It 
« «' 


1.0 
1.0 


<< 

a 


3.0 
3.0 


cement 


paste, 


.125 
.50 




18 


9 




182% 


10 




( it 


1.0 


a 


3.0 


" 


tt 


.33 




166% 


11 




« It 


1.0 


" 


3.0 


a 


a 


.25 




92 


12 




i << 


1.0 


it 


3.0 


tt 


tt 


.166 




94% 



Characteristics. 

When silicate solutions are dried in the presence of inert substances, 
the cement may be regarded as a mass of particles adhesively united; 
and its character must relate quite definitely to the original components. 
In the case of calcium hydroxide another factor enters. The silicate 
tends to precipitate or gel, a rapid rise in viscosity takes place, and a 
quick-setting paste is formed. A great variety of substances react with 
silicate solutions and when the process takes place in a plastic mass the 
same general effect follows ; but it may take place slowly or fast, accord- 
ing to the materials and conditions chosen. 91 It is rarely advisable to 
use enough of the reacting ingredient to decompose the silicate com- 
pletely, so that the great majority of silicate cements are alkaline. 

Setting caused by chemical reaction is usually accompanied by loss 
of ultimate strength and by increase of resistance to water, for silica 
gels are insoluble. Their strength is greatest when they are formed 
in the presence of little water. They are solids, while the soluble silicate 
is liquid even when so viscous as to appear perfectly rigid. A quality 
of toughness inheres in cements in which soluble silicate remains as 
such so long as any water is present. Rock-like masses of hydrated 
silicate show a resilience suggestive of rubber. The rebound of a sledge 
or cutting tool driven into them will amaze the uninitiated. 

91 Behrens, George E. and Josef Veit, U. S. Pat. 1,063,939 (June 3, 1913). 



SILICATE CEMENTS 195 

Addition of Acids and Salts Which React Quickly. 

It has been proposed to improve the character of cements made from 
silica or clay, such as those used to resist acid, by adding small amounts 
of acids or acid salts. Wedge 92 uses sodium bisulfate or nitre cake, 
and Meigs 93 uses chlorides, nitrates, phosphates or sulfates of weak 
bases. Holley and Webb 94 use calcium sulfate or lead carbonate for the 
same purpose. 95 The result is in each case the same, — partial gelation, in- 
creased speed of set, increased resistance to water, and lower ultimate 
strength. Unless time is of extraordinary importance these mixtures 
are inadvisable. 

Calcium Carbonate. 

This criticism does not apply with the same force to substances which 
react slowly. Kuhlmann 96 recommended mixtures of silicate solutions 
with powdered marble for the repair of statuary. Von Fuchs 97 sug- 
gested mixtures of silicate solutions and calcium carbonate for cements. 
Limestone, chalk, marble dust, and precipitated forms of calcium car- 
bonate have been used for making plastic bodies for diverse uses ranging 
from roadways 98, " to fine imitation marble 10 ° for decorative use. It 
remained for Carter, 101 however, to make the observation that reaction 
between silicate solution and calcium carbonate is a function of the 
ratio of sodium oxide to silica in the silicate. Na 2 0, 3.3Si0 2 may be 
mixed to a viscous state with powdered chalk and in a closed container 
the viscosity, a sensitive index of reaction in a silicate solution, remains 
unchanged for days or even weeks. When Na 2 0,2Si0 2 is substituted, 
a rise in viscosity may be noted in a few hours and proceeds steadily 
until the mass becomes solid. This difference explains numerous appar- 
ent contradictions in the literature. Thus Paterson's patent 102 in which 
a road material consisting of calcium carbonate and alkaline silicate is 
described may proceed according to his description and form an in- 

92 U. S. Pat. 1,220,575 (March 27, 1917). 

93 Meigs, Curtis C, U. S.'Pat. 1,237,078 (Aug. 14, 1917); U. S. Pat. 1,252,013 
(Jan. 1, 1918). 

94 Holley, A. E. and H. W. Webb, U. S. Pat. 1,287,995 (Dec. 17, 1918) ; U. S. 
Pat. 1,288,413 (Dec. 17, 1918). 

95 Chance and Hunt, Brit. Pat. 112,966 (July, 1919); Chim. Ltd., 2, 816. 
M Compt. rend., 41, 980-3, 1029-35 (1855). 

97 Dingier s polytech. J., 142, 365-392 (1927) ; Abst. Chew, Zcntr., 28, 86-90. 

98 "Silicate-Macadam Roads," Northwich, England: Brunner, Mond & Co., 
Booklet 271, 1927, p. 6. 

^Lawton, C. F., U. S. Pat. 594,113 (Nov. 23, 1897). 

100 Kallauner, O., Chem. Ztg„ 33, 1174-1175 (1909). 

101 Carter, John D., patent applied for. 

102 U. S." Pat. 1,042,474 (Oct. 29, 1912). 



196 SOLUBLE SILICATES IN INDUSTRY 

soluble mass slowly under the influence of carbon dioxide of the air 
if a silicate of low relative alkalinity (1:3.3) is employed, or more 
rapidly and certainly if the ratio between Na 2 and Si0 2 is 1:2. As 
a practical matter, the former type silicate which Paterson used was 
frequently washed away by rains before any appreciable reaction had 
taken place. The effort to increase the rate or extent of reaction be- 
tween soluble silicates and calcium carbonates 103 ' 104 by adding various 
forms of sugar, which would be expected to help bring the lime into 
solution, have been found not nearly so effective as proper regulation 
of the composition of silicate itself. 

Wall Board. Where conditions permit the application of heat, re- 
action between silicate solution and calcium carbonate may be secured 
in a short time. A wall board consisting of a mixture of finely ground 
calcium carbonate and a silicate solution laid as a plastic mass between 
two layers of paper, and heated at a temperature below that which would 
carbonize the paper, exhibits a very desirable combination of strength 
and light weight, for the cement expands by the liberation of steam into 
an intumescent mass. It compares favorably with gypsum cements, 
which have been widely used in wall boards. 

Roadways. Roadways consisting of coarse stone set in a matrix of 
silicate mortar have been built in many countries. 105 - 106 ' 107 ' 108 Under 
the most favorable conditions they are a great improvement on water- 
bound macadam construction but are not adapted to carry the highest 
concentrations of heavy and fast moving traffic encountered on modern 
trunk highways. 

A typical silicate road may be made from limestone dust mixed with 
Na 2 0, 3.3Si0 2 1.38 specific gravity (40°Baume) at the rate of about 26 
gallons per cubic yard. Enough water is used to make a rather stiff 
grout. This is either laid on the compacted road base, covered with 
two-inch stone and rolled, or mixed with the larger stone before rolling. 

In this way 100 pounds of silicate will bind about 10 square yards 
of road 4 inches thick. Soft limestone is to be preferred because it 
compacts better and it has been found that some of the alkali of the 
silicate penetrates the stone leaving a more silicious layer at the surface, 
which thereby becomes less affected by water. For secondary service 



103 
101 



Butter field, John Cope, U. S. Pat. 808,339 (Dec. 26, 1905). 
Paterson, Edward Alfred, U. S. Pat. 987,597 (March 21, 1911) ; U. S. Pat. 
996,513 (June 27, 1911). 

105 Peter, A., Schweiz. Z. filr Strassenwesen, 12, No. 3, 32 (1926). 

106 Anon., Schweiz. Z. filr Strasseniuesen, 11, No. 24, 303 (1925). 

1OT Caldana and Santambrogio, "Contributo Alia Soluzione del Problema della 
Strada," Milano, 1926. 

108 Gaelle, M., "Revelement des Chaussees" (3rd Note, Paris, 1924). 



SILICATE CEMENTS 197 

these roads have a place, especially in localities where the most suitable 
limestones are available. Except in arid climates, however, it is usually 
impossible to retain a strength of matrix equal to Portland cement 
though this is easily done with a silicate cement which can be kept dry. 1 



09 



Special Cements. 

Great numbers of silicate cements containing fibrous ingredients have 
been proposed for fireproof plastics, insulating compounds, structural 
materials, and the like. 110 " 125 Others that do not contain fibrous materials 
are used for similar purposes and for the protection of surfaces. 126 " 139 

Bituminous Materials. 

Various attempts have been made to combine the advantages of 
bituminous substances with those of silicate cements by emulsifying 
them. 140 ' 141 ' 142 It is possible in this way to produce strong, uniform 

109 Wernekke, Asphalt Tcerind Ztg., 26, 470-471 (1926) ; C. A., 21, 1173. 

110 Keener, Francis M., U. S. Pat. 1,133,380 (Mar. 30, 1915). 

111 Mitchell, Ardon, U. S. Pat. 1,408,760 (Mar. 7, 1922). 

112 Pater, Carl J., U. S. Pat. 1,067,542 (July 15, 1913). 
"'Herbert, Arthur W., U. S. Pat. 1,303,313 (May 13, 1919). 
114 Dunstan, William, U. S. Pat. 1,445,204 (Feb. 13, 1923). 
115 Beadle, George W., U. S. Pat. 1,125,445 (Jan. 19, 1915). 

110 Armstrong, Morgan K., U. S. Pat. 1,076,261 (Oct. 21, 1913). 
117 Oelhafen, John Walter, U. S. Pat. 1,564,706 (Dec. 8, 1925). 
118 Stryker, George B., and Frank A. Mantel, U. S. Pat. 1,436,061 (Nov. 21, 
1922). 

119 Lefebure, Victor, U. S. Pat. 1,650,080 (Nov. 22, 1927). 
120 Lefebure, Victor, Brit. Pat. 268,851 (April 17, 1927). 
m Lennig, Albert M., U. S. Pat. 653,101 (July 3, 1900). 

132 Weintraub-Schnorr, Naum, U. S. Pat. 606,751 (July 5, 1898). 
123 01ney, George, U. S. Pat. 627,008 (June 13, 1899). 
124 Benner, Raymond C, U. S. Pat. 1,573,369 (Feb. 16, 1926). 
^Ffoss, Charles, U. S. Pat. 1,111,021 (Sept. 22, 1914). 
126 Stowell, E. R., U. S. Pat. 819,467 (May 1, 1906). 

127 Willett, Walter E., U. S. Pat. 1,454,780 (May 8, 1923). 
128 Ebbesen, Poulsen Mads, U. S. Pat. 1,570,953 (Jan. 26, 1926). 

129 Suss, Herman M., U. S. Pat. 1,041,526 (Oct. 15, 1912). 

130 Miller, W. E., U. S. Pat. 430,766 (June 24, 1890). 
lsl Gauthier, L., Brit. Pat. 128,905 (May 15, 1919). 

133 Schlotterer, G. K., and R. H. Youngman, U. S. Pat. 1,643,181 (Sept. 20, 
1927). 

133 Morse, Waldo G., U. S. Pat. 1,392,074 (Sept. 27, 1921). 

Dougal, J. W., U. S. Pat. 1,639,629 (July 19, 1927). 

Boxer, Frederick N., U. S. Pat. 430,766 (June 24, 1890). 

Amies, Joseph H., U. S. Pat. 1,470,674 (Oct. 16, 1923). 
137 Pennington, H. R., U. S. Pat. 1,583,169 (May 4, 1926). 
138 Britton, R. P. L., U. S. Pat. 1,477,938 (Dec. 18, 1923). 
139 Kelly, George, U. S. Pat. 830,329 (Sept. 4, 1906) ; U. S. Pat. 870,367 (Nov. 
5, 1907). 

140 Paterson, E. A., U. S. Pat. 1,171,236 (Feb. 8, 1916). 
141 Vail, James G., U. S. Pat. 1,206,056 (Nov. 28, 1916). 

143 Kelly, G., U. S. Pat. 882,891 (March 24, 1908); U. S. Pat. 882,890 (March 
24, 1908). 



134 
135 
130 



198 SOLUBLE SILICATES IN INDUSTRY 

bodies ; but the resistance to water is disappointing. The property of 
silicate solutions which enables them to wet oily surfaces has found use 
in other processes though it is a serious disadvantage here. 

Mixtures Containing Portland Cement. 

Setting Time. 143, 144 The relation between silicate solutions and 
Portland cement has received attention from numerous experiment- 
ers. 145 ' 146 ' 14T Ordinary Portland cement reacts at once with solutions 
containing more than three mols of silica and more slowly with those 
containing two or less. The effect of adding small amounts to the 
gauging water is therefore to increase the speed of set and to reduce 
the ultimate strength, as indicated in Table 73 : 

Table 73. Setting Time and Tensile Strengths. 1 * 8 

Na.O, 3.3Si0 2 , 42.89°Baume 

Tensile Strength 
After 7 Days After 28 Days 
Setting Time lbs. sq. in. 

A Briquets gauged with plain water. 

Initial setting time = 15 minutes 

Final setting time =145 " A v. 616 783 

B Briquets gauged with 2% sodium silicate. 

Initial setting time = 5 minutes 

Final setting time = 35 " 638 720 

C Briquets gauged with 6% sodium silicate. 

Initial setting time = 5 minutes 

Final setting time = 30 " 551 605 

D Briquets gauged with 10% sodium silicate. 

Initial setting time = less than 5 minutes 

Final setting time = 25 minutes 406 468 

Table 74. Setting Time. 

Over 6 hours 
148*4 cc. H 2 " 6 " 

145 1 /' " " Began in 5 " (approximately) 

1421/, " " " " 4 " 

136 " " " " 3 " 

Pretty firmly set in A 1 /* hours. 
Using 30 g. to 120 cc. water — hard in 3 hours. 

Cementation of Water-Bearing Strata. Rapid setting, even at the 
expense of strength, is sometimes of value, 149 as in the closing of open- 

143 Davis, Watson, Eng. News Record, 87, No. 1, 26 (1921). 
'"Cement and Eng. News, 34, No. 1, 34 (1922) 



Silic 


ate 







134 


g. 


41/2 


<< 


71/2 


H 


CI/ 


II 


■372 





145 



McCoy, James P. A., U. S. Pat. 1,286,371 (Dec. 3, 1918). 
146 Gilmore, Q. A., "Limes, Hydraulic Cements and Mortars," Van Nostrand, 
1874, p. 97, 98. 

117 Borntrager, H., /. Soc. Chem. Ind., 20, 477-478 (1901). 

148 Brunner, Mond & Company, Booklet S. S. 232, Northwich, England. 

149 Burke, J. T., U. S. Pat. 1,552,270 (Sept. 1, 1925). 



SILICATE CEMENTS 199 

ings against leaking water and in the process of keeping oil out by 
cementing the wells during drilling; and the control of it by varying the 
amount of silicate used enables the operator to adapt his cement to the 
character of the strata to be sealed. 150 ' 151 » 152 Francois 153, 154 devised a 
technic for the cementation of water-bearing strata in the sinking of 
mine shafts and other engineering works. He found that by pumping 
alternately a solution of aluminum sulfate and sodium silicate into sand- 
stone or other porous formation a gelatinous precipitate was produced 
which under heavy pressure acted like a lubricant and permitted a 
cement slurry to penetrate more deeply than would otherwise be possible. 
This process has been extensively used abroad. Its success depends on 
highly expert manipulation, and pressures up to 180 atmospheres have 
been used. 155 " 169 

Wood-Fiber. Another form of concrete in which silicate solutions 
are used is that of Zuskoski 1T0 in which sawdust or wood-fiber 171 is 
treated with silicate solutions and mixed with cement to make a light 
mass. 172 



^Ztakikawa, Jap. Pat. 37,655 (Dec. 14, 1920). 

1M Wilson, Charles, U. S. Pat. 1,547,189 (April 17, 1924). 

102 



Winkler, Kaspar, U. S. Pat. 1,519,285 (Dec. 16, 1924); 1,530,533 (Mar. 24, 
1925). 

** Francois, A., U. S. Pat. 1,391,678 (Sept. 27, 1921); U. S. Pat. 1,430,306 
(Sept. 26, 1922); "Sinking of Shafts in Mine Pits by Process of Cementing"; 
"Shaft Sinking and Cementation in Water-bearing Rocks," Liege, Belgium, 1922. 

1& * Francois Cementation Company, Ltd,, Bentley Works, Doncaster, England, 
Booklet. 

155 Sadtler, Bishop, Vail, Symposium, Trans. Am, Inst. Chem. Eng., 19 (1927). 

1M Anon., Eng. and Mining I., 125, No. 2, 60 (1928). 

157 Potts, Harold Edwin, U. S. Pat. 1,635,500 (July 12, 1927). 

158 Robertson, I., "The Cementation of the Glasgow District Subway Tunnels." 
Paper prepared by Inst, of Civil Eng. 

139 Dixson, H. O., "Underground Water Difficulties," Wigan Mining School, 5 
(1923-24). 

190 Hassam, A., and T. T. Mawson, Ann. Mines, France, 9, Ser. 11. 

161 Blandford, T., "The Principles of Cementation," Colliery Guardian, 132 
(July 16, 1926). 

1<a Ball, H. Standish, Trans. South Wales Inst, of Eng., 36, 509-74 (1921). 

163 Marriott, Hugh F., "The Francois Cementation Process," etc. Lecture de- 
livered before the Birmingham University Mining Society (May 20, 1919). 

1W Morgan, F. L., "Cementation Methods of Dealing with Underground Water 
Problems." Lecture delivered before the Birmingham University Mining Society 
(Feb. 10, 1921). 

165 Robertson, E. H., Trans. Mining Geol. Inst, of India, 11, 144-160 (1916). 
16a Mitton, H. Eustace, Trans. Inst. Mining Eng. {London), 70, pt. 5, 345-367 
(1925-26). Paper read before Inst, of Midland Eng. (England), (Oct. 15, 1921). 

167 Hassam, A., and T. T. Mawson, Trans. Inst. Midland Eng. (England), 58. 
"Sinking a Shaft by the Francois Cementation Process." 

168 "The Francois Cementation Process," S. African Mining Eng. I. (June 9, 
1923). 

169 Colliery Eng., 1, No. 6, 270-282 (1924). 
70 U. S. Pat. 1,471,876 (March 8, 1922). 

Kelly, Thomas Daniel, U. S. Pat. 1,262,512 (April 9, 1918). 
Wheeler, W. H., U. S. Pat. 1,201,535 (Oct. 17, 1916). 



171 

173 



200 SOLUBLE SILICATES IN INDUSTRY 

Patching Concrete. Silicate solutions are also an aid in patching 
concrete ; the surface to be repaired is cleaned, painted with a thick 
layer of syrupy Na 2 0, 3.3Si0 2 , and dusted while still wet with dry 
cement powder. This sets within a few minutes and provides a surface 
to which new concrete binds firmly. 173 

Iron Reinforcing Bars. A highly alkaline type of silicate has been 
proposed as a means of providing the alkalinity needed to inhibit rust- 
ing at the surface of concrete reinforcing bars. The silicate solution 
is applied to the rods and caused to set by dusting with dry Portland 
cement as in patching, but Na 2 0, 1.5Si0 2 is chosen. The iron is dipped 
in a sticky 45°Baume solution of the silicate, drained, and dusted with 
cement powder. 174 This binds well to the concrete and a safe alkalinity 
at the surface of the metal, which according to Toch, 175 is all that is 
needed to prevent corrosion, is assured. 

Mechanism of the Reaction. It cannot be positively stated whether 
the reaction between Portland cement and silicate solutions is primarily 
a reaction with calcium silicates. Free calcium hydroxide reacts quickly 
with the more silicious silicates and more slowly with the highly alka- 
line. This is also the case with Portland cement. On the other hand, 
old concrete in which free lime may be assumed to be absent has the 
property of forming water-resisting masses with silicious sodium sili- 
cates. Probably both reactions occur, — those with free lime much more 
rapidly than those with calcium or aluminum silicates. 

Portland cement added in small quantities to masses in which the 
primary binder is sodium silicate serves the purpose of giving early 

Table 75. Typical formulas Used to Hasten Set or Increase Resistance to Water. 

30 parts wood flour or residue from corn cobs 
30 parts Na 2 0, 2.06SiO 2 
30 parts Portland cement 
10 parts water 



29 parts graphite 
29 parts Na 2 0, 2.06SiO 2 
28 parts Portland cement 
14 parts water 

72 parts talc 
7 parts Na 2 0, 2.06SiO 2 
7 parts Portland cement 

14 parts water 



62 parts whiting 

33 parts silicate, ratio 1 : 2.92, 1 : 2.47, or 1 : 2.06. 
5 parts Portland cement 

173 Sterne, E. T., personal communication. 

™ "Silicate P's & Q's," Philadelphia Quartz Company, 5, No. 4 (1925), 

175 Toch, Maximilian, hid. Eng. Chem., 15, 665-666 (1923). 



SILICATE CEMENTS 201 

resistance to water and also of taking up water which would otherwise 
have to be removed by drying. 

Other reacting substances can be used to make cements which resist 
water. 

Acid-Resisting Brick Work. Portland cement and silicates of 

soda have been extensively used for setting acid-resisting brick work in 

digester linings for the sulfite process of making paper pulp from 

wood. 176 ' 177 The iron shell is usually separated from the first course 

of brick by a one or two inch backing of cement made from sand, 

Portland cement, clay, and a silicate solution. This is proportioned as 

follows : 

1 part quartz 

1 part fire clay 

2 parts cement 

made up with a silicate solution of such ratio and concentration that it 
takes a preliminary set in half-an-hour or less. The amount needed 
will change with the temperature and with the ratio of the silicate solu- 
tion. Na.O, 3.3Si0 2 , Na 2 0,2Si0 2 . and Na 2 0, 2.5Si0 2 are frequently 
used in this country, the last most often. The bricks are set in a cement 
which contains more silicate and sets as fast as can be worked. The 
second or interior course is laid with great care, sometimes in a silicate- 
Portland cement mixture which is afterward pointed with a glycerin- 
litharge cement, though sometimes the bricks are laid in the more costly 
litharge composition. The resistance of this is also improved by the 
addition of small amounts of silicate, which affect its time of set. If 
Na 2 0, 2.5Si0 2 be used at specific gravity 1.26 (30°Baume), the speed 
of set will increase as the glycerin is reduced. To state it the other way, 
the silicate and litharge (PbO) react promptly when mixed, and more 
slowly as the action is modified by introducing glycerin. The amount of 
litharge, within the limits imposed by a consistency suitable for applying 
with a knife or trowel, has little influence on the setting time, though 
the stiffer mixtures tend to set slightly faster. 



'.-,■ 



Table 76. Effect of Silicate on Setting Time of Glycerin-Litharge Cements. 

Na 2 0,2.5Si0 2 Glycerin PbO 

at30°Baume Parts by Parts by 

Parts by Weight Weight Weight 

4 8 firm in 3 minutes 

4 18 firm in 3 minutes 

4 2 8 firm in 6 minutes 

4 3 8 firm in 10 minutes 

4 4 8 firm in 25 minutes 



177 



Heijne, Otto, Paper Trade J., 80, No. 23, 61 (June 4, 1925). 
Ekstrom, P. G., U. S. Pat. 1,456,303 (May 22, 1923). 



202 SOLUBLE SILICATES IN INDUSTRY 

Increase in concentration of the silicate will also increase somewhat 
the reaction time. These compositions resist for long periods the hot 
calcium bisulfite liquors and such abrasion as results from the circu- 
lation of the pulp. They adhere strongly to brick, but care must be 
used to apply them when they are still thin enough to wet the surfaces 
and no piece of brick must be moved after initial setting has occurred. 
This involves mixing small batches at the point where they are to be 
used. The best plan is to have one worker laying brick, and beside 
him, another doing the mixing in lots only enough to set two or three 
pieces. 

Metallic Cements. 

Compositions for the repair of metal pieces may be made by mixing 
silicate solutions with metallic powders. 178 Zinc and aluminum powders 
react sufficiently with Na 2 O s 3.3Si0 2 to attain a fair resistance to water 
after a few days. Such cements when dry will take a polish and are 
thus suitable for closing defects in castings where the mechanical re- 
quirements are not severe. 

Gas and water-tight repairs to engine cylinders and the like are 
made with cements of this type. Silicates of soda and iron filings are 
rarely used, as the silicate covering prevents the rusting of the iron 
which is desirable to expand and harden an iron cement. When the 
repair is made on iron, the silicate cement adheres best to a rusty surface 
or one that has been scaled slightly by heat. Silicate cements from 
soapstone or other earthy materials which are not hydrous give good 
service on hot iron. 179 

Saturation with Silicate Solutions. 

Structural Stone. Kuhlmann applied diluted silicate solutions to 
marble statuary, plaster, brick, concrete and structural stone for the 
purpose of hardening them and decreasing their tendency to disintegrate 
with age. His expectations have not stood the test of time. It is a 
matter of some difficulty to obtain penetration of a dense body with 
a silicate solution which, when spread upon a surface of very fine 
porosity, undergoes a partial dialysis, with a tendency to leave most of 
the silica near the surface. While this is most clearly observed by at- 
tempting to saturate a piece of hard wood, it must also play a part in the 
treatment of most natural stone in place. It is extremely unlikely that 
Kuhlmann was able to surround every particle of the stones he treated 

178 West, Frank P., U. S. Pat. 1,388,011 (Aug. 16, 1921). 

179 Dunnington, F. P., personal communication. 



SILICATE CEMENTS 203 

with a silicate solution or a gel. If he could not do this the weathering 
of the stone would proceed by the decay of the untreated portions, even 
though the treated parts were perfectly protected. With or without 
the use of precipitating agents such as calcium chloride, no permanent 
results were obtained. 180 ' 181 

According to Gilmore, 182 "There is a variety of other important uses 
to which this silicifying process, as it may be termed, can be advantage- 
ously applied, for our knowledge of which we are chiefly indebted to 
Kuhlmann, Professor of Chemistry at Lille, and Fuchs. We will refer 
to them very briefly in this connection. 

"When a solid body, of any degree of porosity, is immersed in water 
or any other fluid, it rapidly absorbs a certain quantity of the latter, 
until the point of complete saturation is reached ; and if, in addition, the 
fluid possesses reacting powers, certain chemical changes will ensue 
within the pores of the solid body. If a porous limestone, like chalk, 
for example, or a piece of mortar of fat lime, be dipped in a solution 
of alkaline silicate, a certain portion of the silica in solution, after its 
absorption, will part with its potash or soda, and enter into combination 
with the lime, whilst another portion will remain mechanically inter- 
posed in the pores of the solid body, and will, in time, if exposed to a 
current of air, solidify by desiccation. The result will be that, with a 
single immersion, the density and hardness of the chalk or the mortar 
will be augmented, and after several alternate immersions and exposures 
to the air, these properties are attained in a considerable degree. The 
softest varieties of chalk may be thus hardened, so as to become capable 
of receiving a high polish. 

"Upon the sulfate of lime or plaster, the action of the alkaline 
silicate is essentially the same, though more rapid, and is accompanied 
by the inconvenience of giving rise to an alkaline sulfate, which, in 
crystallizing within the pores of the solid body, near the surface, is apt 
to cause disintegration. It is recommended in this case to use the solu- 
tion more diluted, with a view to retard or diminish the effects of the 
crystallization of the sulfate, to such a degree that the indurating solid 
will be able to resist it. 

"The process of silicatization, so named by Kuhlmann, which rests 
upon the principles enunciated above, is of undoubted utility, although, 
as yet, its practical application is attended with difficulties, and fol- 
lowed, not unfrequently, with uncertain results. It appears destined 

180 Dent. Banzcitung, No. 48 (1868) ; Abst. Chcm. Zcntr., 40, 816 (1869). 
L81 01fers, Poly. J., 176, 229 (1865) ; Abst. in Chcm. Zcntr., 36, 656. 



isa 



Gilmore, Q. A., "Limes, Hydraulic Cements, and Mortars," New York : D. 
Van Nostrand & Co., 1874, p. 98-99. 



204 SOLUBLE SILICATES IN INDUSTRY 

to meet with a varied and extensive application, in the industrial and 
fine arts, not only in the conversion, at a moderate cost, of common 
into hydraulic lime of any required degree of activity, and with a fair, 
or at least, encouraging" degree of strength, but in the preservation 
of walls of whatever kind, already constructed unadvisedly of ma- 
terials liable to more than ordinarily rapid decay, whether of brick, 
stone, pise, or concrete ; in the restoration and conservation of statu- 
ary, monuments, architectural ornaments, etc. ; in transforming designs 
cast in ordinary plaster into hard and durable stone ; in rendering 
wood-work ; and, to a limited extent, even cloth fabrics indestructible 
by fire ; and in a multitude of other collateral uses, some of which are 
even now well developed and in practical operation, while others remain 
still in their infancy, giving more or less encouraging promises of 
future utility and value." 

Water and Oil-Resistant Concrete. Portland cement concrete 
differs from sandstone or even marble in two important respects. It 
is chemically more reactive toward the silicate solutions, and the silicate 
treatments which are applied to its surface are directed to decrease its 
permeability and to increase its resistance to abrasion rather than to 
alter the erosion effects of the elements. Its pore structure is often 
such that a silicate solution will penetrate for several inches. 183 

Most cement bodies are more or less porous. This is particularly 
true of Portland cement concretes which set by a process of crystal- 
lization or hydration of insoluble silicates. One method of closing the 
pores consists in applying a silicate solution sufficiently dilute to pene- 
trate and sufficiently unstable to deposit a gel in the capillary openings. 
If the concrete is fresh enough to contain some free calcium hydroxide 
a satisfactory reaction may be had with a 10 per cent solution of 
Na 2 0, 3.25 Si0 2 . The preferred method of treatment is to saturate the 
cement with the silicate on three successive days, which is usually suffi- 
cient to seal the cement so that it will absorb no more. If this is not 
the case, other saturating treatments may follow. A gel, being a 
permeable substance, can never produce water-resistance such as may 
be expected from oily or asphaltic layers, and aside from its essential 
permeability there is probably some separation from the cell walls by 
syneresis. Nevertheless, substantial improvements in water-resistance 
can be made by silicate as indicated in the following graph, from which 
it may be seen that the treated test piece absorbed about half as much 
water as the untreated when both were subject to a thirty-foot head 

183 "Stone Preservation Committee Report, Dept. of Sci. & Ind. Research," 
London: His Majesty's Stationery Office, 1927, p. 22. 



SILICATE CEMENTS 



205 



and that while water flowed steadily through the untreated piece there 
was no flow through that which had been treated. 

If the cement is so old that all 
the free calcium oxide has been 
converted to calcium carbonate, the 
silicate will require longer to de- 
velop maximum resistance to water 
and may not become entirely in- 
soluble until it has absorbed 
enough carbon dioxide from the 
air to cause the gelation of the 
silica. 

When the substance in the pores 
is only a dried silicate solution the 
resistance to oils is very high, for 
dried silicates are glass-like bodies 
and resist admirably liquids which 
do not dissolve them. Free fatty 
acids may be partly saponified if 



A 






**> 


4 




s 
• 
• 




/ 

/ 
/ 
/ 
/ 

• 


/ 
/ 


















• / 


SlU 1 C AT L 


TfltME O 















Fig. 87. — Penetration of Water into 
Concrete with and without Silicate 
Treatment. (Courtesy Brunner, 
Mond & Co.) 



the silicate in the pores has not been sufficiently dried, but no reaction 



Days 



7 
21 



A 



202 
301 



Table 77. Tensile Tests on 1:3 Mortar Briquets. 
(Brunner Mond and Company) 

Ultimate Strengths in lbs. per square inch. 
(Average of four briquets.) 



B C 

Untreated 



120 
190 



270 
419 



D E F 

Standard briquets im- 
mersed for 7 days 
in 5% sod. sil. soln. 
Stored in damp sand 
when not immersed. 



323 



368 



350 



G H I 

Standard briquets 
dipped 3 times at 24- 
hour intervals in 20% 
sod. sil. soln. and 
stored in damp sand. 



321 



342 



359 



takes place in the absence of water. Silicate-impregnated concrete is 
thus an excellent container material for mineral and vegetable oils. 1S4_18S 

184 Moyer, Albert, Concrete, 4, 49 (1910) ; Can, Eng., 19, 707 (1910) ; Concrete 
16, 279 (1920); Concrete Cement Age, 4, 135 (1914); Eng. Record 62, 624 
(1910) ; Proc. Am. Soc. Testing Materials, 10, 351-355 (1910). 

185 "Report of Service Tests on Concrete Floor Treatments," Bur. of Standards 
(Oct. 28, 1920). 

186 "Silicate of Soda and Concrete," Philadelphia Quartz Company, Bulletin 
No. 34 (1925). 

187 Proc. Am. Road Builders' Assoc, 24th Annual Cony. (Jan. 11-15 1927) 
1S8 Huth, F., Farbe und Lack, 606 (1925). 



206 SOLUBLE SILICATES IN INDUSTRY 

Protection against oil penetration is also desirable in factory floors 
and garages. The application is the same as for water-resistance, but 




p IG 88. — Abrasion Test Showing Effect of Silicate Treatment on Concrete. 

the contrast in oil absorption before and after treatment is more strik- 
ing than the results shown above for water. 189 

Concrete Hardening. Silicate treatment of concrete gives it a 
greatly increased resistance to abrasion. This may be shown by rub- 
bing the test piece with sanded blocks under standardized conditions. 
The piece shown in the picture was made in this way. The 2 : 1 sand- 
cement mortar block was silicated for half its length and each end 
subjected to the same amount of rubbing. The narrow fin indicates the 
original thickness of the piece where no abrasion was applied, the next 
step is the silicated part, and the thinnest portion is the original un- 
treated concrete. 

Wear on a concrete floor or roadway means a corresponding amount 
of dust which is inimical to the satisfactory performance of many in- 
dustrial processes. 190, 191 « 192 Saturation with silicate solutions is inex- 
pensive and for many conditions affords a complete solution of the 
problem. 

Curing Concrete. 193 Further use of silicate solutions in connection 
with Portland cement concrete is in connection with the curing process. 
If a coating of silicate be applied to the cement as soon as possible after 
the initial set, that is, when it is hard enough to bear the weight of a 
man without marking, the water escapes less readily than it would 
without the silicate treatment and there is some evidence that the final 
strength of the concrete is improved. 

Advantages claimed for this method of curing are the ease and cheap- 
ness at which it may be applied, the fact that no labor is required for 
removing the curing medium, as in the case of earth or straw, and its 

189 Dulac, A., Brit. Pat. 250,439 (July 14, 1925) ; C. A., 21, 1174. 
190 Stubbs, Robert C, U. S. Pat. 1,315,749 (Sept. 9, 1919). 
191 Brunner, Mond & Co., D\cr, Calico Printer (Aug. 15, 1924). 
192 Remler, R. F., Fibre Containers, 11, No. 2, 16 (1926). 
193 Beightler, Robert S., Eng. News Record, 100, 316 (1928). 



SILICATE CEMENTS 



207 



Cor9iftres3ton Te$ ti 
on 


Concrete Cy/*/*<fe*v 




3ooc 






















* 












V 
























sxtxxr 








■ 




i 








Is. 
' /coo 


m 
























Cured in 






Wife* 


Si'i,<aff of- s oc /a \ 






/ 7 1 /.a 


I 







B 


for" 
*S 28 Pays 9o 





Comprets/on Tests on Concrete Cy tinders 

Fig. 89. 

adaptability to localities where water is not plentiful. Ball indentation 
tests and compression and loading tests of beams indicate that at least 
under optimum conditions the silicate curing treatment will increase the 
strength of concrete. 194 

Another means of indicating the effect of silicate treatment on wear 

194 Remler, he. cit. 



208 



SOLUBLE SILICATES IN INDUSTRY 



&oo 



>3 y°° 

fc *>oo\ 



it 






40O ■ 



3 CO 



>> Zoo 
tco 



Hay 



Beam 7e*/s 
Cured W% 



B 



M/ 



6rct*Jtf/, 

ff-8 
fitt'<j& te 

■S»c/ct 



+000 



3000$ 



ZOCO^ 

v» 



(000 



ZBOays 



flC£ 

69 Coys 



I BO 0+ys 



Modulus of fixture and Compression Tests on Concrete Beams 

Fig. 90. 

is to apply the Continental method of observing the depth of penetra- 
tion of a sand blast applied to the surface. The following graph from 
Otzen 195 indicates that whether the silicating is done early or late there 
is always a striking contrast between the raw and treated pieces. 

195 Otzen, Robert, personal communication, Tech. Hochschule, Hannover (Nov. 
19, 1924). ' 



SILICATE CEMENTS 



209 



Tahle 78. Surface Hardness Test. 

Size of beams 40" x 6" x 8" 

Mix l-l?i-3^> 

Hay cured 14 days 

Age when tested 60 days 

Indentation Loads, Pounds. 

Silicate of soda treated 10,465 

Untreated 8,915 

Difference 1,550 

These data are averages of 25 to 30 determinations. 

Indentation load is the pressure necessary to force a one-half inch steel ball 
one-quarter inch into the concrete surface. 




Fig. 91. — Sand Blast Penetration of Concrete with and without Silicate Treatment. 



The frequency with which it is desirable to repeat silicate treatments 
will to some extent depend upon the amount of traffic. A factory floor 
subject to iron-wheeled truck traffic may need a fresh saturation every 
six months, while many lighter services need it only once. 

Acid-Resistance. More frequent still is the need of repeating the 
silicating where floors are subject to the action of weak acids. Concrete 
does not resist strong mineral acids, and silicate treatment is not suffi- 
cient protection to warrant designing floors for exposures of this sort 
though silicate has done good service when old Moors had to be used 
and ideal conditions could not be met. Concrete floors have been suc- 
cessfully protected against large amounts of weak organic acids by 
silicating at relatively short intervals — in some cases weekly. 



Chapter VIII. 
Adhesives. 

Definition and General Behavior. 

Adhesive substances have had important uses from very early times. 
Solutions of starches, glues, and gums, drying oils, and other colloidal 
substances have been used to cause the adherence of paper, wood, light 
metals, ceramic wares, and objects for decoration or use in all the arts. 
The science by which we shall understand their performance 'has lagged 
behind the art of putting them to use. Before considering specifically 
the function of soluble silicates as agglutinants it may be worth while 
to set down a few points of general application. 

Adherence and Coherence. 

Webster contrasts the ideas of adherence and coherence by citing the 
difficulty of separating a pile of smooth glass plates, which cohere with 
great tenacity. Metals or other dense materials with perfectly fitting 
surfaces exhibit the same phenomenon. His distinction between the 
holding together of two like surfaces such as glass or metal and two 
different substances as wood and glue serves for most of the instances 
with which we are concerned. Adhesives are different from the sur- 
faces on which they are spread. 

Film Formation. 

To perform their office of uniting, they must be able to wet the sur- 
face and form a more or less continuous film. The strength of the union 
produced will be a function of the strength of the film which lies be- 
tween the surfaces to be bound. Adhesives take their grip either by 
specific adsorption or by penetrating surfaces more or less rough or 
porous and by forming protrusions on the film which in the course of 
the process changes from a fluid to a relatively solid condition. 

The materials which fill these requirements are usually concentrated 
viscous liquids which do not tend to crystallize at ordinary temperatures 
and that among the soluble silicates there are numerous materials fitted 
to act as adhesives. 

210 



ADHESIVES 211 

General Characteristics of Adhesives. 

Although its first report did not deal at all with these mineral adhe- 
sives, the Adhesives Research Committee 1 has set forth some consid- 
erations applicable to all adhesive materials as well as to animal glues, 
which they investigated. 

"Glues are most commonly employed for sticking together surfaces 
of wood ; these are relatively rough and uneven, and no matter how 
closely a pair of wood surfaces be pressed together, the actual points 
of contact form probably but a fraction of the area of overlap. Be- 
tween the points of contact are relatively large air spaces. In well-glued 
joints, the glue not only covers the portions of the two pieces of wood 
which touch, but it fills in the spaces which would otherwise be occu- 
pied by air. In this way, only, can a strong rigid structure be obtained. 
Glass surfaces can be ground to such an accuracy that they fit each 
other perfectly. Not so wood surfaces, where the interspaces must 
be filled with an adhesive. For this purpose, an adhesive must obviously 
be, at time of application, a viscous liquid, since a mobile one could not 
be retained in place, as it were, until the joint was made. 

"If, however, glue is too viscous it will not readily fill the interspaces, 
and the joint is consequently weakened. Thus, for each class of mate- 
rial to be glued there is possible an optimum viscosity dependent upon 
size of interspaces and pores of that particular material. This may be 
one underlying reason for a characteristic feature of the glue industry, 
i.e., the selection of numerous special glues for specific purposes. 

"Adhesives, then, must be viscous substances ; since viscosity is gen- 
erally connected with high molecular weight, or at least with high 
molecular association, they are usually substances of complex chemical 
composition." 

The close analogy between the adhesive characteristics of animal 
glues and silicate adhesives is readily seen. 2 ' 3 ' 4 

An extended systematic study of adhesives and adhesive action by 
McBain 5 and Hopkins led to the conclusion that adhesive joints are of 
two types, namely : specific and mechanical. The first are formed 
between smooth, non-porous surfaces and are probably associated with 

1 "First Report of Adhesives Research Committee," Dept. Sci. and Ind. Re- 
search, London : His Majesty's Stationery Office, 1922. 

a "Second Report of Adhesives Research Committee," Dept. Sci. and Ind. 
Research, London: His Majesty's Stationery Office, 1926. 

3 J. Phys. Chem., 29, 188-204 (1925). 

y. Phys. Chem., 30, 114-125 (1926). 

5 McBain and Hopkins, Second Report of Adhesives Research Committee, 
London: His Majesty's Stationery Office, 1922, p. 34. See also McBain, J. W., 
and W. B.Lee, Ind. Eng. Client., 19, No. 9, 1005 (1927). 



212 



SOLUBLE SILICATES IN INDUSTRY 



adsorption phenomena. The latter can be formed by any liquid which 
penetrates porous surfaces and then becomes solid in situ as by cooling, 
evaporation, oxidation or otherwise. Such joints depend largely for 




70 sa 3° 

Fie. 92.— Relation of Viscosity to Temperature for Na 2 0, 3.34SiO,» (43° Baume). 

their strength upon the strength of the adhesive itself, for they are 
essentially cases of embedding the substances to be stuck in the adhesive 
which forms a link that must of itself carry any load placed on the 
system. Specific joints on the other hand may be much stronger than 
the adhesive as in the case of a soft shellac which made joints between 
metals many times stronger than its film strength (nearly two tons per 



ADHESIVES 



213 



square inch). The combination of specific and mechanical adhesions 
may often occur. In general, any liquid which wets a surface and is 
then transformed into a solid may be regarded as an adhesive for that 
surface. 



<0 

































































07 ^ 


< 9. 


J 


9 


1 



Per Cent //a^ O 

Fig. 93.— Relation of Viscosity to Alkalinity for Na a O, 3.34SiO a (43° Baume). 

Set and Viscosity. 

The porosity of the surfaces to be attached will determine the 
viscosity required at a given pressure — more pressure may cause too 
great a penetration which is conveniently resisted by a greater viscosity. 
If there were no other variable the ideal pressure-viscosity relation could 



214 



SOLUBLE SILICATES IN INDUSTRY 



be easily worked out for each particular surface with a given adhesive. 
But an adhesive must set, that is, the liquid must become solid — its 




4o.o 



4/o 



4Z4 



4^0 



0* 



?yrees 



va"/*?^ 



Fig. 94. — Relation of Viscosity to Specific Gravity for Na 2 0, 3.34Si0 2 at Constant 

Temperature (20° C.). 



viscosity must rise. This usually begins as soon as it becomes a film. 
Thus the time element enters. This is variable for each adhesive liquid 
and for each surface. It is usually a vital consideration in industrial 
processes. 



ADHESIVES 215 

If the setting of the adhesive depends upon the transfer of moisture 
from the adhesive to the surface stuck this will primarily relate to the 
area which functions as an absorbent. It follows that thick films will 
set more slowly than thin ones; the amounts of water removed, though 
the same per unit of area, are different proportions of the large and 
small quantities of adhesive. 

The ability of surfaces to absorb will vary not only with porosity 
but with the amount of water already present. Wood or paper, being 
sensitive to the fluctuations of atmospheric humidity, will vary the setting 
time of aqueous adhesives. 

Typical graphs for the viscosity rise of silicate solutions beginning 
with the type Na 2 0, 3.3Si0 2 (Figs. 92, 93, 94) show that the curves of 
increases due to cooling, to reduction in relative alkalinity, and to con- 
centration are of nearly the same shape, but it should here be pointed 
out that air drying never completely removes moisture. The solid film is 
really a highly concentrated silicate solution containing 20 per cent of 
water, more or less, and capable of becoming somewhat fluid when 
quickly heated to temperatures near the boiling point of water. The 
tendency to liquefy may be offset by evaporation. The water-containing 
film is, like the hydrous silicate powders of commerce, capable of being 
dissolved by hot water. It must be modified if completely insoluble 
adhesives are desired. 

Choice. 

The conditions which the finished work is required to withstand will 
have much to do with the selection of an adhesive. Must it resist water ? 
How quickly must the bond be formed ? How long must it endure ? 
Is an alkaline adhesive permissible? What is the cost? These are all 
questions which must be answered before an adhesive can be wisely 
chosen. There are many more, but these will serve to indicate the 
difficulty of reducing all the variables to measurable units and of making 
and choosing adhesive compositions by cut-and-try methods. 

Silicate Adhesives Unmodified by Other Materials. 

Silicate solutions may be used either alone or mixed with modifying 
substances for adhesive purposes. We shall consider first the use of 
solutions containing only water, Na 2 0, and Si0 2 on sundry surfaces. 

Glass. 

Bottles on which syrupy silicate solutions between Na 2 0,2Si0 2 and 
Na 2 0,4Si0 2 have been spilled will often adhere to each other or to 



216 SOLUBLE SILICATES IN INDUSTRY 

wood or stone shelving with snch tenacity that it is impossible to salvage 
them. The grip of silicate solutions on glass surfaces is partly due 
to a slight etching of the glass which at the same time tends to disturb 
the equilibrium between silica and soda, increase the viscosity, and pro- 
duce a more water-resistant film than would be formed on an inert 
surface. 6 Na 2 0, 2.7Si0 2 is often sold in small bottles for the repair 
of china and glassware. The joints when freshly made will not stand 
long immersion in water but become better as the reaction proceeds 
slowly over the course of years. Large surfaces of glass give difficulty 
from slow setting, for evaporation takes place only at the edges. The 
reaction with ordinary flint glass and a 1.41 specific gravity (42° 
Baume) solution of Na 2 0, 2.7Si0 2 is sufficient to cause gelation in about 
two years at atmospheric temperature in a sealed test tube. The same 
liquid stored in iron would show no measurable change in viscosity in 
that time. Silicate solutions have been mistakenly used to fasten tem- 
porary signs on polished plate glass Windows. They are very difficult to 
remove completely. The best method is to apply acetic acid followed by 
hot water and then restore the original polish with fine abrasives and 
rouge. McBain gives the following tension tests of a series of silicate 
solutions on glass : 

Table 79. Tension Tests — Silicate Adhesive betzveen Glass Surfaces. 

Single Coating Double Coating 

Grade of Silicate Lbs. per Sq. In. Lbs. per Sq. In. 

Grade 5 molar ratio 2.0 ...*t ...f 

" 1 " " 2.45 300 200 

" 2 " " 2.9 1,000 500 

" 3 " " 3.0 600 800 

" 4 " " 3.3 600 800 

Experimental sample 4.08 567$ 600 

* Film moist. 

f No test possible as the joints were too weak to withstand ordinary handling. 

$ Maximum values. 

These results are inconclusive in the absence of information that opti- 
mum concentrations, viscosities, and drying times were used. 

Mica. 

Heat-resisting translucent sheets are built up by dipping thin pieces 
of mica in silicate solutions rather thinner than is usually chosen for 
glass and laying them together upon a support until a sheet of the 
desired size and thickness has been formed. It is then pressed and 
baked. Na 2 0, 2.4Si0 2 does this satisfactorily. There is probably some 

6 Norman, John Thompson, U. S. Pat. 949,493 (Feb. 15, 1910). 



ADHESIVliS 



217 



reaction with the mineral. When these sheets are kept dry their elec- 
trical insulating properties are good ; when moist, the insulating prop- 
erties are much reduced and some efflorescence of the exposed silicate 
films is to be expected. 

Asbestos Paper. 

Adjustment of Viscosity. Mineral fibers have for many years 
been made into paper because of their heat-resisting qualities. Parkyn 7 
proposes to use asbestos board for wall board. When asbestos paper 
is to be adhesively united the 
advantage of a mineral and 
incombustible adhesive is obvi- 
ous. Asbestos paper is normally 
very porous. When dry it is 
white in color and pleasing to 
the eye, but water causes it to 
assume while wet a dark greenish 
gray color. Silicate solutions 
thin enough to penetrate the paper 
also cause this color, which re- 
mains after the silicate has dried 
to a solid condition, though it will 
not be entirely dehydrated. In 
order to make a silicate adhesive 
which will not discolor asbestos 
paper, it is necessary to adjust 
the viscosity to a point where 
wetting is at a minimum. Sulz- 
berger s used silicate to render 
asbestos paper translucent for 
copying and transfer purposes. 

Corrugated Paper. Corrugated asbestos paper is made into air cell 
covering for thermal insulation of steam pipes and other conductors, 
or containers for both hot and cold fluids. 

In corrugating asbestos paper the pressure of the toothed roll carrying 
the wavy member to the tips of which the silicate has been applied would 
be great enough to drive the adhesive too far into the porous paper. 
This may be overcome by lightly coating the surfaces which will be 
inside with a diluted silicate solution which serves to stiflen the sheet 

7 Parkyn, Herbert A, U. S. Pat. 1,466,246 (Aug. 28, 1923). 
Sulzberger, Nathan, U. S. Pat. 1,597,301 (Aug. 24, 1926). 




Fig. 95.- 



Alaking Asbestos Air Cell Cov- 
ering, Hand Method. 



218 



SOLUBLE SILICATES IN INDUSTRY 



and at the same time reduce the penetration of the adhesive. This 
sizing silicate should be dried by drawing over a heated surface before 
the adhesive is put on. 

Mill Board. Sheets of asbestos paper dipped in silicates thin enough 
to penetrate them may be pressed together to form a rigid mill board 
of any desired thickness. The composition ordinarily used as an 
adhesive for asbestos is Na 2 0, 3.3Si0 2 . Although there is probably 
some reactions (cf. asbestos and silicate in cements, p. 191) these masses 
are not completely resistant to water. Mill boards have, however, ap- 
peared un the market in which a surface treatment with Portland cement 
has been relied on to make them insoluble. Katz 9 made asbestos products 



If 

to— — 
ill 

*■§■ 

Fig. 96. — Asbestos Air Cell Covering. 
(Courtesy, Johns Mansville Corp.) 

with good water-resistance by adding calcium carbonate as a filler to 
the asbestos paper and then saturating it with Na 2 0,2Si0 2 , which reacts 
relatively rapidly to form an insoluble silicate. The by-product calcium 
carbonate which results from the treatment of dolomitic limestone to 
separate magnesia, is especially useful because its reaction with the 
silicate is somewhat increased by the presence of small amounts of 
magnesium hydroxide. 

Table 80. Typical Analysis of By-Product Calcium Carbonate. 

Per Cent 
Loss on ignition below redness 6.98 

Total loss on ignition 46.9 

Insoluble in HO .27 

MgO in water soluble form .46 

MgO in water insoluble form 2.72 

CaO in water insoluble form 44.25 

A1 2 3 and Fe,0 3 3.76 

98.36 
9 Katz, Henry G., personal communication. 




ADHESIVES 



219 



Pipe Covering. Creped asbestos paper has been made into pipe 
covering by spotting it with a viscous silicate solution as it was being 
rolled into the desired form. Thus the insulating value was retained 
without too greatly increasing the weight or rendering the completed 
structure brittle. 




Fig. 97. — Creped Asbestos Paper Made into Pipe Covering by Spotting with 

Silicate Solution. 



Wood. 

Shearing Strength. Shear tests of silicate joints between walnut 
surfaces indicate the greatest strength with ratio 1:3. The experiments 
on which the chart (Fig. 98) is based took no account of viscosity rela- 
tions but used commercial solutions as received. 10 Work done in 
McBain's laboratory indicates that higher values can be secured by 
adjusting viscosity. It is noteworthy that a silicate of approximately 
the optimum composition was chosen by cut-and-try methods and made 
standard for most adhesive uses of silicate in the wood and paper in- 
dustry long before any strength measurements were made. 

Dove Tail Boxes. Silicate adhesives on wood have been exten- 
sively used for fastening the dove-tailed corners of small boxes made 
from sawed lumber. The type Na 2 0, 3.3Si0 2 is almost exclusively used. 
Its solutions are sufficiently alkaline to give a yellow color to the outside 
surface. Economy demands that the dove-tailed ends be dipped in the 
silicate before fitting. 



10 McBain and Hopkins, loc. cit., "Second Report of Adhesives Research Con: 
mittee," London: His Majesty's Stationery Office, 1922, p. 43. 



220 



SOLUBLE SILICATES IN INDUSTRY 



Plywood. Plywood for temporary service, especially that from soft 
wood, as gum and poplar, when water-resistance is not required, may 
be made with a silicate adhesive. The strength of bond is ample for 
such purposes as shipping boxes for textiles, of which many have been 
used. 11 

Pieces of smooth sawed maple wood fastened together end to end 
under a pressure of about 4.218 kilos per square centimeter (60 pounds 



700 




























\ 
"^ Soo 

4 

\ 300 
S* loo 





















































2.o j.o 4,0 

Mc/ar faf/o -Mo/s St Oz J Mots Afa £ 

Fig. 98. — Shear Tests. Silicate of Soda between Walnut Surfaces. 



to the square inch) with a 1.41 specific gravity (42°Baume) solution of 
Na 2 0, 3.3Si0 2 will develop over night a tensile strength of more than 
52.6 kilos per square centimeter (750 pounds per square inch). It re- 
quires only about 14.0 kilos (200 pounds) to pull the fiber sidewise out 
of gum veneer. 

The ordinary procedure is to use a two-roll glue spreader with fluted 
rolls 20 to 30 cm. (8 to 12 inches) in diameter. The lower roll dips into 

11 For Nomenclature, specifications, and grades used in this industry see 
Paper, 35, No. 12, 503 (1925). 



ADHRSIVES 



221 



the silicate and the depressions cause a larger amount to be carried to 
the upper roll than would be the case if it were smooth. For three-ply 
rotary-cut veneer the center sheets from 0.127 to 0.32 cm. ( 1 /. (l to % 
inch) thick are passed between the silicated rolls and coated on both 
sides at the rate of 415 to 439 kilograms per 1000 square meters (85 to 
90 pounds per 1000 square feet) of surface. This sheet is laid by hands 
protected with rubber gloves upon the dry sheet which is to form the 
outside of the plywood ; the grains of the two pieces are placed at right 
angles. Two dry sheets are laid on top and the operation repeated till 
perhaps thirty centers have been laid. The pile is then trucked to a press 
and enough force put on to flatten the sheets and make a perfect contact. 
The pile is clamped in this position and allowed to stand for several 



102 lbs. 



134 lbs. 



134 lbs. 




202 lbs. 



240 lbs. 



250 lbs. 




Fig. 99. — Broken Test Pieces Showing the Effect on the Face of Gum Veneer of 
Silicate Bonds Ruptured under Various Loads. 

hours, preferably over night, when the sheets may be taken out and 
sawed. 

Pressure should be put on within twenty minutes from the first 
spreading of silicate. Larger amounts are needed than if there were 
no waiting period, but the dry sheets are not so easily wetted as paper, 
and on this account also liberal spreading is necessary. 

Silicate adhesives have the great advantage of introducing a minimum 
of moisture into the wood. The loss of 20 per cent of the weight of 
the silicate, nearly all of which is absorbed by the wood, is enough to 
form a bond permitting the laminated stock to be trimmed with saws. 
The entire process is accomplished without any special attention to 
drying ; ordinary handling gives enough ventilation to dry the plywood. 

Effect of Age. Though the initial strength is ample and the con- 
venience of manufacture great, exposure to water quickly loosens the 



222 



SOLUBLE SILICATES IN INDUSTRY 



bond. Even when the silicate-bound plywood is kept reasonably dry 
there is enough water normally present in the air-dry silicate (about 
20 per cent) and in the wood to permit slow absorption of carbon di- 
oxide and a gradual granulation of the colloidal film. This is often 
erroneously referred to as crystallization. Observation of commercial 
processes leads to the general statement that under dry conditions, but 
without the protection of varnish films or other covering, the silicate 
holds satisfactorily for one to two years on plywood, though, as will 
later appear, its service on paper products is much longer. Carter made 
a study of the eflect of age, using dense maple blocks glued end to end, 
and obtained the following data : 

















































































9° 




























































































































































«/*■'/)_ 


stet^u 




Mqrjl* 


*/£> 




^fa^'/S 


StiOs 




Mil* 




H 


*>7 



>Q 440 
^ 300 



fly* of Bond - months 

Fig. 100.— Effect of Age on Strength of Na 2 0, 3.34Si0 2 Bond on Maple Wood 

Pieces 1 Inch Square. 

For work which must resist water and endure permanently, silicate 
serves in various protein adhesive mixtures. 

Vulcanized Fiber. 

Many attempts have been made to bind sawdust and other forms of 
wood or fiber waste with silicate 12 (see Chapter VII). Other materials 



Oelhafen, John Walter, U. S. Pat. 1,564,706 (Dec. 8, 1925). 



ADHESIVES 223 

may be attached to wood with silicate adhesives. Here it will suffice 
to mention the so-called vulcanized fiber, a dense cellulose sheet made 
by treating paper with zinc chloride solutions until the fibers become 
gelatinous, pressing and washing. This fiber is adhesively laid upon 
sawed lumber or plywood to make trunks. Here the life of silicate 
films is greatly increased because contact with water and carbon dioxide 
is much reduced by coating the outside with paint and varnish. If the 
fiber chosen is of good grade and 0.127 cm. (%o inch) in thickness, and 
proper precautions are used to dry the silicate film, which must be of low 
relative alkalinity, the results are quite satisfactory ; but porous fiber or 
inadequate drying may permit the migration of enough alkali to the 
surface to make an oil varnish sticky. 

The ordinary practice is to apply adhesive silicates cold, but it has 
been found satisfactory to coat the wood rather heavily with silicate 
and allow it to dry to a glossy film. The fiber is then placed dry on 
the silicated surface and both are put into a hot press which melts the 
solid silicate solution and causes it to take firm hold of the fiber and 
set by the combination of further evaporation and cooling. This has 
the advantage of requiring less drying and permitting neater working, 
as no excess silicate is squeezed from the press. 

Wood which has been stained with silicate is difficult to restore by 
treatment with oxalic acid or bleaching agents on account of the pro- 
tective film which keeps the reagent away from the stained fibers. 

Fiber Board. 

The advent of the fiber shipping container made from corrugated or 
solidly laminated sheets of paper has opened a wide field for silicate 
adhesives. The heavier laminated paper products such as wall board, 
cloth board, and paper tubes, have also assumed an important place in 
industry. 13 Each presents its own problems of adaptation of adhesive 
to machine and papers. On this account, and because growth is still 
active, the processes will be separately treated in some detail but always 
from the point of view of the function of the silicate adhesives. The 
transition from wood, which is used once and burned, to paper, which 
can be reclaimed many times is of primary economic significance in a 
country whose forest reserves are being rapidly depleted in the face 
of an expanding industrial life and an inadequate program of re- 
forestation. 14 

13 Malcolmson, J. D., Chem. Age, 28, No. 8, 273 (1920) ; 28, No. 9, 321 (1920). 
"Andrews, O. B., The Shears, 34, 97-105 (1924). 



224 SOLUBLE SILICATES IN INDUSTRY 

Corrugated Paper. 

By this term we understand a structure composed of the actual cor- 
rugated sheet with one or two flat sheets to which the tips of the 
corrugations are adhesively united. Some interesting variations have 
been proposed. 15-19 The specifications of the Freight Container Bureau 
and the Bureau of Explosives, which through the railroads and the In- 
terstate Commerce Commission 20 control the classification of containers 
in the United States, require that the sheet in which the corrugations 
are impressed shall be made of straw. The great bulk of corrugated 
paper is used to make boxes for freight transport, so these specifications 




Fig. 101. — Corrugated Paper. 

are strictly observed. Although they allow rather wide variations in 
composition they are of sufficient interest to record. 

Specifications. 

The thickness of the straw paper for corrugating is 8 to 10 points.* 
The flat lining sheets are of two types, — a board made of old papers 
exclusively, called chip board, and a better sheet used on the outer 
liners. This passes under the misnomer of "jute", though it is usually 
quite free from this fiber ; more properly it is called test board, for it 
must meet definite strength tests proportioned according to the size 
and loading of the box. It is generally made from old papers with an 
addition of sulfite or sulfate pulp and is well-sized with rosin size pre- 
cipitated on the fiber with alum. A liner of more or less pure sulfate 
fiber, known as kraft, is coming into increased favor on account of its 
great strength. The adhesive which combines these three elements, 
a corrugated sheet between two flat sheets, into a shock-absorbing 
structure, is silicate of soda. The composition most generally used is 

ls Fiske, William Grant, U. S. Pat. 145,854 (June 29, 1920). 

18 Howard, Charles H., U. S. Pat. 1,605,953 (Nov. 9, 1926). 

"O'Brien, David J., U. S. Pat. 1,360,142 (Nov. 23, 1920). 

"Wandel, Kurt, U. S. Pat. 1,519,281 (Dec. 16, 1924). 

19 Fairchild, Walter H., U. S. Pat. 1,158,657 (Nov. 2, 1915). 

20 Consolidated Freight Classification, No. 4, 24, Rule 41 (Dec. 20, 1924). 

* i.e., 0.008 to 0.010 inch. 



ADHESIVES 



225 



Table 81. Fiberboard, Pidpboard or Donble-Faced Corrugated Strazvboard Con- 
tainers. Double-Faced Corrugated Strazvboard Facings. 











tr. 




Solid Fiber 


Double- 


faced Corrugated 










.2 




B 


Dard 


Strawboard, Chestnut or 










C/3 








Pine Wood Fiberboard 








</> 


E 


c y 






Facings 


u 


cr 

co 








x -° 




rrt C 


i 




i 




O 




o 

o 

6 




X 

o 
PQ 

o 
*>> 


pqw 

tJ _ 1 c/3 


ISIS U 

^ n <d 


u 

C ° 

C CQ 

Jo 

.£ </3 


*0 C/3 - ~ 
. rt l—H C/3 


~ C/3 

s| 

c </3 


TD </3 
G ^ S_ 

.s ^ a 


>> 

OS 

U 
1 


<U CU 

a, c ^-s 
Ji "+- "^ 

^ ° c3 

^ ,_: o 


£ 




CO 


r^ rt 




JP 


>«H <L> 


££ 


^fe 


S 


r^^CQ 


1 


One 


piece .... 


40 




60 


0.060 


175 


0.016 


85 




175 


2 


" 


u 


65 




65 


0.080 


200 


0.016 


100 




200 


3 


<< 


<< 


90 




70 


0.100 


275 


0.030 


135 




275 


4 


Telescope .... 


40 




60 


0.060 


175 


0.016 


85 




175 


5 


* 




65 




65 


0.080 


200 


0.016 


100 




200 


6 


< 




90 




70 


0.100 


275 


0.030 


135 




275 


7 


Recei 


;sed end . 


40 




60 


0.060 


175 










8 


< 


<< 


65 




65 


0.080 


200 










9 


< 


tt 


90 




70 


0.100 


275 


• ■ • 








10 


One 


piece- . . . 


40 




60 






0.016 


85 




175 


11 


Threefold edge 


65 




65 






0.016 


100 




200 


12 


Solid 


body . . . 


40 




60 


0.060 


175 










13 


n 


" 


65 




65 


0.080 


200 










14 


u 


a 


90 




70 


0.100 


275 










15 


Double strengtl 


i 




















corru 


gated 






















strawboard . . . . 


90 




70 






0.016 


85 




275 



Na 2 0, 3.3Si0 2 though some variation from this standard has been 
practiced. 

"The best method of closing the bottom of a box by gluing is by 
means of a press, where it should be allowed to remain undisturbed for 
at least 3 minutes. 21 The next best method is to glue and immediately 
fill, allowing the weight of the contents to act as a press for at least 
3 minutes undisturbed. The tops may then be glued and the box im- 
mediately reversed, thus bringing the weight of the contents on the top, 
and allowing the box to remain undisturbed for 3 minutes as before; 
the sealing tapes may be applied to the bottom of the box during this 
time. The box may then be reversed and the sealing tape applied to 
the top after which it should remain undisturbed for at least 30 
minutes." Complete and adequate closure can be obtained with silicate 
without the use of tape. 

Manufacture. In order to understand the adhesive requirements of 
this art it is necessary to consider the mechanical conditions imposed 
by the machines in common use. The straw paper is first moistened 



Consolidated Freight Classification, loc. cit., p. 23. 



226 



SOLUBLE SILICATES IN INDUSTRY 



by a jet of steam and then ironed into permanent waves by passing 
steam-heated bronze corrugating rolls. In the best practice, silicate is 
applied to the tips of the corrugations while they are engaged in the 
teeth of a metal roll and the first backing sheet is laid on them under 
substantial pressure limited only by the danger of weakening or defac- 
ing the flat sheet. Under these conditions of heat corresponding to 
three or more atmospheres of steam, and solid contact, the adhesive 
may be applied very sparingly and will set almost instantly to a con- 
dition stronger than the paper. To secure this result the sheets must 
be pressed together very soon after the adhesive is spread ; the machines 
shown in the diagrams will do it in a fraction of a second. 

Thus a single- faced paper with thirty-six corrugations to the foot 
may be made with 0.0488 kilo of 40° silicate per square meter (ten 
pounds of 40° silicate per 1000 square feet). 

The case is quite different with the second sheet. The evolution of 




HBATSO PLATfonrl 



-TOP utA/£R ^~STf?AW ^-OQTTOM UIN£R 

Fig. 102.— Machine for Making Double Faced Corrugated Paper. 

machinery for this purpose has provided means for applying the second 
lining sheet quickly after the silicate is spread. This avoids the need 
for excessive amounts which serve only to delay the set long enough 
to permit wetting and making a good contact with the second liner, 
but it is obvious that no greater pressure can be applied than that which 
the paper truss will carry. For this reason more silicate is required 
to put on the second sheet. It is good practice to use 0.0586 to 0.0732 
kilo per square meter (twelve to fifteen pounds per 1000 square feet), 
but this varies with mechanical conditions. 

When the silicate is applied from below it tends to run into instead 
of away from the point of contact, which makes for economy. These 
machines are run at speeds up to more than a hundred linear feet a 
minute. The first liner sticks without any treatment; the second is set 
by passing over a steam-heated table with a device for maintaining 
contact. Some machines provide insufficient steam table to effect com- 
plete setting, which occurs only after the sheets have been stacked in 



ADHESIVES 



227 



piles. Fans are sometimes provided to remove the steam by blowing 
down the length of the corrugations. 

To make boxes, the finished paper must be scored and as the bend 




Fig. 103. — Making Corrugated Paper. 



paper is sometimes 



is a source of weakness a strip of reinforcing 
silicated to the lining sheet as it moves along. 22 

The history of the various manufacturing processes can be followed 
by a study of the patents given below. 23-46 

22 Bird, Charles S, U. S. Pat. 1,022,923 (April 9, 1912). 

23 Jones, A. L., U. S. Pat. 122,023 (Dec. 19, 1871). 
M Melch, H. B., U. S. Pat. 212,723 (Feb. 25, 1879). 

25 Thompson, R. H., U. S. Pat. 252,547 (Jan. 17, 1882). 

26 Thompson, R. H., U. S. Pat. 430,447 (June 17, 1890). 
27 Ferres, J. T., U. S. Pat. 545,354 (Aug. 27, 1895). 
^Ferres, J. T., U. S. Pat. 657,100 (1900). 

^Hinde, U. S. Pat. 1,005,836 (1911). 
30 Raffel, T. E., U. S. Pat. 1,146,771 (July 13, 1915). 
"Hicks, O. H., U. S. Pat. 1,184,748 (May 30, 1916). 
^Langston, S. M., U. S. Pat. 1,186,997 (June 13, 1916). 
33 Langston, S. M., U. S. Pat. 1,186,998 (June 13, 1916). 

34 Swift, George, U. S. Pat. 1,263,000 (April 16, 1918). 

35 Swift, George, U. S. Pat. 1,410,622 (March 28, 1922). 
38 Swift, George, U. S. Pat. 1,425,914 (Aug. 15, 1922). 

37 Hill, Irving, and Paul A. Dinsmoor, U. S. Pat. 1,473,096 (Nov. 6, 1923). 

^Spaeder, L. J., U. S. Pat. 1,535,503 (April 28, 1924). 

39 Heinrichs, Berg, U. S. Pat. 1,482,894 (Feb. 5, 1924). 

40 Swift, George W., U. S. Pat. 1,492,490 (April 29, 1924). 

"Maston, Edward E., U. S. Pat. 1,493,763 (May 13, 1924). 

^Colgrove, Charles E., U. S. Pat. 1,569,073 (Jan. 12, 1926). 

43 Howard, Charles H., U. S. Pat. 1,605,953 (Nov. 9, 1926). 

"Wagner, Joshua, U. S. Pat. 1,620,174 (March 8, 1927). 

45 Kramer, Joseph, and Albert H. Israel, U. S. Pat. 1,629,511 (May 24, 1927). 

46 Crowell, Charles H., U. S. Pat. 1,631,521 (June 7, 1927). 



228 



SOLUBLE SILICATES IN INDUSTRY 



Effect of Age. Malcolmson 47 has investigated the condition of 
corrugated container board after it had been stuck together with sili- 
cate for ten years and found it still of satisfactory quality. The strength 




W6-ATTE-0 OS.OM. 



Fig. 104. — Double Faced Corrugated Paper. Silicate Applied at F and G. 



TRAVELING GUILLOTINE CUTTER — 
RUBBER COVCRCD PULL ROILS 
HEATED PLATFORM 





I 



QP miner '-dOTTorr Line/* ^-straw 

Fig. 105. — Double Facing Corrugator. 



DOUBLE FACER 




CUTTER 




^— SILICATE rj 

7® 



HEATED Pi-ArroW 



top liner \sr/fAyY L sorrorr liner 



Fig. 106. — Single and Double Facer as Separate Units. 

of the paper is such that no great adhesive strength is needed, so that 
the initial strength of the silicate can be much reduced by carbonating 
without depreciating this product. 

47 Malcolmson, J. D., Fibre Containers, 6, No. 3, 10-11 (1921). 



ADHESIVES 



229 









1 


r « 


— 






? 


\ 


r« > a 


"^^lllifcl^,-^,— . ; . 


■M5k.| 


* 


..~ — 


| 


p 

U 
1 * 

i 


".] i " 






1 

■ 




3 




r 


jt* 


i a ; ■ 





Br^p" 




' | | 


\-1n 


Jp tii._iL»i — 




BssSKLlss 


aafa »- 


^_^ 


,♦ 1 




J*- !*' 




° :X M 










Pf- 


i ■ 


.-*■-, . (■'"" .•■*•■ 


' 


~Jl 








<%fg 


WP.i 


- ■— - ■ 
':3^ • 


(Jk 


^r : - -', 






■\i 


; "^^«wa8s^ 


























^WttRjftf 







Fig. 107. — Making Corrugated Paper. 




Fig. 108. — Corrugator, Single and Double Facer in Tandem. 



230 



SOLUBLE SILICATES IN INDUSTRY 



Effect of Moisture. One of the fundamental economies of the 
paper shipping container is the feasibility of putting it into the beater 
of a paper mill and making it into fresh paper after it has done its 
initial service. This means that it must be possible to reduce it to pulp 
with water. Not only old containers but the trim and waste from the 
combining machines must be reworked. With this, an absolutely water- 
proof adhesive is incompatible. 

Silicate without any additions to increase its water-resistance not 
only makes a board that can be reworked, but if precipitated with alum 








Fig. 109. — Board Made with Silicate 
Containing 9% Na 2 as Applied. 
Water Applied by Inverted Glass 
for 7 Hours. 



Fig. 110. — Board Treated Identically 
with Fig. 109, Differing from It 
Only in That the Silicate with 
Which the Board Was Made Con- 
tained 11% Na 2 0. 



it imparts a hardening effect to the new sheet and improves its surface 
and strength. Silicates are added for this purpose to many paper 
stocks in which they do not occur accidentally, or better incidentally, 
as adhesives. 

Water-Resistance. Rosin size is depended on for water-resistance 
in container board; it is adversely affected by alkalies, and all adhesive 
silicates are alkaline. The remedy lies in using silicates of the lowest 
alkalinity consistent with mechanical necessity, in applying them as 
sparingly as may be to give good adhesion, and in causing them to 
dry in the shortest possible time, thus localizing their effect. 

Water tests were made by inverting a drinking glass full of water on 
sheets made from the same paper but different silicates (Figs. 109 to 
112). 



ADHESIVES 



231 



The photographs show the penetration of water after seven and fifteen 
hours with Na 2 0, 3.3Si0 2 and Na 2 0, 2.9Si0 2 . Translated into the con- 
ditions of a box in a rainstorm, the difference, which corresponds to 
but 2 per cent Na 2 0, is the difference between success and failure. The 
more alkaline silicate is attractive on account of its greater tackiness, 
but for the reason given it should never be used within one thickness 
of paper from the outside of the box. 

This consideration does not apply- to the adhesive used for sealing 
these containers, for the sealing silicate is always at least three layers 
of paper away from the outside and does not penetrate to the surface. 





Fig. 111a. — Board Made with Silicate 

Containing 9% Na 2 as Applied. 

Water Applied by Inverted Glass 
for 15 Hours. 



Fig. 111b. — Board Treated Identically 
with Left Hand Specimen, Differing 
from It Only in That the Silicate 
with Which the Board Was Made 
contained 11% Na a O. 



Alkalinity. The lowest practical alkalinity for adhesive use is near 
Na 2 0,4Si0 2 . 48 The water test was applied to some board made with 
this silicate. When stored dry the rosin size was not affected. Storage 
of a month over water in a closed vessel, followed by the water test, 
gave a sharp contrast between Na 2 0, 3.3SiOo and Na 2 0,4Si0 2 . Figure 
112 is the obverse view. 

Sealing. Corrugated shipping cases are sealed with silicate adhe- 
sive spread by hand or mechanically. As in the manufacture of the 
board, the most economical results are obtained where a firm pressure 
is applied as soon as the silicate is spread. This is easily provided in 

^Stericker, Wm., U. S. Pat. 1,462,835 (July 24, 1923). 



232 



SOLUBLE SILICATES IN INDUSTRY 




Fig. 112. — Corrugated Paper. Comparison of Water Resistance with Silicate, 

Ratio 1 : 3.3 and Ratio 1 : 4. 




Fig. 113.— Automatic Silicate Sealing of Fiber Containers. 



ADHESIVES 



233 



setting up the box and sealing the bottom before filling but much more 
difficult after the container is packed with some light or fragile ware. 49 




Fig. 114. — Silicate Sealing Fiber Containers. Silicate Spread Manually. 

The greatest measure of success is believed to be obtainable with 
a silicate close to the composition Na^O, 2.9Si0 3 concentrated to a vis- 




Fig. 115. — Glassware in Corrugated Paper Box. 

cosity of 800 centipoises which corresponds to a specific gravity near 
1.48 

This solution weighs 1.47 kilograms per liter (12.3 pounds per U. S. 
gallon) and this amount will seal 300 boxes 30.5 X 30.5 centimeters 

48 "Packing for Domestic Shipment," U. S. Dept. of Commerce, Domestic 
Commerce Series No. 10, p. 10, 1927. 



234 SOLUBLE SILICATES IN INDUSTRY 

(12X 12 inches), with careful hand spreading using a brush, or 27.87 
square meters (300 square feet) of flap area. On boxes which have 
been highly sized it is needful to dilute the silicate to obtain the best grip 
on the paper. This process increases the spread but necessitates spe- 
cial precaution to obtain good contact. Ten per cent of added water 
will give a spread of about 9.45 square meters per liter (385 square feet 
per gallon) while 25 per cent increases this to approximately 14.7 square 
meters per liter (600 square feet per gallon). 

The Forest Products Laboratory 50 determined, by a series of tests, 
that maximum strength of the silicated joints of fiber boxes was not 
reached until 4 hours had been given the silicate of soda for setting. 
The tendency of the board to absorb water from the silicate causes 
a weakening of the silicate joint between the jute and the chip. Be- 
fore the board can reach its maximum strength, this water must have 
been evaporated through it, which because of its thickness is a slow 
process. Their tests showed that temperature had an effect on the 
rate of drying of the silicate joint only under extreme conditions ; at 
normal working temperatures no effect could be detected. 

Silicate adhesives when they have set in the air as on brushes or 
machine parts are more difficult to remove than glue or dextrin. It 
is therefore wise to keep all machinery in contact with silicate thoroughly 
clean. This is easily accomplished by treatment with hot water or a 
steam jet at the close of each working period. Failure to attend to 
this may involve a laborious operation of chiseling away the accumu- 
lation or the less satisfactory expedient of dissolving it off with a hot 
caustic soda solution. The other side of the balance is that the silicate 
adhesives are sterile, odorless, and inexpensive. They are supplied at 
controlled viscosities ready to use and thus repay the care required to use 
them. 

Laminated Board 

Specifications. While corrugated board is best adapted for fragile 
goods, there is great demand for a paper container of maximum 
strength which need have no shock-absorbing properties. To meet 
this, chip board is laminated flat with a silicate adhesive. It is not 
economical to make thick paper upon the ordinary paper machines. 51 
Thirty points, that is, thirty thousandths of an inch, is the maximum 
for container stocks on account of the slowness of drying. If there 

50 Hale, H. M., Second Progress Report, Project L-207-4, Forest Products 
Laboratory, Madison, Wis.: March 11, 1919. 

51 Mai com son, loc. cit. 



ADHESIVES 235 

are exceptions for special purposes this is certainly true of chip board 
and container test board, the production of which engages the largest 
paper machines thus far built. They must operate at high speed and 
minimum cost. Sixteen points is the thickness of most of these prod- 
ucts. One machine with which the author is familiar makes a sheet 
154 inches wide, 16 or 20 points thick, and runs at 250 feet per minute, 
producing 178 tons of paper daily. 

In order to make boxboard it is usual to combine chip board inner 
sheets with liners of higher test and water-resistance. The liner when 
folded into a tray must hold water for 6 hours and must meet the 
specifications given below : 

Table 82. Specifications for Solid {Laminated) Box Board. 







Maximum 








Combined 


Maximum 


Minimum 


Required 


Dimensions, 


Gross Weight 


Thickness 


Strength, 


Length and 


Package 


of Board 


Mullen 


Width and 


and Contents 


(In.) 


Test (Lbs.) 


Depth (In.) 


(Lbs.) 


0.060 


225 


60 


40 


0.080 


275 


65 


65 


0.100 


325 


70 


90 



The silicate, according to these specifications, should conform to the follow- 
ing analysis : 

"(a) For manufacturing plyboard the ratio of soda to silica must not be 
greater than 1 to 2.8 with a specific gravity not exceeding 47°Baume at 68° F.. 
and it is recommended that silicate of soda having ratio of soda to silica not 
exceeding 1 to 3.25 with a specific gravity not exceeding 43°Baume at 68°F. be 
used where manufacturing conditions permit. 

"(b) The silicate of soda must be as evenly spread as possible and should not 
exceed in amount from 15 to 18 pounds per 1,000 square feet of each film of 
cement used in the board. 

"(c) For cementing the closures of plyboard boxes the ratio of soda to silica 
must not be greater than 1 to 2.8 with a specific gravity not exceeding 47°Baume 
at 68°F., nor be less than 1 to 3.0 with a specific gravity not less than 41°Baume 
at 68° F." 

Manufacture. Meeting of the specifications is accomplished by 
building up a combined board three-, four-, or five-ply. The silicate 
used is ordinarily Na 2 0, 3.3Si0 2 , but it may be less viscous than that 
used for corrugated board. The usual method of application is to 
draw the inner sheets through a silicate bath and then to bring them 
together with the dry liner sheets between heavy press rolls which 
squeeze out any excess silicate and allow it to drain back into the 
main supply. A series of other press rolls keeps the paper in contact 
as it passes to the cutting end of the machine. The operation is con- 
ducted without heat and very rapidly. Two hundred linear feet per 
minute is usual. As the machine may be less than fifty feet from the 
first press roll to the cut off where the board must be ready to make 



236 



SOLUBLE SILICATES IN INDUSTRY 



into boxes it will be seen that the silicate must set in less than fifteen 
seconds. This is possible by the use of very thin films and great pres- 
sure. Obviously all the water lost to set the silicate must be absorbed 
into the paper, as there is no opportunity for evaporation. If the paper 
contains before combining the amount of water which gives optimum 
strength, the combined board will be weaker than the sum of its plies, 
but if it be drier at first the silicate may add water which gives the 
appearance of increased strength. As the board comes into equilibrium 




Fig. 116. — Laminating Fiber Board with Silicate of Soda. 

with the air its normal strength will appear and it is this which should 
govern the selection of materials to meet a given test. 52 

Under modern practice the silicate films are so thin as easily to escape 
detection. A convenient way to observe them is to cut the board 
diagonally with a sharp knife, moisten the edge, and apply a drop of 
phenolphthalein solution, when the pink color will locate the silicate 
line and show that there is very little penetration into the board. 

A normal spread of silicate for a smooth chip and jute combination 

is near 0.17 kilo of 1.38 specific gravity (40°Baume) solution per 

52 Kress, Otto, and Philip Silverstein, "How Paper is Affected by Humidity," 
L-10, 529 (1917), Forest Products Laboratory, 'Madison, Wis.; presented at 
Annual Meeting Tech. Ass. of Pulp & Paper Industry, New York (Feb. 8, 1917). 



ADHESIVES 



237 



square meter (35 pounds of 1.38 specific gravity solution per 1000 
square feet) of three-ply board. Slightly better spreads can be had by 
using Na 2 0, 3.9Si0 2 on account of its still smaller tendency to penetrate 
the paper. 

Maximum water-resistance is sometimes secured in a board of this 
type by introducing as one of the interior plies a sheet containing a 
film of asphaltic material. 53 

Sealing. Solid fiber boxes are sealed in much the same way as 
corrugated, but it is to be noted that when there are asphaltic layers so 
near the surface that the board will not take up enough water to set the 
silicate in a short time, the bond forms very slowly. 

The design of paper shipping containers has been carefully worked 



VARlA ^ufc SpfctO mc*Am«l 




Fig. 117. — Plan and Elevation of Combiner for Solid Container Board or Wall 

Board. 



out and points of weakness determined by the aid of a rotary drum 
tester which simulates the hazards to which boxes are subject in traffic. 
The silicate bond is always stronger than the substance of the paper. 
The silicate seal for closure stiffens the box by uniting the whole con- 
tact surface of the flaps at top and bottom and when properly made 
never fails. 

Wall Board. Thick combined boards for book-backs, cores for 
wrapping bolts of cloth, lithograph supports for advertising display, 
et cetera, are often laminated in sheet form instead of continuously 
from rolls. Thus any desired thickness can be built up and put into 
a press to set in a few minutes. The time required to build up a pile 
is long enough to make necessary a more liberal spread. Wall board 54 

53 Davidson, Frank B., U. S. Pat. 1,353,323 (Sept. 21, 1920). 
M Sandor, Nikolaus, Ger. Pat. 389,536 (1924) ; Papicr-fabr., 22, pt. 84 (Mar. 2, 
1924). 



238 



SOLUBLE SILICATES IN INDUSTRY 




Fig. 118. — Drum Tester. (By courtesy of Container Testing Laboratories, Inc. 

Rockaway, N. J.) 




Fig. 119. — Drum Tester. (By courtesy of Container Testing Laboratories, Inc., 

Rockaway, N. J.) 



ADHESIVES 



239 



for interior building construction is laminated continuously but differs 
from container board in that the plies arc usually thicker, about 0.127 
centimeter (0.050 inch), and finished with a rougher surface. Built up 
four-ply they require a thicker silicate and a heavier spread, for the 
finished product must be as stiff as possible ; 0.248 kilo per square 
meter (50 pounds per 1000 square feet) of four-ply board is usual. 
This industry has in recent years reached substantial proportions. 

A piece of wall board shown in the cut was built into a house in 
the tropics where it was attacked by white ants. They cut an intricate 
series of passages as shown, but ate the wood pulp down to the first 
silicate layer only. It is not known whether the taste of the silicate or 
the hardness of the film was the determining- factor, but more likely the 
latter as silicate of adhesive grades tastes to us not unlike baking soda 




Fig. 120.— Wall Board Attacked by White Ants. 

and very much milder than the same amount of Na 2 0, as hydroxide. 
The tendency of silicate films to repel vermin is a distinct advantage 
when it is used for containers for the transport of food or other com- 
modities likely to be attacked. 

Miscellaneous Uses. 

Paper Tubes. Paper tubes present a set of adhesive requirements 
quite different from either corrugated or flat laminated papers.* 
Spirally wound tubes are made from narrow strips of paper drawn 
around a mandrel by the friction of leather belts. Except for large 
diameter tubes or tubes made on machines which move slowly enough 
for the silicate film to become sticky after spreading, the chief difficulty 
lies in a tendency of the paper to slip and fold under the traction of 

* Cf. page 244. 



240 



SOLUBLE SILICATES IN INDUSTRY 



the belt. Mechanical improvements are tending to minimize this dis- 
advantage and some small tubes are made with silicate adhesive. Na 2 0, 
3.3Si0 2 is used to make the 12-inch diameter tubes shown in the illus- 
tration and some smaller tubes are made with more alkaline types up 
to Na 2 0,2Si0 2 , but this use has not developed to the extent that would 
be possible with a power-driven spreading device. Na 2 0,2Si0 2 has 
just the needed properties of stickiness and quick set at 61°Baume, 
but its viscosity is too great to permit handling it satisfactorily on 
machines built for the much more fluid hot animal glue solutions which 
become sticky by cooling immediately after spreading. 

A conically wound paper barrel shown in Figure 123 is another 





Fig. 121. — Spiral Wound Containers. 



Fig. 122. — Straight Sided Paper Bar- 
rel Making with Silicate Adhesive. 



variation of the use of silicate adhesives on paper. 55 Convolute or straight 
wound tubes are also easily made with silicate solutions as adhesives. 

Label Pasting. Label pasting with silicates is widely practiced where 
labels printed in black are used, as on rolls of paper. Silicate solutions 
give good adherence on clean tin plate, but on thin papers it is neces- 
sary to avoid colors which are sensitive to alkali. Papers which con- 
tain large amounts of mechanical wood pulp or unbleached fibers are 
likely to show some discoloration when thin sheets are pasted with it. 
This is reduced to a minimum by using Na 2 0,4Si0 2 , spreading it very 
thin, and drying quickly to prevent penetration. 56 

55 Snyder, George C, U. S. Pat. 1,270,889, 1,270,890, 1,270,891 (July 2, 1918). 
^Furness, Rex, /. Soc. Cheni. Ind., 41, 18, 381 R-384 R (1922). 



ADHESIVES 241 

Splicing Felt Paper. Silicate solutions have been found the most 
satisfactory adhesives for splicing felt paper which is to be drawn 
through a bath of hot asphalt for saturating to make roofing because 
it sets quickly and resists for a sufficient time the temperature of the 
bath. 

Silicating Watch Screws. A certain watch manufactory places 
minute screws in position for polishing by drawing them with a par- 
tial vacuum into holes in a polishing head. When the screws are in 
place the head is painted with a viscous silicate which holds them in 



Fig. 123. — Tapered Paper Barrel Made with Silicate Adhesive. 

place. The vacuum is then released and the heads are polished with 
minimum labor. 

Instances of adhesive uses of pure silicates could be multiplied but 
those described will give an idea of the behavior of the adhesive solu- 
tions by themselves, and we shall next consider adhesive mixtures. 

Adhesive Mixtures. 

Mixtures with Insoluble Inorganic Powders. 

Wall Board Requirements. Wall board being much heavier than 
container board and having three thick adhesive layers to help stiffen 
it, is passed more slowly through the combiner than stock with very 
thin silicate films. The viscosity of the films increases more gradu- 
ally, the adhesive is slow to set. Also because the board is heavy and 



242 SOLUBLE SILICATES IN INDUSTRY 

more difficult to handle, the machines are stopped relatively often for 
adjustments, and rolls of paper of 0.050 inch thickness contain less 
area than like weights of thinner stock. On these accounts it is de- 
sirable to use an adhesive which will remain sticky on the part of the 
paper which has been spread and not pressed together. Here surface 
evaporation comes into play and Na 2 0, 3.3Si0 2 will lose its ability to 
wet the dry liner sheet within about two minutes. A natural remedy 
would be to use a more alkaline silicate which remains sticky for a 
longer time. Na 2 0, 2.9SiQ 2 has been used and with it a waiting period 
of about seven minutes is possible. Its behavior on the machine is 
satisfactory — it holds the edges well and gives a minimum loss from 
imperfect sheets. 

Diffusion of Sodium Compounds. The relative water-resistance 
of these two types of silicate was illustrated in describing corrugated 
paper. The wall board being made cold and having three thick layers 
of silicate between heavier paper cannot dry as quickly as container 
board, and this favors diffusion of sodium compounds through the 
board and liability to stain. The mechanism of this transfer has not 
been entirely explained, but it is not a simple case of diffusion of sili- 
cate. There is a sort of dialysis at work which leaves most of the 
silica where it was first laid and the sodium-bearing solution which 
penetrates contains relatively little silica. Similar phenomena occur 
with other alkaline colloids used as adhesives. The remedy is to use 
the lowest practicable ratio of Na 2 in the silicate and to dry the films 
as quickly as possible. 

Addition of Hydrous Clay. In the case of wall board, however, 
this does not provide for the slow setting requirement. Carter 5T solved 
the difficulty by diluting the less alkaline silicate and thus controlling 
the rate of set and then restoring the viscosity by adding a powdered 
hydrous clay. 

The rate of set could thus be controlled to a nicety. Na 2 0, 3.3Si0 2 
could be used as dilute as 1.31 specific gravity (35°Baume). The watery 
liquid made up with clay to the consistency of thick cream yielded an 
adhesive abundantly strong which spread at almost the same rate per 
unit of volume as the pure silicate, but because the mixture contained 
45.3 kilos (100 pounds) of silicate solution and 36.2 kilos (80 pounds) 
of clay the units of sodium oxide per unit of area were reduced and 
likewise the water per unit area. The process has been in satisfactory 
use for several years. 58 

57 Carter, John D., U. S. Pat. 1,188,040 (June 20, 1916). 

58 Thickens, J. H., U. S. Pat. 1,377,739 (May 10, 1921). 



ADHESIVES 243 

Specific data on such a use are apt to be misleading because the vary- 
ing conditions of different clays have very different effects on the vis- 
cosity of the adhesives. These variations are probably a function of 
particle size but have not been fully studied. The viscosity of silicate- 
clay mixtures rises for some time after the ingredients seem to be well 
mixed. This may be due to the wetting of particles which cannot be 
seen because they are covered by liquid masses. These mixtures can be 
stored in tanks and pumped with centrifugal pumps. 59 

Other fillers have been tried but their flowing characteristics are less 
satisfactory, — they spread poorly, or, as the operators say, they work 
"short" and have more tendency to settle out. This may also be merely 
a matter of particle size. McBain G0 concluded that finely divided silica 
had no effect on the strength of a silicate bond. 61 

Addition of Calcium Carbonate. Adhesives made from calcium 
carbonate and Na 2 0, 3.3Si0 2 have been employed for the type of wall 
board which comprises a row of wooden lath laid edge to edge and 
lined on both sides by paper. 62 ' 63 Here again, adjustment of fineness 
and concentration of the silicate are the means of adapting the adhesive 
to mechanical necessities. By using Na 2 0,2Si0 2 a greater resistance 
to water could be secured though the actual silicate used is more soluble. 

Although straight silicate solutions give good bonds on plywood made 
from gum and poplar, the results are less satisfactory on those cut 
from harder woods, such as maple and birch. It has been found that 
good adhesion can be had on these woods by adding to a 1.38 specific 
gravity (40°Baume) solution of Na 2 0, 3.3Si0 2 about 30 per cent of 
its weight of finely divided calcium carbonate. Such a mixture can be 
spread at the rate of 0.236 kilo per square meter (178 pounds per 1000 
square feet) of double glue line and is satisfactory for plywood for 
shipping cases. Other fillers have been tried without success on' these 
woods, but the reason for the special virtue of calcium carbonate is not 
known. 

A mixture of 25 parts 1.71 specific gravity (60°Baume) solution of 

Na 2 0,2Si0 2 , 25 of water, and 60 whiting, when spread upon paper 

boards becomes substantially insoluble in a week, and the board when 

redried is found to be stuck together, but while wet the bond is weak. 

It is strong enough to hold paper but insufficient for plywood. 

30 Thickens, loc. cit., and U. S. Patent Serial No. 3,396, Interference No. 41, 
800 (1919). 

60 "Second Report of Adhesives Research Committee," London: His Majesty's 
Stationery Office, 1922, p. 81. 

61 Schleicher, U. S. Pat. 1,162,712 (Nov. 30, 1915). 

02 Magelssen, N., U. S. Pat. 1,487,255 (March 18, 1924). 

63 Smith, R. H., and R. B. Beal, U. S. Pat. 1,513,191 (Oct. 28, 1924). 



244 SOLUBLE SILICATES IN INDUSTRY 

Silicate-Carbohydrate Mixtures. 

Starches. Starches hoiled in silicate solutions may yield adhesives 
strong enough to be used on wood veneer, that is, having a tensile 
strength up to 35.2 kilos per square centimeter (500 pounds per square 
inch) between maple blocks glued end to end, but they carry much 
more water than the silicate solutions and for most purposes have 
little advantage over them. Some care must be given to proportion the 
mixtures so that they remain homogeneous. Two formulas which have 
been tested are given. 

Table 83. Formulas for Silicate-Starch Mixes. 

1. 

100 parts by wt. Na 2 0, 3.34Si0 2 1.37 specific gravity. 

5 parts of starch, mixed with 4 parts water, and stirred with the silicate. 
Heated until starch loses milky whiteness, becoming nearly clear. 

2. 

50 parts starch 1 e ,. , , ,i 
im ^ , . > btirred together. 

100 parts water J fc 

Heated with 50 parts Na 2 0, 3.34Si0 2 1.38 specific gravity until mixture is 

nearly clear. 

The question as to whether the presence of starch would delay the 
decomposition of silicate adhesives by carbon dioxide was investigated 
with a negative result. 

Dextrin. Silicates may be added to dextrin adhesives for making 
spirally wound paper tubes and other uses where a low tensile strength 
suffices and a high degree of initial "tack" is required.* The adhesive 
him is somewhat more flexible than film that would be formed by the 
silicate alone, but less than the straight dextrin. The stiffening is 
often an advantage. 

Silicate-Casein Mixtures. 

Waterproof Glue. It has long been known that useful adhesives 

can be made from casein, lime, and soluble silicate, 05 ' 6G ' GT but adhesives 

of this type have come into extended use as the result of studies from 

1917 to 1921 by U. S. Forest Products Laboratory, induced by the 

need of water-resistant glues for airplane construction. This work 

eventuated in a patent to S. Butterman C8 which was assigned to the 

United States Government and dedicated to the public. Butterman's 

adhesive proved more satisfactory than any of its predecessors and has 

* Cf. page 239. 

65 Pick, Ger. Pat. 60,156 (1891). 

"■Wenck, Ger. Pat. 116,355 (1900). 

87 Jeromins, Ger. Pat. 154,289 (1904). 

«* Butterman, S. S., U. S. Pat. 1,291,396 (Jan. 14, 1919). 



ADHESIVES 245 

been extensively used. The original formula was modified by increas- 
ing the lime to add water-resistance, and the following, known as 4B, 
is the basis of practice in many industrial plants as a water-proof glue 

for wood. 69 ' 70 

Parts by Weight 

Casein 100 

Water 200-230 

Hydrated lime 20-30 

Water 100 

Sodium silicate 70 

Method of Mixing Casein Glues. 71 Attention must be given to 
the technic of mixing this or other casein glues if success is to be had. 
Dry casein is first soaked in water for 15 minutes, then hydrated lime 
and water are mixed separately and added to the casein with a me- 
chanical agitator in operation at 50-60 revolutions per minute. After 
two or three minutes the silicate solution is put in and the mixing con- 
tinued for half an hour. It is necessary to determine by test what 
amounts of water to use for a particular casein and to reject any 
batches which are too thick or too thin, rather than to attempt much 
adjustment after they are made up. 

Table 84. 

Natural sour casein takes 130-170 parts water 

Mineral acid casein takes 170-200 parts water 

Rennet casein takes about 280 parts water 

Various alkaline salts are able to extend the working life of casein 
glues but the silicates are the most effective as shown by Browne's 
graph reproduced herewith. 72 (Fig. 124.) 

The water-resistance of these glues appears to be due to reaction 
between calcium hydroxide and casein. 73 Dolomitic limes may be used 
if proper allowance is made for their calcium content. Water-resistance 
increases up to 30 parts high-calcium lime and then falls off with 
further additions. The reaction proceeds rapidly unless controlled by 
the addition of silicate, which greatly extends the time during which 
the glue remains in a workable condition. 4B formula gives a glue 
which has a working life of six to twenty-four hours. 7 ^ 

60 Prestholdt, Henry L., U. S. Pat. 1,604,311, 1,604,313, 1,604,317 (Oct. 26. 
1926). 

70 Bogue, R. H., Chem. Age, 30, 3, 103-6 (1922). 

"Dunham, Andrew A., U. S. Pat. 1,391,769 (Sept. 27, 1921). 

72 Sutermeister, Edwin, "Casein and Its Industrial Applications," New York : 
The Chemical Catalog Co., Inc., American Chemical Society Monograph Series, 
1927. 

73 U. S. Dept. Agr., Rep. No. 66, "Glues Used in Airplane Parts," 1920. 
"Dunham, Andrew A., U. S. Pat. 1,391,770 (Sept. 27, 1921). 



246 



SOLUBLE SILICATES IN INDUSTRY 



For some purposes it may be best to make a glue with less than the 
optimum amount of lime for water-resistance. This will have longer 
working life and its water-resistance may be enhanced by the method 



given below. 




flj/tall'nify in 6rt>m £oui fa I eats AaOH f er /OO Grants of Ca-reS* 

Fig. 124. — Influence of Alkalinity of Casein Glues on Their Working Life. 

Casein Glues and Heavy Metal Salts. It was found possible to 
increase the water-resistance of these glues by adding copper salts, 75 ' 76 
and some other soluble salts of heavy metals perform similar service. 77 
The explanation of this behavior is not known but it increases the 
permutations by which these glues can be adapted to longer or shorter 
working life. 

The glue known to the Forest Products Laboratory as No. 11 em- 
bodies this idea as follows : 

Casein 100 

Water 220-230 

Hydrated lime 20-30 

Water 100 

Silicate of soda 70 

Cupric chloride 2-3 

Water 30-50 

75 Butterman, S., and C. K. Cooperrider, U. S. Pat. 1,456,842 (May 29, 1923). 
78 Jones, W. L., "Improved Casein Glue Containing Copper," 8, 4477 (1922), 
Madison, Wis.: Forest Products Laboratory. 
"Henning, S. B., Can. Pat. 226,535 (1922). 



ADHES1VES 



247 



The procedure in the first three steps is the same as for 4B. The 
mixture is brought to a smooth consistency after the silicate is added ; 
then the solution of cupric chloride or an equivalent amount of sulfate 
is added slowly with stirring. It tends to form lumps, but these dis- 
perse to make a smooth violet-colored adhesive of excellent water- 
resistance. 

Silicate solutions may be added to thicken or reduce the cost of glues 
made from casein and caustic soda. 78 These are strong but without 
great water-resistance. 

Properties. Casein-lime-silicate glues make joints on wood which 




Fig. 125.— Plywood Door in Water Soaking without Damage. 



are stronger than the wood fiber 



They will stand prolonged immer- 
sion in water or even boiling. They have somewhat greater tendency 
than animal glues to dull knife edges of woodworking tools, but can 
be easily sawed. Among the many combinations possible it appears that 
casein glues free from lime and containing silicate can be produced 
with a high degree of water-resistance, but the technic of their manu- 
facture has not been divulged. They are said to have no more effect 
on cutting tools than the wood itself. 

78<, Casein Glues, their Manufacture, Preparation, and Application," Madison, 
Wis.: Forest Products Laboratory, revised July, 1923, 



248 SOLUBLE SILICATES IN INDUSTRY 

The spread and hence the cost of these adhesives will depend upon 
working conditions. A thick quick-setting glue will obviously not 
spread as far as a thinner glue which, containing more silicate, may 
remain in working condition for several days. Thirty square feet of 
three-ply panel per pound of dry casein is easily attained. 

Substitutes for Casein. A product of lower adhesive strength but 
otherwise comparable has been made from condensed buttermilk. 

Vegetable proteins offer an attractive source of cheap water-resisting 
adhesive. Soya bean meal 79 has been used and with suitable allow- 
ance for its individual characteristics yields a strong water-resistant 
glue with a wet mix using lime and silicate solution. Other press cakes 
from oil-bearing seeds, such as peanut and cottonseed, are susceptible 
to similar treatment. 80 

Dry Mixtures. Various dry mixtures containing casein and solvent 
are on the market. Most of them can be extended and reduced in cost 
by adding silicate as the final step to the wet mixture, but attempts to 
use soluble forms of silicate in the dry mixture have had very limited 
use. 

It is usually possible to make a better glue from the same casein by 
observing the sequence of steps specified in formula 4B or with the addi- 
tion of heavy metal salts as in formula 11, than by attempting to use 
a mixture which contains protein, solvent, and lime, all coming into 
contact with water at the same time. Dry mixtures generally require 
more solvent, which does not add to adhesive strength or water-resis- 
tance but is only a means of bringing the protein into condition to spread 
and should, therefore, be kept to a minimum. 

A dry product described by Bogue 81 is made by dissolving gum 
arabic in a silicate solution, 1 part of gum in 5 parts 1.38 specific gravity 
(40°Baume) Na 2 0, 3.3Si0 2 evaporated to dryness and ground. This 
is a difficult procedure. 

Gum-silicate mixture 50 mesh 20 parts 

Casein 40 40 

Calcium hydroxide 150 25 

This is to be made up with 45 parts of dry mix in 100 parts water, or 
the following for a wet mixture with gum arabic : 

Casein 47 

Calcium hydroxide 29.5 

Silicate 15.5 

Gum arabic 8 

79 Johnson, Otis, U. S. Pat. 1,460,757 (July 3, 1923); reissued 16,422 (Sept. 
14, 1926). 

80 Osgood, G. H., U. S. Pats. 1,601,506, 1,601,507 (Sept. 28, 1927). 
sl Chem. Age, 30, No. 3, 103-106 (1922). 



ADHESIVES 249 

It is obvious that many other minor ingredients can be used to modify 
the character of these adhesives, as glycerin, shellac, rubber latex, and 
a large number of earthy materials. 82 ' 83 

Blood Adhesives. 

Wood's Glue. Blood adhesives set by heat which coagulates the 
albumin are among the most resistant to water. They also may be made 
up with silicate solutions. Wood 84 calls for : 

1 gallon saturated solution of silicate of soda (presumably 

Na 2 0,3.3Si0 2 1.38) 

2 gallons blood 

3 gallons water 

0.1 ounce ammonia water (if quick drying is desired) 

Good results may be obtained when the ingredients are varied in 
amounts as much as 20 per cent. Heating is carried on at temperatures 
not less than 65 °C. nor more than 93 °C. This mixture, when used to 
join two surfaces, dries and hardens to be waterproof within twenty- 
four hours without applying heat to the surfaces. 

Haskell's Glue. Another glue of this type is that of Haskell. 85 ' 86 
To 45 parts blood albumin and 55 parts water, 9 per cent of sodium 
silicate based on albumin is added and mixed until the mass is a homo- 
geneous syrup. The specification does not make clear the exact char- 
acter of the silicate to be used. It is believed, however, that Na 2 0, 
2.9Si0 2 , specific gravity 1.48, was intended. 

Glue-Silicate Mixtures. 

There are many adhesive mixtures in which silicates occur as minor 
ingredients along with glue. Glue hydrolized with silicate solutions is 
said to be stronger but more brittle than that hydrolized with sodium 
hydroxide. This may be overcome by adding glycerin but the film is 
thus made hygroscopic. 87 An example of the complicated mixture with 
glue is that of Tsukoski, 88 - 80 which calls for : gliopeltis f urcata, glue, 
sodium silicate, potassium dichromate, alcohol, lead oxide or lead acetate. 

82 Isaacs, M. R., U. S. Pat. 845,791 (March 5, 1907). 

83 Dance, Edward L.,*U. S. Pat. 1,478,943 (Dec. 25, 1923). 

84 Wood, W. W., U. S. Pat. 1,270,477 (June 25, 1918). 
83 U. S. Pat. 1,516,567 (Nov. 25, 1924). 

M Drushel, W. A., U. S. Pat. 1,476,805 (Dec. 11, 1923). 

87 Tressler, D. K., personal communication. 

88 Jap. Pat. 38,763 (June 1, 1921). 

89 Bottler, Max, Kunstoffe, 15, 89-91, 114-117 (1925). 



250 SOLUBLE SILICATES IN INDUSTRY 

Other Materials Compatible with Silicate Solutions. 

Various substances which are compatible with silicate solutions may 
be used to modify the character of adhesive films which are primarily 
composed of silicate as well as those which are more complex. 90-94 The 
permutations of the mixtures are infinite. Gum arabic has already been 
mentioned. Other water-soluble gums can be employed. Gum shellac 
can be dispersed in silicate solutions with or without the aid of am- 
monia. Glycerin is a favorite means of retarding drying and thus re- 
taining a degree of flexibility not inherent in the silicate film. Mal- 




Fig. 126. — Rubber Latex Particles Suspended in Silicate Solution. Magnified 1200 

Times. 

colmson extended silicate solutions without loss of viscosity by mixing 
them with sodium chloride brines. 

Rubber latex stabilized with ammonia mixes readily with adhesive sili- 
cate solutions, softening and increasing the flexibility of the film. 95-97 It 
also increases somewhat the resistance to water, but being a discontinu- 
ous material, it cannot protect the silicate entirely from the action of 
water. 

Sugar can also be used. 9S Commercial glucose syrup mixes in the 

90 Malcolmson, J. D., U. S. Pat. 1,379,639 (May 31, 1921). 

91 Dahse, W., Ger. Pat. 318,516 (Aug. 23, 1918). 

92 /. Soc. Chem. Ind., 39, 517A. 

93 Meta, Sarason, Ger. Pat. 316,080 (Nov. 13, 1919). 

^Besele, Lynaz, Ger. Pat. 61,703 (1892). 

93 "Silicate P J s & Q's," 5, No. 5, Philadelphia, Pa. : Philadelphia Quartz Com- 
pany, 1925. 

^Teague, M. C, U. S. Pat. 1,550,466 (Aug. 18, 1925). 

97 See also, Harris, John, U. S. Pat. 1,631,265 (June 7, 1927), which is a modi- 
fication of U. S. Pat. 1,498,270 (June 17, 1924). 

^Hacket, William, Brit. Pat. 20,528 (1900). 



ADHESIVES 251 

cold with adhesive silicates but reacts and causes gelation when heated. 
Many hydrolized products such as corn cob adhesive are miscible. 99 ' 10 ° 
Waste sulfite liquors and vegetable tanning extracts can be mixed after 
a pretreatment with sodium hydroxide. 

Testing Adhesives. 
The art of making and using adhesives has not yet advanced to a 
point where results can with safety be predicated from tests other than 
those which simulate the conditions of service. Except in the cases of 
a few materials which have been intimately studied, as glue, and 
starch, we must rely on actual measurements of bond strength with 
variations of moisture, setting time, or other factors of import in the 
industrial processes concerned. The older literature pays little atten- 
tion to the evaluation of adhesives and the more recent is specific to 
the arts concerned. Wood-gluing, because it makes maximum demand 
on adhesive strength, has had the most attention ; but even here the 
practice of industry is only beginning to be systematic. Much is to be 
expected when more complete and comprehensive studies of adhesives 
have been made. 101-105 

General References 

General references on adhesives in which references are made to 
soluble silicates are given below. 

Breuer, Carl, "Die Kitte und Klebstoffe," Leipzig: Dr. Max Janecke, Verlags- 
buchhandlung, 1922. 

Kausch, "Adhesives and Binding Materials," Kunstoffc, 3, 63-66, 89-92, 110-11? 
127-130 (1913). 

Allen and Truax, "Glues Used in Airplane Parts," U. S. National Advisory 
Committee for Aeronautics, Report No. 66 (1920). 

Standage, H. C, "Agglutinants of all kinds and for all purposes," London : 
Archibald Constable & Co., Ltd., 1907. 

Scherer, "Casein : Its Preparation and Technical Utilization," London : Scott, 
Greenwood & Co., 1911. 

Furness, Rex, /. Soc. Chcm. Ind., 41, 381R-384R. 

Sutermeister, Edwin, "Casein and Its Industrial Applications," New York: 
The Chemical Catalog Co., Inc., American Chemical Society Monograph Series 
1927. 

"LaForge, F. B., U. S. Pat. 1,285,249 (Nov. 11, 1918); Fibre Containers 6 
38-40 (1921). 

100 Sweeney, O. R., Ioiva State College of Agriculture, Bull. 73, 23, No 15 
(1924). 

101 Elmendorf, Armin., Proc. Am. Soc. Testing Materials, 20, 324 (1920). 

102 Forest Products Laboratory, Technical Notes : "Effect of Age on Casein 
Glues," Lo-11, 377, No. F-18, and "Method of Testing Strength of Joint Glues " 
Lo-11, 320, No. F-16. 

103 Wagner, H., Farben-Ztg., 31, 2132 (1926) ; Brit. Chcm. Abstracts, 45, No 32 
638 (1926). 

101 "Second Report of the Adhesives Research Committee," Dept. Sci. Ind. 
Research, London: His Majesty's Stationery Office, 1926. 
103 Vail, James G., Fibre Containers, 6, No. 9, 16 (1921). 



Chapter IX. 
Sizes and Coatings. 

The Nature of Silicate Films. 

Properties of Silicate Films. 

Just as many a prospector has found pyrite and imagined it to be 
gold, so great numbers of experimenters have found that silicate solu- 
tions produce a beautiful, transparent, and colorless film, and have re- 
garded it as a new mineral varnish, not only cheaper, but with out- 
standing advantages over the materials hitherto used. These silicate 
films would be incombustible and odorless ; the supply would be un- 
limited ; the solvent for reducing them would be water. 

Silicate solutions do, in fact, produce handsome films ; but they 
have three inherent limitations : they are slowly soluble in water ; they 
absorb carbon dioxide from the air, and tend to lose their pristine 
beauty by efflorescence ; they lose water and become brittle, which 
eventually means they become discontinuous. 

There are means of limiting the effect of these undesirable charac- 
teristics, so that even though the silicates can never be the universal 
coating medium of which inventors have dreamed they yet serve to 
make films of considerable importance in industry. 

Effect of Ratio. 

Beginning with Na 2 0,4Si0 2 , we obtain colloidal solutions charac- 
terized by the ability to set very rapidly by the loss of small amounts 
of water. A 35 per cent solution assumes the appearance of dry var- 
nish when it has lost 10 per cent of its weight of water. This film is 
least affected by moisture or carbon dioxide, and it passes most quickly 
through a crumbling stage to brittleness. 

As the alkalinity increases, the setting time is lengthened, the solu- 
bility and ability to take up carbon dioxide is increased, and water is held 
more firmly, extending the period in which the film may be bent with- 
out cracking. 

When the last solution which retains its colloidal character under 

252 



SIZES AND COATINGS 253 

all ordinary conditions (Na 2 0, 1.5Si0 2 ) is reached, setting takes place 
only in a dry or warm atmosphere ; solubility is high and the film instead 
of being gelatinous is sticky. Jts ultimate disintegration is more likely 
to be due to crystallization of sodium carbonate than to the brittle char- 
acter which results from dehydration. 

Procedure to Offset Limitations. 

The best means of counteracting solubility of silicate films is to cover 
them with water-resisting media or to cause the colloidal silicate to be 
protected by the formation of an insoluble gel. This is brought about 
by securing the presence of a suitable amount of metastable silica which 
gels when water is evaporated. The latter may be prepared by neu- 
tralizing a part of the silicate solution with acid and preventing imme- 
diate gelation by the addition of more silicate. The gel forms when the 
film begins to evaporate. 1 This is more fully treated in the chapter on 
gels. Materials with which silicate films may be overlaid are paraffin, 
chlorinated naphthalenes, rubber solutions or latex, waxes, gum solu- 
tions, nitrocellulose lacquers, or other colloidal films which are not easily 
saponified. 

Films which are laid upon a surface to alter its properties are subject 
to the same sort of modification as adhesive films. They may be mixed 
with suitable colloids to alter their character. Starch, glycerin, and 
rubber latex are the most useful. It is obvious that any adhesive can 
also be used as a sizing agent, but the reverse is not true since the sizing 
agent often lacks adhesive properties. 

Uses of Silicate Films Without Pigment. 

Coating Papers. 

Method of Application. Manila or chip board for making cartons 
to contain coffee or condiments is much more permeable than the metal 
containers which were formerly used. Its resistance is improved by a 
silicate coating. Na 2 0, 3.3Si0 2 or Na 2 0,4Si0 2 are adapted for coating 
paper. They are spread very thin with steel rolls for smooth papers, or 
with rolls covered with rubber for papers of uneven surface. The 
amount of silicate on the basis of 1.38 specific gravity for Na 2 0, 3.3Si0 2 
varies from 9.81 kilos per 1000 square meters of surface to 98.1 kilos 
(two pounds per 1000 square feet to about 20 pounds). To make a 
light coating under paraffin, 24.6 kilos per 1000 square meters (five 
pounds per 1000 square feet) is a fair average amount. 

'Vail, James G., and John D. Carter, U. S. Pat. 1,129,320 (Feb. 23, 1915). 



254 



SOLUBLE SILICATES IN INDUSTRY 



Silicate films as thin as these, when spread upon a porous surface 
like paper, set very rapidly. It is usual to run coating machines at 
two hundred linear feet per minute and to have the silicate film dry 
enough to permit a final coat of paraffin within about 9 meters (30 feet), 
i.e., within ten seconds. This is important as paraffin will not properly 
wet a moist surface but will "crawl" unless the silicate seems dry to the 
touch. The speed will depend somewhat upon atmospheric conditions 




Fig. 127. — Cartons Sized with Silicate. 



and upon the moisture in the paper. Concentration of the silicate and 
also machine conditions must be adjusted to compensate for changes of 
humidity and temperature. Thus a specific gravity of 1.32 may be right 
for dry warm weather, but a somewhat higher specific gravity with a 
closer set of the spreading roll may serve better when it is cooler or more 
humid or when the paper is not as dry as it should be. As the viscosi- 
ties of the silicates have an important bearing on this use, Na 2 0,4Si0 2 
must be run at a lower concentration than the more alkaline grades. 
It sets faster, but this advantage is offset by greater sensitiveness of 
viscosity to temperature changes. 2 

Grease-proofing. It has been asserted that soluble silicates are not 
adapted to grease-proofing paper. As applied to perfect resistance, such 
as sheet metal gives, this is true, for the silicate film develops hair 
cracks in time. The following tabulation showing the time required 
for grease to penetrate silicated cartons in comparison with plain patent 

3 Paper, 22, 358 (1919). 



SIZES AND COATINGS 255 

coated stock and plain double-lined manila shows the different behavior 
of various oily foodstuffs as well as different cartons. 3 ' 4 

Table 85. Time in Days Required for Penetration of Grease. 
(Each figure is the average of 5 tests.) 

Silicated Plain Patent Plain Double 

Cartons Coated Manila Lined 

Prepared flour No. 1 160 21 4 

Prepared flour No. 2 41 30 13 

Shredded coconut 79 3 2 

Peanuts 5.5 1 1 

Chocolate wafers 270+ 146 104 

Extensive studies have shown that silicated stock is very useful in 
keeping crackers and biscuits fresh. This is due to the fact that passage 
of moisture through the board is delayed. Silicates of soda are soluble 
in water but the untreated paper acts like a wick and the silicate coat- 
ing stops this action almost completely. Oil-bearing materials differ 
greatly in penetrating power and many products which would quickly 
go through untreated paper are held by silicate films. 5 ' 6 

It has also been found that the aroma of coffee and spices is better 
retained in a package made from silicated stock. 7 Using silicate under 
paraffin serves a double purpose. It prevents the softening of the 
fiber stock by partial saturation with paraffin, and it also reduces the 
amount necessary to make a continuous film. The double-coated board 
is largely used to contain soda crackers or other baked products which 
contain little oil but are kept fresh in a dry package. Additions of 
finely divided fillers, such as mica and aluminum bronze, which take 
the form of flakes, help to make grease-resisting films with silicate 
solutions. 8 

Modifications. Silicate-lined paper cartridges were used by Van 
Meter 9 as reaction chambers for generating poisonous gases from solid 
charges and chlorine. Surface sizing of paper has been done with a 
large number of mixtures with silicate as one constituent. A great 
variety of coatings suited to specific needs can easily be worked out 

3 Research Report, Folding Box Manufacturers Assoc. 

4 "Silicate P's & Q's" 5, No. 10, 1925 ; Philadelphia, Pa. : Philadelphia Quartz 
Company. 

5 Artus, W., Chem. Zentr., 28, 749 (1857). 

6 Ellis, C, U. S. Pat. 1,311,595 (1919). 

7 Vail, James G., The Spice Mill, 47, 134-136 (1924). 
8 Cavanaugh, A. J, Jr., U. S. Pat. 1,357,844 (Nov. 2, 1920). 

9 Van Meter, James W., U. S. Pat. 1,419,653 (June 13, 1922); U. S. Pat. 
1,430,772 (Oct. 3, 1922) ; U. S. Pat. 1,654,025 (Dec. 27, 1927). 



256 SOLUBLE SILICATES IN INDUSTRY 

when the properties and compatibilities of silicate solutions are under-. 
stood. 10 ' «' 12 

Among these may be mentioned the process of Wezel, 13 who uses 
horn shavings dispersed with sodium hydroxide and adds a silicate 
solution, and a process of making paper water-resistant by using a 
strongly silicated soap solution on a surface previously prepared with 
lead acetate and zinc oxide in a mixture of starch and gum arabic. 14 ' 15 

Metallic films made from foil laid on a silicate film or deposited from 
solution upon a silicated surface have been proposed. 16 ' 17 

For Memorandum Pads. A silicate coating on bleached paper of 
high grade or on bristol board is used for memorandum pads. The 
silicate surface is easily written on with a pencil and as easily erased 
by rubbing with a moist cloth. The operation may be often repeated 
before the film ceases to be effective. Bleached fiber is chosen for 
this purpose to avoid discoloration in contact with the alkaline film. 

Barrel Testing and Sizing. 

Distinction Between Testing and Sizing. Wooden containers for 
fats and oils must be treated to overcome their natural porosity. The 
practice of the industry involves two steps. The first is to test the 
tightness of a barrel or cask soon after it is set up, and the second is to 
apply a lining or sizing coat near the time when it is to be filled. Bone 
glues, pitch, and casein serve under some circumstances ; but silicates 
of soda are almost universally used for edible oils, lard, and hydro- 
genated fats shipped directly in wooden vessels. 18 

Many barrels for mineral oil are also silicate-sized, and a still larger 
number are tested with silicates over which a sizing of glue may be 
put on. 

Method for Testing. Testing is conducted by putting a gallon or 
more of hot Na 2 0, 3.3Si0 2 diluted to about 1.1 specific gravity into the 
barrel, closing the bung hole and turning the barrel about till the liquid 
covers the entire inner surface. This procedure heats the air and makes 
a pressure within, which drives the liquid into any small openings, 

"Morrison, F. J., U. S. Pat. 1,365,715 (Jan. 18, 1921) ; Papier, 22, 358 (1919) ; 
C. A., 14, 627. 

"Kojima, Yonejiro, Jap. Pat. 42,365 (April 20, 1922) ; C. A., 18, 470. 

"Crowell, Charles H., U. S. Pat. 1,577,450 (March 23, 1926). 

13 U. S. Pat. 686,374 (Nov. 12, 1901). 

"Sekiya, Keiya, Jap. Pat. 41,392 (Jan. 12, 1923) ; C. A., 17, 2645. 

"Menzel, K. C, and Paul Meyerburg, Ger. Pat. 405,299; Papier jabr., 22, 
573-4 (Nov. 30, 1924). 

16 Marino, Pascal, Brit. Pat. 20,012 (Jan. 11, 1912). 

"Diamond Decorative Leaf Company, Brit. Pat. 186,889 (June 14, 1923). 

18 Batchelder, James H., U. S. Pat. 900,256 (May 5, 1908). 



SIZES AND COATINGS 



257 



whence it exudes with a hissing sound which is easily detected. A peg 
driven into a worm hole is adhesively fastened in place. Some porous 
parts of the wood are closed by the silicate itself, and the cooper knows 
when his work is water-tight. The bung is now removed and the excess 
liquid returned to the heater for further use. One-half pound of 
silicate solution, specific gravity 1.38, is needed per 50 gallon barrel 
for testing, though some kinds of wood will absorb more than others. 



ZINC 
CHLORIDE 




SODIUM 
SILICA T E 




10 9 
fafefcM* 



7 6 5 4 

wlwiiitoiinfriiHi'iiiir 



10 12 3 

rtaaflaf- . ....-lii'MiH O.iHiiitiAli^llf 



9 10 



Fig. 128. — Comparative Penetration of ZnCl 2 and Na 2 0, 3.3Si0 2 into Hemlock. 
(Courtesy of Forest Products Laboratory.) 



It is noteworthy that sound wood excepting those varieties which, 
like oak, have natural canals of considerable size is not easily pene- 
trated by silicate s'olutions. Hemlock test pieces put into a vessel from 
which the air was exhausted, then covered with silicate solutions and 
subjected to 50 pounds pressure while immersed, showed a penetration 
of only an eighth of an inch from the sides and less than half-an-inch 
from the ends. Another experiment shown in the cut illustrates the 
great difference in penetration when attempts were made to saturate 
wood with ZnCl 2 and Na 2 0, 3.3Si0 2 . 19 The testing treatment is there- 
fore primarily a means of seeking out and closing actual channels 
through or between the pieces of which the barrel is made. 

Method for Sizing. The sizing coat is made with silicate of higher 
concentration. It is well to choose conditions which will not leave a 
thick covering on the wood. The saw marks on the inner part of the 

^Teesdale, Clyde H., Fifth Progress Report, L-177, Forest Products Labo- 
ratory, Madison, Wis. 



258 



SOLUBLE SILICATES IN INDUSTRY 



barrel should be easily located with the fingers after sizing. Although 
the silicate does not penetrate deeply, thin films do derive a substantial 
measure of protection from intimate contact with wood fiber in barrel 
sizing. Thirty-five degrees Baume, 1.32 specific gravity, is right for 
Na 2 0, 3.3Si0 2 under average conditions. It should be heated to 82° C. 
(180°F.). Enough liquid should be put into the barrel to make a sub- 
stantial pressure ; five gallons is not too much. This will also insure 
heating the staves and the excess liquid can be completely drained out. 
A few accidents are on record in which the pressure has risen to a point 




Fig. 129. — Silicate Sizing Barrels. 



sufficient to blow out the head of the barrel. If too much pressure de^- 
velops, it is better to lower slightly the temperature and concentration 
of the silicate rather than to reduce the amount put in at each opera- 
tion because imperfect drainage is a source of trouble and the larger 
amount of liquid cools more slowly. The amount of silicate (40° 
Baume basis) required for this treatment will vary from 1% to 5 
pounds per 50 gallon barrel, depending on the porosity of the wood and 
the manner of handling. 

It is important to control the concentration of the silicate supply in 
the heater because hot silicate evaporates and the barrel takes up water 
as the film sets. Also the return of solution drained from the barrels 
involves exposure and concentration to a surprising degree. 

Draining is accomplished by placing the packages with the bung 
hole at the lowest point over the return trough. It should be continued 
as long as there is any flow, thirty minutes at least. Spray machines are 
also used for silicate sizing. 

Silicate sets more rapidly than glue in the badly ventilated interior of 



SIZES AND COATINGS 



259 



a barrel. Na 2 0,4Si0 2 has been used experimentally. It sets more 
rapidly than the usual material but requires much more care, due to 
its rapid rise of viscosity with concentration. This has thus far pre- 
vented its adoption, although its lower solubility and alkalinity make 
it attractive. 

Open wooden vessels, such as lard or butter tubs, are best sized by 
filling them full of hot silicate solution and allowing them to stand ten 
minutes or more before draining. 

Conditions for Use. Oils, whether animal, vegetable or mineral, 
with viscosities above 150 centipoises may be satisfactorily held in sili- 







\ :f_ 






i[ 


"^^;': : M 


" ml W 




— 


^^"^^i 




: '■ -Is 



Fig. 130. — Penetration of Turpentine through Wooden Barrel Head. 
Left, Silicate Tested, Glue Lined. Right, Glue Tested and Lined. 

cate-sized containers. Lighter mineral oils are better put into barrels 
tested with silicate and lined with glue, which is more elastic and more 
costly. Turpentine barrels thus prepared have been shown to hold 
better than glue-tested barrels but as turpentine is clouded by contact 
with silicate the practice is not considered advisable. 

Vegetable oils containing free fatty acid make it necessary to be 
careful that the silicate film is well dried before coming in contact with 
oil. If this is done, no appreciable reaction takes place. If a little wet 
silicate remains, the oil is likely to be clouded by a slight saponification. 
This has happened also to barrels which were properly sized and filled 
but not painted on the outside when they have lain awash in the hold of 
a ship. Under these conditions enough water entered the wood to dis- 
solve the silicate somewhat and cloud the oil. 

Time for Sizing. As the silicate film is subject to deterioration if 
long exposed to the air without the protection of the oil, the sizing 
should not precede filling by more than about ten days, although the 
circulation inside a barrel is poor and the film remains intact longer 
than it would were it exposed outside. In some plants drying is hastened 



260 SOLUBLE SILICATES IN INDUSTRY 

by inserting a pipe to draw out air or blow in a warm current. This is 
good practice. Unless so treated, glue sizings are prone to mold in hot, 
damp climates, where a week may be necessary to dry the coat prop- 
erly without forced circulation. Though the silicate sets faster than 
glue and does not nourish molds, better films are formed when drying 
takes place within a few hours. The drier the film, the slower will 
be the absorption of carbon dioxide. 

Fire-Proofing. 

Character of Protection. Von Fuchs coated theatrical scenery 20 
in Munich in 1820, and since that time there have been numerous cases 
in which silicate solutions were used to prevent fire. 21-37 This use de- 
pends upon the presence of a film which is incombustible. It cannot 
give much protection to combustible materials after temperatures ca- 
pable of releasing, inflammable "gases by distillation are reached. When 
the film consists of a silicate containing a substantial amount of water, 
additional protection results from its property of intumescence. When 
rapidly heated above the boiling point of water, steam is driven oil 
with sufficient energy to blow bubbles in the now liquid film and these 
as a result of the concentration solidify, making a porous mass which 
is an excellent thermal insulator. 38 So long as the film retains its 

20 Kratzer, Hermann, "Wasserglas und Inf usorienerde," Hartleben's chemisch- 
technische bibliothek, 2, Wien, 1907. 

21 Andes, Louis Edgar, "Feuersicher-, geruchlos- und wasserdicht-machen aller 
materialen, die zu technischen und sonstigen zwecken verwendet werend," 222, 
Wien: Hartleben's chemisch-technische bibliothek, 1896. 

22 V erhandlungen des V ereins sur Bejorderung des Gezverbfleisses in Preussen, 
20, 49-53 (1841). 

23 Eschenbacher, August, "Die Feuerwerkerei ; oder, Die Fabrikation der Feuer- 
werkskorper," 11, 3rd ed., Wien: Hartleben's chemisch-technische bibliothek, 1897. 

34 Neueste Ertindnngen und Erjahrungen, 40, 566-567 (1913). 
25 Hexamer, C. J., /, FrankUn Inst., 147, 65-70 (1899). 

26 Kaiser, C. G., Poly. J ., 21, 91-92 _ (1826). 

27 Roller, Theodor, "Die Impragnirungs-Technik," 219, Wien: Hartleben's 
chemisch-technische bibliothek, 1896. 

28 Sandham and Abel, Mechanics' Magazine, 67, 531-532, 580-582, 609-610 
(1857). Same, abstract, /. Franklin Inst., 68, ser. 3, 38, 284-285 (1859). Same, 
condensed translation, Poly. I., 149, 194-197 (1858). Same, abstract translation, 
Bull. soc. d'encour. I'ind. nat., 58, ser. 2, 6, 374-375 (1859). 

^Patsch, Albert, Z. ver. deut. Inge., 9, col. 543 (1865). Same, Poly. I., 177, 
492 (1865). Same, abstract, Chem. Zentr., 36, n.s.v. 10, 944 (1865). 

30 Allgemeine Bauzeitung, 5, 36-38 (1840). 

M Ellery, James B., U. S. Pat. 1,435,957 (Nov. 21, 1921). 

32 Hess, Henry K., U. S. Pat. 1,344,891 (June 29, 1920). 

33 Hopkins, N. M., U. S. Pat. 1,507,181 (Sept. 2, 1922). 

34 Tumminelli, Arcangelo, U. S. Pat. 1,126,132 (Jan. 26, 1915). 

35 Scharwarth, John A., U. S. Pat. 1,136,370 (April 20, 1915). 
^ Harris, James E., U. S. Pat. 1,612,506 (Dec. 28, 1926). 

37 Ashenhurst, Harold S., U. S. Pat. 1,353,621 (Sept. 21, 1920). 

38 Arthur, W., loc. cit., U. S. Pat. 1,041,565 (Oct. 15, 1912). 



SIZES AND COATINGS 



261 




1 



Fig. 131.— Effect of Silicate Paint on Yellow Pine, Exposed to the Flame of a 

Meker Burner. 

vitreous appearance, and contains water, which will be the case if it 
is air dried, it is able to swell when heated and thus to delay ignition 




Fig. 132. — Same as Figure 131. Viewed from Under Side. 

from minor sources of heat such as sparks, flashes of flame, or even 
small continuing fires such as might result from the ignition of a 
small leak in a gas conductor. Intumescence is reduced by the intro- 
duction of pigment. 



262 SOLUBLE SILICATES IN INDUSTRY 

The two boxes shown in Figures 131 and 132 give the comparison 
between yellow pine, untreated, and treated with silicate paint. 39 Each 
was exposed to the flame of a Meker burner, which burned a hole 
through the painted wood. The flame did not spread, but passed 
through the hole for more than an hour, leaving the main body of the 
wood unaffected. The untreated wood ignited promptly and would 
have been completely consumed had not the fire been extinguished. 

The problem in designing applications of silicate solutions for fire 
protection is to circumvent the failure of the film by carbonating. This 
may be done by covering and thus reducing exposure, or for hazardous 
factory operations the coating may be renewed at intervals. 40 

Protection of Timbers. Timbers of certain railway tunnels have 
been cheaply protected by spraying them with Na 2 0, 3.3SiQ 2 , 42°Baume 
and immediately throwing against the wet silicate fine sand which ad- 
hered and yielded a silicious coating very resistant to flame or sparks. 
Slaked lime has been used in the place of sand and gives the advantage 
of early insolubility. Similar treatment has been applied to timbers in 
mines. Another method is to allow the silicate coating to dry and then 
spray with aluminum sulfate. 

Protection of Rubber Insulated Wire. Rubber insulated wire 
used in the telephone industry is less liable to burn when a silicate film 
is interposed between the rubber insulation and the outer braided cover- 
ing of cotton protected with fire-resisting salts. The extent of pro- 
tection is reduced by long exposure but is almost complete for the 
first year. 

Silicate-saturated felts have been laid between double wooden floors 
of tongue and groove type and this protective measure has been recog- 
nized in building codes. 41 Na 2 0, 3.3Si0 2 is usually preferred for 
making fire-resisting coatings. 

Protection Against Light Oil Fires. As an example of fire- 
resistance of a film containing pigment, the illustration of a corrugated 
paper box coated inside and out with Na 2 0, 3.3 Si0 2 , specific gravity 
1.18 containing calcium carbonate and lithopone, will serve. The dimen- 
sions were 4" X 4" X 12". One hundred cc. of petroleum distillate, 
50°Baume light, were put into the box and ignited, the flames rising 
around the outside of the second box. The heat was sufficient to char 

39 Gardner, Henry, Bull. No. 4, Paint Mjrs. Ass., Sci. Sec. (1914) ; Drugs, Oils, 
and Paints, 29, 10, 370 (1914). 

40 Patsch, loc. cit. 

41 City of Boston Building Laws, Chapter 550, Section 32, page 103, amended 
under Acts of 1907. 



SIZES AND COATINGS 



263 




Fig. 133. — Corrugated Paper Box Flame-proofed with Silicate Paint. 



the paper nearest the fire but the other paper sheet was uninjured and 
the box was not ignited. 

Mixtures for Fire-Proofing. Numerous compositions of matter in- 
volving soluble silicates have been patented as fire-proofing agents. 
Though they probably represent mixtures which are of service for some 
specific condition, yet they are often unnecessarily complicated. Be- 
cause they shed little light on the properties of silicates only a few are 
cited. 42 " 49 

Automobile Frames. Silicate films are applied to wooden members 
of automobile frames to permit the use of higher temperatures in ovens 
where finishes are baked on the metal parts. Temperatures up to 230° C. 
(450°F.) are used, and the silicate-coated wood is uninjured on 40 
minute exposure. 

Prevention of Oxidation on Sheet Iron and Coating of Metal 
Ware. Similar treatment of sheet iron to prevent oxidation at tem- 
peratures sufficient to cause it without the coating have proved effective. 
They have also been found useful for coating metal ware previous to 

42 Wortelman, G. A., U. S. Pat. 1,397,028 (Nov. 15, 1921). 

43 Welles, C. E., U. S. Pat. 1,436,618 (Nov. 21, 1922). 
44 Vivas, F. S., U. S. Pat. 1,369,857 (March 1, 1921). 
45 Iversen, M. M., Nor. Pat. 33,924 (Jan. 30, 1922). 

46 Locke, J. A., Brit. Pat. 160,801 (March 24, 1921). 
47 Ferrell, J. L., Ger. Pat. 162,043 (1905). 

48 Felix, Charles R., U. S. Pat. 1,643,116 (Sept. 20, 1927). 

49 Young, Ira Benjamin, and Harry R. Haywood, U. S. Pat. 1,505,519 (Aug. 
19, 1924). 



264 SOLUBLE SILICATES IN INDUSTRY 

the enameling process, as the surface is thus more easily kept clean and 
free from rust. 50 

Soluble silicates have been used to moisten asbestos or cellulose fibers 
applied to metal surfaces with phenol-aldehyde condensation products. 51 

Miscellaneous Uses for Silicate Films. 

Half Tone Cuts. An interesting use of a silicate film is involved 
in a method for rapid production of overlays or impressions of half 
tone cuts for printing. A mixture of rosin and emery powder is dusted 
on a freshly inked proof and set by heat. The paper is then dipped 
in a silicate solution, one part Na 2 0, 3.3SiQ 2 , 1.4 specific gravity, and 3 
parts water by measure. This is quickly dried and it imparts enough 
rigidity to withstand the operation of printing. 52 

Silicate-Coated Walls. The outside wooden walls of certain to- 
bacco warehouses are periodically painted with silicate to reduce the 
escape of moisture. 

Silicate has been successfully used to coat old walls which were so 
permeated with soot and grease that plaster could not be applied without 
staining through. A silicate coating prevented the staining and gave a 
satisfactory base for the plaster. Dilute silicate solutions may be applied 
to the surface of new plastered walls to facilitate the adherence of 
paint.* Treatment of metallic surfaces to help the adherence of mag- 
nesium oxychloride cements has been accomplished with or without 
admixture of clay or other minerals. 53 

Sizing on Jute Sacks. Na 2 0, 3.3Si0 2 , specific gravity 1.4, diluted 
with 9 measures of water has a sizing effect on jute sacks used as con- 
tainers for acid calcium phosphate or fertilizer mixtures which contain 
free acid. The acid causes the rapid weakening of the fiber, being most 
troublesome in hot weather. The silicate delays but does not com- 
pletely prevent this action. Calcium acetate and paraffin are also used. 
The latter is effective in cool weather but not in the summer tempera- 
tures encountered in the Southern States where most of the acid phos- 
phate is made. The silicate treatment adds nearly 50 per cent to the 
weight of a sack with a 9 to 1 dilution and somewhat more with a ratio 
6 to 1 between the original solution and water. 

Tree Wounds. Silicate films have also been found useful as a 

dressing for pruning-wounds of trees. They serve the double purpose 

* Cf. page 271. 

60 Nicksch, K., Z. ger. kohleus Ind. (1919); Rev. chim. hid., 28, 267 (1919); 
C. A., 14, 3802. 

^Wirth, J. K., Brit. Pat. 188,187 (Oct. 22, 1921). 

62 St. Paul, Johns, U. S. Pat. 1,441,283 (Jan. 9, 1923). 

"Davies, J., and W. H. 'Miles, Brit. Pat. 186,231 (Aug. 24, 1921). 



SIZES AND COATINGS 



265 



of reducing the loss of sap and of keeping out the spores from which 
spring the fungus growths which cause destruction of the wood. 54 

Two pruning wounds are shown in Figure 135. They were made at 
the same time. The upper one was painted with a viscous solution of 
Na 2 0, 3.3Si0 2 , and healed rapidly and clean while the lower one became 
a host to fungi which would ultimately cause deep destruction. The 





Fig. 134.— A Pruning Wound 
Showing Entrance of Rot. 
(Courtesy of Ohio State Agri- 
cultural Experiment Station). 



Fig. 135. — Healing of Pruning Wound. 
Infection of Untreated Wound by 
Fungus (Courtesy of Ohio State 
Agricultural Experiment Station). 



coating is not necessarily heavy enough to give a glassy film, but the 
treated surface should become dry and hard. It is probable that the 
best results could be had from the most silicious silicate, which would 
not only dry faster, but be less likely to be washed away before gelation 
due to the combined action of sap and carbon dioxide. This action is 
partly mechanical, but the alkalinity of the silicate is useful against 
organisms which thrive in an acid medium. 

Stainproofing Lumber. Moist hot climates give rise to blue stain, 
a fungus growth which readily attacks and disfigures freshly cut 
lumber. It requires an acid medium in which to grow and the lumber 
can be protected by passing through an alkaline bath. Silicates have 

64 Young, W. T., Ohio Agri. Exp. Station Bull., 8, 13-17 (1923). 



266 SOLUBLE SILICATES IN INDUSTRY 

the advantage over other alkaline materials of remaining close to the 
surface and are at the same time less soluble. A concentration of 1.07 
specific gravity is sufficient for Na 2 0, 3.3Si0 2 . 

Parting Films. In spite of their adhesive character and the fact 
that they can under some conditions be laid on rubber surfaces, silicate 
solutions are useful for making parting films between iron molds and 
plastic rubber masses. Particularly in the making of hard rubber 
jars and the like, a silicate film on the mold gives a smooth surface and 
a ready separation. On account of the need of removing this film it 
is best to use Na 2 0, 2.9Si0 2 or even Na 2 0,2Si0. 2 , which can be readily 
cleaned away with hot water. The objection to too great an alkalinity 
is slowness of set. 

Films of more silicious silicates on paper serve as separators for light 
rubber goods before vulcanizing. 

Coatings on Metal. 

Zinc Loss. Remelting of finely divided metal scrap such as turnings 
is, if the alloys contain zinc, subject to a loss by the oxidation of that 
metal. This may be reduced by dipping the turnings into a silicate 
solution of suitable strength to coat each particle with a thin film. 
There is some latitude in the selection of a silicate for this purpose, but 
good results appear to be obtainable with Na 2 0,4Si0 2 at about 1.1 
specific gravity. 

Induration of Defective Castings. Induration of porous metals 
or defective parts of castings has long been practiced and appears to 
yield satisfactory results for steam engine cylinders and other pressure 
vessels made by casting, provided of course that the openings are not 
too large. The most effective method of application is to place the 
castings in vessels from which the air should be exhausted, then to 
immerse them in silicate and finally to apply pressure. This has been 
successfully done with light metal alloys for use in equipment of air 
craft. Another method is to plug up the casting so that the solution 
shall be applied from one side only. Na 2 0, 3.3Si0 2 1.05 to 1.10 specific 
gravity or 3 to 5 measures of water to one of 1.39 specific gravity is 
used according to the degree of porosity and the size of the casting. 
The solutions are used hot, 70° to 90° C, and pressures up to 4.93 
kilograms per square centimeter (70 pounds per square inch) are 
applied and maintained until the solution does not sweat through, or 
for 10 to 20 minutes. 55 

55 Air Service U. S. Army Specifications No. 20,002-A (Sept. 25, 1921). 



SIZES AND COATINGS 267 

In some cases it is sufficient to soak the casting in the warm silicate. 
After the treatment the castings are washed, dried, and subjected to 
double the pressure required of them in service, or not less than 0.703 
kilogram per square centimeter (10 pounds per square inch). The test- 
ing liquid is kerosene. The process is applicable only to castings with a 
degree of porosity which results in but slow seepage of liquid. It cannot 
be expected to close openings large enough to allow spurting of liquid 
under pressure. Aluminum castings are easier to deal with than a metal 
which does not react at all with the silicate, but numerous unpublished 
confirmations of the fact that it serves well on iron are available. 

Silicates have been used as incidental reagents in making metallic 
coatings which are glossy because of the presence of a colloidal com- 
pound which prevents the liberation of hydrogen at the cathode. 56 

Silicate Paints. 
Nature of Paint. 

Requirements of the Paint Film. Paints are systems in which a 
more or less viscous liquid causes the suspension of finely divided matter 
insoluble in the vehicle. They must harden to form films fit for deco- 
rating or for protective service on widely varying surfaces. Silicate 
films alone have been described ; the introduction of pigment increases 
their range to provide color, opacity, or light-diffusing power and added 
resistance to chemical influences. Silicate stains, i.e., soluble colors 
dissolved in silicate solutions, have been proposed but not widely used. 57 

Factors Governing Consistency of Paint. The working proper- 
ties of a paint, its behavior under brush, spray, or dipping, have much 
to do with the ability to make uniform films of appropriate thickness. 
Paint consistency depends upon yield value and mobility, which are 
governed by viscosity of vehicle, ratio between vehicle and pigment, 
the force of flocculation in vehicle and pigment, and particle size of the 
pigment. 58 All these can be adjusted in a paint with a vehicle of soluble 
silicate. It is therefore possible to make a paint with the physical char- 
acteristics desired for spreading, and the limitations of its use will be 
found in the character of the finished film or in some cases the keeping 
quality of the mixture. 

Color of Vehicle. Most liquids suitable for paint vehicles affect 
the color of the film. Silicate solutions, being colorless, have a great 
advantage over oils for coatings of maximum reflecting power. It is 

56 Classen, Alexander, U. S. Pat. 1,491,381 (April 22, 1924). 
57 Puscher, Chem. Zentr., 277 (1870) ; Chem. Zentr., 42, 448 (1871). 
58 Green, Henry, hid. Eng. Chem., 15, 122-126 (1923). 



268 SOLUBLE SILICATES IN INDUSTRY 

believed that the whitest paint known can be made from some of the 
modern types of lithopone in silicate vehicles. Such paints are used 
to make light-diffusing surfaces in apparatus required to produce light 
of known quality for colorimetric and similar work. As a flat white 
is required, Na 2 0, 3.3Si0 2 is used at about 1.16 specific gravity 
(20°Baume). 

Suitable Pigments. 

It was early observed that some pigment materials such as white lead 
react and cause silicate solutions to gel. This may in some cases be 
offset by grinding the pigment previously in a silicate solution and thus 
rendering the surface of the particles relatively inactive. Creuzburg 59 
proposed alternate layers of silicate and of pigment in a vehicle with 
which it does not react, but this is too laborious for modern uses. The 
better means is to choose coloring materials compatible with the silicate, 
as there are enough of them to give a wide range of tints. Clays, silica, 
lithopone, whiting, barytes, and, under some conditions, zinc oxide are 
available for white. Ultramarine or smalt 60 give good blues. Chro- 
mium oxide gives the most satisfactory green, though lead chromate 
ground in silicate and mixed with ultramarine may be used. Ochers 
and umbers make good yellows and browns. Cinnabar or iron oxides 
free from lime serve for reds. Grease-free carbon blacks can be used. 
In addition to these, there are numerous alkali-resisting lakes avail- 
able. 61 Of metallic pigments, aluminum, either pure or alloyed to give 
yellow colors, copper, zinc, and lead can be mixed with the most silicious 
solutions. 

Silicate Vehicles. 

Specific Gravity of Silicate. Any silicate solution with three or 
more molecules of silica may serve as a vehicle for paint. The concen- 
tration chosen will determine the degree of gloss and to some extent 
the tendency to crack. For permanent exposures for decorative pur- 
poses the specific gravity should not be more than 1.19 (24°Baume). 
The vehicle prepared by neutralizing a part of a silicate solution with 
acid and preventing gelation by mixing in a further quantity of silicate 
yields a film which is insoluble in water a few minutes after spread- 
ing. 62 Other silicates without this treatment become insoluble in course 

™ Dingier' s polytech. I., 144, 292-295 (1857) ; Abst. in Chem. Zentr., 28, 428-430 
(1857). 

60 Fisher, Harry C, U. S. Pat. 1,631,628 (June 7, 1927). 

81 Wagner, H. von, Chem. Zentr., 47, 128 (1876). 

63 Carter, J. D„ and J. G. Vail, U. S. Pat. 1,129,320 (Feb. 23, 1915). 



SIZES AND COATINGS 269 

of time by taking up carbon dioxide and forming a binder of gelatinous 
silica similar to the first. It is not always possible to await this slow 
action, however, lest the soluble silicate be washed away. The picture 
shows the comparative weathering of a silicate paint, 1, and 3 com- 
mercial casein paints. 



■ 



Fig. 136. — Comparative Weathering of Silicate Paint. 

Britton 63 proposes a paint vehicle made by peptizing gelatinous silicic 
acid in a silicate solution with the same object. Alkaline bicarbonates 
heated with silicate solutions have also been proposed. 64 

Kind of Silicate. Potassium silicates show less tendency toward 
efflorescence than the corresponding sodium silicates ; and the latter of 
low alkalinity, as Na 2 0, 4.2Si0 2 , less than the ordinary grades of com- 
merce ; but all are likely to show some white "bloom" against the back- 
ground of a dark pigment. Carbonate efflorescence is easily removed 
by washing. 

Light Diffusion. 

Decorative Lighting Effects. A method of avoiding efflorescence 
and adding resistance to water in a silicate paint used as a light diffuser 
in place of frosting on electric lamps is to coat the dry silicate-painted 
surface with dammar varnish. 65-68 A very light coating made from a 
varnish much reduced with turpentine is sufficient. 

Opal glass is simulated by using zinc oxide, French chalk and 
hydrated magnesium silicates. These are ground in a ball mill with 
water and little or no silicate of soda, and the principal amount of silicate 
is put in near the time the paint is to be used. The formulas are the 
following : 

M U. S. Pat. 1,477,938 (Dec. 18, 1923); Brit. Pat. 191,426 (Sept. 7, 1921). 

64 Gallenkamp, W., Ger. Pat. 294,330 (April 1, 1916). 

65 French Thomson-Houston Co., Fr. Pat. 555,691 (March 28, 1923). 

68 British Thomson-Houston Co., Brit. Pat. 113,769; Brit. Pat. 150,598 (Jan. 
8, 1920). 

67 Luckiesh, M., U. S. Pat. 1,464,101 (Aug. 7, 1923). 

68 See also Dixson, James Q., U. S. Pat. 587,799 (Aug. 10, 1897). 



270 SOLUBLE SILICATES IN INDUSTRY 

White Yellow 

French chalk 15 French chalk 26 

Zinc oxide 15 Burnt sienna 13 

Water 25 Water 24 

Sodium silicate sp. gr. 1.375, Silicate 37 

presumably Na 2 0, 3.3Si0 2 . . 45 

This is put on with brush or spray. The glass may have been roughened 
by sand blasting, but this is not essential. The paint hardens in a few 
minutes, when the varnish may be applied by brush or dip. Lamps 
thus treated give a good diffused light with less loss than indirect 
methods of illumination. A further step consists of omitting the varnish 
coating and causing the dried silicate film to become insoluble by dipping 
it in a bath of a reacting salt or acid. Zinc chloride, aluminum sulfate, 
other soluble salts of zinc, tin, and alkaline earth metals, ammonium 
fluoride, ammonium chloride, sodium chloride and sulfuric acid have 
been used. After treatment with the precipitant the coating may be 
washed, after which it is free from efflorescence. For lamp coating, 
the oxides of magnesium, aluminum, zinc, and tin have been used as 
opacifiers. 69 ' 70 

These coatings are cheap, durable, and well adapted to give decorative 
lighting effects. 

Another step has been the application of silicate paints to the inside 
of the lamp bulbs, which, contrary to expectation, have shown a satis- 
factory life in spite of the impossibility of completely dehydrating the 
silicate film. It has been found that good adherence of a sprayed film 
to the glass can be had on surfaces which are scrupulously clean. The 
addition of a small amount of ammonia to the paint reduces surface 
tension and makes adherence easier. 71 

Screens for Lanterns and Motion Pictures. A light-diffusing 
silicate paint adapted for screens for projecting lanterns is made from : 

100 parts Na 2 0, 3.3Si02, 1.38 specific gravity 
15-20 parts rice starch 
200-300 parts water 

This is applied to a glass plate, which then serves as well as ground 
glass. It can also be used for focusing glass for cameras, etc. 72 

The same object has been sought in a motion picture screen of glass 
coated with zinc sulfide in a silicate vehicle. Calcium sulfate is also 
specified, but its quick reaction with the less alkaline silicates makes it 

""Whitmore, James Bryant, U. S. Pat. 1,581,766 (April 20, 1927). 
"British Thomson-Houston Co., Brit. Pats. 185,910 (July 18, 1921); 196,843 
(June 21, 1922). 

"Osgood, Samuel W., U. S. Pat. 1,169,506 (Jan. 25, 1916). 

72 Eberlin, L. W., and S. E. Sheppard, U. S. Pat. 1,421,924 (July 4, 1922). 



SIZES AND COATINGS 



271 



impracticable to obtain a smooth coating. 73 Na 2 0,2Si0 2 might serve but 
is not specified. 



Coatings on Wood. 

Effect of Diluting the Silicate. Sprayed silicate paints on brick, 
stone, or concrete surfaces last for years, but on wood, which is subject 
to changes of moisture and con- 
sequent expansion and contraction, 
they tend to crack. A paint made 
from two parts of whiting and one 
of lithopone with substantially an 
equal weight of the special silicate, 
1.17 specific gravity, containing 
metastable silica resisted exterior 
exposure on a brick wall in Phila- 
delphia for five years. The same 
paint on interior brick and concrete 
remains intact at this writing, eight 
years after it was spread.* If 
checking of silicate coatings on 
wood be avoided by diluting the 
silicate, reducing it relative to the 
pigment, the binding action will 
not be sufficient, and chalky films 
will be formed which do not resist 
even mild abrasion. 

Addition of Rubber Latex. 




Fig. 137. — Spraying a Silicate Paint. 



An improvement consists in grinding the pigment in the silicate and then 
adding rubber latex stabilized with ammonia. 74 ' 75 > 76 If the latex were 
put in during grinding, it would coagulate. Delayed addition of the latex 
improves the brushing consistency of the paint and softens the film 
enough to permit its use on wooden surfaces. The lithopone is floccu- 
lated by the concentration of silicate needed for binder though the same 
silicate at lower concentration is an effective means of deflocculating. 

The limiting proportions of latex are 10 to 20 per cent by weight 
of the vehicle. It is desirable to add 0.1 to 1 per cent of borax or 

"Gilpin, R., Brit. Pat. 166,015 (May 19, 1920). 
* Cf. page 264. 

74 Drefahl, Louis, and Edward Taylor, U. S. Pat. 1,486,077 (March 4, 1924). 
75 Teague, M. C, U. S. Pat. 1,550,466 (Aug. 18, 1925). 

"American Rubber Company, Brit. Pat. 235,888 (June 18, 1924); C. A., 20, 
1004. 



272 SOLUBLE SILICATES IN INDUSTRY 

sodium benzoate to the latex to prevent fermentation of its protein 
content. A typical formula is : 

-r,. , cn , /99.8% lithoponc. 

Pigment 50 per cent ^ Q2% hor ^ 

[90.0% 22°Baume Na 2 0, 3.3Si0 2 treated by 
Vehicle 50 per cent -j Carter process. 

[10.0% rubber latex stabilized with am- 
monia. 

This mixture kept sealed in a can was in good condition after six 
months. It may be applied to damp surfaces. It can be thinned with 
a little Na 2 0,4Si0 2 , 34°Baume, if necessary. It works with either brush 
or spray. 

The extent to which the addition of materials which do not dissolve 
in the silicate are able to modify the films is related to the manner and 
degree of dispersion. Films made from emulsions exhibit primarily 
the properties of the continuous phase. When this is a silicate solution 
the film is therefore affected by water and never exhibits the degree of 
flexibility which might be implied from its rubber or oil content. Emul- 
sions in which silicate solutions were dispersed in oils would corre- 
spondingly lack some of the advantages peculiar to the silicate. 

Miscellaneous Uses. 

Protective Coating for Whitewash. A series of tests by Fink 77 
indicated that silicates may make good protective coatings for whitewash 
and be of service in connection with casein paints. He used the special 
solution containing metastable silica, which is probably not the best 
for use with casein. Arthur, Mitchener, and Withrow 78 recommend 
the use of silicate of soda in mixtures designed to improve upon ordinary 
whitewash as a coating for brickwork, more or less heated, as it is in 
many industrial processes. 

Stereochromic Painting. 79-85 The older literature of the soluble 

77 /. bid. Eng. Chem., 14, 503-511 (1922). 

78 Arthur, Edwin P., \V. B. Mitchener, and James R. Withrow, Ind. Eng. 
Chem., 19, No. 5, 591 (1927). ' 

7S Rivington, /. Soc. Arts, No. 1630, Feb. 15, 1884. 

80 Encyclopedia Britannica, 11th ed., 20, 488-489. 

81 Kleim, A., "Mineralmalerei," Wien, 1881. 

82 Bersch, Josef, "Die Malerfarben und Malmittel," Wien: Hartleben's 
chemisch-technische Bibliothek, 1905, p. 28-37, 180-184. 

83 Feichtinger, G., Poly. J., 210, ser. 5, 10, 440-444 (1873). Same, condensed, 
Chem. Zentr., 45, ser. 3, 5, 74-75 (1874). Same, abstract, Neueste Eriindungen 
und Erfahrung, 1, 60-61 (1875). Same, abstract translation, Bull. soc. chim., 26, 
n.s. 21, 280-282 (1874). 

84 "Peinture murale," Le Montieur scientiiique, 6, 800 (1864). 
83 Pettenkofer, Max, Poly. I., 113, 217-225 (1894). 



SIZES AND COATINGS 273 

silicates lays great stress on stereochromic painting, a form of fresco 
painting devised by von Fuchs and used by artists more or less con- 
tinuously since. It consists in preparing a porous surface of plaster 
upon which a picture is wrought with pigments in any aqueous medium. 
These are then fixed by spraying repeatedly with a hot dilute solution 
of silicate until the plaster is saturated. Potassium silicate is always 
specified on account of its comparative freedom from efflorescence ; but 
if the final step is to apply a solution of ammonium carbonate as di- 
rected by Cremer, 80 and washing with distilled water to remove the 
potassium carbonate formed, it seems that a sodium silicate would be 
satisfactory. Numerous notable mural paintings have been done by 
this process; success depends upon the preparation of a uniform porous 
ground and the use of colors specially prepared for the process. They 
must not only be resistant to alkali, but they must be mixed with gum 
arabic or other colloids such as silicates, which modify and control their 
behavior. In some cases it is advantageous to use colors ground 
in silicate solutions. The finished work after drying is treated with 
a solution of paraffin in benzol, which has the effect of brightening the 
colors and keeping the water away from them for a time. 

Metallic Paints. Paints with a silicate vehicle and metallic pigment 
are serviceable on hot surfaces where they reduce radiation losses and 
withstand for a long time the effect of temperatures up to red heat. 87 
Aluminum powder reacts sufficiently with silicates, even Na 2 0, 4.2Si0 2 , 
to make it unsafe to store in tight cans which may be exposed to enough 
heat to cause the can to burst from the pressure of liberated hydrogen. 
When mixed immediately before use, it makes a pleasing and highly 
durable coating for furnace doors, stoves, and other hot apparatus in 
which heat conservation is an object and where a paint containing 
organic material would readily burn off. Edwards 8S gives the following 
precautions : 

"However, not all brands of sodium silicate have been found to be 
equally effective. If there is excessive frothing when the aluminum 
bronze powder is mixed with the solution, this is an indication that it 
is not, perhaps, the best grade which can be secured for this purpose, 
although, unless the frothing is excessive, it need not necessarily inter- 
fere with the successful application of the paint. It is found that dilut- 

8a "Beitrage zur technik der Monumental Malverfahren," Diisseldorf, 1895. 

87 Coblentz, W. W., Architecture and Building, 55, 93 (1923). Coblentz, W. W, 
and C. W. Hughes, Bur. Standards Tech. Paper No. 254, 171-187. 

88 Edwards, Junius D., "A Treatise on the Physical Properties of Aluminum 
Paint and Its Uses in Industry," Pittsburgh : Aluminum Company of America, 
1924. 



274 SOLUBLE SILICATES IN INDUSTRY 

ing the silicate to a density of 22° to 28 Baume gives a vehicle of the 
proper consistency. . . . The surface to which the paint is to be applied 
should be sufficiently rough, however, to assure the proper bonding of 
the paint. In case of doubt, the adherence can be tested by preliminary 
experiment. It is essentially, however, an interior paint, although mod- 
erate success has been had with the application of it to exterior cement 
work. In the latter case, the sodium silicate seems to combine with 
and become insolubilized by the concrete surface, with the result that 
very good adherence is usually secured. In some cases, where rain 
destroyed the adherence of the paint film, the difficulty proved to be due 
either to the vehicle or to the fact that the cement work was new. Such 
a vehicle only costs about 25 cents per gallon, so that it makes a very 
economical paint for uses where its properties are satisfactory." It is 
important to have the surfaces free of grease or oil. The presence of 
a small amount of soap in the paint appears to reduce the surface 
tension and facilitate spreading. 89 

One and a third to one and a half pounds of aluminum powder per 
U. S. gallon of 22°Baume Na 2 0, 3.9Si0 2 give a paint which works well 
on concrete and brick interiors and on exterior concrete which has been 
sufficiently aged. These should be mixed within a few hours of use to 
avoid frothing, as bubbles of hydrogen make uniform spreading difficult. 
Only silicates high in silica are suitable for this use. 

Decorative Coatings on Wallboard. Gold or aluminum bronze 
paints make decorative and permanent coatings on wall board or wood 
surfaces. If these surfaces are very porous it is best to give them a 
sizing coat of silicate. The coatings do not entirely prevent rusting 
of iron. 

Pulley Dressing. Silicate paints containing abrasive material have 
been used to increase the traction of wooden and steel pulleys, which 
are thus enabled to take better hold of belts for the transmission of 
power. 90 

Printers' Ink. Small additions of any silicate solution thoroughly 
mixed into printers' ink are a convenient means of increasing its vis- 
cosity. Many a print shop keeps a can of silicate handy against the 
time when the ink works a little too thin on the presses. The more 
silicious grades are preferable for this purpose. Similar results are to 
be had in oil paints, which develop a better pull on the brush when a 
little silicate is ground in with the pigment. This should never be done 
in a paint for exterior use, as it lowers the resistance of the film to 

"Seideman, Leon, U. S. Pat. 1,452,445 (April 17, 1923). 
eo Benford, David M., U. S. Pat. 1,383,692 (July 5, 1921). 



SIZES AND COAT IX OS 275 

water. Amounts of the order of one per cent give a marked change 
in flow, partly due to saponification and partly to the emulsifying action 
of the silicate. 91 

Coating Heat Exchangers. Imison and Russell ° 2 describe the use 
of a silicate paint to protect iron heat interchangers used for the oxida- 
tion of ammonia. This consisted of 73-75 per cent barium sulfate in 
a finely divided condition and 10 per cent Na 2 0,4Si0 2 . It was reduced 
to a painting consistency with watgr and applied to the iron surface 
which had been heated to 200° C. This process was several times re- 
peated and resulted in a coating which would stand a full red heat and 
long service without corrosion of the metal. It was found very difficult 
to make satisfactory coatings on large apparatus. 93 » 

Refractory Paints. Other silicate paints have been proposed to 
impart refractory properties to bricks 94 but have found a rather limited 
use. For high temperatures something more than a film is needed. A 
mixture of 75 per cent carborundum and 25 per cent silicate solution 
may reduce chemical attack at the surface but must be supported on a 
foundation capable of resisting the temperatures encountered in fur- 
naces or gas retorts. 95 

Paints made from silicate solutions and clay form glazes on furnace 
linings and glass pots which reduce the penetration of gas or fluxing 
liquids. 

Silicate solutions have been used to toughen the coating of electron- 
emitting electrodes in thermionic valves. 96 

Electrodes for Welding. Wire electrodes for arc welding are 
coated with silicate paints containing asbestos to prevent oxidation at 
the high temperature applied for a short time in this process. 97-99 

Pottery Glazes. Ceramic colors painted upon surfaces to be deco- 
rated with the aid of a silicate binder which sets in the air and permits 
of easy handling have been found convenient and economical, 100, 101 and 
zinc silicate glazes applied in this manner have yielded some of the most 
beautiful crystalline effects. Kraner 102 found that a step in the prepara- 

"Bourcet, P., and H. Regnault, Ger. Pat. 415,062; Zcllstoff u. Papier, 5, 267 
(July, 1925). 

02 /. Soc. Chcm. hid., 41, 37-45T (1922). 

93 Imison, C. S., personal communication. 

94 Stowell, E. R., U. S. Pat. 774,003 (Nov. 1, 1904). 

BS Chcm. & Met. Eng., 24, 1070 (1921). 

"Krogh, A. T., Brit. Pat. 255,830 (July 23, 1925). 

97 King, Jesse C, U. S. Pat. 1,312,256 (Aug. 5, 1919). 

98 Boorne, William Hanson, Brit. Pat. 185,580 (Sept. 14, 1922). 

"Holslag, Claude J., U. S. Pat. 1,451,392 (April 10, 1923). 

100 Keram. Rundschau, 28, 239 (1920). 

101 Fenaroli, Pietro, U. S. Pat. 1,164,710 (Dec. 21, 1915). 

102 /. Ceram, Soc., 7, 868 (1924). 



276 



SOLUBLE SILICATES IN INDUSTRY 



tion of these glazes could be omitted by using a silicate solution as 
binder for the glaze materials and calculating the soda and silica of 
the silicate as part of the final composition. In this way the alternative 
of frit, weakly attached with an organic binder which had to be burned 
out at a low temperature prior to the final firing, was avoided and 
decorative effects of rare beauty were obtained. Zinc silicate crystals 




Fig. 138. — Crystalline Zinc Silicate Glaze. 



are able to absorb certain coloring materials, such as the oxides of 
cobalt, manganese, copper, uranium, nickel, and iron in such a way 
that bright colored crystal masses appear upon a background of con- 
trasting color. It is not possible to present this adequately in mono- 
chrome, but the author possesses two vases similar to those shown in 
the cut. Their surfaces are strewn with delicate blue crystal tracerv 
on a background of brownish buff, most pleasing to the eye. Many 
color combinations are possible. 

A silicate solution of 47°Baume (13.7% Na 2 0, 32.9% SiOo, and 
53.4% H 2 0) is not appreciably absorbed by whiteware or faience bis- 
cuit with as much as 10 per cent water absorption. This may be used 



SIZES AND COATINGS 277 

with a willemite or zinc silicate glaze without affecting its fusion prop- 
erties. The silicate and glaze ingredients are mixed to a smooth con- 
sistency and applied to the surface of the ware by dipping or brushing ; 
the coating is then allowed to dry to the similitude of a thick varnish. 
The pieces may then be handled without danger of injury. The water 
is not completely removed on air drying and some intumescence is noted 
in the early stages of firing, but the coat soon settles back without loss 
of material from the surface. The batch weight used was the following: 

Per Cent 

Sodium silicate 49.69 

Flint 19.46 

Zinc oxide (ZnO) 17.95 

Titanium oxide (Ti0 2 ) 7.94 

Water 4.96 



100.00 



Coloring materials were added as required, but always in small 
amounts. 

Optimum conditions for firing consisted in raising the temperature 
uniformly to 1200° C. in 10 to 13 hours and cooling to 900° C. between 
the 16th and 17th hours. 

The success attained with this process suggests that a silicate vehicle 
may be of use for sundry other ceramic uses where an impermeable 
surface is required with or without decorative quality. 

Dry Paint Mixtures. 

Since hydrous silicates of several ratios are available in powder form 
and these are much more soluble than the anhydrous powders of like 
ratio, it appears logical to make some of the paint mixtures in dry form, 
requiring only the addition of water. This has been done. They require 
more care than the wet preparations. If cold water is to be used, it is 
generally necessary to use more silicate to allow for something less than 
complete solution. The mixtures should be stored in air-tight metal 
containers to prevent the decomposition of silicate by carbon dioxide. 
The danger of separation of the dry silicate from other ingredients must 
be guarded against. If casein is present, the most favorable sequence 
of reaction is not possible. Some silicate may be decomposed by lime 
before it performs any useful function. Nevertheless there are many 
silicate paints which, with a little study, could be prepared dry with a 
gain in convenience to the user ; and there are several known factors 
to supplement the method of trial and error. 



278 SOLUBLE SILICATES IN INDUSTRY 

Patent Literature. 

The patent literature of silicate coatings is voluminous. Ingredients 
such as casein, glucose, glue, glycerin, pigments, and fibrous materials 
can be mixed with silicate solutions in innumerable permutations. The 
patents cited are typical. 103-119 

Analysis. 

The analysis of silicate paints is difficult unless the ratio between 
Na 2 and SiOo in the original vehicle is known. If the silica content 
of the pigment is not known, it is difficult to assign the proper source 
to all the silica found. As in the case of cements, reactions take place 
which may render ultimate analyses misleading. 120 

Paper Sizing. 
Silicate Sizing. 

Relation between Soluble Silicates and Rosin. The process of 
sizing paper consists in depositing upon or among the fibers which form 
the sheet colloidal substances so chosen as to modify the finished product 
to fit it for specific uses. Rosin is the material mostly used, and its 
primary contribution is to impart a resistance to water. It does not 
give to paper all the desirable qualities, and as forest reserves are de- 
pleted its cost increases. These two considerations have led to the use 
of several other colloids which serve in some instances by themselves 
and in other cases in an accessory capacity. 

The soluble silicates fall into this group. To understand their place 
in the industry it is necessary to have clearly in mind their relation to 



103 Philipp, Ferdinand, U. S. Pat. 300,890 (June 24, 1884). 
°*Fewins, Frank N., U. S. Pat. 443,361 (Dec. 23, 1890) 



105 Bibikon, N. A., U. S. Pat. 421,229 (Feb. 11, 1890), 
109 McLennon, Charles J., U. S. Pat. 872,960 (Dec. 3, 1907). 

107 Connolly, J. P., Can. Pat. 177,506 (June 5, 1917). 

108 Sharp, Robert, U. S. Pat. 1,309,782 (July 15, 1919). 

109 Hutchison, A., Brit. Pat. 153,081 (July 28, 1919). 

110 Isaacs, M. R., Brit. Pat. 150,551 (Oct. 8, 1919). 

111 Morrison, Freeland, U. S. Pat. 1,365,716 (Jan. 18, 1921). 
m Mees, E. F., U. S. Pat. 1,396,970 (Nov. 15, 1921). 

113 Walsh, M. J., U. S. Pat. 1,415,282 (May 9, 1922). 

114 Keedwell, C. A., U. S. Pat. 1,476,016 (Dec. 4, 1923). 

113 Sulzberger, N., U. S. Pat. 1,518,944 (Dec. 9, 1924). 

1,fl P16nnis, Rudolf, U. S. Pat. 1,487,471 (March 18, 1924). 

117 Blombery, George Frederick, U. S. Pat. 1,582,117 (April 27, 1926), 

1,s Gaudry, Tanciede, U. S. Pat. 1,604,904 (Oct. 26, 1926). 

119 Bristow, John J. Rucker, U. S. Pat. 1,635,110 (July 5, 1927). 

120 Coffignier, C, Rev. chim. ind., 28, 299-301 (1919). 



SIZES AND COATINGS 279 

the process of sizing with rosin. 121 ' 122 Both are alkaline colloidal mate- 
rials, for rosin is always dispersed by making a soap which contains 
more or less free rosin. In their alkaline condition they are not re- 
tained by cellulose fiber and would be lost in the process of making 
paper unless a precipitant were used. Various salts and acids have been 
tried, but the one in almost universal use is aluminum sulfate, known as 
papermaker's alum. The theory of rosin sizing has not been set forth 
in such a way as to be completely satisfying, but it is evident that both 
aluminum hydroxide and colloidal rosin play a part in giving the paper 
the ability to resist the penetration of water or aqueous inks. It has 
been assumed that rosin sizing and soluble silicates are incompatible. 123 
This is an error. It is necessary to add a sufficient amount of alum 
to precipitate both silicate and rosin when they are used together, just 
as they must each be precipitated when they are used separately. 124 
Pulp which has been treated with rosin size and just enough alum will 
not be properly sized if made alkaline with silicate. When the silicate 
is precipitated with alum both are in condition to be retained and to 
affect the finished paper. 

Characteristics of Silicate Sizing. Though the silicate precipi- 
tate does not impart waterproof qualities to paper, except as it assists 
in retaining rosin or increases the hydration of the fiber, it hardens it 
and makes a smoother surface. It increases strength ; it reduces the 
tendency of cut sheets to curl, improves color by helping to retain pig- 
ments, and likewise helps to save small fibers which would otherwise 
have to be recovered from the waste waters, if saved at all. 125 It makes 
possible a good printing paper which is not susceptible to discoloration, as 
rosin-sized papers are, on exposure to light. Mineral sizing is mostly 
used in connection with and supplementary to rosin sizing. In addition 
there are sundry operating advantages which will be mentioned later. 

The extent to which silicate sizing is useful in paper was pointed out 
by Klemm, 126 who distinguished between the need for paper surfaces 
to resist water and those which should have good printing quality 
without necessarily passing a water test. 

Effect of Alum on Rosin and Silicate. When rosin size is diluted 
to the concentrations encountered in paper sizing, small additions of 

m Papeteric, 43, 1058-1066 (1921). 

122 Vail, J. G., Chem. & Met. Eng., 25, 823-824 (1921) ; Abs. /. Soc. Client. Ind., 
40, 884a; C. A., 16, 492; Ind. Digest, 1, 337 (1921) ; Paper Trade I., 73, No. 17, 
32-34 (1921) ; 74, No. 1, 49; Paper, 29, No. 6, 19-20 (1921). 

12:1 Bert, Henry, Fibre Containers, 6, No. 2, 14 (1921). 

124 Vail, J. G., Fibre Containers, 6, No. 3, 16 (1921). 

125 Stericker, Wm, Paper. 33, No. 7, 8 (1923). 

126 JVochbl. Papierfabr., 38, 1983 (1907) ; 40, 1007 (1909) ; C. A.. 1, 2490, 



280 



SOLUBLE SILICATES IN INDUSTRY 



alum cause precipitation which increases with increase of precipitant 
until the separation is nearly complete. In contrast to this, silicate 
solutions become turbid. Their opalescence increases as alum is added, 
but separation begins only if almost all the alum needed has been 
put in. It thus appears that while a slight under-dosage of alum may 
cause minor losses of rosin size it may result in the entire loss of 
silicate. Silicate flocculation is similar in appearance to that of alumi- 
num hydroxide. The floes increase in size and slowly settle to the 
bottom of the containing vessel when alum has been added to about 
pH 5. 

Nature of the Precipitate with Alum. The composition of the 
precipitate varies with the alkali-silica ratio of the silicate. This may 
be due only to the fact that more alum is required to neutralize the 
larger amounts of soda, but the precipitate seems to be something more 
than a mixture of aluminum hydroxide and silica. A hot solution of 
acid potassium sulfate has little solvent effect on freshly precipitated 
silica but dissolves aluminum hydroxide. The floe which results from 
precipitating silicate with alum is soluble in hot solutions of acid sodium 
or potassium sulfate. This suggests but does not prove a combination. 
There may be some aluminum silicate formed. 127 The floe always 
carries sodium out of solution, presumably adsorbed, as its amount 
does not vary greatly with changes in the composition of the precipi- 
tate. Precipitation of the silica is more nearly complete in the more 
concentrated solutions and it is believed that this is also true of the 
solutions of lower relative alkalinity, though accurate data on this point 
are lacking. Certainly the silica in Na 2 0,4Si0 2 is less stable in solution 
than that in Na 2 0,2Si0 2 . 

Table 86. Precipitation of Silicate by Alum. 
Solutions Used 

Amount of Amt. Alum 

Concentration Silicate .00169 

Silicate Composition Per Cent Solution, cc. A1 2 3 per cc. 

Na 2 0, 3.86Si0 2 1.56 51 65 

Na 2 0,3.3Si0 2 0.13 401 47 

Na 2 0,2.45Si0 2 1.25 36 51 

Precipitate 

Per Cent 
Per Cent Na 2 + Per Cent Per Cent 

Si0 2 in Ppt. Per Cent Undeter- Total of Total 

Silicate Composition Dry Basis A1 2 3 mined Si0 2 Ppt. A1 2 3 Ppt. 

Na 2 0, 3.86Si0 2 81.1 14.5 4.5 89.4 83.3 

Na 2 0,3.3Si0 2 68.0 36.3 5.4 43.9 80.5 

Na 2 0, 2.45Si0 2 73.6 21.7 4.7 83.3 100.0 

127 Carter, J. D., unpublished records of the Philadelphia Quartz Company. 



SIZES AND COATINGS 281 

Blasweiler found that the yields from metasilicate in the process used 
above were very low and concluded on this account as well as because 
of the greater cost of the silicate that this is uneconomical compared 
with Na 2 0,3Si0 2 . 

Experience with production on a large scale points to the desirability 
of using the highest ratio of silica attainable. The limit in this direc- 
tion is reached not because there is any silicate solution too silicious for 
paper sizing, but because solutions with more silica than Xa 2 0,4Si0 2 
are too costly (cf. Chapter VI). Xa 2 0, 3.3Si0 2 can be produced at 
lower cost than any soluble silicate with less base because the solubility 
of all more silicious products is so much slower that they seriously re- 
duce the output of manufacturing equipment. 

Blasweiler 128 ' 129 did not find that more than 72 per cent of the silica 
used was retained in the finished paper when the precipitation of Xa 2 0,- 
3.3Si0 2 was conducted in the presence of pulp. As sodium chloride or 
any other electrolyte except the alkaline hydroxides will tend to reduce 
the stability of silica sols, he considered the possibility of increasing 
the yield by adding sodium chloride to salt out the silica, but found it 
uneconomical. 

The precipitate always contains water. Example 2 of the foregoing 
table contained 18.4 per cent of water which could not be removed at 
100° C. Under the conditions of drying paper, it is not likely that the 
silicious deposit is ever dried below 25 per cent water and it generally 
carries more than that into the paper. 

The solubility of the precipitate in a large amount of water, as in the 
dilution of stock for the paper machine, is appreciable. When the pre- 
cipitation was conducted in a solution neutral to litmus the solubility 
was greater (28.8 per cent of the silica content) than when a slight 
excess of alum was added (12.9 per cent) ; with a large excess of alum 
the solubility was 12.42 per cent, which indicates little advantage from 
excessive alum. 130-132 

Precipitants Other Than Alum. Precipitants other than alum 
have been tried 133 but have not come into general use. Magnesium 

^ Blasweiler, Th. E., ''Die Verwendung von Wasserglas zum Leimen von 
Papierstoff," Berlin: Otto Eisner Verlagsgesellschaft. 1922, p. 17. 

129 Blasweiler, Trans, of above by L. \V. Codd, "The Use of Sodium Silicate 
for the Sizing of Paper," London : Constable & Co., Ltd., 1926. 

130 Blasweiler, Th. E., op. cit., German edition, p. 23; Papicrfabr., 19, 809-816 
875-877, 992-997, 1108-1111, 1217-1223 (1921); Paper, 28, Xo. 22 20-22- No ?4 
20-22; 29, No. 6, 19-20; Paper, 34, Xo. 22, 1011 (1924). 

131 A. R., Papeterie, 43, 1077; 44, 58-61 (1922). 
™Papermakers Monthly /.. Xo. 4, 122-123 (1911). 
133 Klason, Papicr-Ztg., Xo. 34, 1315 (1907). 



282 SOLUBLE SILICATES IN INDUSTRY 

sulfate 134 gives low yields and the alkalinity of magnesium hydroxide 
is objectionable in the paper. Mixtures of aluminum and magnesium 
sulfates have also been tried. Ferrous sulfate was investigated by 
Carter, 135 who found that the salt would produce satisfactory sizings 
for dark colored paper. Like alum, it yields smaller precipitates as 
the amount of water is increased. The most satisfactory results were 
obtained when rosin size and silicate had been well beaten with the 
liber and the ferrous sulfate was added as solid crystals just previous 
to the discharge of the beating engine. A solution of Carter's which 
had been kept in a closed vessel over night was found to yield 58 per 
cent ash. This is probably due to partial oxidation of the iron in 
solution. 

Electric Charge. Pure paper pulp, colloidal rosin, and colloidal 
silica all bear negative charges. In the case of cellulose, the charge may 
be reversed by intimate contact with aluminum sulfate. 136 The acidity 
necessary to reverse the charge on colloidal silica is not reached under 
any conditions appropriate to paper sizing. Gordon 137 found the charge 
negative at pH 3.567 and positive at 1.217. The presence of opposite 
charges may assist in the retention of the silicious precipitate, but 
simple filtration in the process of forming the sheet of paper also plays a 
part. 

Use of High-Ratio Silicates. In using the higher percentages 
within the range employed in practice, it will be found that the stock 
holds water somewhat longer on the wire. This permits better felting 
of the fibers and is one of the elements in improving strength. This 
action is not enough to be a disadvantage from an operating point of 
view in most papers up to 6 per cent Na 2 0,4Si0 2 , 1.3 specific gravity, 
based on the dry fiber stock. At 10 per cent it is usually appreciable 
and may necessitate either greater suction or slower operation of the 
paper machine. 

Retention of Filling Materials. As will be seen from Table 
87, 138 the use of silicate precipitated in the pulp aids the reten- 
tion of filling materials and counteracts their tendency to reduce 
strength. 139 ' 140 ' 141 

1M Frohberg, A., Wochbl. Papierfabr., 44, 4250-4252 (1913). 

135 Carter, John D., unpublished records of the Philadelphia Quartz Company. 

136 0stwald, W., and R. Lorenz, Kolloid Z., 32, 11-76, 119-137, 195-209 (1923). 

137 Gordon, Neil E., Colloid Symposium Monograph, New York : Chemical 
Catalog Co., 1924, Vol. 2, pp. 119-121. 

13s Blasweiler, op. cit., German edition, p. 25. ,. 

13a Brit. Pat. 177,137 (Nov. 24, 1921) ; Fr. Pat. 543,763; and Paper, 31, No. 20 
(1920). 

™Papeteric, 41, 634 (1919). 

141 Altmann, P. E., Ger. Pat. 288,106. 



SIZES AND COAT IS CS 283 

Retention of Colors. So also, silicates may help the retention of 
colors partly by the mechanical process of filtering them out of the water 
in which they are suspended with fiber and partly by adsorption of color 
on the silicate precipitate. Basic dyes are strongly adsorbed, sub- 
stantive dyes weakly, and acid not at all. Acid dyes therefore wash 
out. Magnesium sulfate is the best precipitant for holding basic colors; 
aluminum sulfate is best for substantive colors ; and calcium salts are 
intermediate in both cases. Color lakes of this type have been offered 
on the market. The retention of silica is best with alum and a basic 
dye. 142 ' 143 

Manipulation of Silicate in the Mill. 

Role of Silicate. The manner of using silicate in paper will depend 
upon the objects sought and the conditions obtaining in the mill. To 
illustrate, thin translucent paper known as glassine is made from a 
stock which is thoroughly hydrated in the beating engine. Silicate 
should be added early in the operation and left alkaline in order to assist 
the mechanical treatment which induces the pulp to take up water. It 
is allowable to do this because the presence of silica so modifies the 
action of the alkali that it does not injure the strength of the cellulose. 
Then, shortly before the beater is dropped, alum is added to precipitate 
silicate and rosin size together. 

Very different is the procedure in the case of a cheap writing paper. 
The beating time instead of several hours may not be more than an 
hour, and colors sensitive to alkali are often used. Here the silicate 
must be put into the water with the pulp, and alum for precipitation 
added as soon as possible to give time for coloring after the silicate has 
been neutralized. 

Or again the principal object of adding silicate may be to increase 
strength, to retain clay or other filler, or to control a tendency of small 
fibers to stand up above the surface of the sheet. 

Kind of Silicate. As alum is needed to cause precipitation of the 
silica in proportion to the amount of soda present, the more silicious 
silicates are usually chosen by the papermaker. 

Na 2 0, 3.86SiOv, 1.3 sp. gr., requires about 25 lbs. papermaker's 

alum (18% AL>0 3 ) for 100 pounds silicate. 
Na-O, 3.3Si0 2 , 1.4 sp. gr,, requires about 33 lbs. of alum per 100 

pounds silicate. 

142 Heuser and Behr, Papierjabr., 1-6 (1923); Paper, 31, No. 18, 7-12 (1923). 
143 Heuser, Paper Maker, 64, 433 (1922). 



284 



SOLUBLE SILICATES IN INDUSTRY 



05 



S 1-1 

S a! 



< 



be 

c 

ID 

u 
-t-> 

co 



G co 

O ° 



•O 

'1 



a <a nop 

is <j co co 

CO 



O 



■OV 



"d< 

+ 



•(MfO 

•cm ^q 

"co CM* 



'O 
co 






2 i £ . 

"53 M-t OS H »Q 



5 



be cu 

a •£ 
« is 

hJco 



H « 



bc< 



p -oo 

rf ■>*■ 'Tj- CO 



u CO 



a 



CO 



1- - n O 

is"* 

0-i 



O s-h j_ 



\o o *© o 

CO CM y— 1 co 



as TJ 

+J <U o t>> "3 CM 
O <s> CM "^" "^ t^ 
HP 



I -Ort 0! . . • . • 

^ CQ >"» . 
a) -gp Q 

U 05 ^ O p CM CM O O 

u ."S • •- co olodod'— ''— ' 



vo 
<o 

o 



O co 

do 

++ 



Tf l_0 • LO ON LO O CO 

<^n -— ; • CM 00 "■* "-O LO 
CM co ' co' t-h t-i t-H r-H 



O 

o 



00 o 

LO O 
CO VO 



OO • O o O lo rf 

CM 1—1 • 00 O "t" fM ir > 

■ CM no • CM rv) Tf 00 no 

CO co • co co CO CM CM 



• O O O NO CO 

• Tt ON NO !>. CM 

'^tiovdo'^ 



ooo>hn 

NOOOOOtrH 



000 

LOLOLO 



000 -ooooopppopo 
i-h' «-5 ■ r -('Kdd^od-H'\dK'Ni 

1— I 1— I 1 — I 1— I 1 — I r-H co 



Ph 



o< 



co 

<4H 

o 

'l2 



MO CQ 

CQo 

o 00 
00 CO 
CO 



>. 
_o: 

U 



^-i" w 

Q* 



S-* 



1- u, 



+-> -4-> +-) 

ai aS as 



O 



o 

X,' -aj -aJ 

<CQCQ 



u 

U 

c 

CM 

pq 



03 

5^ ON 
OJ u • 

5/3 O O 



^^t 






.u^ss^: 



^^ OJ 03 

rt 2 rt - 

S C u u 



00 00 
co co 



Lo^ 



cococouUcoH 



OvS3'y5>vS5vvS>"sP'sS>>5) v C>vS> ■s.O 



^ 



^ 



LO 1— I t— I 1 — I 



0000000 

CM CM r-. CM 



Si ^ iJ £ £ tf aT 

o3 o3 a3 a3 03 -H *j 
(J C d (j o o! oS 

— •" us s ^ .y .y 

CO U CO CO CO ^ ^ 

OOLOL0000055: 

MCOrHr-l(Nlr-lrHrH^I< 



OS Cfl 

Hco'coi 



CMcorfLONOt^OOONO'— 'CMCOTj-LONOt^OOON 



SIZES AND COATINGS 



285 



fe 



£ co° co 

CO 



■59 

>co 

CO 



lo£°° 



. CO 00 
• co CO 



• O >0 

. CO ^H 



in 



5u 

O rt 



GO £ 






' co co 'co 



-J. 



03 



' r " 3 tr",, Q o 
^ £ C ex] c\) 



H 



J 



QO • Q CO 

OOO • O co 

co 00 • l^» \Q 

•rf CO • "*t" co 



OOQ 
co O 

CO CM 



H 



best 
+3 C 



,00000 

5 v- odododo'cK\dt^t^ovdcdr>!t< 
r « — i 



ufL, 



> 



i-il t/3 

u(2 



VO 



•Q O^OcoOcooOcopOOOO 

C « tsdio'd v 0O , 0' T tfNCA'd ( 0>0 
^ K CMCO'^cO'^r'^-cococoCN^fCNjrv) 



r; c ^ i- 

;_ to u rt 

<u <- • •- Ph 



in o3 <l> i jr 1 



■ \JD n M O On ^t t 
. u-j co_ MO rf Tf On ON 

; c\i co' co' as \6 o <-< 



\0 rH CM r\) ro —i 
(~vj co # O »-j Tf <N1 
<M* ON O iO r-J rvj 



O 



o 






CO 
co 
CO 

•LOCNIO O 

■0\NO « 

:^oo : : : : : 4 

• -oQ -c 

• • ON co <u 

• • xn 

. .NVO 3 



<u.2 o_ 



w i3 o]H^ 



- 



^pq 






co 



G 

3 



kU 



'OJ 



Wo 
o 00 
00 CO 
CO 



-iNO'ONrt 
Oi-IOKIT/O 



U 



u 



< 



Si m 

03 U 



£ j? c? ►; >> £ « 

00 -O -o jfl ^rt -TO c 

- -uG -~ 

c« oi n) rt 2 rt « 
U U U c c U u 



oE 





o3 

( 1 ^ -4-< 



o 

<PQpq 

o o 

rn 00 00 

-nco co 

fe 4) OJ 

03 rt 



tvqn- 



cocOcoUUcoh 1 



o3 rG 7G 

E-iloco 



r.G C ctf «« . . 

O >^ U- Vh u "^ 

00 03 'O nj *0 c« <« 

^ o3 03 
OJ <U (U - « 

03 03 «3 o3 03 ■*-• -y 

U C U CJ (J 03 03 

u u 



CO — 



Ov^v? 1 'NP'tNp>S 3 'Npv5i> N p>P^C) 



^ 



^ 



OO 



oo ooooo 

!-H ^H ^H (NJ (>J ^H (>) 



OO^o 

Ojco i-H 



couco'coco^-^ 

lOOOOO^I ^ 
i-« CM ^h ^H ^H r< ^ 



si 
H 



-HNfOTfiO^ONOOOvO^MCO^tiOMDtsOOON 



286 SOLUBLE SILICATES IN INDUSTRY 

Technic. Silicate may be manipulated to avoid interfering with 
colors, and it may with advantage be used wherever hydration is desir- 
able and an increase of ash permissible. Wherever hardness or smooth 
surface is sought silicate sizing will help but often at some sacrifice of 
bending properties. The balance between these opposing tendencies will 
often determine the amount of silicate to be added. Mills making the 
most various kinds use from 2 to 10 per cent. 

The texture of a silicate precipitate depends on the dilution of the 
silicate and the alum. Under the conditions occurring in the beater a 
light flocculent product, well adapted to harden and increase the strength 
of the paper, is produced, but if the chemicals were mixed in relatively 
concentrated condition the material thrown out would be granular, 
sandy, or lumpy, just as would be the case if dry alum were mixed with 
a strong solution of rosin size. When the light flocculent precipitate is 
dried, it hardens to a horny consistency, too hard to be crushed easily 
by the hand. In this hard condition it still retains a considerable amount 
of water, which contributes largely to its toughness. 

Effects of the Silicate. The effect of retaining this material in 
the substance of paper is shown first of all by an increase in the ash 
of the paper. 144 A study involving 550 tons of paper and an examina- 
tion of 1,200 samples gave an average of 1 per cent in ash with an 
average addition of 3.48 per cent of liquid silicate based on dry fiber. 
The amount of dry alum necessary for the precipitation of the silicate 
was 25 per cent of the weight of the silicate solution. The average 
retention was 66 per cent of the total silica in the silicate, plus the 
Al 2 O s of the alum. There is good reason to suppose that the use of 
larger proportions of silicate would not only produce more marked 
effects on the paper but would be accompanied by a higher percentage 
retention. 

The hardness and the finish of the paper were determined by the 
combined judgment of several experienced papermakers, as there was 
no method of reducing these qualities to a numerical standard. From 
comparison of sheets, which differed only by the silicate content and 
the alum requisite for its precipitation, the statement is warranted that 
the use of silicate in every case produced a harder and a smoother sheet. 
The Mullen tests of the papers in this series when averaged showed a 
gain of 12 per cent in favor of the papers containing silicate. Ink, 
resistance was studied in four different grades of paper by the floating 
method with standard ink. In one case the silicated sheets gave the 
same values as those with rosin sizing only, but in three of these grades 

^Furness, Rex, Paper-maker & Brit. Trade /., 73, 107 (March 1, 1927). 



SIZES AND COATINGS 287 

the papers containing silicate showed better ink resistance than those 
which contained none. This may be attributed to the increased retention 
of rosin in the paper, there being no reason to believe that sodium 
silicate can of itself increase the resistance of paper to water or to an 
aqueous ink. 

In studying the effect of the addition of silicate to the beater, it was 
observed that the increment of ash increased over a period of several 
hours, sometimes reaching its maximum as late as 7 hours after stock 
containing silicate came on the machine. This is interpreted to mean 
that a larger precipitation of the silicate and better retention develop 
as the white waters from which the silicate has been precipitated are 
returned to the machine and to the beaters. 

The higher retention of the silicate precipitate is not wholly due to 
the accumulation of silica in the water, but it has been shown experi- 
mentally that prolonged agiiation increases the amount of precipitate 
even in the absence of pulp. Thus it may be expected that those papers 
in which the manufacturing routine provides a long beating will not 
only retain the silicate better on account of closer texture of the sheet, 
but will also have the advantage of more complete precipitation of the 
silica. This is of minimum importance in those mills where most of 
the water is saved for recirculation, but may be very significant where 
beating time is short, or where the mill works but a few hours on one 
kind of paper. 

Trimmings Put to Use. The waste of the fiber container industry 
consisting of trimmings from the manufacturing process and of con- 
tainers which have served their intended purpose provides a large 
amount of stock to paper mills. The silicate used as adhesive in this 
stock may now be turned to good account by precipitating it with 
alum and making a better finished paper board. Though silicate which 
is not neutralized is detrimental to rosin sizing, these clippings, which 
may contain 7 per cent by weight yield a satisfactory surface when 
this is properly precipitated. 145 

Combinations with Soluble Silicates. 

Rosin Saponified by Silicate. Blasweiler, who worked under the 
authoritative guidance of Emil Heuser. also studied the use of soluble 
silicates in conjunction with other colloids for sizing paper. He found 
that the proposals to make concentrated size by using silicates to sa- 
ponify rosin at low temperature offered little advantage over the ordi- 

lw Vail, James G., Fibre Containers, 6, No. 8, 16 (1921). 



288 



SOLUBLE SILICATES IN INDUSTRY 



u 
o 


O 


* 

-G 

u 


.5 


10 

•SI 




'c3 


O 


s- 


OJ 


CO 



o 

+ 



■o 

co 



NO 
O 



+ 



© 



G^ 
CD H c/5 



LO ^1" 

00 "* 

CO CO 



lo i— i CO O 






OO 

On CO 



G 



C/i o 



S v„ CO 



oo 

ON ON 

co CO 



OOQ 

no© o 

coCM 



G «5 •■} 5P, t— i»-h . i— i co On 

rt Q«H ++ + I I 



o 
o 

CO 



Soo o 

^t-o o 

00 <0 i—i (O 

co co CO CM 



+ 



$ 



8 



<o 



CO 

oo 

w 

M 

< 



<D 

to 

5 



O 

g£ pq 

^G 

PwO « ^ 

m 

Sou .o 

*-l — ?>»•« (/} 

<U J£ *-■ ■" ' rrt 



T.-9 






Q u 



CO 



On 
O 



O 
co 



co CM lo NO "O co 



G 



C/3 

o 

2 



8,2 



-oo 

-O co 



© v^ 



CM 



a 



1^ 


On 
CM 


© 


cm' 



On 

LO 



CM 

NO 



CM 

CO 



a u 


u 


SX 


S 


oO 


C/] 


y nj 




u£^ 



'53 o 

CO O* 



- O iUGo 
' ."G00 

~a a 
<u CJ 

<G;G 

"S't/5 

o 

05 ° 
to ^ 

G 

.5 O 

<o G 

LO ^ 



.S js 

CO +■> 

9 G 

^^ 

LO 

© 



!^3 ^ —i '(75 

I O «5 O 
+ CM «> ^ 

^ + -G 3 

In 2 

O G o g 

< co o 



, vo_i 

U '-' 'V 

rt oo u 

>u'lo H 

pq^ ^ 

•4-> 

G - 

00 -M |_ 

cd rt-a 

Pm 
d 



• S bi.S 

w C (fl 

qa o 



<u • -G • 

*J -H tS -H 



oJi- as 

Pm^Ph 

E+E 

o - o 

CO.GC/i 
to 

°^ 2 

bflyCs bJO 

ce^ c 
._ LO .„ 

o 



a; 

LG 



as 

a. 

B 
o 
U 



lo NO t^ 00 On 



SIZES AND COATINGS 



289 







■d2 

rt co 




■*-> 

rj 

<U 

•4-> 

03 


VO 




J3 

V 

in <u 




o rt 
P^S 


o <u 


P-i 

U 

V 

O 


oo 




00 • 


# 




t_0 >-0 »— I >-0 

rnrHVO T— 1 








.S is 


co ' 


■ 




co CO CO CO 






co' 


E w 
















•a 
















Unsize 

Tearing 

Length 


o • 

CO • 






3640 
3640 
4300 

3640 






O 
O 
CXI 


llary Test 
per Hour 
Printing 
Varnish 


oo 






O O>-0 




• 


CM 


aw cO 


OO 


. 




OOO ; 




• 


r-H 


o'o 


. 




irinO ; 




. 


i— 1 



l. co i rt 

<3 



Ph 



CM On 00 

00 """! ^ 



n p 

CO 
co 

CO* 

q 



bo i> 



° H j_ 



9M5 
fe cffl< 



S!s 



n3 C 



on" 



IsIj 



<L> O 






bo 

.s 






:cocvi 



\OC\) 



'3 : 
o . 

°„ 

. -00 
'Oco 



rt O u 



c/3 o 

p^ 

CO © 



o w 

„ - <u 

- s *■ 

o c 
pjj — 

i_o 

©' 



o^<v 
eMpq 

•S°co 

•gco 

-rd «3 

<D U 

'Sco 
rt ° 

.si 

UO *« 

© 



n3 

U 03 Jd 






ci 



. o - ° 



oo • >> 

c 



-o 






a 



(U 



<3J 



XJ 



co 
H 



OS 



^+ C 






^i= 



^coo 



oS a3 
.^- CL( ^cj 

CO u •" 

^ J «CO 

10 Ouo 
, CO 

+ o + 

■S bo.a 

S C w 



eye 



oi '^ oS 
PU^Ph 

a, a 

£+6 

O J-J O 

co-Sco 
bJOvo ho 

C 6^ C 



to ^o r^ oo o\ 



290 



SOLUBLE SILICATES IN INDUSTRY 



nary practice of using rosin size and silicate separately. 14G ' 147 Even 
when immediate precipitation of silica is avoided the size tends to de- 
posit silica on dilution before the addition of alum. Saponifying in dilute 
solution immediately before addition to the pulp gave better retention 
of silica and some gain in strength. 148 

Other Materials. Fatty acid soaps have also been used in sizing 
paper. They are compatible with soluble silicates and adapted to give 
water-resistance with better bending properties than rosin. 149 ' 150 ' 151 
Bakelite has been used, but its advantages over rosin are not commen- 
surate with the present difference in cost. 152 ' 153 

The advantages of increased retention of other colloidal sizing ma- 
terials are had when silicate sizing is used in conjunction with animal 
glue, casein, montan wax, or starch. 154-162 

Silicates and Starch. Starch, in particular, when heated in a sili- 
cate solution until it swells becomes involved in the silicate precipitate 

Table 89. Sizing ivith Silicate and Starch. 
(Blasweiler) 

Strength Figures 

with Starch Without Starch Increase in + or — 

Tearing Tearing Tearing Tearing 

Kind of Sizing Length Stretch Length Stretch Strength Strength 

mm. % mm. % 

5% swollen starch 3800 3.68 4150 3.76 350 9.2 +0.08 

5% swollen starch, ppt. . 3800 3.68 4350 3.40 550 14.5 -0.20 
10% swollen starch, ppt. 3800 3.68 4550 3.80 750 21.5 +0.12 
10% raw starch and 
10% sodium silicate, 

38° Be., ppt 3650 3.15 4300 3.50 650 17.8 +0.35 

5% starch, 5% sodium 

silicate, 38°Be., ppt... 3650 3.15 4280 3.67 630 17.3 +0.52 
10% starch, 10% sili- 
cate, 38°Be., swollen, 
ppt 3650 3.15 4600 3.48 950 26.0 +0.33 

The silicate used was Na 2 0, 3.3Si0 2 

146 Kuldkepp and Graf, Ger. Pat. 245,975 (Oct. 20, 1909). 
147 Clapp, Albert L., U. S. Pat. 1,345,317 (June 29, 1920). 
^Sommer, George G., Ger. Pat. 257,816 (Aug. 20, 1911). 
149 Kolb, Papicrfabr., 19, 1141-1144 (1921) ; C. A., 16, 493. 
130 Blasweiler, loc. cit. 

151 West, Clarence J., Ind. Eng. Chem., 14, 858-860 (1922). 

152 Holzverkohlungs-Industrie Akt.-Ges., Ger. Pat. 338,396 (1921). 

153 West, Clarence J., Paper Trade J., 73, No. 15, 52 (1921). 
154 Clapp, Albert L., U. S. Pat. 1,592,294 (July 13, 1926). 
155 Muller, Ger. Pat. 317,948 (1920). 

157 Possanner, E., Chem. Ztg., 38, 100 (1914). 

158 Ger. Patents reviewed by West, Paper Trade L, 75, No. 1, 55 (1922). 
1M Mosley, J. F., Brit. Pat. 226,850 (Aug. 24, 1923). 

160 Reichard, F., Brit. Pat. 177,137 (Nov. 24, 1921). 

161 See also Fr. Pat. 543,763: Paper, 31, No. 20 (1920). 

lfl2 Altmann, P. E., Ger. Pat. 288,106. 



SIZES AND COATINGS 291 

in such an intimate way that the retention is increased, 60 to 70 per 
cent of that used being found in the paper. 163 

Silicate which has been boiled with starch and precipitated with 
alum exhibits a horny texture quite different from the corresponding 
precipitate without starch. Although raw starch is flocculated by alum 
it is poorly retained in paper, but it imparts a pleasing finish and is used 
in numerous mills. Whether viewed as a modification of silicate sizing 
with starch in minor proportion or as a means of retaining starch with 
silicate in the lesser role, the combination is a useful tool in the hands 
of the skilled papermaker. 164-167 

Advantages of Silicate Sizing. 

From an operating point of view the advantages of silicate sizing 
include : 

1. Good formation of the sheet and satisfactory removal of water by suction. 

2. No sticking on the press rolls. 

3. As a result of the above, increased life of the felts. 

4. Quick and complete sedimentation of the white waters. 

5. Increased retention of filling materials without sacrifice of strength. 

6. Economy in coloring. 

In addition, the qualities imparted to the paper, though they vary ac- 
cording to the kind of stock and method of manipulation, may be sum- 
marized : 

1. A small though definite increase in strength. This is of the order of 10 
per cent. 

2. Increase of rattle or snap of the paper. 

3. Better feel — i.e., a smoother surface free from protruding fiber ends. 

4. The combination of quick absorption of printers' ink with hardness which 
makes a clean impression for offset and other rapid printing processes. 

5. Reduction of the tendency of cut sheets to curl. 

The kinds of paper in which silicates are being used include a wide 

range, but a few are listed with the principal advantages sought. 

Bristol board stiff smooth surface, generally with starch and rosin. 

Kraft increased strength and reduction of mechanical treat- 
ment to affect hydration. 

Book clay or talc retention without loss of strength. 

Envelope small amounts to improve finish. 

Straw denser, stiffer sheet, low cost. 165 

Greaseproof better hydration. 

Glassine same to increase transparency. 

Writing better finish and formation. 

163 Lutz, Alfred, "Ber. d. Hauptvers. d. Vereins d. Zellstoff und Papier 
Chemiker," 1907. 

164 Blasweiler, Th., Wochbl. Papierfabr., 56, 89-93 (June 13, 1925). 
163 Fues, Wochbl. Papierfabr., 44, 835-841, 1223 (1913). 

188 Wrede, Hans, Wochbl. Papierfabr., 44, No. 10, 835 (1913) ; C. A.. 7, 2114. 
167 Wrede, Hans, Papierfabr., trans, in Paper, 31, Xo. 12, 11-14 (1923) ; Papier- 
fabr., 23, No. 18, 293 (1925). 

" Papeterie, 43, 1077; 44, 58-61 (1922). 



ies 



292 



SOLUBLE SILICATES IN INDUSTRY 



<0 

s 



S <U 





>> 


Mews 




"3 


paper 




CCC.Su 




cu 


oi 01 m u 4J 


nS 


CJ 




c 


m 


C G C o o 
<U <U <DcN|CM 


2 


o 


.S.S.S-L-j- 

"55 '55 '55 "1 r 


O 


A 


o o o . . 


.CM 


t 


•h l- U ty fj 

<u <u <u <; <t* 

cu cu cu 


< + 




U, U U n « 


n m 


.s 


<+H M-l M-H , s/-^ 

CO CO CO /-v ,-v 

o3 rt ajCJCJ 


oo 


N 


.S.S.Sww 


mm 


c/5 


•"»_•■. — / 




CO CO ' CO _£? _« 

o o c>Z2Z<> 


<< 




^^$£ 


^ 




CO CO CO CM CM 


CM CM 


»-. 


• • -t^l>» 


•O 


.— 


• • ■©© 


• o 



^ 



c ooo^oa oo 






G> 



CO 



CC 



m 



m 






_ C/3 



oo 
oo 



N 2 fc £fooooo 
•71 S3 ¥ 9, o o o o o 

£> <^co 



o er> 

co co 



oo 
oo 



o 



fe 



C 

CD 


\ONC7\00 


On VO 


ooooo 


— 'O 


!h 




















1/2 






















>. 










>, '• 




^s 










CIS • 


















*o 










a '. 




a 










d ' 




.5 










.5 j 




!5 










•5]s 






"0J3 

.s 








S^ 




o 

CM 


"5 

<u 

03 


»0, 

PC 


"0, 

PC 


> 


++ 


PC 

o 


+ 

PQ 


o 


o 

cc 

CO 


o 
CO 


l* v-. i_ 

*0 T3 »t3 


00 CO 
CO co 


t/3 












0, 


<L 


<L> <V <D 


CD CD 






■+- 




•*-> 4—' 




n 


Ct 


o3 a3 03 


03 o3 




o 


/■~ 


u u u 


CJ CJ 


































/ 


<r 


CO CO CO 


CO CO 




u- 


^ 

3 


OOO 


O LO 










I— ( 1— ( 


CO 





o 
o 



o 

G 

03 



CO 



+ 

o 



<u 


g£ 


<u 


Ih 


U< CJ 


M-l 


MH 


CO 


rt .5 


03 


q 


.5 u 


CO 


CO 


O 

1-H 


2^ 




O 


£ 


^^ 


CO 


CO 




CM 


• 


CO 



lO 



o 
o 



o 





-f 




CM 




o 




On 




i-H 






1 




1 . Q 


> 
'3 




3 


o ■ 

CM • 








+ : 


CO 




CU 


<u . 




rrt 






a 


c > 


rt 


03 ' 


'. > 




c; 


CJ 


























IS} 


-V 


iyj 


CO 


£M 


-C 


PQ • 


^ 


o 

00 

CO 


^ 


o 

oo • 


a 




Ci 


co • 



co O co vo 

"co O 'co <J 

u *^ U -*-" 03 

t> uB^ cu *?. 

i <~> *-h i r^ »— t cu 





o* 


& 


a 


a3 


o3 a, 


03 


O 


O o3 


o 


CO 


co O 


CO 


i 


" CO 


1 


rt 


a i 




^ 


>5>- o3 




CO 


CO 


co 


03 


as co 


03 




CS 
















O 


O •" 


O 




O 


ci 


-a 
<u 

CU 




cu 


co 


CO <j 


,a 


a 


c^ 


a 


o 


o -. 

+j 03 


>. 


+J 


•t; >> 


O 


O 


o O 


co 


CJ 


CJ CO 


^ 


^ 


^ 


LO 


LO 


LOLO 


o 


o 


OO 



On 



On 



< 



C 

03 



^^j >~' cu <— ' l ~-' l — ' <~? 



O 
O 



oo 



CM 


O 


O O 


T— 1 y—l 


^ 


£? : 


to 


LO • 


+ 


ex : 

«5 . 


03 


O . 

CO 

i 


O 


a • 


CO 

I 


£ : 


a 




X 


CO 




rt ; 


CO 




a 


^_t 








o • 






O 




_ *<u *n *(u 




_S oo c oo 

-^co gco 


55 -X - 


% a v a 


v cu 


^•^^fS 


LO ^LO M 


o 


c^ 



LO ON 



2^ 
oo 



LO o 

oo 



LO 

r— C 

a 
o 

CO 

I 

a 



03 



"Om! 



. O 

_.CQ S 
<v° <v 

cu 00 Q 
coco T" 1 

. S - a! 

2 w >> 

^'^LO 
LO O 



SIZES AND COATINGS 



293 



o 

CM 

+ 

G 



bfl bfl 



£ 

o3 
CM 



a 

CM 



CM 

<U CM 



O 



On 



< 






-c 






nS 


O 


o 


o 


© 


<U 


1— 1 


T— I 








rt 






o 
























CO 




CM 

CO 



CM On 



>J) o 

rag 

o 

CO <u 



o 

; + 

*o3 g^o 

.g - a o 

C G CM 
CM CM 



.G 

a 



CO 

*0 
G 
o3 



CO 



O 
CM 



o 

CM 






o 

CM 



o 
o 



O 
tT 



r3 



O 
CM 



+ + 



-G 


,G 


,G 


J3 


u 


u 


(J 


o 


u 


Ui 


t_ 


Ih 


a 


o3 


aJ 


aJ 




-i-> 






CO 


CO 


CO 


CO 


g 


G 


G 


G 


<u 


<u 


cu 


<u 


















o 


o 


o 


O 


£ 


£ 


£ 


£ 


co 


CO 


co 


co 


^ 


^ 


^ 


c£ 


LO 


o 


LO 


O 




T ~~ t 




1 






o 


o 






CO 


CO 



o 

o 



LO 



42 CQ 

co 

LO 



■spq 

o 



lo rt 2 
go go 

^CM £CM 

co co 

^ + ^ + 



COvO CO 
-oj CO CN' 



t5r l 
$> co o^co 

LO T-H 



03 

u 

g 

03 



CO 



G 

03 

G 

15 



'5 
o 

£ rt 

o3 13 
G aJ 



o 

o CM 



^ 



O 

o 



o 



LO o3 
,G~ 

-4-J 

•r o3 

£ G 

co O 
co CM 



+ 



<u 



U 



GO 
O CO 



<D CO 

-c Jr 
<u £ 

CO p 

* C 

<u ,_ 

•-^ (U 

o 

Is 

CU o 
° CO 

03 03 co 

03 



co j^ 



- 



sS « 
% g s 

G G !L> 

" — , rt 

-a cj 

■55 "G --h 

O <L) 

-g gH 
^^ • 

*G ' — co 
G N n3 

g'lt; > 

.G -t- 1 

cu > G 

N . *-' 

*2 a3 ^ 
fig 

-G <u^ 

- M X 

°.s «« 

-t-j C -*- 1 
fafl'G: bC 

G c G 

bo « bp 

rj Lh _G 

*n — - 'S 

03 03 re 



u 



aj 



•-.£ G 
cs o 
.2<g; 






^ 



03 

t|JS 

Wo, 
£.> 

03 fcJO 



294 SOLUBLE SILICATES IN INDUSTRY 

Any printing paper which is not required to withstand aqueous inks 
may be made without the danger of discoloration which is characteristic 
of all rosin sized papers on long exposure to light. 

Textile Processes. 
Silk Weighting. 

Reason for Weighting. Silk weighting has been referred to as a 
"nefarious practice", 169 but the public view of substituting one substance 
for another is in process of change, and recently advertisements have 
appeared in which the advantages of weighted silk are set forth. 170 

The moral aspect is no longer a matter of concern when the buyer 
knows what he is purchasing, and the seller points out its advantages 
with candor. There can be no question that the weighting of silk has 
been carried in some cases to a point where its value was much depre- 
ciated. It is also true that some properties useful in the making of 
certain textiles, notably ribbons, are imparted by weighting. The better 
draping qualities of weighted fabrics is often a determining factor. 
We are here concerned only with the process which employs soluble 
silicates. 

Method. Raw silk contains a soluble gum which accounts for 18 
to 25 per cent of its weight. This is first more or less completely re- 
moved in a soap solution. The weighting is done in a 28°Baume, 1.239 
specific gravity, solution of tin chloride, containing 0.5 to 1.5 per cent 
free hydrochloric acid, which is kept cold. The treatment continues 
for an hour during which time the silk gains 12 to 15 per cent in 
weight. 171 Cotton under similar treatment would gain 0.5 to 2 per cent. 
The mechanism of the reaction is not known. It was thought to be 
a matter of hydrolysis, but as the silk will take up 11 to 12 per cent of 
stannic chloride from an anhydrous solution in benzol, this is plainly 
not the whole explanation. Stannic chloride forms compounds with 
amino acids, and a similar process may take place in the silk. Hy- 
drolysis of course takes place in the washing which is the next step, 
so that stannic hydroxide is present when the silk is put into a 5°Baume, 
1.036 specific gravity, solution of disodium hydrogen phosphate at 54° C. 
(130°F.) and worked for an hour. This cycle may be repeated ac- 
cording to the weight desired, each pass through tin and phosphate 
baths adding about 15 per cent to the weight of the silk. 

169 Encyclopedia Britannica, 1 1th ed., vol. 25, p. 103. 

170 Advertisement in Silk Journal, Textile Dyeing Co. of America (1927). 
171 Roscow, James, U. S. Pat. 1,602,840 (Oct. 12, 1926). Cf. McDowell, Joseph 

Curry, U. S. Pat. 1,558,104 (Oct. 20, 1925). 



SIZES AND COATINGS 295 

The silicate is used as a single final treatment at 5° Baume, 1.036 
specific gravity, and 65 °C. (140°F.). The weight added by the sili- 
cate depends upon the amount which the tin and phosphate baths have 
put in. 172 - 173 Two passes of these enable the silicate to add 12 to 15 
per cent, 3 passes about 20 per cent, and 4 passes up to 30 per cent. 

Aluminum sulfate may be used after the tin and phosphate baths to 
further increase the weight. The silk is made acid with a 5 to 8 per 
cent solution of sulfuric acid and worked in a 3.5° to 4.5°Baume alumi- 
num sulfate bath at 35°C. and finally in a silicate bath of 4°Baume, 
42 °C. The extent of weighting by this method is dependent upon the 
amount of tin phosphate in the silk as well as upon the details of manipu- 
lation. Increase of concentration or temperature of the silicate makes 
for greater weight. So does longer time of treatment, but skill is essen- 
tial to obtain silk of proper strength and free from any trace of floccu- 
lent deposit which would cause dyes to take unevenly. The silicate 
should never be used above 63°C. (145°F.). A final process to increase 
weight which has come out below expectations is to put silicate 1.5 times 
as heavy as the silk to be treated in a 10 per cent soap solution and treat 
the silk for an hour at 42 °C. As much as 15 per cent can be added 
in this way. It is necessary to add more weight than is expected in the 
finished silk as some is lost in the dyeing or bleaching processes which 
follow. This may amount to 20 per cent. Details of technic are set 
forth by Ley 174 with elaborate precautions essential to success in this 
complicated and difficult art. He also describes a combination of cutch 
and logwood weighting with tin phosphate and silicate. 

A total weighting up to 50 per cent of the boiled-off silk seems to 
have very little influence on strength and 100 per cent weighting is suit- 
able for many purposes. Ribbon silks are often weighted up to 250 per 
cent on the basis of fiber after removal of gum. 

As the process plumps the fiber and improves its luster and feel, it is 
generally used for such goods as hosiery and ribbons. This gives a 
better result than the thin fibers of untreated silk. 

The procedure may be varied to permit weighting either in skeins or 
as woven or knit goods. An increasing amount of silk is now weighted 
in the piece. 175-177 Mayer says that it is almost universal in Germany, 

172 Knup, J, Brit. Pat. 6,728 (1904). 

173 Weidmann, U. S. Pat. 780,924 (1905). 

Ley, Hermann, "Die Neuzeitliche Seidenfarberei," Berlin: Springer, 1921. 

Rossbach, Helmut, Deut. Farben Ztg., 57, 586-587 (1921) ; C. A., 15, 3754. 

Trotman, S. R., Textile Recorder, 25, 46-49 (1924), reprinted in Dyestuffs. 

Posselt's Textile I., 29, 111-132 (1921). 



171 

175 

176 



296 SOLUBLE SILICATES IN INDUSTRY 

where the mineral content of silk frequently runs from 40 to 75 per cent, 
of which 40 per cent may be silica. 178-182 

The great mass of moderately weighted silk performs its intended 
function without difficulty and gives complete satisfaction at a cost not 
to be attained with the pure fiber. 183 

The industry has reached substantial proportions in this country, 
having consumed in 1922, approximately 6,250 tons. 

Requirements of the Silicate. Silicate for silk weighting is re- 
quired to be crystal clear, and because the life of the treating bath is 
terminated by the appearance of silicious floe which would cause dyes 
to take unevenly if deposited on the outside of the fiber, it should be 
as stable as possible. A good test is to reduce the concentration to 
5°Baume, boil for five minutes and allow to stand for an hour, at the 
end of which time it should be clear and free from floe. The ratios 
used in the industry vary from Na 2 0, 2.4Si0 2 to Na 2 0, 3.3Si0 2 , the 
more alkaline being preferred, as the silk or the precipitate formed in 
the silk adsorbs sodium in a manner analogous to other silicious pre- 
cipitates. Some of this is removed from the silk during washing, but 
the bath eventually becomes unstable and must be discarded. 184 

Color. Many acid colors which are popular on pure silk are not 
readily adsorbed by tin-weighted silk and require great care in manipu- 
lation. Basic dyes are easily applied on tin-weighted silk. Very heavy 
weighting followed by exposure to sunlight may cause the fiber to 
become tender. In some cases, reddish colored spots appear which may 
be guarded against by a treatment with weak ammonium thiocyanate. 
Tendered silk is restored by treatment with hydrofluoric acid. 185 

Test for Weighting. The presence of mineral weighting is easily 
detected by burning a strip of silk. Pure silk burns completely, and 
heavily weighted goods leave a white skeleton of ash. A quick quan- 
titative method consists in comparing X-ray photographs of weighted 
silk with those of standard samples. 186 A more exact procedure is 
based on extraction with 2 per cent hydrofluoric acid at 60° -70° for 20 

178 Mayer, Hermann, "Das Wasserglas," Sammlung Vieweg, No. 79, 1925, 
Braunschweig : Friedr. Vieweg & Sohn Akt.-Ges. 

179 Neuhaus, Ger. Pat. 75,896 (Jan. 25, 1893) ; 305,275, 305,770. 
180 Keiper, Melliands Textileberichte, 3, 181 (1922). 
181 Heermann, Chem. Ztg., 35, 829 (1911). 
182 Sisley, Chem. Ztg., 35, 621-622 (1911) ; C. A., 6, 158. 

183 Dyestuffs, 26, No. 11, 167 (1925). 

184 Cole, George Warren, Jr., Fr. Pat. 562,658 (Feb. 23, 1923). 

185 Textile Colorist, 26, 167 (1925). 

18a Tondani, Carlo/ Giorn. chim. ind. applicato, 4, 17 (1921) ; C. A., 16, 1872. 



SIZES AND COATINGS 297 



minutes followed by 2 per cent sodium carbonate at 60° -65° which re- 
moves the tin-silicate weighting. 



187 



Dyeing and Printing. 

Mordants. Silicate solutions are effective as fixing agents for iron 
and chromium salts used as mordants, especially the arsenates and 
phosphates, which are rendered insoluble in a bath of one of the more 
silicious grades. Colloidal silica itself serves as a mordant for aniline 
green. The fiber is prepared by passing through a silicate bath followed 
by a weak acid. 188-193 Dilute silicate baths protect cotton dyed with 
sulfur colors, which sometimes develop enough acidity to cause hy- 
drolysis and weakening. 

Printing. In textile printing, silicates serve where a viscous alkaline 
medium is required to apply a color or reagent in such condition that 
the design shall remain clear and sharp. 194 Particularly is it useful 
in the application of vat colors, where they are not only cheaper but 
give better results than potassium carbonate which is often recom- 
mended. 

After indigo has been discharged with hydrosulfite and the goods have 
been washed, a silicate bath will brighten the white parts of the pattern 
without risk of weakening the goods. It is also said to brighten 
colors. 195 ' 196 At least, experience in washing shows that silicate has a 
protective action as a result of which colors of washed goods are 
brighter than when soap only is used to cleanse them. Silicate pre- 
cipitated locally in the fiber by a printing process previous to dyeing 
yields shaded figures. 197 

Alkaline Reagents. Silicate solutions, on account of the buffer 

action of the silica which prevents too great activity of the alkali, are 

chosen as alkaline reagents in various textile processes. Their action 

can be further regulated by additions of sodium chloride or sodium 

187 Cook, A. A., Textile World, April 15, 65-67; May 22, 131-133 (1922) ; C. A., 
16, 2782-2783. 

"Bolley, Chem. Gazette, 13, 58-59 (1855). 
Favre, Camille, Z. angew. Chem., 19, pt. 2, 1476 (1906). 
Gobels, Albert, Neueste Erfindungen und Erfahrungen, 17, 18-20 (1920). 
Joclet, Victor, "Die Kunst und Feinwascherei in ihrem ganzen Umfange," 
63, 3rd ed., Wien: Hartleben's chemisch-technische Bibliothek, 1879. 

192 Joclet, Victor, "Die Woll and Seiden Druckerei in ihrem ganzen Umfange," 
46, Wien: Hartleben's chemisch-technische Bibliothek, 1879. 

^Knecht, Rawson and Lowenthal, "A Manual of Dyeing," 1. Philadelphia, Pa.: 
Lippincott, 1910, p. 203. 

194 Soxhlet, V. H., "Die Praxis der Anilin-Farberei und Druckerei auf Baum- 
wollwaaren," Wien: Hartleben's chemisch-technische Bibliothek, 184, (1890). 

195 Dent. Farben. Ztg., abstract in /. Soc. Chem. hid., 1, 279 (1882). 
Griine, W., Deut. Musterztg, No. 6 (1854) ; Chem. Zentr., 26, 71-74. 
Kasuya, Saburo, Jap. Pat. 40,695 (Nov. 18, 1921) ; C. A., 17, 1893. 



188 
189 
190 
191 



196 
197 



298 SOLUBLE SILICATES IN INDUSTRY 

sulfate. Thus cellulose acetate and cotton may with advantage be dyed 
in silicate baths. 198 ' 199 

Sizing. 

The art of textile sizing and finishing makes incidental or rather 
specialized use of silicate solutions to modify other colloids which are 
the basic materials of the art. Starches, dextrins, gums, glues, clays, 
and other fillers are all compatible in appropriate proportions with 
soluble silicates as appears from discussions of adhesives and other 
uses where the silicates of soda play a larger part. 200 ' 201 

Sizing materials in contrast to adhesives should be able to penetrate 
the surfaces on which they are laid, 202-204 which suggests that silicates 
should not be used at high concentrations. Some sizes are made with 
silicate and a precipitant such as aluminum sulfate, liberating silica, 
which plays the role of filler and gives to the size the combination of 
high viscosity and penetrating power. 

Numerous mixtures which contain silicate 205 have been proposed for 
textile sizing and finishing processes, a region in which the art has run 
far ahead of the science. The starches and gums used are for the most 
part miscible 206 - 209 with silicate. 

Mercerizing. 210 

A mixture of sodium hydroxide, 28°Baume, 100 parts, and silicate 
of soda, 1.39 specific gravity (41°Baume), 10 parts, was investigated 
by Hubner and Pope 211 with respect to claims that it would mercerize 
cotton without tension. They found that the luster of the fiber, though 
increased, was much less than with a pure sodium hydroxide solution. 
The shrinkage was less and the affinity for coloring matters was in- 
creased. This is a very clear bit of evidence of the restraining action 
of silica upon the caustic alkali. 

198 Richardson, L. G., Brit. Pat. 175,846 (Dec. 18, 1920) ; C. A., 16, 2230. 

199 Dorr, G., Riv. gen. mat. color., 18, 101-102; C. A.. 2950-2951 (1914), 



200 



For example, Walen, Ernest D., U. S. Pat. 1,587,094 (June 1, 1926). 
^Whewell, W. H., Text. Inst. L, 2, 43 (1911). 
202 Posselt's Text. I., 25, 53-54 (1919). 
^Feary, N. A., Brit. Pat. 128,691 (1919). 

^Poulson, A., Brit. Pats. 165,365 (Sept. 24, 1920); 169,103 (Sept. 24, 1920). 
205 Taylor, Alfred, U. S. Pat. 52,906 (Feb. 27, 1866). 

206 Pickard, R. H., /. Text. Inst., 10, 54-55 (1919) ; /. Text. Inst., 9, 18-22 (1918). 

207 Lamb, M. C., and A. Harvey, /. Soc. Dyers Colonrists, 33, 19-20 (1917). 

208 Mayer, op. cit., p. 42. 

m Polleyn, F., "Die Appreturmittel und ihre Verwendung," 134, 2nd ed., rev., 
Wien : Hartleben's chemische-technische Bibliothek, 1897 ; "Dressings and Finish- 
ings for Textile Fabrics," translated from the German ed. by Charles Salter, 
London: Scott, Greenwood, 1911. 

^Meister, Lucius, and Briming, Brit. Pats. 10,784, 11,313 (1897). 

211 /. Soc. Chem. Ind., 23, 409 (1904). 



SIZES AND COATINGS 299 

Degumming Silk. 

Silicate solutions have been successfully used for boiling off or de- 
gumming silk, usually in combination with sulfonated oils. Properly 
controlled, they can displace part or all of the olive oil soap usually 
employed, with a substantial saving in cost. 212 

212 Textile World, 71, No. 1, 59 (1927). 



Chapter X. 
Deflocculation and Detergency. 

Characteristics of Soluble Silicates Which Affect Their 

Detergent Action 

The suitability of silicate solutions for various detergent uses has 
been for many years a matter of active controversy. The colloidal 
phenomena which constitute the familiar processes of washing have 
engaged the attention of some of the ablest investigators of modern 
times. A great deal has been learned, enough to show that it is not 
yet possible to determine with precision the best and most economical 
materials and technic for washing. It is beyond the scope of this 
treatise to deal with washing procedure and the problem of selecting 
washing materials, but it may be possible to sift fact from fancy by 
considering separately some of the actions of soluble silicates which 
bear upon the study of washing and to view at the same time other 
industrial uses which depend upon characteristics which have a part in 
detergent action. 

The opinion of Vincent x that a mixture of 80 per cent silicate and 
20 per cent soap has merit for general use as a detergent is worthy 
of careful scrutiny, for it is based upon extensive scientific work. Let 
us examine the factors one at a time. 

Deflocculation. 

Rate of Sedimentation of Clay. The sedimentation of clay from 
water may be greatly delayed by small additions of alkaline compounds, 
among them the soluble silicates. Other materials of small dimensions 
are similarly suspended. The deflocculation is accompanied with a 
reduced viscosity of the suspension and this facilitates the removal of 
impurities which exist in particles of larger size than the clay sub- 
stance or which are less affected by the dispersing action of the silicate 
than is clay. Quartz, feldspar, siderite, pyrite, ilmenite, biotite, mica 
and ferric oxide are thus separated, in some cases quantitatively, by 
settling, after which the clay can be recovered by long settling or more 

1 J. Phys. Chem., 31, 1305 (1927). 

300 



DEFLOCCULATION AND DETERGENCY 



301 



rapidly by a chemical treatment to cause flocculation, as, for instance, 
neutralizing' the silicate with acid. 2 This is in accord with Stokes' law : 
2r 2 g 



V 



in which V = velocity of settling, r = radius of 



9K (d-d 1 )' 

particles, K = viscosity, d 1 = density of fluid, d = density of particles, 
and g = gravity constant. Viscosity is the primary factor in the rate of 
sedimentation when the radius is constant. 

Bleininger considers the physical changes to be complex and postu- 
lates the formation of a lyophile pseudo-emulsoid substance resulting 
from the subdivision of clay particles under the influence of hydroxyl 
ions. 3 When silicates are used, the silica constitutes such a substance 
which may tend to prevent further decrease of viscosity and thus 
further delay the settling of fine particles. 

Effect of Silicate on Viscosity of Clay Suspensions. If this is 
the correct conception, it follows that different clays with different 



ah 
• 
































"> 
































•> 






--^£~„. 


'«./.> B.Jj 






















l&t!A *..!. 


• B*, 








r ""i;. 


" *•«<>; 


a.<, 








9 .< 


J 


<0 


» 




> ./ 


c -ts. 



Pmr Ct.r #i t O itts-o, 



Fig. 139. — Effect of Silicate on Viscosity of Clay Suspensions. 

assortments of particle sizes and different degrees of adherence between 
particles to be dispersed will behave quite differently in the presence 
of alkali, and so it is. Measurements of viscosity of relatively con- 
centrated suspensions of clay in water show that the addition of silicate 
solutions causes a rapid drop in viscosity, which is much greater per 
unit of added Na 2 than when viscosity is lowered by sodium car- 

2 Bleininger, A. V, Bur of Standards Tech. Paper No. 51 (1915) ; U. S. Pat. 
1,528,908 (Mar. 10, 1925). 

3 Shorter, S. A., /. Soc. Dyers Colourists, 34, 135-138 (1918). 



302 



SOLUBLE SILICATES IN INDUSTRY 



bonate. Even on a weight- for- weight basis the silicate is more effective 
in some cases and the range of minimum viscosity is wider. 

The reduction of water made possible by the lower viscosities makes 
it possible to produce by casting processes bodies of improved density 
with decrease of losses from shrinkage cracks and with greater mechani- 
cal strength. Another interesting application of this property is in 
adding clay to soap. 4 Tensile tests show that the point of maximum 
deflocculation is not necessarily the point of greatest strength, but the 
following table shows the advantages of reagents and indicates that 
silicate solutions can produce useful results. 

Table 91. Tensile Strength of Castings. 





(Ble 


ininger) 


Na 2 C0 3 




Silicate 






Na 2 C0 3 


Less than 


Silicate 


Less than 






Max. 


Max. 


Max. 


Max. 




Without 


Defloccu- 


Defloccu- 


Defloccu- 


Defloccu- 




Reagents 


lation 


lation 


lation 


lation 




(kilos 


(kilos 


(kilos 


(kilos 


(kilos 




per 


per 


per 


per . 


per 


Body Containing as Clay 


sq. cm.) 


sq. cm.) 


sq. cm.) 


sq. cm.) 


sq. cm.) 


North Carolina kaolin.... 


1.063 


1.262 


0.985 


1.034 


1.25 


Georgia kaolin 


4.77 
7.17 


6.14 
10.8 


5.52 
9.65 


7.10 
11.75 


6.3 




9.25 


Florida kaolin 


4.62 


4.95 
4.76 


4.44 
5.18 


3.97 
4.15 


4.39 


Body B 


6.4 



This fact is generally recognized in the ceramic industry * and most 
cast wares are made from clay suspensions in which the viscosity has 
been reduced by silicate either alone or combined with sodium carbon- 
ate. 5 Mixtures of clay and water are subject to changes in viscosity, and 
those slips which have been liquefied by alkalies, although they are more 
stable, tend to thicken or become further deflocculated on standing. 
These changes are reduced when some excess above that required for 
maximum deflocculation is used. Reactions which take place slowly 
may change the concentration of hydroxyl ions, but the buffer effect 
of silicate will tend to hold it nearer constant. 

The effect of the reagents, used to reduce the viscosity of clay slips, 
upon the plaster molds in which the ware is cast has been considered by 
Kail, 6 who found'that reaction between sodium carbonate and calcium 
sulfate could lead to serious pitting and eventual disruption as concen- 

4 See Feldenheimer, Wm, and W. W. Plowman, U. S. Pat. 1,321,516 (Nov. 
11, 1919). 

* Other materials may be deflocculated at the same time ; for example, see 
Bellamy, Harry T., U. S. Pat. 1,585,010 (May 18, 1926). 

5 Vail, James G., /. Am. Cer. Soc, 6, No. 4, 610 (1923). 

6 Kail, G. A., Sprcchsaal, 60 (1), 8-9 (1927). 



DEFLOCCULATION AND DETERGENCY 



303 



tration increased with repeated absorption of the liquid part of the slip 
and drying for a fresh cycle. He observed, however, that sodium 
silicate solution (Na 2 0,2Si0 2 ) had no deleterious effect upon the molds 
up to a concentration of 0.5 per cent in the clay. This may be partly 
due to a tendency of the silicate to remain at the surface of the mold 
and partly to a smaller tendency to reaction under the conditions of this 





















^< 






































^ 


















/ 


i / 
















,(f 


jt — ■ ' 
















* / 


















, 


-' ,.<X 
















XT" 


► -< 
















_...»•• 














.-' 


>.— — "(( 




\~^\ 












-••1 


t'l 




'^—^ 


• ' 














<* - ♦ , — "< 


i-* 












--.-• 


i -t 


i — " 






































\ 








\ 








2.7 




\ 










\ 












\ \ 








A ' 
\ 






2.6 






l '; 








\ 












\ \ 




\ ( 


) 


\ 






25 






\ ' 


i 






\ 






2.4 
















\ 










*. 








-\ 




X 








*. 








\ 




2.3 








\ 








■ \ 
< 


t 


El 








*. < 


1 










t«- 2.2 
o 








\ 










^ 


« 2/ 








\ \ 










1 






\ 




\ c 


") 






— no i ^incore 

— No,0- 4.00 Sit 




\ 










\— 2.0 


>? \ 


\ 










V 


1 






\ 










.C 1.9 


Vn. 2 Silicate 




•. 










o 


f/p n. ? ?? C/7 


7 


f\ 










V 1.6 
a. 
1.7 




"e~ -'•-'-'•"• 


'g 




r. 












\ ( 


»\ 








hu.J Jf/ILUftf 






( \ 








1.6 


N 


o z uc?.5d5n 


>2 




\ V 


rz 












N. \ 








15 


No A Silicate 
No e 0-I.8l SiC 








\ 






1. 






x^ 






/.4 














1 1 1 








*^^ 



. O 

2 



000 .005 .010 .015 .020 .025 .030 .035 .040 045 

Additions of Sodium Silicate 

in Increments of .005 Percent NajO 

Fig. 140. — Effect of Ratio of Silicate on Viscosity and pH of Clay Slip (McDowell). 

use. It should further be pointed out that a more silicious ratio would 
not only deflocculate better but, containing more colloidal silica, would 
be still less likely to corrode the plaster molds. Kail recommends 
that additions of Na 2 CO a should not be more than 0.1 per cent and 
that where more liquefying effect is needed it should be obtained with 
silicate. It is not seen why silicate should not be used in the first 
instance. 

Effect of Varying Ratio on Deflocculation. McDowell 7 has 
studied the effect of silicates of varying ratio upon deflocculation of a 
V. Am. Ceram. Soc, 10, 225-237 (1927). 



304 



SOLUBLE SILICATES IN INDUSTRY 























*<o 








































i-*" 




































"■ — 




0) 














•^•^ 








3 










"• 


f *^."'^ 










*£ 




. 


-.7ZS*£ 














IP 
















i 






















CL 












\ 


















I \ 




\<„ 




No.4 Silicate 

n n . i o i an — 










\ \ 




V 






2.6 






\ \ 












'3 










\ • 




i 


















v> 






\ 




















_A 






%" 






\ '• 






\ a'~ si ■ ? zz> c:n — 








\ ' 






\ /i 


1/pV c 




^2 




u. 






\ 






V 










<+- oo 






\ 


*, 




\ 










2.2 






\ 


•, 






\ 








d) 








► • 






\ 








c 








i \ 






\ 








,- on 








\j« 






\ 








Q 20 








\ \ 






\ 








> 








\ *. 




\ 






o 








\ \ 




\ 


■\ 






^i , ^ 








\ \ 








\ 






a /■£ 




t 




\ M 






\ 










NO.I on/cart 













< 






/Va 2 t 


2 \ 


\ 








v. 








1 


i \ 










> 


1.6 






' o C 7 : * 




















0-3.3 






, 




i 










No z 


3 Si0 2 


NiIn 




















^^^-rf-J^-- 




1.4 

















.000 .005 .010 .015 .030 .025 030 .035 .040 045 

Additions of Sodium Silicate 
m Increments of .005 Percent Na E 

p IG 141 — Deflocculation of Florida Kaolin with Silicates of Varying Ratio 

(McDowell). 







1 1 








L f 




























1 












— -i^i-- -+ ? 


t— • T 














^s^" 
































































\ 












£.6 










\ 




















\ 










2.5 










\ 




















1 


s 






















l 










\ 








1 


"--J 




^2.3 




\ 












~"-"J 








\ 














k -. 


U. 2.2 

O o , 




\ 














\ 




\ 














N i 


2.1 




\ 




A'/? / ^iliratp Mr, D 400 KiD. 


£ 2.0 




A 




NaOH Soluh 


'"V" 




•"-2 




1 


















A 








oj AS 


1 


















1.8 




































CC i -7 


1 




































\\ 




















































1.5 










i 








IA. 






jf '^ 



10 
8-± 

_ Q. 



ao 



.02 .04 .06 .08 0.10 0.12 0.14 0.16 0.18 

Percent Additions of Na 7 



Fig. 142.— Deflocculation of Florida Kaolin (McDowell). 



DEFLOCCULATION AND DETERGENCY 305 

series of clays and measured the hydrogen ion concentration in the slips. 
The clays behaved differently but it was found that the reduction in 
time of flow through an orifice was greatest per unit of Na 2 in the 
mixture when a silicate of ratio 1 : 4 was used. 

It is interesting to note that the maximum rate of flow was in each 
case reached while the slip was on the acid side of neutrality. Com- 
paring the more silicious silicates with sodium carbonate and sodium 
hydroxide, the silicates were found to have the greatest effect per unit 
of alkali. 

Shop men notice that silicate produces a "stringy slip" compared 
with sodium carbonate, which yields a slip with high surface tension, 
if both are brought to minimum viscosity. The former is advantageous 
in casting clay wares. Silica sol prepared by Bradfield's method had no 
appreciable effect. 8 It is not a deflocculating agent. 

McDowell offers an explanation of the potency of silicate solutions 
as due to the adsorption of positive sodium ions on colloidal silica. 
Thus their equilibrium with hydroxyl ions is disturbed and the latter 
may then become more active in forming hydroxyl ion complexes with 
positively charged particles and ions and thus reach maximum charge 
for that system. 

Flocculation and Deflocculation by Silicates. Many other finely 
divided substances are deflocculated by silicate solutions, including most 
silicious minerals, while many sulfide minerals undergo the reverse and 
are flocculated. 9 This is a fortunate circumstance, for the condition 
favorable to the concentration of ores by flotation is to have the valuable 
minerals in a flocculated condition. By causing the worthless parts of 
the ore to deflocculate they are kept out of the froth and separated. 
Silicates of soda are useful reagents to render the gangue particles 
unfloatable, while the valuable minerals are carried up in the froth 
from which they are recovered. 10 " 13 

Flotation. Silicate solutions are particularly useful in flotation cir- 
cuits in which it is desired to recover two valuable minerals separately. 
Even relatively high concentrations (0.25 per cent in one instance) 
deflocculated the gangue without causing either zinc or lead sulfides to 

8 7. Am. Chem. Soc, 44, 965-74 (1922). 

9 Kohl, t H., Ber. deut. keram. Ges., 3, 64-77 (1922) ; C. A., 16, 4311. 

10 Weinig, Arthur J., and A. J. Palmer, Quarterly of the Colorado School of 
Mines, 21, 2 (1926). 

11 Edser, Edwin, 4th Colloid Report, Scientific and Industrial Research, London : 
His Majesty's Stationery Office (1922), p. 263 et. seq. 

12 Edser, Edwin, U. S. Pat. 1,337,548 (April 20, 1920). 

33 Wright, C. A., J. S. Parmelee and J. I. Norton, Bur. of Mines, Bull. 205 
(1921). 



306 SOLUBLE SILICATES IN INDUSTRY 

float. It was then possible to deflocculate the zinc blende and float the 
galena by adding soap, after which dilution was sufficient to cause the 
zinc blende to be removed separately while the silicate maintained the 
gangue deflocculated and unfloatable. 

The technic of differential flotation is complicated and difficult, but 
silicates of soda are well recognized as useful controlling agents be- 
cause of their property of selective deflocculation. 14 ' 15 

As in clay deflocculation, attention to the time factor is important. 
Silicates, as Kohlrausch showed, do not quickly reach equilibrium, and 
will not therefore necessarily give the same results with the same con- 
centration and different times of contact. 

The kinds of silicate most suitable for deflocculation appear not to 
have been investigated in any published work, from the point of view 
of flotation, but empirical testing has led to large-scale use of Na 2 0, 
2Si0 2 and NaoO, 3.3Si0 2 . 

Technic of Application. Borcherdt 1G ' 1T has elaborated a technic 
for the application of soluble silicates to certain ores of zinc. The first 
step is to rid the ore pulp of some of its colloidal constituents by de- 
flocculating and decanting them, a variant of the method already de- 
scribed for refining clay. 18 Na 2 0, 3.3Si0 2 accomplishes this at less 
cost than other available reagents. The second step is to use silicate 
solutions for controlling the flotation operation itself. If colloidal 
gangue minerals are not deflocculated they will contaminate the froth 
which, aside from impurity, becomes very difficult to handle. 

Differential Flotation of Variety of Ores. Silicate is available 
to induce differential flotation of a great variety of ores, among them 
not only sulfide ores, but oxidized or non-sulfide minerals and those 
which have been sulfidized. Copper, lead, zinc, tin, tungsten, molyb- 
denum, silver, antimony, coal, and calcium phosphates have been treated 
by processes in which soluble silicates serve as deflocculants and control 
flotation. 19 " 21 

14 Fahrenwald, A. W., Bur. of Mines Report, 2700 (Aug. 1925). 
"Minerals Separation, Ltd., Brit. Pat. 154,870 (March 9, 1920); C. A., 15, 
1129. 

16 Borcherdt, W. O., U. S. Pats. 1,446,375 (Feb. 20, 1923); C. A., 17, 1415; 
1,446,376, 1,446,377, 1,446,378, 1,445,989 (Feb. 20, 1923); 1,454,838 (May 8, 1923). 

17 Borcherdt, W. O., Can. Pats. 232,145, 232,148-9, 232,151 (June 19, 1923) ; 
233,601 (Aug. 14, 1923) ; C.A.,17, 3154. 

18 Electro-Osmose A. G., Brit. Pat. 143,920 (1920) ; C. A.. 14, 2908. 
w Edser, E., and L. A. Wood, Brit. Pat. 168,927 (March 20, 1920) ; C. A., 16, 

405. 

20 Edser, E., H. L. Sulman, and F. B. Jones, Brit. Pat. 159,285 (Nov. 20, 
1919) ; C. A., 15, 2173. 

21 Broadbridge, W., and E. Edser, Brit. Pat. 171,155 (1920) ; C. A., 16, 985. 



DEFLOCCULATION AND DETERGENCY 307 

The amount used varies greatly with individual cases. Varlcy re- 
ports 0.0951 kilogram per metric ton (0.0863 pound per short ton) 
of ore treated as average for lead, lead-silver, molybdenum, tin, and 
miscellaneous in 1920. — A mill which uses silicates in both lead and 
zinc circuits employs 0.498 to 1.494 kilograms per ton (1 to 3 pounds 
per ton), the upper limit being set by the point at which pyrite begins 
to be deflocculated and carried into the froth. 23 ' 24 

Other Uses of Deflocculating Power. It is obvious that defloccu- 
lation of useless materials is a help, not only when simple decantation 
is used, but in other hydraulic means of separation, as wet screening, 
jigging, or table concentration in which for practical purposes the 
deflocculated mineral becomes a part of the liquid. Amounts of the 
order of 1.992 kilograms per ton (4 pounds per ton) of dry ore are 
effective. 25 Five per cent is the highest figure which has been noted. 

High speed mechanical disintegration in the presence of much water, 
as in the "colloid mill," is fostered by the presence of a colloid of the 
same sign as the material to be dispersed. Thus, 10 parts of a silicate 
solution per hundred of zirconium oxide were effective in separating it 
from the minerals with which it was associated ; and phosphates, feld- 
spars, or other raw products are rendered colloidal and available for 
fertilizers by the same process. 2G ' 2T 

Measuring Detergency by Deflocculation. Fall 28 attacked the 
problem of measuring detergency by choosing a standard and easily 
determined material which should be as nearly as possible typical of dirt. 
A very finely divided manganese dioxide was used and its defloccula- 
tion by various detergent solutions studied. Its behavior was ascer- 
tained to be similar to that of ferric oxide, clay and lamp black. A 
series of soaps and alkaline compounds including silicates of soda was 
considered. A good bibliography was also assembled. 

Soaps were found* to exert their greatest suspending power in the 
range 0.2 to 0.4 per cent concentration while caustic soda, sodium 
carbonate, trisodium phosphate and all the silicates show T their greatest 
ability to peptize solid dirt in the range 0.0125 to 0.05 per cent. The 

™Bur. of Mines Serial No. 2203 (1921). 

23 Marquand, A. B., personal communication ; also Eng. & Min. J. Press, 5-8, 
756-762 (1926). 

*Morley, Walter S., Trans. Am. Inst. Mining and Met. Eng., No. 1085M 
(1921); C. A., 15, 3436-3437. 

23 Borcherdt, W. O., U. S. Pat. 1,448,514 (March 13, 1923); 1,448,515 (March 
13, 1923). 

' 26 Plauson, L. Ed., Brit. Pat. 196,944 (Oct. 28, 1921); /. Soc. Chan. Ind., 42, 
622A; C. A., 17, 3672. 

"Plauson, L. Ed., Brit. Pat. 195,655 (June 28, 1922) ; C. A., 17, 3743. 

28 /. Phvs. Chem., 31, 801-849 (1927). 



308 



SOLUBLE SILICATES IN INDUSTRY 



silicates are more like soap in their action than any of the other 
materials. 

The other alkaline salts do not always act as suspending agents and 
when they do they suffer a decrease as the temperature is raised. Soaps 
and silicates are also more effective at 40° C. than at 75 °C. The most 



































- 


T./l 


„s. v 












.... 


; 








' 




8 - 


S///C0 


r -^ .4W.a 






QI'L 


. n,i J", 










— 


I 


~/»- n 


s 


*^~ — 














1 


/ A 












































A 
< 
t 
























Vj 










































* 


s 



Determent ConcenTrmtie* - % 

Fig. 143. — Deflocculation of Manganese Dioxide at 40°. 

silicious silicate, ratio 1 : 4, was found to be best at concentrations above 
0.15 per cent and at its optimum concentration, 0.025 per cent, was able 
to suspend substantially the same as olive oil soap at its optimum 
concentration. 

In terms of efficiency per unit of weight the silicate is much more 
effective, while if the comparison be placed upon units of cost the con- 
trast is still more spectacular. 



Table 92. Comparison of the "MnOz Values" of Various Compositions of Three 
Different Silicates of Soda at 40° and at 75° C. 



1 gram portions of M11O2 ground in a colloid mill (No. 

50 cc. portions of silicate of soda solutions. 

Values given represent centigrams of Mn0 2 present in 
as calculated from an analysis of 25 cc. of suspension*, 
average of duplicate determinations. 



2 \ 

one liter of suspension 
These values are the 



Cone. 


"S' 


Brand * 


"K" 


Brand 8 


"BW 


Brandf 


er Cent 


40° 


75° 


40° 


75° 


40° 


75° 


0.5 


292 


240 


219 


205 


40 


61 


0.3 


382 


261 


316 


247 


219 


200 


0.15 


396 


287 


394 


300 


396 


300 


0.05 


434 


346 


430 


342 


431 


344 


0.025 


445 


351 


431 


342 


452 


348 


0.0125 


436 


348 


433 


334 


437 


313 


0.0062 


427 


216 


297 


247 


404 


227 


0.0031 


278 


000 


41 


000 


203 


38 


0.0015 


36 


000 


000 


000 


19 


000 



* "S" Brand is Na 2 0, 3.97Si0 2 , specific gravity 1.30. 
"K" Brand is Na 2 0, 2.92Si0 2 , specific gravity 1.48. 
t"BW" Brand is Na,0, 1.62Si0 2 , specific gravity 1.68. 



DEFLOCCULATION AND DETERGENCY 



309 




Fig. 144. — Deflocculation of Manganese Dioxide by Silicate. 



Table 93. Comparison of the "MnOi Values" of Various Concentrations of Fiv^ 

Different Commercial Soaps. 

1 gram portions of MnOa ground in a colloid mill (No. 1). 

SO cc. portions of soap solutions. 

Values given represent centigrams of MnOa present in one liter of suspension 
as calculated from an analysis of 25 cc. of suspension. Values given are the 
average of triplicate determinations. 

At 40°C. 



Cone. 


Olive Oil 


Tallow 


Palm Oil 


Green Arrow 


Silicated 


'er Cent 


Soap 


Soap 


Soap 


Soap 


Green Arrow 


2.0 


412 


327 


302 


387 


278 


1.4 


440 


427 


377 


435 


384 


0.8 


468 


496 


420 


475 


486 


0.4 


453 


532 


512 


522 


505 


0.2 


435 


539 


550 


520 


522 


0.1 


336 


328 


335 


285 


323 


0.05 


162 


334 

At 75 


278 
3 C 


320 


360 


2.0 


322 


316 


299 


325 


282 


1.4 


352 


372 


342 


348 


341 


0.8 


427 


433 


409 


427 


416 


0.4 


433 


455 


453 


448 


432 


0.2 


416 


460 


455 


457 


450 


0.1 


153 


322 


304 


250 


261 


0.05 


85 


123 


141 


134 


219 



310 SOLUBLE SILICATES IN INDUSTRY 

When soap is used at concentrations below the optimum, silicates 
have more effect in increasing the suspending power of the solutions 
than other alkaline salts. Also the range of concentrations in which 
silicates are effective is greater. The effect is also obtainable through 
a fairly wide range of ratios. 

Table 94. Comparison of the "MnO* Values" of Various Concentrations of Differ- 
ent Alkaline Solutions at 40° C. and at 75° C. 

1 gram portions of Mn0 2 ground in colloid mill (No. 2). 

50 cc. portions of alkaline solutions. 

Values given represent centigrams of Mn0 2 present in one liter of suspension 
as calculated from an analysis of 25 cc. of suspension. These values are the 
average of duplicate determinations. 



Cone. 


"S" 


Silicate* 


NaOH 


Na 2 C0 3 


Na 3 P0 4 


Per Cent 


40° 


75° 


40° 


75° 


40° 


75° 


40° 75° 


0.5 


292 


240 


000 


000 


000 


000 


000 40 


0.3 


382 


261 


000 


000 


000 


000 


000 140 


0.15 


396 


287 


17 


52 


000 


12 


70 274 


0.05 


434 


346 


232 


231 


30 


99 


350 290 


0.025 


445 


351 


347 


269 


110 


196 


365 291 


0.0125 


436 


348 


373 


252 


284 


234 


273 248 


0.0062 


427 


216 


333 


140 


203 


140 


125 113 


0.0031 


278 


000 


17 


000 


68 


17 


40 000 


0.0015 


36 


000 


000 


000 


000 


000 


000 000 



*"S" Silicate is Na 2 0, 3.97Si0 2 , specific gravity 1.30. 

The similarity between the deflocculating action of silicates and that 
of soaps is striking. Its bearing on the efficiency of washing processes 
needs further study, but it is quite evident that large amounts of 
silicate relative to soap will stably suspend dirt at low cost. 

The deflocculating power of silicate solutions has been used to pro- 
duce a lithopone of extraordinary dispersion and light-resistant quality. 
Ultramarine is also graded by deflocculating with silicate. 29 

Moses 30 found that small additions of silicate solutions could so 
disperse the clay substance in a road base that practically all the water 
was colloidally adsorbed and did not expand when reduced to tem- 
peratures below freezing. This meant in practice that a road could 
be built of earth and yet be free from danger of heaving with frost. 

Relation of Deflocculation to Washing Practice. Deflocculation 
is a vital consideration in washing practice, for a large amount of the 
ordinary soil of clothing or other materials which we need to cleanse is 
not soluble in any permissible reagent and must be removed in a state 
of suspension. Deflocculation makes this possible. 31 

"Drefahl, Louis C, and Edward A. Taylor, U. S. Pat. 1,486,077 (Feb. 4, 1924). 

30 Moses, D. V., personal communication. 

31 Fall, P. H., loc. cit. 



DEFLOCCULATION AND DETERGENCY 311 

Spring 32 was able to deflocculate a specially purified carbon black, 
also silica and alumina, with soap so that they would pass without 
even discoloring a filter paper which completely held them when no 
soap was present. 

Richardson found that a suspension of unusual stability could be 
made by shaking lamp black containing free fatty acid and hydrocarbon 
oil with a dilute silicate solution. The same degree of stability could 
not be secured by shaking lamp black which contained only neutral 
hydrocarbon oil in a soap solution. 33 

Use of Deflocculation. Deflocculation, then, is the result of specific 
relations between the substance to be dispersed and the reagent. Silicate 
solutions deflocculate quartz permanently, i.e., disperse it to a point 
where Brownian movement overcomes gravity, and sedimentation does 
not occur. 34 Most silicious minerals are readily dispersed by silicate 
solutions. These constitute the principal part of dirt which is to be 
removed by washing. Pyrite, and many other sulfide minerals, are 
flocculated in silicate solutions, a characteristic which is employed to 
separate valuable sulfides or sulfidized minerals from silicious gangues. 
The method has proven very valuable in the treatment of lean ores by 
flotation. 

Wetting Power. 

Conditions Necessary for Wetting. Substances which are de- 
flocculated in aqueous solutions must first be wet, and washing is the 
release from wet surfaces of contaminating material. 35 Any evidence 
that silicate solutions cause water to spread in an even film over a sur- 
face bears, therefore, upon the problem of their detergency. 

Water stands in drops upon an oiled surface but does not wet it. This 
is also true of many substances which are quite free of oil or grease. 
Sulman 36 found that the angle between a surface and a liquid which 
stands upon it is, within certain limits, definite and characteristic. It 
makes a difference whether a position of equilibrium is attained by 
means of the liquid spreading over a dry surface or by recession from a 
surface which has been covered. A drop of water moving down a win- 
dow pane meets the glass at different angles on the upper and lower 

33 Spring, W., Rec. Trans. Chim., 28, 120-135, 424-38 (1909) ; 29, 1-17 (1910) ; 
Z. Chem. lnd. Kolloidc, 4, 161 (1909) ; 6, 11, 109, 164 (1910). 

33 Ind. Eng. Chem., 15, 241-3 (1923). 

34 Edser, Edwin, Fourth Colloid Report, Sci. & Ind. Research, London: His 
Majesty's Stationery Office. 1922, p. 169. 

35 Traube, I., and K. Nishizawa, Kolloid Z., 32, 383-392 (1923) ; C. A., 17, 2982. 
, "Bull. Inst. Mining & Met., 29, 44 (1920). 



312 



SOLUBLE SILICATES IN INDUSTRY 



sides. Sulman suggested calling the difference between the maximum 
values the hysteresis of the contact angle. Edser says that alkalies, par- 
ticularly sodium silicate, reduce both contact angle and the hysteresis. 
For quartz, both may be reduced to zero. The condition necessary for 

wetting is the reduction of the 

I contact angle to zero, so silicate 

^R §jf solutions wet silicious minerals 

generally more readily than water 
is able to do. A simple experiment 
with almost any kind of textile will 
indicate that this is also true of 
animal and vegetable fibers. 

These phenomena have to do 
with the inter facial tension be- 
tween liquid and solid, which in 
turn relates to the surface tensions 
of both liquid and solid. Nuttall 3T 
says, 

"For the liquid to wet, T 3 must be 
> Ti + V where 

Ti = surface tension liquid/air. 
T 2 = surface tension solid/air. 
T12 = surface tension liquid/solid. 

Owing to the difficulty of measur- 
ing either T 2 or T 12 there is no 
proof that this holds in all cases, 
though it has been demonstrated 
for some. 38 If this is accepted, it 
follows that lowering of the 
liquid/air surface tension will im- 
prove wetting power. But the 
situation is more complicated than 
this. The surface tension of the surface to be wet has a great influence 
on the interfacial tension, and disturbing influences such as the concen- 
tration of soap or saponin in the surface may work large changes. 

The wetting power of silicate solutions is illustrated by an experi- 
ment suggested by Vincent 39 in which heavy lubricating oil in a six 
millimeter glass tube is covered with water. The adherence between 




Fig. 145. — Experiment Illustrating the 
Wetting Power of Silicate Solutions. 



37 Nuttall, W. H., 5th Colloid Report, Scientific and Industrial Research, Lon- 
don : His Majesty's Stationery Office, 28-47 (1923). 

^Rontgen, A. J., Wied, Ann. Physik und Chemie, 2, 321 (1877). 



DEFLOCCULATION AND DETERGENCY 



313 



the oil and the glass is such that the water does not separate them. 
When, however, a solution of Na 2 0, 3.3Si0 2 at a concentration of three 
to four per cent is used instead of the water, it penetrates between the 
glass surface and the oil, allowing the drop to rise to the surface as 
illustrated in Figure 145. 

Drop Number. The drop number of soap solutions against kero- 
sene is, within limits, a good measure of their wetting power. 40 Applied 




Fig. 146. — Effect of Sodium Carbonate and Silicate on Surface Tension of Soap 

Solutions at 40° C. 

"Star" Silicate is Na 3 0, 2.61Si0 2 , Specific Gravity 1.41. 
"BW" Silicate is Na.O, 1.62Si0 2 , Specific Gravity 1.68. 



to other solutions, the measurement of interfacial tension by this method 
may be misleading. Soluble silicates when added to water alone do 
not sensibly affect the drop number against kerosene, 41 yet they do 
reduce the angle of contact — in some cases to zero. Though they have 
no appreciable effect on the interfacial tension in the absence of soap, 42 
they materially reduce the interfacial tension between soap solution and 
kerosene. 

39 Vincent, loc. cit. 

40 Hillyer, /. Am. Chem. Soc, 25, 511-532, 1256-1265 (1903). 

41 Richardson, loc. cit. 

42 Edser, 4th Colloid Report, Scientific and Industrial Research, London : His 
Majesty's Stationery Office, 1922, p. 263, ct scq. 



314 SOLUBLE SILICATES IN INDUSTRY 

Millard 43 measured the surface tension of soap solutions with added 
alkaline compounds against benzene by the drop method at 40° C. Two 
types of silicate of soda were included. Figure 146 recalculated to 
show the effect of units of Na^O in various combinations on surface 
tension shows that silicates, though less effective than sodium carbonate, 
have a marked influence. 

Table 95. Drop Numbers for Soap Solutions ivith Added Sodium Silicate at 100° C. 



91 
76 
59 
45 
33 
13.5 13.5 

0.20 0.25 









(Richardson) 




Per Cent 










Soap 










0.25 


56 


62 




70 


0.20 


44 


48 




55 


0.15 


34 


39 




47 


0.10 


26 


31 




36 


0.05 


18 


23 




27 


0.00 


13.5 


14 


\4 


14 




0.00 


0.05 


0.10 


0.1 



Per cent Na 2 0, 2.83Si0 2 added 
Each of the above drop numbers is the average of two or more tests. 

Richardson believes that soluble silicates increase the surface tension 
of soap solutions toward air, as indicated by decrease of the drop 
number. 44 ' 45 

Viscosity and Film Formation. The colloidal character of silicate 
solutions differentiates them from other alkalies with which they have 
been grouped. Experience indicates that their effect on surface tension 
is, like that of gums and gelatin, only a part of the story as far as 
ability to wet surfaces is concerned. 46 Considerations of viscosity and 
of film formation were found by Clark and Mann to be of great im- 
portance in emulsincation, which is closely related to wetting and 
deflocculation. The colloidal character of silicate solutions gives them 
viscosities much higher than other alkaline salts and though the avail- 
able data are meagre, it is well to bear this in mind when considering 
industrial uses of soluble silicates which depend on wetting power. 47 

Wetting Power and Washing Processes. The value of wetting 
power has perhaps been too little stressed in discussing washing proc- 
esses. Any surface which has been completely wet by a detergent 
liquid has been separated by a film from other substances with which 
it may have been contaminated. When this condition is attained, 

i3 Ind. Eng. Chcm., 15, 810-811 (1923). 

44 Shorter and Ellingworth, Proe. Roy. Soc. (London), A, 92, 231-247 (1916). 

45 Elledge and Isherwood, /. hid, Eng. Chem., 8, 793-794 (1916). 

46 Briggs and Schmidt, /. Phys. Chem.. 19, 479 (1915). 

47 Clark, G. L., and W. A. Mann, /. Biol. Chcm., 52, 157-182 (1922). 



DEFLOCCULATION AND DETERGENCY 315 

mechanical processes will do much toward complete removal regardless 
of the occurrence of defiocculation or the formation of emulsions, help- 
ful though these processes are. 

There are several industrial methods which appear to depend pri- 
marily upon the ability of silicate solutions to wet surfaces which have 
been covered with an oily layer. 

Recovery of Bituminous Material from Sand.. To recover 
bituminous materials from sands or rock in which they occur naturally 
it is advantageous to wet the sand with a watery medium, thus allowing 
separation. This has been done with waters to which various colloidal 
or alkaline substances have been added. The soluble silicates which 
combine these two characteristics have served well in a process proposed 
by Fyleman 48 but developed independently by Clark 49 > 50 in connection 
with the bituminous sands of Alberta. 51 Plant-scale separations have 
been carried out using an average of 1.518 kilograms (3.25 pounds) 
Na 2 0, 3.9Si0 2 per ton of sand containing 12 to 17 per cent bitumen, 
the maximum amount of sand in the concentrate being 11 per cent, the 
minimum, 5.5 per cent. A temperature of 50° to 90° C. was employed 
for the silicate treatment. The selection of the most silicious silicate 
solution to be had commercially was the result of a series of tests, and 
indicates the value of colloidal characteristics for wetting the sand. 
Weathered material does not work satisfactorily. The freshness of the 
sand, the type of treatment with silicate and the mechanical mixing are 
intimately connected. 52 

Fyleman proposed the use of his process to release oil from sands 
so far depleted that crude petroleum would not otherwise flow from 
them. In the laboratory this works out very well but in the field its 
value depends upon the absence of soluble salts which may react with 
the silicate and retard the flow. 53 The method is to pump the silicate 
solution, 0.5 to 2 per cent Na 2 0, 3.3Si0 2 , into the lower part of the sand 
so that the oil may rise above it into an opening from which it can be 
recovered. 54 

48 Fyleman, M. E., Trans. Soc. Chem. Ind., 41, 14 (1922); Brit. Pat. 163,519 
(1921). 

48 Clark, K. A., 3rd Annual Report, No. 8, Scientific and Industrial Research, 
Council of Alberta (1922) ; 4th Annual Report, No. 10, 59-73 (1923). 

M Clark, K. A., and S. M. Blaire, Report Scientific and Industrial Research, 
Council of Alberta, No. 18, 4-28 (1927). 

^Eglofr, Gustav, and Jacques C. Morre.ll, Can. Chem. & Met.. No. 2, 33 (1927). 

sa Clark, K. A., personal communication. 

53 Silicate P's & Q's, 6, No. 1 (1926), Philadelphia, Pa.: Philadelphia Quartz 
Company. 

54 Stroud, Ben K., U. S. Pat. 1,575,944 (March 9, 1926) ; U. S. Pat. 1,575,945 
(March 9, 1926). 



316 



SOLUBLE SILICATES IN INDUSTRY 



Purification of Mineral Oils. Mineral oils which have been used 
for lubricating the crank cases of internal combustion engines, for 
insulating electrical transformers or for oil-immersion switches become 
contaminated with finely divided carbon which cannot be removed by 
filtration. The recovery of these oils will, in the future, assume a 
greater importance than it has in the past. 



70 
GO 
50 

40 



1 ' Figure J } ' ' 

Effect of eoncen+rahon of sj //cafe 
Oil '.' silicate - /2.S : / t?tf ro/ume 

40l 




Fig. 147. — Clarification of Mineral Oil by Silicate of Soda (Van Brunt), 



10 

6o 

50 

4o 
30 
20 



10 









Figure c. 
Effect of ratio of silicate to 












C 


rank case oil treated 


i$Z- — 


I 






























V 

o 




















i 






51 










' 










i 






1 




















- 6A 
















HC 


W(2S > 













12 16 20 24 26 32 36 40 

Fig. 148.— (Van Brunt). 



44 48 



Van Brunt and Miller 55 ' 56 found that by agitating mineral oils con- 
taining such colloidally dispersed carbon with a relatively concentrated 
silicate solution they could cause it to pass completely into the silicate. 
As the silicate solution is much heavier than the oil it is a simple matter 
to throw the oil upon a body of water and allow the silicate droplets 
as they quickly settle out to carry the carbon past the interface into 

55 Van Brunt, C, and Miller, P. S., hid. Eng. Chem., 17, 418 (1925). 
59 Van Brunt, C, hid. Eng. Chem., 17, 966-7 (1925). 



DEFLOCCULATION AND DETERGENCY 



317 



the aqueous layer, leaving the oil free of suspended matter. It then 
remains only to remove the light fractions by heat to obtain an oil ready 
for re-use. They worked with oils from the crank case of internal 
combustion engines. 

Na 2 0, 3.3Si0 2 at various concentrations yielded a sludge which sepa- 
rated slowly from the oil at room temperatures, as indicated by Figure 
149. It is evident that higher concentrations are more effective. Fol- 




Fig. 149. — Reclamation of Crank Case Oil. 

Left hand tube — Oil poured on water. Center tube — After the silicate and 
suspended materials have dropped out of the oil and passed into the water layer. 
Right — Same after settling. 



lowing this suggestion, Na 2 0, 3.3Si0 2 specific gravity 1.38, was tried in 
various amounts. Relations between silicate and oil by volume indicate 
that there is nothing gained by using more than 1 : 16 for sedimentation 
at ordinary temperatures. Raising the temperature to 80° C. brought the 
whole clarification of a 5 cm. layer of oil lying on water within 5-6 
minutes and amounts of silicate solution down to 1 per cent were found 
to be sufficient for some oils. 

Contaminated crank-case oils are not simple suspensions of carbon 
in hydrocarbon liquids, and some were found which did not yield to 



318 



SOLUBLE SILICATES IN INDUSTRY 




> 



O 



U 



u 




— 



< 



C 

o 
U 



X 



o 

u 



u 



o 






DEFL0CCULAT10N AND DETERGENCY 319 

this treatment, either hy failing to clarify or hy producing a sludge 
which was not easily dispersed hy water. All these were brought into 
line by adding a mixture of acid manganese resinatc and stearic acid 
in the proportion of 1 : 200 and 1 : 1000 respectively, followed by a 
1:40 by volume addition of Na 2 0, 3.3Si0 2 , specific gravity 1.38. A 
single exception was an excessively dirty sample which required twice 
the amount of silicate. 

Better dispersion of the sludges and hence easier operation of 
mechanical devices was secured by using a still more concentrated sili- 
cate, — Na 2 0, 1.6Si0 2 , specific gravity 1.67. 

The method of agitation found to be most satisfactory is to break 
up the silicate into small droplets, just enough to give complete contact, 
but not enough to form an emulsion which may occur if too much agita- 
tion is used in a relatively clean oil. This can be prevented by adding 
carbon black. Air was also found to be essential and must be broken 
into fine bubbles during the period of agitation. The authors comment 
that this is undoubtedly connected with the fact that not only the more 
polar bodies in the oil but also the silicate tend to enter the oil-air 
interface. They promise a theoretical discussion of the action of the 
silicate solution from the point of view of colloid chemistry. 

This should be of great interest. The observation may, however, be 
made that the process seems to be essentially a wetting of carbon, col- 
loidally dispersed in the oil, by a silicate-soap solution heavy enough 
to settle rapidly from the oil and soluble enough to be easily dispersed 
in water. 

The presence of resin or oleic acid would guarantee the formation 
at least of traces of soap and acidic materials ; manganese or other 
metallic salts would cause a precipitate in the concentrated silicate 
which might, like the carbon black, favor the separation. This, of 
course, is not a complete description of the observed phenomena, but 
the process affords a striking example of the ability of silicate solutions 
to wet surfaces which completely repel water, as well as their part in 
suspending carbon after bringing it into water. Soap solutions and 
other alkaline salts were tried and found greatly inferior to the silicates. 

Other workers have used silicate solutions to wet colloidal carbon 
and removed the sludge with the aid of centrifugal apparatus. While 
oils of satisfactory quality may thus be produced it is neither so con- 
venient nor economical to completely free the sludge from oil as in the 
Van Brunt method. 57 

"Rhodes, F. H., and H. J. Haon, hid. Eng. Chcm., 17, 25 (1925) ; cf. Flowers, 
A. E., F. N. McBerty, and R. Reamer, hid. Eng. Chcm., 17, 481-485 (1925). 



320 SOLUBLE SILICATES IN INDUSTRY 

Clark 58 is of the opinion that positive charges on the colloidal carbon 
have to do with the ease with which the silicate solution wets it. 
The result of his centrifugal process is said to yield from contaminated 
switch oil a product of superior resistance to emulsification, reduced 
acidity, and a dielectric strength comparable to new oil. The carbon 
from arcing switches under oil and from burning motor fuel in an 
engine cylinder appears to be equally amenable to wetting by silicate 
solutions. 

Silicate solutions have been used in mineral oil refining to remove 
traces of acid from lubricating stocks. As the relatively concentrated 
solutions employed are heavier than other neutralizing agents they can 
be quickly and completely settled from the oil at a saving of time. In 
some cases the operation has been carried out in a few hours at low 
temperatures such that a sodium carbonate solution would remain sus- 
pended for weeks. 59 

Vegetable Oil Refining. Vegetable oil refining also employs sili- 
cate solutions either alone or in connection with the well known method 
of refining with caustic soda. Procedures vary according to the nature 
of the particular oil, but in each case the alkali causes the separation 
of a flocculent precipitate containing soap and much of the coloring 
matter of the oil. Silicate solutions are able to wet this soap without 
forming troublesome emulsions, if appropriate conditions are observed, 
and a denser residue with consequent higher recovery of oil is obtained 
due to the weight imparted by the silicate. 

Two methods are recommended for linseed oil, — one employing 
Na 2 0, 3.3Si0 2 and NaOH, the other using Na 2 0, 1.6Si0 2 alone. The 
first uses 0.15 pound per gallon of a mixture consisting of 3 volumes 
of 1.79 specific gravity (22°Baume) NaOH and 1 volume of 22°Baume 
Na 2 0, 3.3Si0 2 , for each per cent of free fatty acid in the oil. 60 This 
mixture is emulsified by stirring at atmospheric temperature, and then 
slowly heated until a flocculent precipitate separates — in the language of 
the trade, till it "breaks." The soap and silicate settle rapidly, and the 
oil is decanted, washed to free it from traces of soap, treated with 
fullers' earth and filtered, giving a light colored sparkling oil. 

The second method requires 0.1 pound of Na 2 0, 1.6Si0 2 , 1.67 specific 
gravity (58°Baume), for each per cent free fatty acid and heating to 
not more than 70° C. Otherwise the procedure is the same as above. 

38 Clark, L. H., personal communication. 

^Michler, J. R., Chem. Ztg., 21, 853; /. Soc. Chem. Ind., 16, 1009 (1897); 
Otto, O. T., Brit. Pat. 158,252 (Jan. 17, 1921) ; C. A., 15, 1954. 

60 Hartman, F. E., "The Truth about Ozone," Scottdale, Pa.: U. S. Ozone 
Co., 1922. 



DEFLOCCULATION AND DETERGENCY 321 

Soft water should be used in washing the oil, as calcium compounds 
tend to cause emulsions that are hard to break. 

Cottonseed oil is the most important subject of this refining method 
though it is applicable to peanut oil and most of the liquid fats. The 
technic must be varied according to the quality of the raw oil. In wet 
seasons the seed often heats before the oil is pressed from it and enzyme 
action increases the content of free fatty acid. Such oils produce a 
large precipitate in refining and consequent loss which may be reduced 
by the use of silicate. The art of the refiner consists in knowing how 
much alkali to add and at what concentration, the time of agitation 
before heating, and the temperature to use in breaking the emulsion. 
All these must be adjusted to the quality of the crude oil because they 
affect the color, flavor, and value of the final product. A large mill 
working by the silicate process obtained an increase of 1.7 per cent 
yield on prime crude cottonseed, and the advantage is much greater 
when high free acid or abnormal color has to be dealt with. 61 

Variations of the general method including the use of sodium car- 
bonate and different sequences of the steps have been patented, but 
essentially it depends upon the wetting and weighting of the flocculated 
albuminous and other impurities by silicate solutions which form a 
dense soap stock and increase the recovery of oil suitable for an article 
of diet and commanding a corresponding price. The practice is well 
established and has for years been used on a large scale. 62 ' 63 

Purification of Fats and Fatty Oils. Fats and fatty oils may also 
be purified by treating their solutions in ether, benzene, or other volatile 
solvents with silicate solutions. A compact dry soap settles out quickly 
and the solvent is recovered by distillation. Na 2 0, 3.3Si0 2 at 1.38 
specific gravity is recommended. 64 ' 65 

Solvents such as those used by dry cleaning establishments are also 
amenable to purification by agitation with silicate solutions which settle 
readily. 66 

Anti-Dimming Compounds. Compounds designed to cause the 
spread of rain drops in an even film upon glass frequently contain 
soluble silicates. Such compounds are important means of improving 
vision through the windshield of an automobile or through glass pro- 

61 The Balance, 2, 3 (1925), Fort Worth, Texas: Fort Worth Laboratories. 

^Chisholm, Jesse C, U. S. Pats. 1,007,642 (Aug. 31, 1911) ; 1,056,261, 1,056,262, 
1,056,263, 1,056,264 (March 18, 1913). 

"Holbrook, George M., U. S. Pats. 1,169,154, 1,169,155 (Jan. 25, 1916). 

M Salmonson, H. W., Brit. Pat. 13,970; Brit. Pat. 165,635 (May 20, 1920); 
C. A., 16, 847. 

^Telenga, Jan., N. Y. J. of Commerce (Jan. 28, 1922). 

6a Hey, H., Brit. Pat. 164,931 (April 27, 1920) ; C. A., 16, 600. 



322 SOLUBLE SILICATES IN INDUSTRY 

tectors for marine or other observers. They also serve to prevent fog 
on mirrors used for dental work. 67 

They were used also in connection with gas masks during the war, 
more than 9 million units of a compound in the form of sticks having 
been delivered to the American armies before the signing of the 
armistice. The formula used for this purpose was : 

100 parts 85 per cent turkey red oil, 

15 parts NaOH or equivalent Na 2 C0 3 , 

5 parts paraffin oil, 

5 parts Na 2 0, 3.3Si0 2 , specific gravity 1.38. 

The composition may be varied as set forth in patents 68 dedicated to 
free use by any person in the United States. 

Sulfonated rape-seed or cottonseed oils may be used and water in 
varying amount to make a consistency suitable for saturating cloth, foi 
paste, or sticks similar to those in vogue for shaving soap. 

Variations of this idea are possible without losing the effect of the 
silicates. Ridgeley 69 had good results from a mixture of soap, glycerin, 
and silicate. 

Differential Wetting of Valuable Minerals. Differential wetting 
of valuable minerals, notably gold and platinum-bearing sands, is secured 
by flowing the ore pulps against a surface prepared with a mixture of 
petroleum grease, animal oil or fat, and silicate of soda. The ores are 
said to adhere while the gangue materials do not. 70 

Emulsification. 

Types of Emulsions. The interfacial tension between silicate solu- 
tions and oils is very low. This favors wetting and the formation of 
emulsions, of which there are two types, oil in water and water in oil. 
The emulsions formed in detergent operations are of the type in which 
water is the continuous phase, while oil is the continuous phase in 
emulsions in which crude petroleum comes from the earth, bearing large 
amounts of water. 71 ' 72 

Great stress has been laid upon the importance of emulsifying oils 
and fats as one of the fundamentals of washing. It has already been 
indicated that such materials can be separated from surfaces to which 

OT Carleton, P. W., Ind. Eng. Chem., 21, 1105-1111 (1919). 

^Kuhn, H. A., U. S. Pats. 1,394,773, 1,394,774 (Oct. 25, 1921). 

60 U. S. Pat. 1,556,714 (Oct. 13, 1925). 

70 Luckenbach, Roger, U. S. Pat. 1,478,237 (Dec. 18, 1923). 

71 Clayton, W., "Theory of Emulsions and Emulsifications." London: Churchill, 
1923. 

"Bancroft, Wilder D., "Applied Colloid Chem.," Chap. IV, New York City: 
McGraw-Hill Company, 1921. 



DEFLOCCULATION AND DETERGENCY 323 

they have been attached by interposing an aqueous film without neces- 
sarily making an emulsion. 73 

Emulsifying Power of Silicates. Hillyer 74 stated that sodium 
silicate would not emulsify cottonseed oil which had been treated with 
dilute sodium hydroxide to remove free fatty acid, but he specified 
neither the composition nor concentration of the silicate, a frequent 
error of those who are not familiar with the variety of substances which 
is included in the term silicates of soda. 75 

Stericker's 76 experiments show plainly that emulsions can be formed 
with silicate solutions in any but the most refined grades of mineral 
oil and that in the case of the more silicious silicates results can be 
secured which are not at all in accord with those which would be 
expected from a consideration of the drop numbers. This method gives 
results which run fairly parallel to the emulsifying power and detergency 
of soaps, but are quite misleading when applied to silicates. Richard- 
son's and Millard's 77 drop numbers already cited, would lead to the 
assumption that sodium carbonate is a more efficient emulsifying agent 
than any silicate, but Stericker found that emulsifying power in sili- 
cates toward mineral oils increases with decreasing alkalinity and that 
Na 2 0, 3.9Si0 2 is more effective than sodium carbonate. Pure hydro- 
carbon oils are but slightly emulsified by silicate solutions and the 
emulsions are unstable. Kerosene is more readily emulsified than a 
U.S. P. petroleum for medicinal use. A colored fraction from Cali- 
fornia crudes, 0.87 specific gravity, is still more readily emulsified. 
The presence of unsaturated hydrocarbons may account for the differ- 
ence. Saponifiable oils are readily emulsified by silicate solutions and 
since they are more effective than sodium carbonate it is evidently not 
wholly a matter of soap formation. The addition of a small amount of 
saponifiable oil to the purest mineral oil causes it to emulsify with 
silicate. 

The purified oil yielded two kinds of emulsions, but both were un- 
stable. The optimum conditions for water in oil were 70-90 per cent 
and a 5 per cent solution of Na 2 0, 3.3Si0 2 , shaken at 20° or 80° C. 
Small amounts of oil in water were obtained with 2 to 4 per cent of 
oil and 0.5 per cent solution of Na 2 0, 3.3Si0 2 or Na 2 0, 3.9Si0 2 . 

73 Mees, R. T. A., Z. Deut. Ol und Fett hid., 42, 235-237 (1922) ; Chem. Week- 
blad, 19, 825 (1922) ; C. A., 16, 2422; bj, 302-304 (1923) ; C. A., 17, 2514. 

74 /. Am. Chem. Soc, 25, 511 (1903). 

"Stericker, William, Ind. Eng. Chem,, 12, 1026 (1920). 

™Ind. Eng. Chem., 15, 244 (1923). 

77 Richardson, A. S., Ind. Eng. Chem., 15, 24-3 (1923); Millard, E. B., Ind. 
Eng. Chem., 15, 810-811 (1923) ;Briggs and Schmidt, J. Phys. Chem., 19, 479 
(1915). 



324 SOLUBLE SILICATES IN INDUSTRY 

The mineral oils which were less refined gave emulsions which 
creamed out, as did those made by Pickering 78 with soap. All the 
silicates had some emulsifying power, but under optimum conditions 
practically all the separated layer could be diluted with silicate solution 
or with water, showing that the oil was still dispersed and, like defloccu- 
lated solids, in condition to be rinsed away. Some of these emulsions 
made with lubricating oil remained emulsified at atmospheric tempera- 
ture for a month without much separation. In this case, Na 2 0, 3.9Si0 2 
at 0.6 per cent and Na 2 0, 3.3Si0 2 or carbonate at 0.4 per cent were best. 

With all but the purest oils the best emulsions with silicate-soap mix- 
tures were better than could be made with soap alone. 

The emulsifying powers of silicate solutions are considered by 
Vincent 79 to be due to soaps formed from fatty acids in the oils which 
silicate has been observed to emulsify. Most dirt encountered in prac- 
tical washing contains some saponifiable material so that oils are emulsi- 
fied by silicate detergents even in the absence of soap. He points out, 
however, that while emulsification is a helpful adjunct to washing, it is 
not essential as oils may be removed from surfaces from which they 
are released by the wetting action of detergents even though they are 
not fully dispersed as emulsions. If the silicate solution is able to 
squeeze in between the junction of oil and fabric or skin, that is, to wet 
the surface to be cleaned and displace the oil, then the oil may be re- 
moved by rinsing regardless of its degree of dispersion; and this is 
known to occur. 

The action may also be viewed as the detergent wetting the oil and 
solutions able to wet oily surfaces are seen to have detergent value. 
In one sense wetting and emulsification are different only in degree, — 
an emulsified oil may be considered as superlatively wet. 

The optimum concentration of soap for forming emulsions for de- 
tergent purposes lies in the range 0.05 to 0.1 per cent, while defloccula- 
tion by soap is most effective at 0.2 per cent to 0.4. Vincent says : 

"If a particular soap bar were composed of 80 per cent sodium 
silicate, (Na 2 0) 2 ,(Si0 2 ) 3 and 20 per cent soap, and if this detergent 
were used at a concentration of 0.3 per cent, the actual soap concen- 
tration would be 0.3 X 0.2 = 0.06 per cent. This is within the con- 
centration of 0.05-0.10 per cent necessary to emulsify oils. 

"The silicate concentration in the detergent solution would be 
0.3 X 0.80 = 0.24 per cent. The Mn0 2 value of "S" Brand silicate 
(Na 2 0, 3.97Si0 2 , specific gravity 1.30), (Na 2 0) 2 ,(Si0 2 ) 3 . 9 r, at 40°C. 

78 /. Chem. Soc, 91, 2001 (1907). 
79 /. Phys. Chem., 31, 1296 (1927). 



DEFL0CCULAT10N AND DETERGENCY 325 

is approximately 390. Whereas, the MnOo value of the soaps studied 
exclusive of olive oil soap, at 0.24 per cent and 40° C. is approxi- 
mately 520. 

"This means that the silicate would suspend 390/520 = 75 per cent 
of the solid material that pure palm oil, tallow, Green Arrow, or sili- 
cated Green Arrow soap would suspend. 

"At the above concentration and temperature olive oil soap exhibits 
an Mn0 2 value of about 445. Thus, the silicate would be 390/445 = 
87.5 per cent as efficient as pure olive oil soap in the suspension of solids. 

"By making a bar of soap which contains 20 per cent soap and 80 
per cent sodium silicate, the soap would cleanse the liquid dirts, and the 
silicate would suspend the solids 75-90 per cent as efficiently as would 
pure soap alone. In reality this percentage would be higher, due to the 
fact that the soap, as well as the silicate, would suspend the solids to a 
certain extent. 

"The emulsifying powers of such a silicated soap were investigated 
and found to be excellent." 

Concentration and Alkalinity of Silicate Solution. The con- 
centration of silicate solutions is an important factor in forming emul- 
sions. Those which stand heating to 80° C. are best made with silicates 
of 5 per cent or lower concentrations, while those which can be depended 
on to break at 70° to 80° C., as in the oil refining processes, are more 
concentrated. This is fortunate, as the lower concentrations are those 
appropriate to washing. One of the best emulsifiers consisted of 0.3 
per cent neutral soap plus 0.1 or 0.2 per cent Na 2 0, 3.3Si0 2 . The soap- 
silicate mixtures proved in all cases to emulsify better than soap alone. 

The evidence seems conclusive that from the point of view of dis- 
persing oils and fats, silicate solutions rightly chosen and applied are 
effective alone, and when mixed with soap they perform this part of 
the detergent process better than a pure soap can do. 

What the factors are which determine the concentration, relative 
alkalinity, and temperature at which silicate will emulsify or cause the 
coalescence of dispersed oil or water do not appear to be fully known, 
but experimental evidence and experience in industry show that both 
can be done. Barnickel 80 has studied the breaking of petroleum emul- 
sions in which oil is the continuous phase. From the foregoing, it 
might be supposed that a highly alkaline and relatively concentrated 
silicate would be best. 81 Since calcium and magnesium tend to induce 
water in oil emulsions, and sodium soaps, the oil in water type, it follows 

80 Barnickel, William, U. S. Pat. 1,093,098 (April 14, 1914). 
^Bhatnazar, S. S., Report Faraday and Physics Soc, 27-31 (1921). 



326 



SOLUBLE SILICATES IN INDUSTRY 



that water-softening agents help to break the natural petroleum 
emulsions. 82 " 87 




Lathering. 

Formation of Foam. Aeration of liquids and the formation of 
froths and foams take place under the most diverse conditions. Edser 88 

concludes that the only condition com- 
mon to frothing liquids is that their 
surface tension is not normal. It may 
be reduced, as in the case of soap solu- 
tions or the slightly soluble oils used in 
flotation, or slightly increased, as in 
the case of electrolytes, among them 
silicates of soda. Pure liquids do not 
foam. The stability of foams may be 
greatly increased by concentration of 
such substances as soap, saponin, in- 
soluble solids, or liquids in the films. 89 
These change the films, in some cases 
at least, to plastic solids. 90 Thus the 
materials removed in washing tend to 
stabilize soap lathers. 

Effect of Silicate on Lathering. 
Silicate solutions alone cause foam, but 
it is evanescent. They do not concentrate 
in the surface films as saponin and 
soap do, but they are able to increase 
and to stabilize foams produced by 
soap. Clay and silica added to 0.2 per 
cent Na 2 0, 3.3Si0 2 solution produced a 
good suds. 91 Mineral oils also stabilize 
the foam produced by silicate solutions. 






Fig. 151. — Effect of Silicate on 
Lathering. 

The tubes contain the same 
amount of soap solution. The one 
on the left contains silicate ; that 
on the right does not. 



82 Clowes, /. Phys. Chem., 29, 407 (1916). 

"Barnickel, Wm. S., U. S. Pats. 1,223,659 and 1,223,660 (April 24, 1917). 

84 Mathews, R. R., and P. A. Crosby, /. Ind. Eng. Chem., 13, 1015 (1921). 

85 Donnan, F. A., Report, Faraday and Physics Soc., 18-21 (1921). 

88 Parsons, L. W., /. Ind. Eng. Chem., 14, 797-798 (1922). 

87 Dodd, H. V., Chem. Met. Eng., 28, 249-253 (1925). 

88 Fourth Colloid Report, Sci. & Ind. Research, London : His Majesty's Sta- 
tionery Office, 314-320 (1922). 

89 Freundlich, Kapillarchemie, 302 (1909). 

90 Wilson, R. E., and E. D. Ries, Colloid Symposium Monograph, 1, 145 
(1923) ; presented in preliminary form at A. C. S. meeting, Rochester, N. Y. 
(April, 1921). 

91 Stericker, loc. cit. 



DEFLOCCULATION AND DETERGENCY 



327 



There is some disparity in the literature respecting the effect of sili- 
cates upon the lathering power of soap. This is doubtless due to differ- 
ent silicates and conditions chosen for experiments. 92 

Figures 151, 152 and 153 show experiments in which soap alone 
and soap with silicate were put into freshly boiled distilled water and 




Fig. 152.— Effect of Na 2 0, 3.34Si0 2 , 1.01 Specific Gravity (2°Baume) Silicate on 

Volume of Lather. 



shaken alike. A 0.5 per cent solution of a high-grade flake soap, well 
known on the market, was used. 93 

Lathering Power and Detergency. Under optimum conditions 
silicate is a more effective promoter of lathering in soap than is sodium 
carbonate. 

If an amount of oleic acid soap just below that required to make a 

92 Rasser, E. O., Seifensieder Ztg., 48, 290, 309, 355, 368 (1921) ; Textilberichte, 
4, 277-84 (1923). 

93 " Silicate P's & Q's, 6, No. v (1926), Philadelphia, Pa.: Philadelphia Quartz 
Co. 



328 



SOLUBLE SILICATES IN INDUSTRY 



lather in distilled water be chosen, an addition of sodium carbonate 
will enable the liquid to foam when shaken. When the same amount of 
alkali is added as silicate the foam is more voluminous and much more 




CC ef Silicate 



Fig. 153.— Effect of Na 2 0, 3.34Si0 2 , 1.04 Specific Gravity (6°Baume) Silicate on 
Volume of Lather in 100 cc. Distilled Water. 

stable. As shown in Figure 154, the original turbidity declines with the 
addition of soda ash, but the substitution of silicate for carbonate yields 
an entirely clear solution under the lather. 

Lathering power has been proposed as a measure of detergency. 94 
^Chapin, Robert M., Ind. Eng. Chem., 17, 461-465, 1187-1191 (1925). 



DEFLOCCULATION AND DETERGENCY 



329 



It is quite obvious that some materials detached from fabrics in washing 
are carried away in the suds. This is a useful property, and soaps 
which lather well are usually good 
detergents, but the value of lather as 
an index of detergency has a place 
in the public mind out of proportion 
to its worth. Foams have good wet- 
ting power because the outside sur- 
faces of the bubbles have higher 
surface tension than the inside, so 
that they tend to flatten out against 
a surface of contact. 95 

The permanence of soap lathers 
has to do with the viscosity of the 
films and the thickness of bubble 
walls. Silicates evidently stabilize 
soap lathers, but the mechanism of 
the process has not been investi- 
gated. Silicates may cause an in- 
crease in the surface concentration 
of the soap. 95 ' 9G 




Fig. 154. — Effect of Silicate of Soda 
on Soap Suds. 

First tube .055 g. Na oleate 1000 cc. 
distilled H*0. 

Second tube .055 g. Na oleate 1000 
cc. distilled H 2 0. .015 g. Na 2 CO s 
equivalent to .008 g. Na 2 0. 

Third tube .055 g. Na oleate 1000 
cc. distilled H 2 0. .03 g. Na 2 0, 3.25Si0 2 
equivalent to .007 g. Na 2 0. 



Lubrication. 

Silicate solutions in common with 
soap and other alkaline materials 
have a slippery feel when rubbed 
between the fingers. It seems prob- 
able that this characteristic may have 
a helpful influence in freeing dirt 
from a state of entanglement in the fibers of goods as they are moved 
about in washing. 98 

If there were formed upon the surface of either fabric or foreign 
material a film such as those described in the following chapter, it 
would at first assume a soft gelatinous condition. Gelatinous films are 
very slippery and yield under moderate pressure with a lubricating 
effect. It seems likely that such films are formed, for small amounts 

95 Shorter, S. A., /. Soc. Dyers Colorists, 34, 136-138 (1918). 

96 Leimdorfer, /. Chem. Umschau, 30, 149-151, 157-161 (1923). 

^Rasser, E. O., Seifensieder Ztg., 48, 268-269, 290-291, 309-310, 355-357 (1921) ; 
C. A., 15, 2992. 

98 Lamborn, L. L M "Modern Soaps, Candles, and Glycerin," New York : Van 
Nostrand, p. 21-32, 1906. 



330 SOLUBLE SILICATES IN INDUSTRY 

of silicious ash accumulate in all fabrics washed in silicate solutions. 
From our knowledge of their behavior, we may assume that the silica 
which forms the ash was highly hydrous when laid down. There are 
no data as to the extent to which lubrication plays a part in detergency, 
but it is a factor which must be studied before our knowledge is 
complete. 

Solution. 

Solvent Effect of Soap Solutions. The solvent effect of soap 
solutions was investigated by Pickering," who found that they would 
dissolve appreciable amounts of benzene and hydrocarbon oils. Silicate 
solutions do not do this, but the action of soap is not prevented by the 
presence of silicates. The best naphtha soaps which contain petroleum 
hydrocarbons to the extent of 10 per cent or more have at least an 
equal amount of silicate and go into solution without separation of the 
mineral oil. It is also usual for soap makers to add small amounts of 
mineral oils along with the silicate in the final mixing of laundry soaps 
to smooth the texture, and this oil does not reappear as the soap is 
dissolved for use. 

Fatty Acids Saponified by Silicates. The presence of silicates 
may also hinder the precipitation of calcium soaps from hard water. 
Silicates are, besides, able to saponify fatty acids which go into solution 
and these, as we have seen, have a marked effect upon emulsifying 
and deflocculating power. 100 This is particularly important because 
small amounts of fatty acid are present as part of the soil in many kinds 
of washing. 

Starches Hydrolized by Silicates. Starches may be hydrolized 
and brought into solution by the alkalinity of silicates. Starched goods 
are notably easier to wash clean because when the starch is dissolved 
in washing, the support of the foreign substances is taken away and 
they are free to float. 101 

Albuminous materials are dissolved by silicate solutions as by other 
alkaline reagents. 

Solvent Action of Silicates in Straw Paper Industry. The 
solvent action of silicate solutions upon the non-cellulose constituents 
of straw has been employed experimentally, 102 though with quantities 
of several tons, for reducing wheat straw to pulp for making the straw 

"Pickering, S. V., /. Chem. Soc, 111, 86-101 (1917). 

100 Shorter, S. A., J. Soc. Dyers Colourists, 36, 299-304 (1920) ; C. A., 15, 1222. 

101 de Keghel, M., Rev. chim. ind., 30, 171-178 (1921) ; C. A., 16, 1020. 

102 Dixon, U. S. Pat. 52,545 (1866) ; Cobley, T. H., Brit. Pat. 13,096 (1896). 



DEFLOCCULATION AND DETERGENCY 331 

paper used in the container industry. The method has the advantage, 
over the usual treatment, of freedom from the encrusting action of lime 
on the paper machine and the ability to harden the paper by precipitation 
of silicate with aluminum sulfate. The pulp thus requires no washing 
in contrast with the use of about 40,000 gallons of water per ton of 
paper in the lime process. 103 The paper is of satisfactory quality, but the 
amounts of silicate required make the reagent cost greater than the cost 
of lime. Schwalbe 104 mentions the use of silicate solutions for the 
removal of straw, weeds, etc., from raw cotton fiber. 

Soap-Sparing Action of Silicate Solutions. 

Precipitation of Calcium and Magnesium from Hard Water by 
Silicate. Decomposition of soap by reaction with calcium and mag- 
nesium compounds from hard water is costly for several reasons. Soap 
which takes part in the reaction is not available for washing. The 
insoluble soaps formed constitute dirt, which, on account of. its adherent 
character, is exceptionally difficult to remove. Even though enough 
soap be used it is difficult to attain satisfactory cleansing and the color 
and feel of the fabric are inferior. 

An ideal addition to soap would be one capable of reacting com- 
pletely with hard waters without forming any insoluble soaps. Such a 
material is not known. Silicate solutions, like soaps, are able to pre- 
cipitate quantitatively the calcium and magnesium from hard water. 
Richardson 105 investigated the problem of what occurs when both are 
present in the same solution, to find whether softening of the water 
would be at the expense of silicate or soap. He found that both the 
typical reactions, in which calcium chloride represents hard water and 
sodium oleate represents soap, take place. 

1. CaCl 2 + 2Na(Ci 8 H 33 2 ) = CaCGaH^O*)* + 2NaCl 

2. CaCl 2 + Na 2 0, 3Si0 2 = CaO, 3Si0 2 + 2NaCl 

He found that the calcium silicate precipitate could react with calcium 
soap in reversible fashion, of which the following is typical : 

3. Ca(C 18 H 33 2 ) 2 + Na 2 0,3Si0 2 ^ CaO,3Si0 2 + 2Na(Ci 8 H 33 2 ). 

The equilibrium of such a system will determine the distribution of 
water-softening effect but with such complicated materials as soaps and 
silicates an exact interpretation seemed hopeless. The following general 
conclusions were reached : 

103 Dedrick, C. H., U. S. Pat. 1,682,834 (Sept. 4, 1928). 

104 Schwalbe, "Chemie der Cellulose," 1911, Berlin: Gebriider Borntraeger. 

105 Richardson, A. S., Chem. & Met. Eng., 25, 594 (1922) ; hid. Eng. Chem.. 15, 
241-243 (1923) ; /. Soc. Chem. hid., 42, 364 A. 



332 SOLUBLE SILICATES IN INDUSTRY 

"I — The distribution of the water-softening effect of a silicated soap 
between silicate and true soap will depend primarily upon the relative 
solubility of the precipitated soap and the precipitated silicate. 

"2 — The relative solubility of precipitated soap and precipitated sili- 
cate may vary with the nature of the soap, the composition of the silicate, 
the nature of the hardness of the water, and with the temperature. 

"3 — Other things being equal, increase in the proportion of true soap 
in the mixture favors water-softening at the expense of soap and in- 
crease in the proportion of sodium silicate favors water-softening at the 
expense of silicate. 

"With reference to possible differences due to differences in the 
character of the true soap, preliminary experiments indicated no essen- 
tial differences in the soap-sparing effect of sodium silicate when mixed 
with sodium oleate and when mixed with a selected commercial brand 
of 'pure' soap. The subject was not pursued further, and sodium 
oleate (from Eastman's 'practical' oleic acid) was used throughout the 
remaining experiments. Sodium oleate solutions have the very great 
practical advantage of not forming gels except at high concentrations." 

The soap-sparing effect with various soaps indicated no essential 
difference. 

"The effect of varying the composition of the sodium silicate was 
studied in some detail. Within practical limits the water-softening action 
of a given amount of sodium silicate of varying composition showed 
little change, except that increasing Na 2 content of the silicate re- 
sulted in a slight but distinct increase in its water-softening action 
toward temporary hardness. In all the experiments reported in detail 
in the present paper, the composition of the silicate used was Na 2 0, 
2.83Si0 2 . 

"Effect of Different Types of Hardness and of Temperature. 
The effect of different types of hardness and the effect of temperature 
upon the efficiency of sodium silicate as a water softener in the presence 
of soap is very marked, as illustrated in the experiments of Tables [96 
and 97]. In these experiments 50 cc. of the various hard waters men- 
tioned in the tables were titrated at room temperature, 28°C. (± 1.5), 
and at the boiling point with a solution containing 1 gram of sodium 
oleate per 100 cc. In the room temperature experiments, the titration 
was carried out in a four ounce tall form bottle and at frequent intervals 
the bottle was shaken in an approximately uniform manner. In the 
experiments at the boiling point, the same amount (50 cc.) of the vari- 
ous hard waters was boiled in a 200 cc. round bottom flask at a slow 
and approximately uniform rate. In each case the amount of soap 



DEFLOCCULATION AND DETERGENCY 333 

necessary to produce a distinct foam and the amount necessary to fill 
the vessel with foam was determined. The same procedure was re- 
peated after first adding to 50 cc. of each of the hard waters 1.5 cc. of 
a 5 per cent solution of sodium silicate (0.075 gram solid). 

"The temporary hard water was a calcium bicarbonate solution origi- 
nally containing 600 parts CaC0 3 per million, but at the time of its 
use the hardness had been reduced to approximately one-half this value 
by precipitation and sedimentation. The St. Bernard tap water, which 
is a deep well water, showed a hardness of 330 parts (CaC0 3 ) per 
million by the soap method. A complete analysis of the St. Bernard 
water was not made, but by analogy with similar water from the same 
neighborhood it may be assumed that the normality of the magnesium 
present was about one-half that of the calcium present. 

Table 96. Showing Grams of Sodium Oleate Necessary to Produce Foam from 

50 cc. of Various Hard Waters, with and without 0.075 g. Sodium 

Silicate Added to the Water. 

Nature of 0.0025M 0.0025'M Temporary St. Bernard 

Hard Water CaCh MgCl 2 Hardness Tap Water 

Without .silicate 28°C. 0.10 0.11 0.15 0.17 

With silicate 28°C. 0.10 0.01 0.15 0.12 

Without silicate 100°C. 0.10 0.09 0.04 0.125 

With silicate 100°C. 0.01 0.01 0.01 0.01 

Table 97. Showing Grams of Sodium Oleate Necessary to Fill Vessel with Foam 

from 50 cc. of Various Hard Waters, with and without 0.075 g. 

Sodium Silicate Added to the Water. 

Nature of 0.0025M 0.0025'M Temporary St. Bernard 

Hard Water CaCh MgCla Hardness Tap Water 

Without silicate 28°C. 0.145 0.22 0.20 0.30 

With silicate 28°C. 0.15 0.13 0.20 0.19 

Without silicate 100°C. 0.145 0.115 0.08 0.155 

With silicate 100°C. 0.09 0.01 0.11 0.09 

"Tables [96 and 97] indicate that sodium silicate is much more effec- 
tive toward magnesium hardness than toward calcium hardness and also 
much more effective at 100° C. than at room temperature. Confirmation 
of these conclusions is obtained from the experiments shown in tables 
[98 and 99], in which the same hard waters were titrated in the same 
manner as described above, except that the silicate was not added sepa- 
rately, but was introduced by using a solution containing 1 gram sodium 
oleate with 0.5 gram sodium silicate per 100 cc. 

"Table [100], which is for the most part self-explanatory, shows some 
of the typical results of our further study of the effect of tempera- 
ture, and also the effect of the proportion of silicate used, upon the 
water-softening or soap-sparing action of sodium silicate. The experi- 



334 SOLUBLE SILICATES IN INDUSTRY 

Table 98. Showing cc. of Soap Solution Necessary to Produce Foam from 50 cc. 

of Various Hard Waters, with and without Addition of Sodium 

Silicate to the Soap Solution. 

Nature of 0.0025 M 0.0025M Temporary St. Bernard 

Hard Water CaCl 2 MgCl 2 Hardness Tap Water 

Without silicate 28°C. 10 11 15 17 

With silicate 28°C. 10 9 14 13 

Without silicate 100° C. 10 9 .. 12.5 

With silicate 100°C. 7 3 . . 4 

Table 99. Showing cc. Soap Solution Necessary to Fill Vessel zvith Foam from 

50 cc. of Various Hard Waters, with and without Addition of 

Sodium Silicate to the Soap Solution. 

Nature of 0.0025M 0.0025'M Temporary St. Bernard 

Hard Water CaCl 2 MgCl 2 Hardness Tap Water 

Without silicate 28°C. 14.5 22 20 30 

With silicate 28°C. 15 20 19 21 

Without silicate 100°C. 14.5 11.5 .. 15.5 

With silicate 100°C. 10 5.5 .. 6.5 

merits at 25°, 50°, and 75 °C. were carried out according to the room- 
temperature procedure already described, except that a water bath was 
used for temperature control. 

Table 100. Showing cc. of Solution Containing 1 Gram Sodium Oleate per 100 cc. 

Together with Varying Amounts of Sodium Silicate, Necessary 

to Produce Foam from 50 cc. St. Bernard Tap 

Water at Various Temperatures. 

Grams silicate 
per 100 cc. soap 
solution 0.0 0.1 0.2 0.3 0.4 0.5 1.0 2.0 4.0 

11 10 10 

"l "\ '6.5 

"The results shown in Table [100] not only show an increase in the 
water-softening by silicate as the proportion of silicate to soap increases, 
but also show that a certain minimum of silicate must be present with 
soap in order to effect any water-softening at all by silicate. At ordi- 
nary temperature this minimum is considerable, even for a hard water 
high in magnesium. At 100° C, however, any practical quantity of 
sodium silicate was found to have a distinct soap-sparing effect. In fact, 
careful analysis of the table will show that in some cases the apparent 
weight of soap conserved per gram of silicate used was several times 
the theoretical value calculated from reactions (1) and (2). We are 
at a loss to explain so great a discrepancy, although it is partially ex- 
plained by the fact that soap wastage is greater than indicated by reac- 



Temperature 














25°C. 


17 


17 


17 


16 


16 


13 


50°C. 


17 


16 


14 


13 


13 


13 


75°C. 


15 


14 


13 


13 


13 


13 


100° C. 


12.5 


6 


5 


4 


4 


4 



DEFLOCCULATION AND DETERGENCY 335 

tion ( 1 ) , much sodium soap being dragged down by the insoluble soaps. 

"Since much of the water supply of this country is quite hard and 
since a considerable proportion of the household laundry work, if not 
the greater part of it, is done at 100°C, it is highly probable that the 
water-softening action of sodium silicate has been a large factor in 
the success of silicated soaps. The above experiments, however, empha- 
size the impossibility of prescribing an ideal amount of silicate for use 
in such soaps, because each kind of hard water and each washing 
temperature present a separate problem." 

Vincent found that a mixture of 20 per cent soap and 80 per cent 
silicate was practically twice as effective as pure soap for softening 
water containing iron and that the advantage of adding the silicate 
separately before the soap was very small. Sodium silicate is much 
better than sodium carbonate for this purpose on account of the sili- 
cate's ability to form a negative sol. The iron is dispersed rather than 
precipitated. 

Effects on Fabrics. 

Control of Alkalinity. Perhaps the most important effect of 
colloidal silica in detergent processes is its ability to modify the action 
of sodium oxide and to resist changes in hydroxyl ion concentration. 
It has already been shown that sodium is adsorbed on silica in solu- 
tion, 106 ' 107 and we shall have further occasion to deal with this prop- 
erty in considering gels. Solutions of soluble silicates do not behave 
like solutions containing the same concentrations of sodium as hydrox- 
ide. The more silicious grades actually reduce 1 the alkalinity of soap- 
sodium carbonate mixtures used in ordinary laundry practice. In these 
respects the silica is analogous to fatty acids in soap. The concept of 
the multi-charged colloidal micelle explains the high conductivity in di- 
lute solution and fits the facts of experience with detergent processes 
using either silicates or soaps. Adsorbed sodium is much less active 
than free caustic alkali. 

Glass bottles cleaned with hot dilute sodium hydroxide or carbonate 
solutions soon become dull and unattractive. Silicate solutions after 
thorough rinsing leave the glass lustrous. 

Ordinary tin plate is quickly discolored on contact of a few days with 
cold sodium hydroxide solutions. Exposure to a solution of Na 2 0, 
3.3Si0 2 containing the same percentage of Na 2 leaves the tin bright. 

109 Bogue, R. H., /. Am. Chew, Soc, 32, 2575-2582 (1920). 
107 Stericker, Wm, Client. & Met. Eng., 25, 61 (1921). 



336 



SOLUBLE SILICATES IN INDUSTRY 



Accidental exposure of the sensitive tissues of the mouth to a 40 
per cent solution of Na 2 0, 3.3Si0 2 is a trifling annoyance. A like 
amount of Na 2 as hydroxide would cause a painful injury. 

Strength of Fabric. In detergent use the modifying action of 
silica is shown by its effect on the strength of cotton fiber. A careful 
and extended study of Zanker and Schnabel showed that cotton washed 
in boiling solutions of soap and sodium carbonate with and without 
silicate would show the contrast between silicated and silicate-free de- 
tergent solutions. They used four materials : 

1. Neutral boiled soap, 60 per cent cottonseed, 40 per cent palm kernel oil. 

2. The same made with 20 per cent 1.38 specific gravity, Na 2 0, 3.3Si0 2 and 

5 per cent NaOH solution, presumably enough to produce Na 2 0, 2Si0 2 . 

3. Washing powder, 30 per cent fatty acid, containing soap and Na 2 C03 only. 

4. The same, plus 20 per cent 1.38 specific gravity, NaaO, 3.3Si0 2 and 5 per 

cent caustic soda lye. 

The solutions contained 5 grams each of soap and soap powder per 
liter of water. It is to be noted that the conditions of this study, in 
which a relatively large amount of Na 2 was present, some of it added 

as hydroxide, were particularly 
severe. They also differed from ordi- 
nary washing in the absence of 
mechanical action on the fiber. The 
samples were boiled for an hour at 
each operation, though without me- 
chanical agitation. The strength was 
determined by breaking individual 
fibers. The fiber was rinsed well 
after each washing, dried and allowed 
to come to equilibrium with the air 
before testing. Fifty measurements 
at least were averaged for each point 
(Fig. 155 and Table 101). 

The strength increased slightly 
for the first ten washes, probably 
due to shrinkage or a slight mercerizing action. The increase was less 
in the silicated detergent and the final loss of strength after many 
washes was smaller. This can only mean that the silica has a modify- 
ing effect on the alkali in washing. The assumption of Zanker and 
Schnabel 108 that the weakening of the fiber is a measure of detergency 
and that these experiments show soap to be a more active washing agent 
is not warranted in view of the complex nature of the washing process. 
108 Zanker and Schnabel, Seifenfabrikant, 37, 249-253, 279-282 (1917). 













I 

V 

z °>s 




,\ 


*t 




</) 
i 

z 

u. 
o 

z 
u 
u 




\/v° 














a. 
a 








^^"^ 



Number of Washes 



Fig. 155. — Effect of Silicate on the 
Strength of Cotton Fiber. 



DEFLOCCULATION AND DETERGENCY 337 

Kind 109 recognized how difficult it is to perform washing experiments 
with only one variable and obtain consistent results. He used Na 2 0, 
3Si0 2 and found an increase of strength in cotton fiber after 30 

Table 101. Effect on the Strength of Cotton Fiber of Silicates in Detergents. 

Strength, Per Cent 
Without With 

Number of Washings Silicate Silicate 

100.00 100.00 

10 107.02 105.84 

20 102.13 104.62 

30 96.29 101.58 

40 96.28 96.69 

50 97.30 96.87 

60 91.52 99.89 

70 85.32 97.17 

80 88.72 96.65 

90 86.09 96.48 

100 82.74 93.36 

110 82.30 90.66 

120 81.03 89.91 

130 78.28 88.82 

140 79.39 87.50 

150 77.06 85.83 

160 72.58 82.22 

170 70.89 82.20 

180 68.24 82.24 

190 70.14 81.36 

200 71.56 83.38 

washes but a loss on linen after the same treatment about twice as 
great as that caused by an olive oil soap. Heermann 110 also found 
small losses with 50 washes when detergents containing silicate were 
used, less than 5 per cent on cotton and 14 per cent on linen, which 
compares favorably with pure soap. 

Effect of Ash. Kind's high ash figures compared with Zanker and 
Schnabel are probably due to inadequate rinsing, and this condition 
may also have something to do with the loss in strength of linen 
fiber. 111 " 113 

Some statements indicating an injurious effect of the silica deposit 
upon fibers require examination because they have been widely quoted. 
It has been said that the deposited silica takes up water, expands, and 
disrupts the fiber. No experimental evidence is offered in support of 

109 Kind, W., "Die Wirkung der Waschmittel auf Baumwolle und Leinen," 
Ziemsen, Wittenberg and Halle, 1902; Chem. Ztg., 47, 457-460, 484-485 (1923). 

110 Heermann, P., Z. angew. Chem., 36, 101-103, 106-111 (1923) ; Mitt. Material- 
prufungsamt, 39, 65-72 (1921) ; C. A., 17, 885; cf., C. A., 15, 2993. 

111 Heermann, P., and H. Somner, Textilberichte, 3, 238 (1922). 

112 Farrel and Goldsmith, /. Soc. Ryers Colourists, 195 (1910). 

113 Leimdorf er, J., Seifensieder Ztg., 1271 (1908); 48, 519-520, 539-541 (1921); 
C. A., 15, 3406. 



338 



SOLUBLE SILICATES IN INDUSTRY 






•T3 
S 
Q 






^ 



si G 



a e 

to bo 



to 

s 

o 



a 



<4> 



8 



w 
►J 
m 
< 
H 



W rS 




GOCM CM Q 
t^CM CM NO 
On 00 ^'fO 



00 CM rf 00 OO 
t^co CM > »-h CO 
O CM t-H CM rf 



CM 



CM CM r-i VO CM O CM Tf vOO 00 O NO Tt NO NO O 00 O 

»^N "">""> "^ no on oq looo r>.'-j cv|ts t~>. co o on tF 

OO CM CM o' ON NO u-j co t^ o'i-h CM NO CO MD cm' ""> M0 



00-t CO CM 
1^00 CM CM 

00t-J coco 



rfCM 00 Q Tt- 

IO00 N >0 O0 



NO 
ON 

<0 " CM 



O - * TfVO OMD CM NO CM CM 00CM CMO CM CO NO 00 00 
rrvo t-i CM t^ «-h 00 VO On •— i t^ r-H co Tf On NO -^J- co tj- 



t-< t— i rt - NO On tJ- vo LO 



CO ^F On VO "3" co rf 

t-h NO O »— • i— i 1 * H O O fJ lfi 



rf 00 Tftf- rt- "<t <0 co NO ON co O «-■'«*■ O NO ■>*■ O On 
oo oo t-^oo t^r^ ooi^ co cm i^c^ io^- in co rf -^l- rj- 



■<— i «— i -^ O CM CO loCM COO NO'-" O0t^ OO On On CM 00 CM 

OO On On t-i O CM r- 1 CM r- 1 On O On On OO «— • On t-i On O 

1— i T— • T— I T— I T— I T— I T— I T-H T-H r— I T— I t-H T"H T— I 

tJ-co CM On O On t^ NO Tf co 00 On On NO Q On rj- CM On 

OO On On 00 l^. On 00 00 lo rj* l>» NO lo lo no rf- lo lo t>» 



lovO t^co CO'* VOK CO Tf CM co i-t Tfr N fO m N 29 
OnO O »-h CMCM ^r^ OO OO i-t O »-• O h O 2 

T-H T— It— ( t— It— I i — Ir— I t— It— I t— I 1 — I t— It— I T-H t — I t— I T-H T—l 



■^"lO r^ON 00 IN. O CM O* t-H CM IN. 00 CO 1— I 00 NO *-• 

OnOn 0000 OnOn OOn In, lo OnOn 00 in, 00 On lo tN, On 



CMCM iO NO lo CM lom lo CM lo CM loco rt On vo MD CM 

t-hO «-h O CM CM coCM r-i O OOn OO CM 00 H Q\ O 



UH UH UH UH Uh OH OH O H H H H 



*o 



<4= 



bo 



LO 

CM 



03 



.-o 



a, 
o 



CM 



O 



CM 



C 
03 



CO 
CO 



CO 
co' 

q 

o3 
CM 



03 * J 

J 3 



^^ 



OS 

a os 

o3nd 

o o 

en i/3 



03 3 
O OS 
c/J O 



LOlO ^fc£ lOlO 
t— i O t-H |H 1—5 O 



03 

*o 

O 



^ CO 

CO tG 



o3 trt 

s * 

^ .a* 

H-> 

cO oS 

O o 

CO 



03 



T3 
O CO 



^S. ^ 



^ 
* 



-a 

c 

CO 



J3 



TC O tS 

to 

OS 

t* 



^ CO 
CM CO 



CO 



DEFLOCCULATION AND DETERGENCY 339 

Table 103. Effect on the Ash of Cotton Fiber of Silicates in Detergents. 

(Kind) 

Original ash content of the fiber 

Detergent without silicate after 

Detergent with silicate, number of washes. 





Per Cent Ash 




0.45 


10-100 washes 


. , . 0.45-0.60 


of washes. ... 10 


0.95 


20 


1.82 


30 


2.35 


40 


3.16 


50 


4.12 


60 


5.14 


70 


5.45 


80 


5.75 


90 


6.57 


100 


6.92 



this. 114 Silica is always deposited in a hydrous condition from silicate 
solutions under conditions appropriate to washing. The hydrous silica 
contracts on drying, and like other silica gels does not increase in volume 
when put into water. Further, examination of the fibers under a micro- 
scope does not reveal that those containing high ash are broken after 
many washings with ironing between, and there is no evidence that the 
deposit depreciates the strength of the fiber, and only when the deposit is 
large is there any noticeable tendency toward a harsh feel or added 
stiffness. 115 Linen, silk, and wool are somewhat more affected by sili- 
cate solutions than by neutral soaps, but this must be regarded as a result 
of the somewhat greater alkalinity of the silicates used. In short, the 
rather persistent idea that silica in wash liquors is harmful appears to be 
the inheritance of an older literature rather than the result of systematic 
study in the light of present knowledge, not only of chemical theory, 
but of the behavior of soluble silicates. 116-126 The tradition has come 

114 Keilmeyer, "Farberlehrling," p. 73, from Schwalbe, "Die Chemie der Cellu- 
lose," Berlin: Borntraeger, 1911. 
115 Zanker and Schnabel, loc. cit. 
11<5 Vohl, Berliner Musterzeitung (1872). 

117 Calvert, /. Chem. Soc, 18, 70-77 (1865). 

118 Schelhass, Bayerisches Gewerbeblatt, 203 (1872). 

119 Euler, F., Leipziger Fdrber Ztg., 59, 81-82; C. A., 4, 1240 (1910). 

120 Leimdorfer, J., Seifensieder Ztg., 48, 519-520, 539-541 (1921) ; C. A., 15, 3406. 

m Griin, A., and Jungmann, Seifenfabr., 37, 507-510, 529-531, 553-555, 579-581, 
003-606 (1917) ; /. Soc. Chem. hid., 37, 411A; C. A., 12, 2693. 

122 Romagnoli, A., Seifensieder Ztg., 33, 67 (1906); Chem. Zentr., 77, 1, 714 
(1906.) 

133 Kiihl, H., Chem. Ztg., 43, 354-355 (1919); /. Soc. Chem. hid., 38, 589A; 
C. A., 13, 3018. 

124 Chevreul, "Recherches chimique sur les crops gras d'origin animals" (Paris, 
1815-1823, reprinted 1889). 

125 Berzelius, Muspratts Handbuch der tech. Chemie, 6, 3rd ed., 1067 (1874-80). 
128 Davidsohn, J., and G. Weber, Seifensieder Ztg., 35, 775, 798-800; Chem. 

Zentr., 79, II, 836 (1908) ; C. A., 3, 1224. 



340 



SOLUBLE SILICATES IN INDUSTRY 



clown into some rather recent writings, but there are now reports avail- 
able from which a clearer appraisal of the facts may be gleaned. 127-129 
It is sufficiently evident that undesirable results can be had by using the 
wrong silicate or the wrong concentration, and some of the conflict 



BO 












/60'f 




f 






























*> 






























i 












/oo'f 




%*> 






























\ 
















\jA 
















%40 
















v» 




























Wf 




x 30 
















































Vj 20 
















V 






D**e 


ryettt: 3S 


tap - / Silk 


ate 























1 S 






N»* 


» her »f 


Rinses 









Fig. 156.— The Effect of Temperature on Rinsing Efficiency. 



of statement is doubtless due to the use of different or unsuitable sili- 
cates or conditions, often to both. 130-135 

Rinsing. It has been suggested that silicate detergents might not 

^Loffl, K., Kunststoffe, 6, 239-40 (1916); C. A., 11, 1327. 

128 Schwalbe, "Die Chemie der Cellulose," Berlin: Gebruder Borntraeger, 1911. 

129 Rev. chim. ind., 266 (1924) ; Text. Inst., 16, A 203 (1925). 

130 Zanker and Schnabel, loc. cit. 

131 Kind, W., "Die Wirkung der Waschmittel auf Baumwolle und Leinen," 
Ziemsen, Wittenberg and Halle, 1902. 

132 Vail, J. G., Chem. Age, 30, 19-20 (1922) ; C. A., 16, 993. 

133 Jackson, H., "Cantor Lectures on Detergents and Bleaching," London: 
Trounce, 1907. 

134 Vail, James G., Chem. & Met. Eng., 31, No. 5, 183-184 (1924). 

135 Stericker, Wm, loc. cit. 



DEFLOCCULATION AND DETERGENCY 



341 



be readily removed in the rinsing process. The slow building up of 
ash in the fiber is a partial answer. Direct comparison of the removal 
of alkaline salts used with soap under conditions encountered in laun- 
dry practice shows that a certain silicate-carbonate mixture was not as 
completely removed by a given amount of rinsing at 60° F. as carbo- 
nate alone but at 160° F. the silicate mixture was slightly better than 



















V 












/60'F 




«i -jo 
























































/oo'f 




>» 

*& 


























60°/*- 


































V 



















































Dete 


rfe* ?•' 3 i 


~oaf - / Soa 


. fir/. 





O / Z J 4 3- 

A/i/mjber *f /f<'n*es 

Fig. 157. — The Effect of Temperature on Rinsing Efficiency. 

the carbonate as shown in Figures 156 and 157. Rinsing properties 
should not therefore be a bar to the use of silicate detergents. 136 

Action on Various Fabrics. Stericker 137 tested various fabrics 
by soaking in 5 per cent solutions of a series of silicates from Na 2 0, 
3.9Si0 2 to NaoO, 1.6SiO z at 20° and 80°C. and compared the effects of 
sodium carbonate and sodium hydroxide. The samples were rinsed in 
distilled water and examined microscopically. Na 2 0,2SiOo and the more 

138 Procter and Gamble Research Staff, Laundry Age, 182 (April 1, 1927). 
137 Philadelphia Quartz Company, unpublished report of. 



342 SOLUBLE SILICATES IN INDUSTRY 

alkaline silicates increased the luster of cotton, but the fibers did not 
swell, as in a sodium hydroxide solution. 138 ' 139 

Twenty strips of cotton sheeting, 1 inch wide, were soaked in the 
solutions indicated for 3 hours. 140 The solutions were maintained at 
63 °C. during the entire time. The tensile strength of the strips was 
then determined on a motor-driven Scott tester. The strips were tested 
while wet in order to eliminate errors due to differences in humidity. 
Each run was duplicated so that the figures given below represent the 
average of forty tensile strength determinations. 

Concentration 

Material . 0.05% 0.5% 5.0% 

Water 37.5 

Na 2 0, 3.34Si0 2 37.6 37.7 

Soda ash 37.5 37.3 37.0 

Caustic soda 39.2 38.0 31.7 

It will be noted there is practically no change in strength with Na 2 0, 
3.34Si0 2 or soda ash. In concentrations below 0.5 per cent, caustic 
soda increased the strength but at 5.0. per cent caused a decided de- 
crease. 

"The following tests were run on samples of all silk crepe de chine. 
Five per cent solutions of Na 2 0, 2.47Si0 2 , Na 2 0, 3.34Si0 2 , and Na 2 0, 
3.96Si0 2 , and of soda ash had no appreciable effect on this silk either 
at room temperature for 23 hours or at 63°C. (176°F.) for 3 hours. 
Since Na 2 0, 2.47Si0 2 is the most likely of these three silicates to cause 
damage, a sample of silk was soaked in it for a week at room tem- 
perature. Even at the end of that time there was no evidence of damage. 
Nineteen hours at room temperature in 5 per cent solutions of Na 2 0, 
1.62Si0 2 and Na 2 0, 2.03SiO 2 did not injure samples of silk, but 3 hours 
at 63° C. was sufficient to damage them. With Na 2 0, 1.62Si0 2 , the woof 
threads were thinned to about half their normal size. With Na 2 0, 
1.23Si0 2 there was evidence of tendering, but not nearly to such a 
great degree. Caustic soda at room temperature destroyed a portion 
of the silk and greatly tendered the remainder. At 63° C. it dissolved 
the silk entirely. 

"With samples of flannel, only part of which was wool, the most 
delicate indication of injurious action was the appearance of a yellow 
color in the solution used to soak the samples. At room tempera- 
ture after 19 hours there was only a barely perceptible yellowish tinge 
with Na 2 0, 3.34Si0 2 and Na 2 0, 3.96Si0 2 . The solution of soda ash 

138 Rev. chim ind., 266 (1924) ; Text. Inst., 16, A, 203 (1925). 

139 /. Home Economics, 17, No. 12,728 (1925). 

140 Danley, Mary, personal communication. 



DEFLOCCULATION AND DETERGENCY 343 

and the other brands of silicate were distinctly yellow while the caustic 
soda solution was very yellow. Under these conditions the caustic 
had dissolved all the wool. Na 2 0, 1.62Si0 2 , Na 2 0, 2.03SiO 2 , and 
Na 2 0, 2.47Si0 2 , and soda ash all seemed to dissolve some wool. The 
amount dissolved decreased in the order named. The flannel remained 
soft in all cases. 

"At 63° C. the action of these materials was intensified. At the end 
of 3 hours not only caustic soda but Na 2 0, 1.62SiOo as well had dis- 
solved all the wool. Na 2 0, 2.03 Si0 2 had left spots of wool and Na 2 0, 
2.47Si0 2 about half of the original amount. Soda ash had dissolved 
enough to be perceptible but Na 2 0, 3.34Si0 2 and Na 2 0, 3.96Si0 2 had 
not. Wherever there was any wool left, it had become yellow and 
was matted. When wet, it was slippery and slimy. When dry, it was 
stiff and hard. It will be recognized that these tests are very drastic 
and simply show tendencies, as the use of alkalies at this concentration 
and temperature is unheard of." 

Linen is similar to cotton in that it is essentially cellulose. Since 
there was no damage to cotton and since cellulose is not injured by 
dilute solutions of alkaline salts, it is believed that the various grades 
of silicate of soda will have no effect on it. It seems at least safe to 
say that Na 2 0, 3.34Si0 2 and Na 2 0, 3.96SiO<> will not injure it in any 
way. The same reasoning applies to viscose, Chardonnet, and cupra- 
ammonium rayons since all of these are essentially cellulose. No pre- 
dictions are offered concerning cellulose acetate rayon. 

These tests do not represent working conditions since the concen- 
tration of any of these materials in the wash-wheel should not exceed 
0.5 per cent (one-tenth the amount used here). They intensify any 
possible injurious action so it can be discovered in a few days or 
hours in place of the many weeks required in actual laundry prac- 
tice. Any recommendations based on these experiments therefore will 
err on the side of over-caution. 

Effect on Color. The silicate solutions have been shown to exercise 
a protective effect on cotton in the wash, as compared with soap and 
sodium carbonate mixtures. Colors are also more permanent when 
silicate is used in the wash. Every soap maker knows that the more 
silicious types will reduce the free alkalinity of soap 141 but even these 
exercise a more active effect upon the skin than a neutral soap. 142 Strong 
silicate solutions should not be recommended for the bath or for wash- 
ing the most delicate silks and woolens. More data are needed, though 

ia Zanker and Schnabel, loc. cit. 

142 Edeler, A., Ind. Eng. Chem., 17, 196-197 (1925), 



344 SOLUBLE SILICATES IN INDUSTRY 

some very successful washing of flannels has been done with washing 
powders containing silicate, and there is evidence that with control of 
ratio and concentration it may have a place both in scouring raw wool 
and in degumming silks. 143-147 

It should be pointed out, however, that the concentration of ratio 
1 : 4 of 0.25 per cent found by Fall to give maximum deflocculation had 
a pH of only 9.4 in distilled water, was scarcely perceptible to the taste 
and did not cause a slimy feeling when rubbed on the hands. Its 
alkalinity is very mild. 

In addition to its restraining action on alkali and its effect on the 
ash of textile fibers, colloidal silica in the wash resists the tendency 
of cotton goods repeatedly washed in sodium carbonate to turn gray. 
It has been assumed that the whitening action of silicate detergents was 
the result of the deposition of silica, which builds up in the fibers. If 
this were so we should expect colored goods to assume a dull or milky 
cast, but actually they are brighter than when no silicate is present. 

This may be partly due to the much lower solubility of dyestuffs in 
silicate or silicate soap mixtures than in solutions of pure soap. 148 

McDowell 149 believes that the better color of dyed goods which have 
been treated with silicate solutions is due to the deposition of a pro- 
tective film. He found indanthrene and other vat colors after kier 
treatment in the presence of silicate became insensitive to chlorine 
bleach to such an extent that goods with designs in color could be 
bleached by the methods ordinarily used for "gray" goods without the 
need of any after treatment to restore an altered color. 

Carter 150 found that the improvement in color of white goods did 
not run parallel to the increment of ash, and also that the ash could 
be almost completely removed without sacrifice of the better color in 
comparison with goods having identical treatment except for the sili- 
cate. 151-152 The explanation of this effect on color remains to be 
found, but something may be learned by analogy in considering the 
soluble silicates in bleaching processes. 

Peroxide Bleaching. Peroxide bleaching is best done in a mildly 

143 Thies, F., Z. angew. Chem., 36, 312-314 (1923) ; C. A., 17, 3424. 

144 Milson, J. R., U. S. Pat. 1,430,099 (1922). 

145 Am. Chemist, 2, 357 (1872). 

146 Van Baerle and Company, /. Soc. Arts, 20, 840 (1872).' 

147 Grothe, H., Musterzeitung, 24, 340; Chem. Zentr., 46, Ser. 3, 6, 830 (1875). 

148 Vincent, G. P., /. Phys. Chem., 31, 1305 (1927). 

149 McDowell, J. D., U. S. Pat. 1,558,104 (Oct. 20, 1925). 

150 Carter, J. D., Ind. Eng. Chem., 18, No. 3, 248 et seq. (1926). 
7ot*ii^Aj* 3ffn jCriri3.r)pl lor at 

152 Grothe, H., Musterzeitung, 24, 378 (1876) ; /. Chem. Soc., 31, 757 (1877) ; 
Chem. Zentr., 7, 92-93 (1876). 



DEFLOCCULATION AND DETERGENCY 345 

alkaline bath from which oxygen is liberated in such a way as to give 
maximum bleaching effect. When colloidal silica is present, the bath, 
though still effective for bleaching, is stabilized and does not decom- 
pose or lose oxygen on standing at the rate which obtains when alka- 
line compounds other than silicate are used. Silicates also act as pre- 
servatives and stabilizers for solid bleaching compounds which decom- 
pose in water to yield hydrogen peroxide. 153-1G1 Such are perborates, 
percarbonates, persulfates, and peroxides of the alkali metals. 

Weber 162 compared the losses of oxygen from a one-volume bath 
of hydrogen peroxide at 37° C. without the addition of alkali and 
with varying quantities of ammonia and silicate, probably about Na 2 0, 
2Si0 2 . When no ammonia or silicate was added there was no loss of 
hydrogen peroxide. With addition of 0.5 cc. of 0.897 specific gravity 
ammonia to 500 cc. of 1 volume hydrogen peroxide, the loss in 3 hours 
was 20 per cent of the hydrogen peroxide present, and ten times this 
amount gave a loss of 69.7 in the same time. Under like conditions 
with silicate the maximum loss of hydrogen peroxide in the baths was 
less than 1 per cent, i.e., probably not greater than the experimental 
error. 

Peroxide baths neutralized with silicates are suitable for bleaching 
wool, silk, cotton, and rayon, or fabrics in which these fibers are mixed. 
When a close adjustment of alkalinity is necessary, baths should be 
made up a day before using because the silicate solutions are more 
alkaline when first made up than they are after coming to equilibrium. 

The experiments shown in Figure 158 were made in the absence 
of fiber, but trials with 135 to 180 kilos (300 to 400 pounds) of wool 
showed that one third the cost of hydrogen peroxide can be saved by 
neutralizing with silicate of soda. 163 

"If too much silicate is used, it will give a yarn rather harsh to the 
touch ; for example, 2.265 kilograms of silicate to 90.86 liters hydro- 



153 
154 
155 



Schaidhauf, Alois, U. S. Pat. 1,225,872 (May 15, 1917). 

154 Wade, Harold, Ger. Pat. 152,366 (Oct. 21, 1920) 

" Kind, W., Seifensieder Ztg., 42, 598-599 (1915) ; C. A., 9, 2971 ; Textilberichte, 
2, 325-326 (1921) ; C. A., 16, 2416. 

159 Palmetto, Textile World J., 52, No. 17, 29 (1917) ; C. A., 11, 1550. 

'"Deutsche Gold und Silber Scheideanstalt, Ger. Pat. 357,956 (March 13, 
1919); Chem. & Met. Eng., 28, 33 (1923); Aus. Pat. 98,668 (May 29, 1922); 
Brit. Pat. 196,839 (June 6, 1922) ; C. A., 17, 3760. 

158 Moore, K. R., Am. Dyestuff Reptr., 7, No. 19, 11, 16-17 (1920) ; C. A., 15, 

159 Surpass Chem. Co., Brit. Pat. 158,531 (1920). 

160 C. A., 15, 2000. 

1(31 Roessler, Ger. Pat. 357,956. 

162 Weber, G., /. Soc. Dyers Colourists, 39, 209-214 (1923). 

163 Weber, he. cit. 



346 



SOLUBLE SILICATES IN INDUSTRY 



gen peroxide (5 pounds of silicate to 20 gallons hydrogen peroxide), 
12 volumes, will give a harsh yarn. But it is possible to use silicate 
of soda and obtain a bleached wool beautifully soft and full, unim- 
paired in every way, and for this only 0.453 kilogram silicate of soda 
(1 pound) should be used for 90.86 liters of 12 volume hydrogen 
peroxide. The white obtained also is better than that given with a bath 
neutralized with ammonia. In addition, it has a protective influence, 
and any iron which may accidentally be present in the goods or any 
copper in the form of stains, will not damage the fiber in the presence 
of silicate of soda. The bath will last with continuous replenishing for 
one week to a month, depending on the quality of the yarn used. 



















\***^£=: 








































































ISa KH,OH 
ID.. (f#,Olt 



£().. NH f O" 



Fig. 158. — Deterioration of Peroxide Baths Neutralized with Ammonia and Silicate 

of Soda. 



Piece goods are bleached in jiggers; a six volume bath gives the best 
results, and here again silicate of soda should be used for neutralizing. 
Hydrogen peroxide gives equally good results with botany or cross- 
breds, either with yarn or finished goods. 

"In order to obtain uniform results, it is important to standardize 
the methods of working for the particular quality of the goods under 
treatment, using the weight of goods as a basis. 164 The same concen- 
tration of liquor, the same quantity of sodium silicate, and the same 
temperature should be used for each lot." 

The action of hydrogen peroxide is catalytically stimulated by ferric 
oxide, often to the extent of causing holes in silk or wool fabrics on 
which particles of rust have lodged. Other substances have a similar 

1M Smolens, H. G., Oil, Paint, Drug Rep., 109, No. 13, 60 (1926). 



DEFLOCCULATION AND DETERGENCY 347 

effect and dirty goods always lose more strength than clean in hydro- 
gen peroxide bleaching. 165 

A commercial formula for cotton bleaching with sodium peroxide is 
as follows : 

To 100 gallons of cold water, add : 

4^4 lbs. 66° sulfuric acid. Heat to 100° F. and sprinkle slowly into the 

bath; 
4 lbs. sodium peroxide powder. Heat to 190° F. and add 
5 lbs. silicate of soda solution (Na0 2 , 10.5%; Si0 2 , 26.7%; Baume 42°) 

which has been previously diluted in two gallons of warm water. 

The protective action of silicates is probably due primarily to their 
ability to keep ferric hydroxide deflocculated 166 and thus unable to 
exert a local action, but inasmuch as the same action of silicates may 
be observed in cotton boiling with sodium hydroxide, in washing with 
soap, and in bleaching, it seems likely that the negatively charged silica 
tends to surround positively charged particles of ferric compounds 
with a film which prevents their adherence to fibers bearing a negative 
charge. If the film should form, it would mechanically prevent floc- 
culation and appearance of the iron in spots. The protective action 
is not sufficient to prevent damage if actual rust specks are dropped 
on the fabric during bleaching. Silicates of very low iron content are 
demanded for this use, but it is doubtful if the iron ordinarily present 
in commercial silicates would do other harm than to increase the rate 
of liberation of oxygen. This is, however, important in some factories 
where the routine is on a strict time schedule. 

Silk may be bleached in a bath containing peroxide, silicate, and soap 
for 8-12 hours at 50° C. 167 ' 168 

Peroxide baths can be used to bleach whites in striped goods where 
the color may be fast to peroxide and sensitive to chlorine bleach. They 
are also of use for stripping colors which are sensitive to peroxide. 169 " 171 

Smolens 172 has found that wool and silk as well as their mixtures 
with cotton may be advantageously bleached in baths containing more 
peroxide and much more silicate than formerly thought permissible, 

165 Heermann, P., Z. angew. Chem., 36, 107 (1923) ; Z. dent. 61- Fett-Ind., 41, 
No. 22, 338-341 (1921). 

16fl Griin and Jungmann, Seifenfabrikant, 37, 507-510, 529-531, 553-555, 579-581, 
603-606 (1917) ; C. A., 12, 2693. 

187 Emmons, Am. Dyestuif Rep., 382-384 (1923). 

188 Ley, "Seidenf arberei," Berlin : Julius Springer, 1921, p. 53. 
160 Humphries, R., Textile Recorder, 28, 11-13 (1925). 
170 Reichert, J. J., Brit. Pat. 176,747 (June 13, 1921) ; C. A., 16, 2418. 

171 Kind, W., Seifcnsieder Ztg., 49, 761-762, 773-774, 785-786, 798 (1922) ; C. A., 
■ 17, 892. 

172 Smolens, H. G., personal communication. 



348 



SOLUBLE SILICATES IN INDUSTRY 



thus securing good color in a short time without as much injury to 
the fiber as might have come from a weaker bath in a longer time. 
Peroxide solutions which have been stabilized with phosphoric acid 




Fig. 159. — Effect on Cheesecloth of Sodium Hypochlorite Treatment with and 

without Silicate. 

and neutralized with silicate solutions have the advantage of contain- 
ing a buffer salt in addition to the silicate. This simplifies the control 
of baths which are continuously replenished by the addition of re- 



o Z 
j "J 



— o 

< Z 



V, 

lv£ 

\ 
\ 
\ 

\ 

\ 



TIME IN MINUTES 



Fig. 160. — Effect on Cheesecloth of Sodium Hypochlorite Treatment with and 

without Silicate. 

agents and increases the life of those which are used to exhaustion. 
Electrolytes have an unfavorable effect on the color obtainable and 
as the disodium phosphate formed is a poor electrolyte the phosphoric 
acid-sodium silicate bath is one of the most efficient. 173 

Hypochlorite Bleaching. Sodium hypochlorite, unlike hydrogen 
173 Smolens, H. G., Oil, Paint, Drug Rep. (March 22, 1926). 



DEFLOCCULATION AND DETERGENCY 



349 



peroxide, is stabilized by silicate solutions only in the presence of 
bleachable material, but Carter 174 found that the weakening action 
of hypochlorite bleach was decreased by putting silicate solutions into 
the bleaching bath when the chlorine value is high enough to cause 
rapid attack on cotton goods. The effect on color is marked. When 




Fig. 161. 



-Effect of Silicate with Sodium Hypochlorite Bleach on Sheets of 

Sulfite Pulp. 



silicate is present a given amount of hypochlorite yields a much whiter 
colored cotton independent of the increment of ash. 175 

Wood pulps made by the sulfite process Carter found to give better 
colors when silicates were added to calcium hypochlorite baths. The 
results thus secured were better than could be had with any concen- 
tration of calcium hypochlorite alone. 

Table 104. Silicates Used in the Folloiving Tests. 





Per Cent 


Per Cent 








No. 


Na 2 


Si0 2 


Mol 


. Ratio 


°Be. 


1 


10.5 


26.7 


1: 


2.60 


42 


2 


19.4 


30.6 


1: 


1.62 


58.8 


3 


8.9 


29.0 


1: 


3.33 


41 


4 


13.7 


32.9 


1 


2.56 


52 


able 105. Chlorine Values 


of Hypochlorite Solutions 


with and 


zmthout Silic 




Chlorine Va 


ue, Grams in 25 cc. 
After Warm- 








Silicate No. 1 




ing to 49° C. 




Loss o 


f Chlorine 


Grams 


Original 


for 1 Hour 




Gram 


Per Cent 





0.04342 


0.04342 




None 


None 


0.25 


0.04342 


0.04342 




None 


None 


0.5 


0.04342 


0.04342 




None 


None 


1 


0.04342 


0.04342 




None 


None 


3 


0.04342 


0.04342 




None 


None 


5 


0.04342 


0.04342 




None 


None 



174 Ind. Eng. Chem., 18, 248 (1926). 

175 Mandelbaum, R., Ger. Pat. 330,192 (1920) ; C. A., 17, 858. 



350 



SOLUBLE SILICATES IN INDUSTRY 



Table 105. Changes in Chlorine Value of Hypochlorite Solutions with am 

without Silicate — (Continued) . 

Chlorine Value, Grams in 25cc. 



Silicate No. 1 




After Warming 


Loss 


of Chlorine 


Grams 


Original 


To 49 c 


C. for 3 hours 


Gram 


Per Cent 





0.04175 




0.04033 


0.00142 


2.5 


0.5 


0.04175 




0.04033 


0.00142 


2.5 


3 


0.04175 


Boile 


0.04033 
d 20 minutes 


0.00142 


2.5 





0.04000 




0.03858 


0.00142 


3.5 


0.5 


0.04000 




0.03858 


0.00142 


3.5 


1 


0.04000 




0.03575 


0.00425 


10.6 


3 


0.04000 




0.03781 


0.00319 


7.9 


5 


0.04000 


Stood 


0.03823 
open 1.5 hours 


0.00177 


4.4 





0.04400 




0.04224 


0.00176 


4.0 


0.25 


0.04400 




0.04224 


0.00176 


4.0 


0.5 


0.04400 




0.04331 


0.00069 


1.6 


1 


0.04400 




0.04367 


0.00033 


0.7 


3 


0.04400 




0.04331 


0.00069 


1.6 


5 


0.04400 




0.04261 


0.00139 


3.2 






Boiled 1 hour 









0.03857 




0.03716 


0.00141 


3.6 


0.5 


0.03857 




0.03680 


0.00177 


4.5 


1 


0.03857 




0.03716 


0.00141 


3.6 


3 


0.03857 




0.03680 


0.00177 


4.5 


5 


0.03857 




0.03645 


0.00212 


5.5 




Warmed to 


38° C. for 2.5 ho 


urs 







0.03290 




0.03115 


0.00175 


5.3 


1 


0.03290 


38°C. 


0.03115 

for 2.5 hours 


0.00175 


5.3 





0.11575 




0.11257 


0.00318 


2.7 


1 


0.11575 


Stood 


0.11257 
open 2.5 days 


0.00318 


2.7 





0.11575 




0.08868 


0.02707 


23.3 


1 


0.11575 




0.09062 


0.02613 


21.7 



Four similar tests gave similar results. 



Table 106. Chlorine Value in 5° Baume Calcium Hypochlorite Solutions in Presence 
of 10 Grams Unbleached Wood Pulp with and without Silicate. 



Grams 



Hypochlorite Solution 



Chlorine Value Remaining 
Without With 1 Gram 

Silicate Silicate No. 3 



32 


Open 1 day 


None 


0.0177 


40* 


Open 2 days 


0.0354 


0.1062 


40* 


Open 2 days 


0.0354 


0.0708 


50 


Closed 1 day 


0.0088 


0.0708 


50 


Open 1 day 


0.0088 


0.0880 


60 


Open 2 days 


None 


0.0265 


40 


Open 20 hours 


0.0354 


0.0531 


40 


Closed 2 days 


0.0177 


0.0354 



* Different pulps were used in these two tests. 



DEFLOCCULATION AND DETERGENCY 



351 



Table 107. Effect of Silicate on Decomposition of Hypochlorite in Presence of 

Bleached Cellulose. 

Chlorine Value, Grams in 25 cc. 







After 








Silicate No. 1 




Warming 


Minutes 


Loss c 


)f Chlorine 


Grams 


Original 


to49°C. 


Warmed 


Gram 


Per Cent 





0.19822 


0.19043 


10 


0.00779 


3.9 





0.19822 


0.18866 


30 


0.00956 


4.8 





0.19822 


0.18406 


60 


0.01416 


7.1 





0.19400 


0.18692 


30 


0.00708 


3.6 


0.5 


0.19400 


0.18692 


30 


0.00708 


3.6 


1 


0.19400 


0.18833 


30 


0.00567 


2.9 


5 


0.19400 


0.18656 


30 


0.00744 


3.8 


10 


0.19400 


0.18610 
To 82 °C. 


30 


0.00790 


4.7 





0.06830 


0.05166 


10 


0.01664 


24.3 





0.06830 


0.05166 


10 


0.01664 


24.3 





0.06830 


0.05024 


10 


0.01806 


26.4 


0.5 


0.06830 


0.05343 


10 


0.01487 


21.7 


1 


0.06830 


0.05343 


10 


0.01487 


21.7 


2 


0.06830 


0.05131 


10 


0.01699 


24.8 


3 


0.06830 


0.05237 


10 


0.01593 


23.3 


4 


0.06830 


0.04777 


10 


0.02053 


30.0 


5 


0.06830 


0.05308 


10 


0.01522 


22.2 


6 


0.06830 


0.05267 


10 


0.01563 


22.8 


7 


0.06830 


0.04316 


10 


0.02514 


36.8 


8 


0.06830 


0.05024 


10 


0.01806 


26.4 


9 


0.06830 


0.05308 


10 


0.01522 


22.2 


10 


0.06830 


0.05024 


10 


0.01806 


26.4 



In this case the silicious precipitate appears to be the effective agent. 
Other alkaline earth salts could be substituted with good effect. When 
less than the full effect of the bleach was secured it was found that 
the silicate was about equal to 1/3 of the bleach. The results could 
not be obtained by substituting sodium carbonate for silicate, though 
sodium hydroxide with calcium hypochlorite gave better colors than 
calcium hypochlorite alone. The best colors were obtained when silicate 
was used. 176 ' 177 ' 178 

Vincent 179 is of the opinion that the conservation of strength of 
cotton fabrics bleached with hypochlorite in the presence of silicates is 
simply a case of the action of alkali. The unstable hypochlorite forms 
nascent oxygen, the real bleaching agent, according to the following : 



NaCIO + HOH 
HCIO 



NaOH + HCIO 
HC1 + (O). 



176 Anon., Textilechem. Color., 633 (May, 1922) ; hid. Chimique, 9, 407; C. A., 
16, 4354. 

Forbes, E., U. S. Pat. 1,401,901 (1921) ; C. A., 16, 1017. 



178 Polleyn, F., "Dressings and Finishing for Textile Fabrics," London 
Greenwood, 1911, p. 177. 



Scott, 



7. Phys. Chem., 31, 1310 (1927). 



352 SOLUBLE SILICATES IN INDUSTRY 

The activity of the solutions is increased by acids and depressed by 
alkalies so that the silicate would tend to conserve chlorine by keeping 
it from reacting - . The same argument would apply to the observed im- 
provement of fabric strength in the presence of silicate, but would 
not account for the observation that even though the bleaching reaction 
may be less the color attained is better. Evidently the silica has some 
part in this phenomenon, which is, after all, the one of industrial im- 
portance. If the bleacher can use less chlorine, reduce the loss of fiber 
strength, and at the same time obtain a better white, he has gained on 
three counts. Vincent postulates a gain in strength due to silica ad- 
sorbed on the fibers, which needs proving. 

The increase of ash is very small in the first few treatments and the 
increase of strength is marked. It might be due to a mercerizing 
action. Further, the character of silica deposited on the fiber as a 
hydrous, amorphous, and tenuous layer is not such as to lead one to 
expect it to cause an appreciable effect on strength. The differences in 
strength with and without silicate increase with the number of treat- 
ments both in detergent and bleaching experiments as the amount of 
silica retained also gains, but the concept of a protective action of 
silica seems more tenable than the idea of silica's adding much strength 
to cotton fibers. The strength of papers may indeed be improved 
by silicious deposits, but this is probably a cementing action. 

Vincent showed the improved color of fabrics bleached with hypo- 
chlorite in the presence of silicate to be due to the more ready removal 
of colored material, not identified, which appears to be a by-product of 
the bleaching. This may be due to a protective action, which prevents 
its adsorption or absorption during bleaching which would be expected 
if the silica were deposited as a film. He says this is unquestionably 
an advantage and sufficient reason for adding silicate to bleaching 
solutions. 

Silicates in Detergent Practice. 
Silicates Alone. 

Overall Washing. Silicate solutions alone have a limited use in 
cleansing operations. They are suitable for reclaiming oily cotton 
waste of the sort employed for cleaning machinery. Mechanics' over- 
alls and other very dirty textiles are well cleaned with Na 2 0, 3.3 Si0 2 
to Na 2 0,4Si0 2 in hot solutions containing about 2 per cent solids. 180-183 

Neueste ErHndnngen u. Erfahrungen, 2, 69 (1875). 
Stericker, Wm, Ind. Eng. Chem., 15, No. 3, 244 (1923). 
Meyer, R., Dingier 's Polyt. J., 227, 280-289 (1878) ; Chem. Zentr., 9, 281-282; 
/. Chem. Soc., 34, A, 534-535 (1878). 

183 Kunheim, L., Polyt. Centralblatt, 414 (1857) ; Chem. Zentr., 28, 288. 



180 
181 
182 



DEFLOCCULATION AND DETERGENCY 353 

Metal Cleaning. For vigorous detergent action where there is no 
risk of damage to the material cleansed, as in preparing metals for plat- 
ing or enameling, sodium metasilicate is useful. 184 Staley 185 used a 
more silicious silicate and rated it below trisodium phosphate 
(Na 3 P0 4 ) without considering whether other silicates would or would 
not fall into the same relative position. This is a good example of the 
risk of ignoring the great differences between silicates of different 
composition. 

De-inking Printed Paper. The removal of printers' ink from 
paper without attack upon mechanical wood pulp, so that white paper 
may be made from waste, can be accomplished with Na 2 0, 3.3Si0 2 in 
a solution of less than 1 per cent, either hot or cold. 186-189 The paper 
is pulped, soaked in the silicate, washed, and remade into paper. The 
pigment is deflocculated and washed away. Stronger reagents can be 
used on paper made from chemical pulp. 

The effect of silicate ratio on de-inking of paper was studied by 
Briggs and Rhodes, 190 who proposed their technic of measuring color 
of the de-inked paper as an index of detergent power. This requires 
the assumption that ink is a typical dirt, to which the present writer 
cannot assent and while a more representative material might be sub- 
stituted it would be very difficult to standardize all the variables to a 
satisfactory degree. 

Their comparison of de-inking reagents shows silicate solutions to 
be effective and suggests the degrees in which other materials approach 
the detergent action of soap. It should be noted that a suspension of 
fullers' earth in sodium hydroxide solution contains sodium silicate. 

184 See also: Hutchins, Nancy A., U. S. Pat. 930,965 (Aug. 10, 1909). 

185 Staley, H. R, The Ceramist, 6, 554-560 (1925) ; Ceram. Abstracts, 4. 332. 

188 Jespersen, T., U. S. Pat. 1,424,411 (Aug. 1, 1922) ; C. A., 16, 3394; cf. Paper, 
35, 510. 

187 Stutzke, R. W. G., U. S. Pat. 1,545,707 (July 14, 1925). 

^Henkel, Hugo, and Otto Gessler, U. S. Pat. 988,874 (April 4, 1911). 

^Bancroft, W. D., Chem. & Met. Eng., 23, 454-456 (1920). 

190 Colloid Symposium Monograph, New York: Chemical Catalog Co., 4, 311 
(1926). 





White- 


De-Inking 


Concentration 


ness 


(Per Cent) 


5 grams per liter 


0.79 5 


100 


10 grams per liter 


0.76 4 


95 


OAN 


0.72! 


84 


5 grams per liter 


0.71 7 


83 


0.1N 


0.715 


82 


0.02N 


0.70o 


78 


OAN 


0.69 3 


75 


10 grams per liter 


O.683 


71 


0.02N 


O.680 


70 


OAN 


0.67« 


69 


10 grams per liter 


0.66s 


65 


10 grams per liter 


0.64 4 


55 


OAN 


0.62 8 


46 




O.6O3 


30 


10 grams per liter 


0.59 7 


26 


0.01JV 


0.56, 





O.OliV 


0.56o 





O.OliV 


0.55 





(Saturated) 


0.55a 






354 SOLUBLE SILICATES IN INDUSTRY 

Table 108. Comparison of Detergents. 

50 grams of printed paper pulped 30-40 minutes in 1 liter of solution. 

Pulped, washed. 

Pulping Solution 

Sodium oleate 

Fullers' earth in 0.02iV NaOH 

Sodium silicate, "O," Na 2 3.3Si 2 0, 

1.39 specific gravity 
Sodium resinate 
Sodium hydroxide 
Sodium hydroxide 
Borax 

Gelatin in 0.02AT NaOH 
Sodium hydroxide (70° -55°) 
Sodium carbonate 
Gum arabic 
Gelatin 
Sucrose 
Distilled water 
Egg albumen 
Sodium chloride 
Calcium chloride 
Aluminum chloride 
Calcium hydroxide 

The comparison of three commercial ratios did not show a marked 
superiority of any one. 

Table 109. De-Inking with Sodium Silicate. 

10 grams paper pulped 30 min. Pulped, washed in water. 
Concentration Whiteness 

Equivalents Na 2 "S" Brand "O" Brand "C" Brand 

per Liter Si0 2 : Na 2 0=3.89 Si0 2 : Na 2 0=3.23 Si0 2 : Na 2 O=2.0 

0.2 0.69e .... 0.63 

0.1 0.73 0.72 3 0.70o 

0.05 0.7L. 0.71a 

0.02 0.69„ 0.69 0.69 

Silicates in Conjunction with Other Materials. 

Sodium Hydroxide. Kier boiling of cotton is done with sodium 
hydroxide as the primary reagent. Five per cent on the weight of the 
goods is usual. Up to 1 per cent of Na 2 0, 3.3Si0 2 , because it assists 
emulsification and prevents rust stains, has found place in commercial 
practice. More alkaline silicates are also used. 191 ' 192 

Sodium Chloride. Sodium chloride added to silicate solutions has 
the property of flocculating grease and insoluble dirt to a degree which 

^Beltzer, F. J. G., Rev. gencr. chim., 12, 285-298 (1909); Chcm. Zentr., 80, 
1597; C. A., 4, 237-238. 

182 Trotman and Thorp, "The Principles of Bleaching and Finishing Cotton," 
Philadelphia, Pa.: Lippincott, 1911, p. 109. 



DEFLOCCULATION AND DETERGENCY 355 

makes it useful as a rough test for following the progress of a wash- 
ing operation. A measured amount of wash liquor is treated with salt 
brine, centrifuged, and the volume of precipitate taken as an index. 193 
Salt also has the property of preventing the adherence of oily dirt to 
metal surfaces, as the buttons of overalls, or the drums or shells of 
metal washing machines. Very satisfactory cleansing of overalls was 
obtained as follows : 194 

1st bath — Cold rinse in 8 inches water (with load) 5 min. 

2nd bath — 8 inches water 82°C, 4.53 kilograms (10 pounds) silicate 

of soda and 4.53 kilograms sodium chloride, 15 min. 
3rd bath — 10 inches water 82°C, 3 min. 
4th bath — Repeat second bath. 
Enough 5-min. hot rinses until last rinse comes clear from wash 

wheel. 
This formula is used in a 36 x 54 wheel, 50 overalls to the load. 

The single objection to this method lies in the labor required to 
polish metal parts of machinery on which this solution has dried before 
rinsing. 

The same idea is of use in making platers' cleaning solutions. Sodium 
metasilicate and salt will remove obstinate grease films and leave sur- 
faces in condition to receive films of electro-deposited metals or of paint. 

Sodium Carbonate. Since 1876 mixtures of sodium carbonate and 
silicate have been on the market as detergents. 195 In Germany, the name 
"Bleichsoda" (bleaching soda) is applied. It antedates any washing 
powder containing active oxygen or chlorine and depends upon the fact 
that it prevents discoloration from rust and has a gradual whitening 
effect on fabrics resulting from the action, not yet fully explained, of 
colloidal silica. 195-200 A typical material of this sort is a powder con- 
taining the following : 

23 per cent Na 2 0, 3.4Si0 2 , 1.35 specific gravity (38° Baume) 
57 per cent Na 2 CO 3 .10H 2 O 
20 per cent Na 2 C0 3 

Aluminum Oxide. Since colloidal properties are recognized as help- 
ful in detergent operations, the idea that the ability to act as a mordant 

193 Wakefield, citation in Silicate P's & Q's, 5, No. 6 (1925), Philadelphia, Pa.: 
Philadelphia Quartz Company. 

194 Schupp, Arthur R, Am. Inst, of Laimdr., Quarterly, 26 (October 15, 1924). 

195 Bailey, Broadus, U. S. Pat. 1,635,244 (July 12, 1927). 

196 Welter, A., Brit. Pat. 136,841 (Dec. 18, 1919) ; C. A., 14, 1416. 

197 Mayer, "Das Wasserglas," 33, Friedr. Vieweg & Sohn Akt.-Ges., Braun- 
schweig (1925). 

138 Geisenheimer, G., Compt. rend., 118, 192-194 (1894); abstracts in /. Ckem. 
Soc., 66, 189; Chem. Zentr., 65, 456; J. Soc. Chem. Ind., 13, 727; Chem. News, 
69, 69. 

m Beltzer, F. J. G., Rev. chim. ind., 21, 233-238 (1910); C. A., 4, 2982-2983 
(1910). 

""Kuhl, H., Seijensieder Ztg., 45, 459 (1918). 



356 SOLUBLE SILICATES IN INDUSTRY 

could be added to a carbonate-silicate mixture by introducing aluminates, 
which also yield colloidal solutions, is attractive. These compounds have 
found a rather limited place in laundering because they are more costly 
and have little advantage over the mixtures which contain carbonate 
and silicate only. The loss of strength in cotton, wool, and silk is said 
to be less than with sodium carbonate, which is also true of the car- 
bonate and silicate mixtures. 201-204 The aluminous compound from a 5 
per cent solution did not injure the goods when they were ironed with- 
out rinsing. Special merits claimed for various silicate mixtures would 
outrun the scope of the present treatise, it is obvious that many permu- 
tations of detergent substances may be useful. 205-207 

Silicates and Soaps. 

Historical. Thus far we have considered silicated washing reagents 
from the viewpoint of detergent action. This is fundamentally sound, 
but the maker of soaps must consider also their appearance and the 
conditions of their manufacture. Sheridan 20S took out the first patent 
for a silicated soap in 1835. Thomas followed in 1856, 209 but in this 
country it was not until the period of the Civil War, 1861-1865, that the 
practice assumed any considerable importance. At that time the supply 
of rosin from the southern states was shut off from northern soap fac- 
tories, which, together with high prices and general shortage of fats, 
induced the use of silicates to extend the available supply. 

When there was no longer a shortage, the use of silicates in soap 
continued in vogue and the total amount steadily increased until again 
during the World War the necessity of conserving fats as comestibles, 
particularly in central Europe, caused a larger reliance on silicates 
for detergent work. Upon the return of peace the experience gained 
during the emergency gave the silicated washing materials a still 
stronger foothold and they are to-day accepted by the public with great 

201 Kayser, Adolf, Brit. Pat. 6934 (March 23, 1909) . 

302 Guernsey, F. H., U. S. Pat. 1,419,625 (June 13, 1923) ; C. A., 16, 2761; Brit. 
Pat. 200,175 (July 4, 1923). 

203 Cowles, U. S. Pat. 1,445,004 (Feb. 13, 1923). 

204 Guernsey, F. H., Am. Dyestuff Rep., 12, 176-181, 208, 217-218, 277-280, 438- 
439, 496-497, 563-570 (1923). 

205 Marcus, Robt., Ger. Pat. 322,088 (Aug. 22, 1917) : C. A., 15, 2160. 
208 Ewe, Geo. E., Pract. Drug. 41, No. 3, 22-23 (1923) ; C. A., 17, 1861. 
^Barlocher, Otto, Ger. Pat. 318,151 (May 4, 1918) ; C. A., 15, 1974; Ger. Pat. 

314,909; C. A., 15, 1974. 

208 Sheridan, Joseph Charles, Brit. Pat. 6894 (1835). 

208 Simmons, Wm. H., "Soap, Its Composition, Manufacture, and Properties," 
p. 66, London: Pitman, 1917. 






DEFLOCCULATION AND DETERGENCY 



357 



freedom when offered side by side with soaps which contain no 
silicate. 210 - 214 

Boiled Soap. When soap has been finished by boiling with suc- 
cessive changes of alkali and separated from the liquors containing the 
glycerin, it is usually delivered to a mixing device called a crutcher 
which assures its homogeneity. While the soap is hot and viscous and 
under agitation of a heavy stirring device, the silicate is put in. The 
first effect is to thin the soap, but if the amount and quality are appro- 
priate to the soap in question, and the temperature is right, an unctuous 
texture develops quickly and the soap is smoother than before. 

As soap and silicate are not miscible in all proportions, it is necessary 




Fig. 162. — Crutching Silicate into Soap (Top View) 



to have regard to several factors in adding silicate. In general, softer 
fats yield soaps which will carry less silicate. Hydrogenated oils carry 
less than tallow. The more silicious silicates are able to take up alkali 
from the soap colloid and this may lead to a grainy condition in which 
soap and silicate are separated, a part of the silicate in the continuous 
phase. This condition may be obviated by proper selection of the grease 
stock on the one hand — harder stock for highly silicated soaps — and on 
the other, by adjustment of alkali. Na 2 0,2Si0 2 in solution mixes freely 

210 G. E. J., Seifenfabr., 39, 253-256 (1919) ; C. A., 13, 2770. 
m Guillin, R., Report of lab., Soc. des Agriculteurs (France: 1917-8); Bull., 
Soc. des Agriculteurs (France: 1919) ; C. A., 13, 2409. 

212 P. L., Seifensieder Ztg., 49, 623-624; C. A., 17, 1160; Oil Colour Trade J., 
1221 (1922). 

213 Mayer, loc. cit., 3. 

** Seifensieder Ztg., 29, 775 (1908). 



358 



SOLUBLE SILICATES IN INDUSTRY 



with a well saponified stock. Many soapmakers practice the addition of 
varying amounts of sodium hydroxide to silicate of the approximate 
composition Na 2 0, 3.3Si0 2 in order to make smoother mixtures. 215 ' 216 
These generally work out to an amount of sodium hydroxide less than 
that required to bring the ratio to Na 2 0,2Si0 2 . The relatively stable 




Fig. 163. — Drawing Hot Silicated Soap from Crutchers into Frames. Same 

apparatus as foregoing picture. 

behavior of Na 2 0,2Si0 2 when mixed with soap suggests the presence of 
sodium disilicate or possibly NaHSiOo in which the alkali-silica ratio 
is the same. It should be pointed out that a considerable time after mix- 
ing is necessary for the silicate-caustic solution to come to equilibrium 
and, as indicated in discussing the constitution of silicate solutions 

a5 Gathmann, H., "American Soaps," Chicago: Gathmann, 1893, p. 72, 187, 
214, 236. 

ae Leimdorfer, J., Kolloidchem. Beihefte, 2, 343-398 (1911). 



DEFLOCCULATION AND DETERGENCY 



359 



(Chapter II), it is not proven that, even then, the solution is identical 
with one made by dissolving glass of the same ratio. 

The concentrations at which silicate is added to soap vary widely; 
Na 2 0,2Si0 2 may be put in as a viscous liquid at 17 specific gravity, 
and lower concentrations of this and the more silicious types of silicate 
are employed according to the final result desired. 

The amounts put into twenty brands of laundry soap sold on the 




Fig. 164. — Silicated Soap after Removal of Frames. 

American market in 1922 averaged 11.86 per cent anhydrous silicate in 
the finished soap and ranged from 1 to nearly 25 per cent. 217 

After soap and silicate have been well incorporated in the crutcher 
the mass is run into frames to cool, as shown in the illustration. Here 
separation may take place if the mixture is unstable. To avoid this it 
is well to let the soap leave the crutcher at as low a temperature as is 
consistent with clearing the apparatus, and to cool the frames as rapidly 
as convenient. The frames should also be taken at once to a place 
where they can remain undisturbed till the soap has fully set and the 
sides can be stripped off ready for cutting into bars and cakes. Devices 

217 Federal Trade Com. vs. Procter and Gamble, Docket 852, Exhibit No. 16. 



360 SOLUBLE SILICATES IN INDUSTRY 

which chill the hot soap by refrigeration so that it solidifies in a few 
minutes are applicable to silicated soaps. 218-246 

Cold Made Soaps. Although a large proportion of commercial soap 
is made by boiling with sodium hydroxide solutions and salting out the 
soap curd, other methods are also compatible with the use of silicates. 

218 Storer, F., Chem. News, 8, 17 (1863); Repertoire de chimie applique, 5, 
5-7 ; Poly. J., 168, ser. 4, 18, 463-464. 

219 Poly. J., 178, 416 (1865) ; Chem. Zentr., 37, n.s., 11, pt. 1, 559-560 (1866). 

220 Schnitzer, Guido, Poly. J., 203, ser. 5, 3, 129-132 (1872) ; Le Moniteur scien- 
tifique, 14, ser. 3, 2, 350-352 (1872) ; J. Chem. Soc, 25, 10, 340 (1872). 

^Droux, M. S., Am. Chem., 4, 438 (1874). 

222 Kingzett, Charles Thomas, "History, Products and Processes of the Alkali 
Trade," Longmans, 1877, p. 175-177. 

223 Muspratt, James Sheridan, "Encyclopedia of Chemistry," 2, Philadelphia, 
Pa. : Lippincott, 1877-80, 779-780. 

224 Artus, Willibald, "Grundziige der Chemie in ihrer Anwendung auf das prak- 
tische Leben," 64, Wien : Hartleben's chemisch-technische Bibliothek, 1880, 
p. 247-248. 

223 Pro. Am. Pharm. Ass., 31, 68 (1883). 

226 Brannt, William T., "Practical Treatise on the Manufacture of Soap and 
Candles," Baird, 1888, 218-219, 382-385, 408-409, 421-422. 

227 Engelhardt, Alwin, "Handbuch der praktischen Toiletteseifen-Fabrikation," 
163, Wien: Hartleben's chemisch-technische Bibliothek, 1888, 109-110. 

228 Gadd, W. Lawrence, "Soap Manufacture," G. Bell, Technological hand- 
books, 1893, p. 106-112. 

229 Carpenter, William Lant, "Treatise on the Manufacture of Soap and Candles, 
Lubricants and Glycerin" (2nd ed., E. & F. N. Spon, 1895), 143-145, 198-200. 

230 Engelhardt, Alwin, "Handbuch der praktischen Toiletteseifen-Fabrikation," 
136, 137, Wien: Hartleben's chemisch-technische Bibliothek, 1896, 49-50, 350-351, 
185-187 

231 Cameron, James, "Soaps and Candles," 2nd ed., Churchill, 1896, 27-31, 111-115. 

232 Hurst, George H., "Soaps ; a Practical Manual of the Manufacture," London : 
Scott, Greenwood, 1898, 47-49, 243-244, 309-311, 342-344, 359-360. 

233 Bach, Karl, Neueste Erfindungen und Erfahrungen, 29, 81 (1902). 

234 International Correspondence Schools, Scranton, Pa., Chem. Tech., 3, Inter- 
national library of technology, 18-20, 2 ser. 44, 3-5 (1902). 

235 Andes, Louis Edgar, Neueste Erfindungen und Erfahrungen, 30, 100-102 
(1903) ; "Praktisches Rezeptbuch fur die gesamte Fett-, 01-, Seifen- und Schmier- 
mittel-Industrie," Wien: Hartleben's chemisch-technische Bibliothek, 1909, 56-88, 
186-190. 

23a Stiepel, C, Seifenfabr., 24, 225-227; Chem. Zentr., 75, 1, 1112 (1904). 

237 Ubbelohde, Leo, "Handbuch der Chemie und Technologie der Ole und Fette," 
1-3, pt. 2, Leipzig: Hirzel, 1911, 592-596. 

238 Z. angew. Chemie, 21, pt. 1, 1025 (1908). 

230 Peter, Julius, Z. angew. Chemie, 26, pt. 2, 138 (1913). 

240 Schmidt, R., Z. angew. Chemie, 26, pt. 2, 311 (1913). 

241 Simmons, William H., "Soap ; Its Manufacture, Composition, and Properties," 
London: Pitman, 1917, 25-26, 66. 

243 Lamborn, L. L., "Modern Soaps, Candles, and Glycerin," 3rd ed., New 
York: D. Van Nostrand & Co., 1918, 115-118. 

M Schuck, E., Am. Perfumer, 14, 355-356 (1919) ; C. A., 14, 854. 

244 Wiltner. Friedrich, "Die Fabrikation der Toilettseifen und der Seifen- 
snezialitaten," 3rd ed., Wien : Hartleben's chemisch-technische Bibliothek, 1920, 
179-180. 

245 Wright, Charles Romley Alder, "Animal and Vegetable Fixed Oils," 3rd ed., 
Griffin, 1921, 834-835. 

^Deite, Carl, "Handbuch der Seifenfabrikation," 5th ed., Berlin: Springer, 
1921. 



DEFLOCCULATION AND DETERGENCY 361 

So-called cold soaps, in which all the products of reaction are included 
in the cake, have a limited use and have long been made with silicate. 
Typical formulas are the following : 

33.98 kilograms (75 pounds) tallow 

11.33 " (25 " ) coconut oil 

33.98 " (75 " ) caustic soda 35.5°Baume 

56.63 " (125 " ) NaaO, 3.34Si0 2 , 41°Baume 

9.06 " (20 " ) potassium carbonate sol. 36°Baume 



144.98 kilograms (320 pounds) Soap 

33.98 kilograms (75 pounds) tallow 

11.33 " (25 " ) coconut oil 

31.71 " (70 " ) caustic soda 35.5°Baume 

45.3 " (100 " ) Na 2 0,3.34Si0 2 , 41°Baume 

7.70 (17 " ) potassium carbonate 36°Baume 



130.02 " (287 " ) soap 

Refined cottonseed oil up to 30 to 50 per cent can be substituted for 
an equal weight of tallow, if the tallow is hard. If the tallow is soft 
or mixed with grease, less oil should be used. The soap will not be 
quite so hard and will take longer to harden, but it will be a good wash- 
ing soap. In these formulas the amounts of caustic are calculated so as 
to include the proper excess for the silicate to take up. 

Potassium carbonate is used in these soaps to improve texture and 
solubility. Sodium carbonate can be substituted at the cost of less 
attractive appearance. 

Fatty acids are also directly saponified with sodium carbonate or 
silicate or mixtures of these. This method is advantageous where 
soaps are to be highly silicated and the amount of water which is neces- 
sarily present in the curd soap plus the amount introduced by the 
silicate is too great to yield a cake of satisfactory texture. 247 The fatty 
acids can be saponified in the presence of relatively small amounts of 
water and by their aid a cake containing a large amount of silicate 
can be made without the need of a drying process, which would too 
greatly increase the cost of laundry bar soaps. Numerous formulas 
have been proposed, of which the references given below may be taken 
as typical. 248 " 254 

217 Blasweiler, T. E., Ger. Pat. 320,829 (April 11, 1919) ; C. A., 15, 2009. 

248 Lara, R, U. S. Pat. 1,335,246 (March 30, 1920) ; C. A., 14, 1616. 

^Pech, P. L. E., U. S. Pat. 1,462,243 (July 17, 1924) ; C. A., 17, 3108. 

^Shields, Fred W., U. S. Pat. 1,481,811 (Jan. 29, 1924); Soap Gazette, 26, 
134. 

251 Reinfurth, N., Brit. Pats. 146,223 and 146,224 (June 26, 1920); C. A., 14, 
3541. 

^Stiepel, C, Seifenfabr., 24, 225-227; Chem. Zentr., 75, 1, 1112 (1904). 

253 Berge, Seifensieder Ztg., 47, 641-643 (1920) ; C. A., 14, 3809-3810. 

^Kalle and Company, Ger. Pat. 381,108. 



362 



SOLUBLE SILICATES IN INDUSTRY 



Result of Use of Silicate. Though silicate makes soap softer up 
to the time of setting, it makes a firmer finished cake. 255-257 Silicated 
soaps are apt to contain more water than the same stocks without sili- 
cate. Silicates cause gelation of sodium and potassium oleates in lower 
dilution than sodium carbonate. 



Table 110. Sodium Olcate and Sodium Silicate. 
(Fischer) 

Concentration of Mixture Remarks 

5cc. m sodium oleate + 9cc. H 2 + lcc. m/ 2 sodium silicate Mobile liquid 
5cc. " " " + 8cc. " + 2cc. " Less mobile liquid 

Sec. " " " + 7cc. " + 3cc. " " " Viscid 

5cc. " " " + 6cc. " + 4cc. " " " Very viscid 

5cc. " " " + 5cc. " + 5cc. " " " Solid gel 

5cc. " " + 4cc. " + 6cc. " " " Solid gel 

5cc. " " " + 3cc. " + 7cc. " Beginning separation 

5cc. " " " + 2cc. " + 8cc. " " " Great dehydration 

and separation 
5cc. " " " + lcc. " + 9cc. " " " Great dehydration 

and separation 
5cc. " " +10cc. mA sodium silicate Great dehydration 

and separation 
Sec. " " " +10cc. H 2 (control) Mobile liquid 



Table 111. Potassium Oleate and Sodium Silicate. 
(Fischer) 



Concentration of Mixture 



Remarks 
silicate Mobile liquid 
Mobile liquid 
Mobile liquid 
Mobile liquid 
Viscid liquid 
Viscid liquid 
Viscid liquid 
Solid gel 
Solid gel 
Viscid liquid 
Mobile liquid 



As the soap dries it becomes harder and less soluble so that very old 
samples of highly silicated soaps are hard to dissolve in cold water and 
if wetted and dried at intervals of a few days the cake tends to be 
covered with a hard silicious film, but this is only evident in the soaps 
containing the higher amount, and in any case does not appear when 
a piece is completely dissolved at one operation, as in the family wash. 

The use of solutions containing silicate and sodium hydroxide which 



5cc. m potassium oleate -- 9cc. H 2 - lcc. m 


A sodium 


5cc. " '' ' 


4 + 8cc. " +2cc. 


i >i 


5cc. " 


' + 7cc. " + 3cc. 


( << 


5cc. " 


' + 6cc. " + 4cc. 


< (< 


5cc. " " ' 


+ 5cc. + 5cc. 


" 


5cc. " ' 


+ 4cc. + 6cc. 


' " 


5cc. " 


+ 3cc. " + 7cc. 


i a 


5cc. " 


' + 2cc. " + 8cc. 


1 a 


5cc. " 


• + lcc. " +9cc. 


( a 


5cc. " 


' +10cc. m/: sodium silicate 


Sec. " 


' +10cc. H 2 (control) 





255 Fischer, M. H., "Soaps and Proteins," New York: Wiley, 1921, 194 et seq. 
"•Fischer, M. H., and G. D. McLaughlin, Kolloidchem., 15, 1-102; 16, 99-133, 
134, 175179 (1922) ; C. A., 17, 25. 

*"Lederer, E. L., Z. angew. Chem., 37, 637 (1924). 



DEFLOCCULATION AND DETERGENCY 



363 



have not reacted fully leads to a final product which irritates the hands 
in use and is more likely to be disfigured with a white efflorescence of 
sodium carbonate. Simmons 258 describes the use of Na 2 0,2Si0 2 and 
says that it reduces the tendency of sodium carbonate, even when added 




Fig. 165. — Addition of Silicate to Potassium Oleate. 

as such, to appear as a bloom on the surface of soap, while McBain 
speaks of silicated soaps as especially likely to form carbonate on ex- 
posure to the air — differences which may easily be due to the type of 
silicate and the manner of its introduction into soap. 259 




Fig. 166. — Addition of Silicate to Sodium Oleate. 



Leimdorfer considers that the prevention of efHorescence by silicate 
on a soap which had contained free alkali is a matter of adsorption of 
sodium hydroxide on silica. When the capacity of silica to adsorb is 

^Simmons, W. H., "Soap, Its Composition, Manufacture, and Properties," 
London: Pitman, 1917, 66. 

239 4th Colloid Report, Sci. Ind. Research, London : His 'Majesty's Stationery 
Office, 1922, 244-263. 



364 SOLUBLE SILICATES IN INDUSTRY 

exceeded the bloom reappears and when there is not enough alkali the 
silicate coagulates the soap and efflorescence may again take place. 260 

The silicate-soap complex has an emulsoid character which is largely 
affected by the viscosity of the two phases, particularly the continuous 
one. Fischer points out that the hydration, which causes the soap to 
stiffen, is a process which requires considerable time. Following this 
lead he was able to add water to silicate soap mixtures which had 
separated, wait until the water had been taken up and then work the 
mass into new batches of soap which were smooth and satisfactory. 
The opinion is here offered that the efflorescence of silicate-soap mix- 
tures is more dependent upon whether the system is a well hydrated and 
fine grained emulsion than upon any exact relation between Na 2 and 
SiOo. This is supported by the fact that the white silicated soaps now 
popular in America are made with silicates which, according to the older 
teaching, should be impossible. Yet they are smooth and show little 
tendency to bloom. Silicates, like other electrolytes, can salt soap out 
of solution but the satisfactory mixture is an emulsion of two viscous 
hydrophile colloids in which most of the silicate is a finely dispersed 
phase. When the emulsion is relatively gross the silicate characteristics 
are more in evidence. The ability to control the efflorescence of added 
carbonate is primarily a matter of including it in a viscous, highly dis- 
persed vehicle. 

In America the practice of using the silicates with more than two 
mols of silica is widespread. The soap is finished slightly alkaline in 
the boiling kettle and the silicate, Na 2 0, 3.3Si0 2 , or somewhat more 
alkaline, is used to take up the free alkali. 261 

Silicates reduce the tendency of soaps containing rosin to be sticky. 
They improve texture and gloss and tend to increase the translucent 
appearance of soap. 262 

Much of the older literature refers to soluble silicates in soaps as 
fillers. 263 The distinction between inert materials added to soap and 
those which assist detergent action has 264 - 266 been aptly recognized by 
the U. S. Bureau of Standards 267 in the use of the term "builders" 

280 Kolloidchem., 2, 343-398 (1911). 

2<H Edeler, A., Ind. Eng. Chem., 17, 196 (1925). 

292 Weber, K. L., Seifensieder Ztg., 49, 458-460, 479-481, 494-495 (1922) ; C. A., 
16, 3224. 

263 Seifenfabrkant, No. 15 (1885) ; Chem. Zentr., 16, 967-968 (1885). 

^Artus, Dingier 's poly. L, 178, 416; Chem. Zentr., 37, 559-560 (1866). 

285 Andes, L. E., "Wasch-, Bleich-, Blau Starke- und Glanzmittel," Hartleben's 
Chemisch-techniche Bibliothek, Wien, 1909. 

™Dingler's poly. I., 222, ser. 5, 22, 501 (1876) ; Chem. Zentr., 56, ser. 3, 16, 
956-957 (1885). 

2m Bur. of Standards Circ. No. 62, 3rd ed., 1-24 (1923). 



DEFL0CCULAT10N AND DETERGENCY 365 

and in specifications calling for a harcl-water laundry soap containing up 
to 20 per cent matter insoluble in alcohol. 

In view of the foregoing, it will be seen that the question of whether 
the use of silicates in soap constitutes adulteration or no, becomes highly 
technical. Silicates are not soap ; mixtures of silicate and soap, or either 
of them separately, are useful washing agents. Silicates are cheaper 
than soap and this fact should be taken into account in setting the price 
of mixtures. A case before the Federal Trade Commission in which 
this point was raised ended by the withdrawal of that part of the com- 
plaint concerning silicates. The testimony showed that the largest ton- 
nage of soap sold in the competitive marked in the United States is 
made up of the silicated brands. 268 

Silicates also have their place in chip soaps and soap powders, where 
their function is not essentially different from that in cake soaps. 269-271 

Specific formulas might be multiplied at length, but they are on record 
for those who are specially interested and they do not add greatly to 
our understanding of the nature of silicate solutions. 

Small amounts of Na 2 0, 3.3Si0 2 in soap prevent free fats from be- 
coming rancid on storage. Additions of 1 per cent of a 1.38 specific 
gravity solution are sufficient. The nature of the action has not been 
explained, but it evidently has to do with free fatty acids and experience 
indicates that colloidal silica has an active part because like quantities 
of other alkalies including sodium carbonate are less able to keep the 
soap sweet. Sodium hydroxide is effective until it is carbonated, and 
the value of silicate may have to do with its ability to prevent decom- 
position by carbon dioxide of the air to the less potent carbonate. There 
is thus a function for silicate in soaps in which its detergent properties 
are not involved. The amounts needed are small. It is permissible 
to use them in toilet soaps or those designed for the most delicate uses. 
In fact the practice of adding small quantities of silicate to shaving 
creams and alkaline cosmetics, to permit the use of aluminum containers 
which would otherwise be attacked, indicates that the mixture contain- 
ing silica is milder than the original product. 

Analysis of Detergents Containing Soluble Silicates. 

Separation of Soap and Silicate. The basis of separation between 
soap and soluble silicate is the insolubility of the latter in alcohol. It 

268 Federal Trade Com. vs. Procter & Gamble, loc. cit. 

299 St. D., Chemisettes Repertorium, 29, 11, 400 (1905); Seifensieder Ztg., 32, 
814. 

270 Steffan, M. O., Seifensieder Ztg., 48, 589-591, 612-614, 631-632 (1921) ; C. A., 
15, 376. 

^Siebel, R., Z. deut. Ol-Fett-Ind., 45, 739-741 (1925) ; C. A., 20, 999. 



366 



SOLUBLE SILICATES IN INDUSTRY 



is necessary that the moisture content of the soap should be low and 
that there be little water in the alcohol. The U. S. Bureau of Stand- 
ards 272 recommends 94 per cent at least. A 10 gram sample after 
digesting, hot, with 200 cc. neutral alcohol is filtered on a tared filter, 
washed with hot alcohol, and dried on a tared filter at 100° to 105° C. 
for 3 hours. This residue includes sodium silicate, sodium carbonate, 
and sodium borate. The other salts may be determined by well known 
methods of analysis, but the interpretation of the results respecting 
silicate is difficult. In the first place, the precipitate is not completely 
dehydrated at 105 °C. in 3 hours, and secondly the ratio between Na 2 
and Si0 2 is usually different from the silicate solution put into the soap. 
As all the soluble silica is in the precipitate it is best to determine it and 
then to calculate back to the silicate known or assumed to have been 
added to the soap. If there is no material insoluble in water the orig- 
inal soap may be charred for the determination of silica. There is no 
analytical method available for determining how much of the sodium 
oxide in a soap of unknown history was introduced as silicate. 

Determination of Free Alkali. Determination of free alkali in 
the presence of silicate also requires some interpretation. Edeler 273 
determined free alkali in the alcoholic extract of silicate solutions alone 
and mixtures of silicate solutions with neutral alcoholic soap, with the 

Table 112. Titrations of Alcoholic Filtrates from Silicated Soaps. 



Free Na 2 in 

Soap Before 

Adding 

Silicate, 

Per Cent 

0.0 
1.21 

2.32 
5.02 



Resulting 

Ratio 
Na 2 0, Si0 2 
(Molecular) 

1 : 3.22 
1 : 2.54 
1:2.12 
1 : 1.52 



Cc. N H 2 S0 4 to 

Neutralize Alcoholic 

Filtrate * 



0.05 
0.30 
0.50 
2.40 



0.05 
0.40 
0.50 
2.60 



Apparent Free 

Na 2 in Silicated 

Soap, 

Per Cent 

0.01 

0.07 

0.10 

0.52 



* Each analysis was made in duplicate on separate samples. 



Table 113. 



Na0 2 
Per Cent 

9.18 
11.37 
13.48 
17.72 
23.97 



Titrations of Alcoholic Filtrate from Sodium Silicates of Varying 
Composition. 



Si0 2 
Per Cent 

29.71 
28.18 
26.13 
26.50 
23.48 



Ratio 
NaO : Si0 2 
(Molecular) 



3.33 
2.55 
1.99 
1.54 
1.01 



Cc. N H 2 S0 4 
Neutralize Alcoholic Filtrate 



Soap Absent 

(1) (2) 

0.10 0.10 

0.25 0.25 

0.55 0.60 

2.20 2.20 

9.40 9.60 



212 Bur. of Standards Circ. No. 62, 3rd ed., 22 (1923). 
273 Edeler, A., hid. Eng. Chem., 17, No. 2, 196 (1925). 



Soap Present 

(1) (2) 

tr tr 

0.05 0.05 

0.30 0.35 

1.40 1.45 

8.05 8.35 



DEFLOCCULATION AND DETERGENCY 367 

result shown in Tables 112 and 113. From this it appears that the more 
alkaline silicates give up a part of their soda content to neutral soap. It 
is well known to soapmakers that the silicious types of silicate are able to 
reduce the free alkalinity of an alkaline soap when the two are mixed 
in course of manufacture. 

The determination of free alkali in a silicated soap by alcoholic ex- 
traction is thus a purely arbitrary procedure. The amount which ap- 
pears will depend upon the ratio of the silicate present and will vary 
with the amount of water and silicate, i.e., upon the degree of hydrolysis. 
A more effective method as far as evaluation of the detergent is con- 
cerned could be worked out on the basis of the pH of the detergent 
solution at the concentration and temperature employed for the 
wash. 274 " 285 

Testing Detergency. 

Practical Washing Tests. Analysis of a washing material may 
give useful information as to its origin and reveal some of its essential 
properties, but as yet the information thus gained must be construed 
with great caution and in the light of experience with actual washing 
operations. 

Many workers have sought to establish simple tests by which de- 
tergency could be determined by measuring accurately one of the 
characteristics which affect the process of cleansing. 286 Such are the 
measuring of drop number, lathering power, and deflocculation, each of 
which is of use under a limited set of conditions. 287 Each fails to take 
fully into account the complicated nature of the washing process. Until 
the whole series of phenomena is more fully understood it seems logical 

™Proc. Am. Pharm. Ass., 42, 608-609 (1894). 

275 Chem. Zeit., 20, pt. 1, 20-21 (1896) ; /. Chem. Soc, 72, pt. 2, 159-160 (1897). 

276 Hussein, Ahmed, Pharm. J., 74, ser. 4, 20, 821 (1905). 

277 /. Pharm. Chim. (6) 21, 496-497; Chem. Zentr., 76, II, 81 (1905). 

-^Braun, K., Chem. Repertor., 31, 355 (1907); Z. angew. Chem., 21, pt. 1, 
1028-1029 (1908). 

279 Isnard, E., Ann. Chim. anal., 19, 98-100 (1914); /. Soc. Chem. hid., 33, 
362-363; Chem. Ztg., 85, I, 1522; C. A., 8, pt. 2, 2077 (1914). 

^Leitch, Harold P., Ind. Eng. Chem., 6, 811-812 (1914). 

^Deite, Carl, "Manual of Toilet Soap Making," trans, from Ger. by H. Keane. 
2nd ed., London: Scott, Greenwood, 1920, 326-327. 

^Sheeley, M. B., Chem. Bull, 8, 275-276 (1921). 

^Beedle, F. C., and T. R. Bolan, /. Soc. Chem. hid., 40, 27-29T, 74T (1921) ; 
C. A., 15, 1925. 

284 Ind. Eng. Chem., 14, 1159-1163 (1922). 

285 Jones, H. E., Brnnner, Mond & Co. Booklet L-237. 

^McBain, J. W., R. S. Harbone, and A. M. King, /. Soc. Chem. hid., 42, 
373-87 (1923). 

^Hillyer, H. W., /. Chem. Soc, 25, 511 (1903); Chapin, Robert M., Ind. 
Eng. Chem., 17, 461-465, 1187-1191 (1925); Spring, W., Rec. Trans. Chim,, 28, 
120-135, 424-438 (1909). 



368 SOLUBLE SILICATES IN INDUSTRY 

to resort to actual washing tests to evaluate detergents. But even this 
is beset with difficulties. Different fabrics do not behave alike when 
soiled with the same dirt. It is no simple matter to soil any kind of 
goods with perfect uniformity, so that concordant results can be had 
only with repeated tests of the same materials and even if this is accom- 
plished it does not follow that the standardized experiment will faith- 
fully represent the conditions of actual practice. Dirt is anything we 
wish to remove, and its chemical nature exceedingly miscellaneous. 

Faragher 288 groups the materials encountered in industrial laundering 
into albuminous substances, such as blood and egg stains ; vegetable 
dyes, which cause fruit and wine stains ; fats and oils, including hydro- 
carbon greases and oils ; acid and alkali stains ; body excretions and 
waste epithelial cells; old starch; and street dirt and soot. So we shall 
have to apply reservations even here. A beginning has, however, been 
made. 

Standard Soiling. Attempts to produce standard soils have been 
numerous, often based on convenience rather than on close analogy to 
working conditions. One of the best mixtures is that proposed by 
ShukofT and Schestakoff. 289 It is a mixture of lamp black with a solu- 
tion of lanolin in benzene. The importance of uniform application of 
the soiling agent is stressed* Another mixture consists of linden char- 
coal, mineral oil, and fatty acid, while indigo colloid and a solution 
of machine oil in gasoline with and without starch have been em- 
ployed. 290 ' 291 

Almost all the mixtures lay stress upon some form of finely divided 
carbon, doubtless partly because it is so easily seen. This may be mis- 
leading because other forms of dirt are quite as important in launder- 
ing, and it does not necessarily follow that a reagent which derlocculates 
carbon will react in the same way with clay or silica. For this reason 
the mixture of ShukofT and Schestakoff would more nearly simulate 
actual working conditions if clay or other silicious material were added. 
Starch generally makes washing easier by preventing the dirt from 
working into the fabric and by interposing a film which is easily wetted. 
Asphalt is not a normal soiling material and should not be used in a 
study intended for application to ordinary laundry practice. 

There is a tendency to use a large amount of soiling material in test 

^Rogers and Aubert, "Industrial Chemistry," Chapter XXVIII, by W. F. 
Faragher, New York : D. Van Nostrand & Co., 1912, 582-583. 

288 Chem. Zta., 35, 1027 (1911). 

290 Z. deut. Ol-Fett-Ind., 41, 338-341. 

261 Textilberichte, 2, 37-38, 61-62 (1921). 

* Note : A useful bibliography on the hydrolysis and detergency of soap 
solutions by L. W. Bosart was published in Ind. Eng. Chem., 14, 1150 (1922). 



DEFL0CCULAT10N AND DETERGENCY 369 

washings, which is inadvisable, as detergent action depends in part upon 
the amounts of dirt and reagent. 

Microscopical Examination. 292 A microscope is a very useful 
accessory to detergent testing. Two samples of cloth which look alike 
to the naked eye may show striking differences when thus examined. 293 
Many of the effects of detergents are cumulative and become evident 
only after many cycles of washing, rinsing, and ironing. An occasional 
treatment with an abnormal amount of sodium carbonate seems to make 
little difference on white cotton goods, but if continued it yields a gray 
color by reflected light and, by transmitted light, a brownish tint. 

Development of Standard Practice. The American Oil Chemists' 
Society has a committee on the evaluation of detergents which, in co- 
operation with various industries, is studying a test which by actual 
washing and measurement of color of standard fabrics having a standard 
soil will seek to put in the hands of investigators a set of conditions 
which will at least give results that can be duplicated. Until some such 
device is perfected we shall not be able to discriminate between different 
soaps for any one kind of washing or know accurately the place of 
silicate solutions in detergent operations short of the long process of 
trial and error conducted in practical operations over extended periods 
of time. This method, though it leaves much to be desired from a 
scientific viewpoint, yet yields authentic information to careful ob- 
servers and it is thus that soluble silicates are accepted to-day on a 
large scale for both domestic and commercial washing. 294 ' 295 

292 Detergent Com. reports in /. Am. Oil Chem. Soc, 1925, et seq. 

293 Stericker, Wm., unpublished report. 

""Keit, DeuL Washerei Ztg.; Seifensieder Ztg., 48, 41-42 (1921) ; C. A., 15, 
1413. 

^Hoyt, L. R, et al., Oil & Fat Ind., 3, 156; d, 29-34 (1927) ; C. A., 21, 1198. 



Chapter XI. 
Gelatinous Films and Gels. 

Conditions Necessary for Gel Formation. 

The coalescence and gelation of silica sols is determined by a set of 
conditions which have been only partly explored. Liesegang acidified 
a silicate solution with hydrochloric acid in excess. This stabilized the 
sol as a mobile liquid. When a piece of solid sodium hydroxide was 
dropped into the tube an alkaline layer was formed in which the sol 
was also fluid. Between the two, a thin film of gel progressed slowly 
upward in the tube. As the alkaline layer increased by diffusion it 
dispersed the gel, which continually formed anew at the point where 
neither acid nor alkali was in sufficient excess to prevent gelation, while 
both alkaline and acid sols in the same tube remained liquid. Gels may 
be formed in both acid and alkaline solutions by adjusting to concen- 
trations of silica appropriate to the particular conditions, a variety of 
which will appear as we consider the industrial uses of silicious gels. 
Purity, time, and temperature play important roles ; but these influences 
affect the rate of coalescence rather than the fundamental tendency 
of sols to progress to larger and larger aggregation and finally to gel. 
After gelation the particles still tend toward rearrangement leading to 
syneresis and finally to crystal structure. 1 

The properties of the gel are changed by altering the amount of 
liquid present when it is formed. The number and size of the inter- 
spaces affect porosity, capillarity, and reaction rate of processes which 
occur at the surfaces. The presence of colloids other than silica may 
also affect the reactivity and usefulness of the gel. 

For convenience in grouping the uses of silicious gels in industry, 
an arbitrary distinction is made between those gels which embody the 
entire reacting liquid and those which are formed as films. 

Gelatinous Films. 

Formation by Cataphoresis. 

The passage of a direct electric current through a silicate solution 
causes cataphoresis. The positively charged sodium ions migrate toward 

1 Scherrer, P., Nachr. Ges. Wiss., 96, 100 (Gottingen, 1918). 

370 



GELATINOUS FILMS AND GELS 371 

the cathode and the negatively charged silica toward the anode. Unless 
the solution is agitated the concentration of silica at the anode surface 
soon reaches a point at which the sol is no longer stable, and a thin 
transparent film of gel is formed. This partially, but not completely, 
polarizes the cell and the current flows in much reduced amount, for 
the gel is a porous structure and contact can be maintained through 
it between the cathode and the main body of electrolyte. To the extent 
that current passes, however, the gel increases in thickness and finally 
the resistance increases to a point where there is practically no flow. 
Reversal of the poles will cause the gel to be dispersed unless the anode 
coating has become dehydrated, which may occur if there is enough 
current to cause a large local rise of temperature. The physical char- 
acter of the film, like that of other gels, alters with concentration and 
any factor which afTects the amount of silica present at the moment 
of gelation. So it is with all silica gels. 

Prevention of Corrosion. 

Cleansing of Aluminum Ware. Metallic aluminum is rapidly at- 
tacked by hot solutions of sodium carbonate. Corrosion of aluminum 
wares cleansed with ordinary soda was measured by Seligman and 
Williams, 2 who found a loss of 5.3 grams per 100 sq.cm. in 24 hours 
at 75°C. with 5 per cent Na 2 C0 3 . 10H 2 O, and 80 grams were dissolved 
by a 1 per cent solution at 100° C. Pitting and discoloration may take 
place even at atmospheric temperature. High-ratio silicate solutions of 
the same sodium content do not attack aluminum. If a piece of alumi- 
num is partly immersed in 1 per cent solution of Na 2 0, 3.3Si0 2 and 
subsequently put into a 0.1 per cent solution of sodium hydroxide, 
bubbles of hydrogen appear at once on the untreated surface, but the 
silicate retards the action upon the treated part. NaOH solutions up 
to 0.5 gram per liter are practically without action on the silicate- 
protected surfaces. When a finger or even a soft rag is drawn across 
the treated surface it may be seen that the protection has been removed 
in the path traversed by finger or cloth. Close inspection will reveal 
the presence of a soft silicious gel upon the surface of the metal. In 
the first moments of contact between silicate solution and aluminum 
the metal begins to dissolve. Positively charged metallic ions are pres- 
ent at the exposed surface; they cause a concentration of negatively 
charged colloidal silica which was already tending to coalesce. The sol 

2 Seligman, Richard, and Percy Williams, I. Inst. Metals, 28, 297-298 (1922) ; 
C. A., 16, 3803-4. 



372 



SOLUBLE SILICATES IN INDUSTRY 



becomes unstable and separates as a protective film of gel upon the 
surface. 

Small additions of silicates to carbonate solutions present the same 
phenomenon. The attack by a 5 per cent NaoCO 3 .10H 2 O solution is 




Fig. 167. — Corrosion of 8 Cu — 92 Al Sand Cast Porosity Cups. ZD Treatment vs. 
Norton Process vs. Heat Treatment Only 150 Hours in 20 Per Cent Salt Spray. 

ZD 8 Hr. Process (left). ZD 24 Hr. Process (left center). Norton 24 Hr. 
Process (right center). Heat Treatment Only (right). 

arrested by one hundredth this amount of silicate of the more silicious 
kinds. Seligman and Williams found that 5 per cent Na 2 0, 2.2Si0 2 
did not attack the metal at 75 °C. 

Rohrig 3 extended the study to sodium sulfide solutions and found 




Fig. 168.— Soft- Annealed Sheet Aluminum — A. S. Spec. 11058 Exposed 120 Hours 
to Spray of 20 Per Cent Salt Solution. 

No treatment (left). Treated Z-D Process (center). Twice Treated Z-D 
Process (right). 

that similar films could be formed to protect aluminum containers for 
chemical reactions. 

z Chem. Ztg., 47, 528-529 (1923) ; C. A., 17, 2983. For similar action on iron, 
see Rawling, Francis George, U. S. Pat. 1,566,118 (Dec. 15, 1925). 



GELATINOUS FILMS AND GELS 373 

Zimmerman and Daniels 4 treat aluminum and alloys containing it 
by heating in silicate solutions and, after draining, baking the film at 
temperatures above the boiling point of water. A bright surface of 
metal may be preserved by immersing in Na 2 0, 3.3Si0 2 1.1 specific 
gravity for 2 hours at 65 °C. (150°F.), removing the metal from the 
bath and baking for 20 hours at 148°C. (300°F.). A cast duralumin 
cup after treatment resisted a 20 per cent salt spray for 120 hours with- 
out signs of corrosion, though an untreated cup was corroded after 3 
hours. A cup made from 90 per cent aluminum and 8 per cent copper 
when filled with a mixture of gasoline and water showed corrosion 
after 24 hours, but when treated it resisted corrosion for 135 days. 5 

Zinc Plates for Dry Battery. Zinc plates for dry battery cans 
can be made to corrode more evenly by treating them with a solution 
containing soluble silica. .Detergent action doubtless plays a part in 
this, but the thin film of gel which is deposited is also a factor in pre- 
venting localized action. 6 

Solution of Lead Retarded by Film. A series of observations 
by Thresh 7 points to film formation under conditions of extreme dilu- 
tion. The plumbo-solvent moorland waters of certain districts in Eng- 
land have given frequent concern to the authorities on account of lead 
poisoning. Pure water does not dissolve lead, but water containing dis- 
solved oxygen causes lead to go into solution, giving the water an alka- 
line reaction. The alkalinity of natural waters is not, however, a re- 
liable index of their solvent power toward lead. 



Table 


114. 




Amt. of 

Lead in 

Drawn-off 




Appearance of 


Oxygen 


Liquid 


Value 


Liquid after 


Used, 


Pts. per 


ofpH 


Acting on Lead 


Per Cent 


100,000 


9 


Turbid 


90 


9.35 


9 


Clear and bright 


19 


0.165 


9 


Clear and bright 


24 


0.75 


4.5 


Clear and bright 


24 


1.85 


4.5 


Dull 


76 


2.05 


4.5 


Dull 


80 


7.0 



Substance Added 

Lime water 

Lime water and silicic acid. . . . 
Lime water and citric acid.... 
Sodium silicate and citric acid 

Citric acid only 4.5 

Hydrochloric acid (iV/22) . 

Conductivity water was adjusted to pH 9 by adding lime water and 
dissolved 9.35 parts per million of lead. In the presence of colloidal 

4 U. S. Pat. 1,540,766 (June 9, 1925). 

B Zimmerman, A. C, and Daniels, S., hid. Eng. Chem., 17, 359 (1925). 

"Breyer, F. G., and W. H. Finkeldey, U. S. Pat. 1,451,758 (April 17, 
1923) ; C. A., 17, 1926. 

7 Thresh, John C, "Examination of Waters and Water Supplies," 3rd ed., 
Philadelphia: Blakiston, 1925, 128-134. 



374 



SOLUBLE SILICATES IN INDUSTRY 




Fig. 169a. — Duralumin as Cast. No Silicate Treatment. Immersed 30 Days in 

Distilled Water. 




Fig. 169b. — Duralumin Heat Treated. No Silicate Treatment. 
Immersed 30 Days in Distilled Water. 



GELATINOUS FILMS AND GELS 



375 




Fig. 169c. — Duralumin Machined. No Silicate Treatment. 
Immersed 30 Days in Distilled Water. 





Fig. 169d. — Duralumin Machined. Treated by Z-D Process. 
Immersed 30 Days in Distilled Water. 



376 



SOLUBLE SILICATES IN INDUSTRY 






Fig. 170a. — Duralumin 'Machined. No Treatment. Exposed 120 Hours to Spray 

of 20 Per Cent Salt Solution. 







Fig. 170b. — 8% Cu— 92% Al Machined. No Treatment. Exposed 120 Hours to 
Spray of 20 Per Cent Salt Solution. 



GELATINOUS FILMS AND GELS 



377 





Fig. 170c. — Duralumin Machined. Treated by Z-D Process. Exposed 120 Hours to 
Spray of 20 Per Cent Salt Solution. 





Fig. 170d.— 8% Cu— 92% Al Machined. Treated by Z-D Process. Exposed 120 
Hours to Spray of 20 Per Cent Solution. 



378 SOLUBLE SILICATES IN INDUSTRY 

silica only 1.65 parts per million were dissolved. Although both 001- 
loidal silica and soluble silicates retard the oxidation and solution of 
lead the latter are more effective. This is probably due to the texture 
of the film. Five parts per million of silica as soluble silicate are 
enough to reduce the solution of lead to a safe point in distilled water, 
but in the presence of carbonates or sulfates a much smaller quantity 
is sufficient. 

Table 115. Effect of 24-Hour Exposure on Solution of Lead. 

Silicic Acid Sodium Silicate as Silicic Acid 

In nigra, per lOOcc 0.75 1.0 1.5 2.5 0.3 0.6 0.75 1.0 

Oxygen used 0.95 0.94 0.95 0.37 0.87 0.325 0.130 0.15 

=Lead oxidized 12.3 12.15 12.3 4.8 11.25 4.2 1.7 1.95 

Appearance of liquid. . Sheeny Turbid Turbid Clear Dull Clear Clear Clear 
Lead in liquid 5.5 3.25 1.0 0.05 5.75 0.02 0.02 0.01 

The amount of lead which can be tolerated is somewhat debatable 
but Thresh believes no harm can come from a water in which it never ex- 
ceeds 0.5 part per million. The fact that the reaction is not com- 
pletely suppressed suggests the formation of a gel film which is slightly 
permeable ; but a film formed from a concentration of 5 parts per 
million would necessarily be tenuous ; and a more even covering is to 
be expected from soluble silicate in which the degree of dispersion is 
greater than when silica, unprotected by sodium, is in a more advanced 
state of coalescence. 8 

Wet films of gelatinous silica as thin as these are not visible. They 
are not only very thin but translucent. 

The following is a comparison showing the behavior of an English 
lake water before and after treating with silicate. 

Table 116. Effect of Silicate Treatment. 

Treated 
with Silicate 
Untreated of Soda 

pH 6 7.5 

Electrical conductivity 33 46 

Oxygen removed in stagnant water in 24 

hours, pts. per million 9.0 pts. per million 1.6 

= Pb oxidized, pts. per million 115.6 " " " 20.7 

Pb in solution, " " " 18.1 " " " 0.1 

Pb in deposit, " " " 49.0 " " " 0.0 

Pb on foil, " " " 48.5 " " " 20.6 

Si0 2 Trace 8.5 

Water from one of the most dangerous reservoirs at Glossop in 
Derbyshire was treated with silicate. Some days later a test of 17 

8 Thresh, John C, Analyst, 47, 459-468, 500-505 (1922) ; C. A., 17, 3733. 



GELATINOUS FILMS AND GELS 



379 



houses showed 14 in which no lead could be detected ; the others 
showed 0.3, 0.2, and 0.15 part per million. The untreated water would 
have contained near 0.9 part per million. 

Prevention of Rusting of Iron. In the course of his work on 
the control of lead corrosion with silicates, Thresh observed, as Speller 
had done, that the rusting of iron was also inhibited. In Paignton, 
where the water is carried for 17 miles through iron mains, great an- 
noyance had resulted from rusty water and frequent cleaning of the 
pipes was necessary to prevent complete stoppage. Sodium carbonate 
treatment did not improve the situation. When silicate was added some 
rust was deflocculated and thus removed, but in three days the water 
became clear and bright and continued in this condition. Ten parts 
per million of silica as silicates are usually sufficient to control the 
rust in a municipal supply. Change in the pH of water such as that 





Black Galvanized 

Fig. 171. — With Silicate Treatment. 



Black Galvanized 

Fig. 172. — Without Silicate Treatment. 



induced by silicate treatment for corrosion may also serve to kill 
water-borne bacteria of the typhoid and cholera groups. 9 

Speller and his collaborators have worked upon the corrosion of 
iron in hot water. They found that this corrosion is a function of the 
dissolved oxygen content of the water and not primarily due to carbon 
dioxide as has often been assumed. It is not necessary to rehearse here 
the theory of corrosion except to say that dissolved oxygen can remove 
films of hydrogen which polarize cathodic areas of metal and when this 
occurs more iron passes into solution. 10 ' n ' 12 

The interposition of a silicious film prevents this transfer and stops 

9 Atkins, W. R. G., /. State Med., 31, 223 (1923) ; App. Chem. Rept., 8, 516. 

10 Speller, F. N., "Corrosion," reprinted from ''Petroleum Development and 
Technology in 1926," Am. Inst. Min. Met. Eng., 1927. 

Speller, F. N., "Corrosion, Causes and Prevention," New York : McGraw- 
Hill Book Co., 1926. 

"Whitman, W. G., E. L. Chappel, and J. K. Roberts, hid. Eng. Chem., 16, 
665 (1924). 

12 Bancroft, W. D., /. Phys. Chem,, 28, 785 (1924). 



380 



SOLUBLE SILICATES IN INDUSTRY 



corrosion. The effect is most easily seen by plotting the specific rate 
of corrosion based on oxygen absorption against time with and with- 
out the silicate treatment. 

Here, as in the case of lead corrosion, the protective film does not 





<D^< 


o 
































Viltho 


vt St/to 


\te 


o 










« 
V. 

5v 

% 


O 


























































*"" 















wA Sti 


'cafe 










'< 








■ ~ TS » 


1 i 


' 


\ i 


f i 


1 / 


1 


t /■ 


» /6 10 XO 32 g* 



CLayS of Continue** Flow 

Fig. 173. — Corrosion Due to Water Flowing through Clean Black Steel Pipe 

at 43° C. 

completely prevent the reactions which cause corrosion. Its per- 
meable gel structure allows some reaction to occur. As a matter of 
experience, however, it has been found that that which continues 
after the film has formed is usually negligible. 



*aT urAr&ie to 



<?ai-0 WATS& 




GUST/COW TAilK 






Fig. 174. — Application of Silicate to Prevent Rust in a Laundry Water Heater. 



The technic of rust control of hot-water supplies with silicate solu- 
tions consists first in providing a concentration of about fifteen parts 
per million of Na 2 0, 3.3Si0 2 to form the film, after which a dosage of 
five to ten parts per million suffices to maintain an adequate degree 



GELATINOUS FILMS AND GELS 381 

of protection. Intermittent dosage may also be used but if the water 
is allowed to flow too long without silicate the film will be more or 
less dispersed and the protective effect will gradually decline. 13 

The deposition is greatest near the point where silicate is injected 
and it is best not to depend on protection in hot water through more 
than two hundred feet of pipe without a supplementary feeder. As 
previously indicated, cold water lines carry useful amounts of silica 
for miles. This conforms to the idea of gel formation, for colloidal 
silica proceeds to coalescence and gelation more rapidly at higher 
temperatures. 

Gels are mechanically weakest when first formed, so weak in fact, 
that good films cannot be laid on surfaces where water is boiling ac- 
tively or otherwise strongly agitated. 

The hardening process or rearrangement of the gel particles by 
syneresis involves shrinkage which might expose portions of metal 
if no silica were present in solution to repair the defect. This and 
the tendency of the gel to disperse slowly are perhaps the principal 
reasons why the addition of Si0 2 to the water must be continued. 

It was at first assumed that the film formation depended upon the 
formation of insoluble silicates, that is, upon heavy metal or alkaline 
earth metal salts in the water. Later it was found that good protection 
could be had in zeolite-softened water of zero hardness or even in 
distilled water. It is of course essential to apply the silicate in a way 
which enables the film to cover all the system, for otherwise corrosion 
would be concentrated in those parts not protected. 14-16 

Convenience dictates that a solid silicate be used for hot-water sys- 
tems in homes and laundries as this requires a minimum of attention. 17 
Na 2 0, 3.3Si0 2 is best on account of its slow rate of solution. Na 2 0, 
2Si0 2 dissolves too fast at first and then tends to become incrusted by 
reaction with calcium and magnesium in the water. The advantage 
of a more even dosage is available for laundries and large installations 
by feeding a controlled amount of silicate solution into the water. This 
avoids not only variations in silicate concentration,' but variations in ratio 
between Na 2 and Si0 2 inseparable from dissolving the solid on a 
small scale. 

13 Russell, Robert P., Starch Room Laundry Jour., 94 (Dec. 15, 1923). 

"Ghem. & Met. Eng., 31, No. 15, 583-584 (1924). 

15 Texter, C. R., /. Am. Water Wks. Assoc., 10, 764-772 (1923); Fire and 
Water Eng., 74, 157-161 (1923) ; /. Sanitary and Heating Eng., 102, No. 10, 329 
(1924) ; Power, 58, No. 15, 588 (1923) ; Nat. Assoc. Building Owners and Manuf., 
117, March 15, 1924. 

18 Speller, F. N., and C. R. Texter, Ind Eng. Ghent., 16, 393-394 (1924). 

"Speller, F. N., U. S. Pat. 1,531,992 (March 31, 1925). 



382 



SOLUBLE SILICATES IN INDUSTRY 



Silicate may serve the double purpose of film former and binder 
for deoxidizing reagents in the form of briquets. 18 ' 19 

Analyses of scale from pipe systems in which corrosion has been 
stopped are not very satisfactory because of the difficulty of distinguish- 
ing between rust and the gel film. A further source of contamination 
lies in the calcium and magnesium compounds present in most natural 
water. Iron may be an essential part of the film, at least it is always 
evident in films from iron pipe. The small tendency of the film to build 
on itself may be due in part to the depletion of iron at the surface. The 
silicious film is in this respect very different from the calcareous pro- 
tective films which stop rusting in very hard waters, and then build 
up serious obstructions to pipe lines. 

Several partial analyses of silicious films, from Speller, are presented 
as typical. 

Table 117. Composition of Silicious Films from Silicate Treated Hot Water 

Systems. 

Location Iron Lime Silica 

Chicago, Illinois 9.65 1.74 4.40 

Detroit, Michigan 16.05 1.78 5.30 

Pittsburgh, Pa 53.75 5.75 2.93 (hot water tank) 

" 62.72 0.72 2.36 (1" pipe from raw hot 

water) 
" 36.10 0.80 18.50 (after sodium silicate treat- 

ment) 

" 47.50 1.48 12.54 (%" pipe from hot water 

line 30' from sodium sili- 
cate treatment tank) 

Pittsburgh water 23.4 0.64 28.64 

" 2.8 .... 30.08 

" 4.55 1.24 5.22 



Wherever the "red water plague" appears a judicious use of silicates 
will bring it to an end. 

Silicate Films for Preventing Corrosion in Condenser Systems 
in Refrigerating Machinery. Silicate films for preventing corro- 
sion have been successfully applied to condenser systems serving re- 
frigerating machinery. Whitman, Chappell and Roberts 20 found that 
0.250 kilo per m 3 (15.6 pounds per 1000 cubic feet, about 76 parts 
per million of Si0 2 ) of a 1.4 specific gravity solution of Na 2 0, 3.3Si0 2 
reduced the corrosion rate in a recirculating system by 98 per cent and 
gave a high operating efficiency. Sodium dichromate also forms pro- 

18 Speller, F. W., U. S. Pat. 1,531,991 (March 31, 1925). 

19 Weidlein, E. R., "Strange Uses of Common Materials," Management and 
Administration (Dec, 1923). 

20 Whitman, W. G., E. L. Chappel, and J. K. Roberts, Refrigerating Eng., 12, 
158-165. 



GELATINOUS FILMS AND GELS 



383 









Corrosion of •Eron <?/*/ $fee/ 
in Atmospheric Cond enser Tests 

Vs 

Cost of Treatment 0a sett an 

I0OO cu.f? of irate r Treated 








100 
* 










































































.V, 

< 












































i 


» a 


* 2 


3 


O 4 


4 


£0 7o 00 90 



Ctsf of Treatment" /'« Cents 

Fig. 175. 









Corros/on at Tran a/id Steet 
in fltntesfiAer/c Cono'etser Fesf 












rs 
Concentration of ftetara'tr 






* 

** 




















1 




















s 





























































Tarfs ft' At/Ui'i of ffetardtr in Water 

Fig. 176. 



tective films, 21 but they are not permissible in potable waters nor do they 
endure in contact with pure water after the reagent is removed, as do 
the silicate films. 

Use of Silicate Solutions in Sodium Chloride Brines. The use 

21 Russell, R. P., J. K. Roberts and E. L. Chappell, Mass. Inst, of Tech., 
Serial No. 187, 62, No. 93 (1927). 



384 SOLUBLE SILICATES IN INDUSTRY 

of silicate solutions in sodium chloride brines is practiced in some 
plants. 22, 23 It clarifies the brines and reduces corrosion ; but silicates 
are not the ideal medium for this purpose because the brine hastens 
coalescence, and tends to cause an uneven film, with a tendency to 
pitting. They have the advantage over chromates, however, that they 
do not cause the poisoning known as "chrome itch". 

Boiler Compounds. 

When soluble silicates are used as boiler compounds there always 
forms upon the inner surface of the boiler metal a thin silicious film, 
which is sometimes obscured by the use of extracts containing tannin 
which color the deposit so that it nearly matches the iron surface. Such 
films have a use in reducing corrosion and appear to have no appre- 
ciable effect upon heat transfer. They are very thin, highly hydrous, 
and, like the films used in the condenser systems, do not offer enough 
resistance to the conduction of heat to constitute an objection to their 
use. 

A certain boiler operating in closed circuit with a high grade dis- 
tilled water was treated with a silicate solution to control corrosion. 
Over a period of weeks in which no make-up water was added the 
concentration of silica and of sodium declined steadily, another bit 
of evidence of the deposition of a film. Sodium is carried out of so- 
lution adsorbed on silica as it is in precipitation processes. 24 Films 
formed under the conditions of boiler practice are never visible until 
the metal is dried, when they look like a thin covering of frost. Many 
proprietary boiler compounds contain silicates of soda, the general 
function of which is to cause scale-forming material to precipitate in 
a flocculent condition in which it can be blown from the boiler, rather 
than as a crystalline, hard, adherent scale. For example, see the patents 
of Schenitza 25 and Campbell. 26 

Silicious films formed in laundries and in textile establishments 
either for the purpose of preventing corrosion or incident to the use 
of the silicates as reagents for bleaching help to prevent the staining 
of goods by rust. The silicates thus added also soften the water, 
save soap, and of themselves exert detergent action. 27 ' 28 

22 Whitman, W. G., E. L. Chapell, and J. K. Roberts, loc. cit. 
B Neff, J. W., Ice and Refrigeration, 6, 7, 383 (1924). 

24 Hecht, Max, personal communication. 

25 Schenitza, Philipp, U. S. Pat. 1,617,350 (Feb. 15, 1927). 

26 Campbell, James R., U. S. Pat. 1,278,435 (Sept. 10, 1918). 

27 Russell, R. P., Starch Room Laundry I ., Dec. 15, 1923. 

28 Am. Ass. Textile Chem. Colorists, 47-51 (1926); Am. Dyestuff Rep., 15, 
61-65 ; C. A., 20, 896. 



GELATINOUS FILMS AND GELS 385 

Electrolytic Baths. 

A variation of the application of silicious films to prevent corrosion 
consists in adding small amounts of silicate solutions to baths under- 
going electrolysis. A thin film deposited upon the anode in the elec- 
trolytic reduction of nitrates or nitrites to ammonia practically elimi- 
nated the attack upon the iron anodes and greatly reduced the losses 
of nitrogen. A current density of five hundred amperes per square 
meter and an addition of 0.5 per cent of silica as silicate were em- 
ployed. 29 

With Silicate Without Silicate 

Bath tension 2.2 volts 3 volts 

Losses of nitrogen About 5% As high as 60% 

Utilization of current About 90% Below 50% 

Corrosion of anode Almost imperceptible Several mm. per annum. 

Galvanized Iron. 

Galvanized iron is difficult to paint, but after treatment in a hot 1 
per cent solution of silicate, which deposits a gel, it takes paint readily 
after drying. The gel presents a porous absorbent film which though 
very thin establishes a contact between metal and oil. 

Egg Preserving. 

Egg preserving seems little related to the process just cited, but con- 
sideration of the mechanism by which the respective results are se- 
cured shows them to be closely akin. 

Technic. Of the many uses of silicate solutions, the practice of 
employing them for the preservation of eggs is, perhaps, the most 
familiar. Under the name of "waterglass," silicates of varying com- 
position, concentration, and fitness for the work are sold and regularly 
used by great numbers of householders. 

The process is essentially one of gelatinous film formation. The 
shell of the egg must be protected against the entrance of bacteria which 
cause decay. For this reason it is necessary to start with fresh, prefer- 
ably sterile eggs. They should not be washed, as this removes a natural 
mucilaginous film and increases the danger of infection before the 
silicious gel has formed an effective seal. It is probable that both the 
albuminous constituents of the shell and the calcium compounds reduce 
the stability of the silica and thus aid the formation of gel. A silicate 
near the composition Na 2 0, 3.3Si0 2 is best. It should be diluted just 
enough to allow the eggs to sink (about 4°Baume) and put into a 

"Griiner, V., U. S. Pat. 1,311,506 (July 29, 1919). 



386 SOLUBLE SILICATES IN INDUSTRY 

stone crock or other tight container. One U. S. gallon of specific 
gravity 1.38 will suffice for 50 to 80 dozen eggs, according to size 
of eggs and shape of container. The eggs are laid in the solution and 
kept covered by two inches of liquid till ready for use. 

More dilute solutions can be used, but comparative tests indicate that 
when this is done the quality of the eggs after storage of six months 
or longer is inferior. Sometimes, especially if the container has not 
been tightly covered and the silicate has concentrated or absorbed much 
carbon dioxide, the whole of the liquid will gel. This does not affect 
the quality of the eggs; but because it is unpleasant to some people to 
put their hands into the soft gel to remove the eggs for use, a more 
stable silicate has been proposed. Na 2 0,2Si0 2 under ordinary con- 
ditions of storage remains clear and liquid 
in contact with the eggs, but the preservation 
is not so good as that secured with the solu- 
tions containing more silica. This is manifest 
in an earlier thinning of the tgg albumin and 
a depreciation of flavor due to the entrance, 
by dialysis, of trifling amounts of Na 2 0. 

High Quality of Eggs. Under opti- 
mum conditions, i.e., the right composition 
and concentration of silicate, storage in a 
temperature not above 25 °C. and proper 
Fig. 177.— Preserving Eggs ^gg quality at the beginning of preservation, 
in Silicate Solution. silicate storage gives eggs which are scarcely 

to be distinguished at the end of six months 
from fresh ones. It will always be observed that the shells have become 
harder and more brittle due to the silicious deposit in their pores. The 
sealing of these makes it necessary to prick a pinhole in one end of the 
egg before boiling, for otherwise the expansion of the ever-present 
bubble of air would cause the shell to burst. 

Storage beyond a year is rarely desirable, though eggs will keep 
sweet in a silicate solution for at least two years. The membranes 
in the albumin weaken with time; but the thin whites are especially 
adapted for beating, as for making cakes, when they form a firmer 
mass of bubbles than do fresh whites. The uses to which stored eggs 
may properly be put are largely a matter of preference. Up to a 
year, they are quite wholesome and certainly adaptable to making 
cakes and custards, and to other cooking. Six months is perhaps as 
long as prime flavor can be expected in eggs served boiled or poached, 




GELATINOUS FILMS AND GELS 387 

but this is equally true of other storage methods. When care is 
used to place sterile eggs in silicate within a few hours after laying, 
it is still possible after six months to break them into a dish and then 
carefully pick up the yolk by surrounding it with the thumb and four 
ringers and find the white sufficiently strong to be lifted also. This 
is a test used by poultrymen to characterize fresh eggs. 

Dependence of Process on Gel Formation. Evidences that this 
process depends upon gel formation are the facts that other alkaline 
solutions have little value for preserving eggs, that dialysis of sodium 
oxide into the eggs will take place if the alkalinity of the solution is 
too high, and that eggs removed from the solution are protected for 
a longer time than fresh eggs, i.e., until the shrinkage of the gel per- 
mits the entrance of organisms able to cause decay. A bibliography 
of the literature of tgg preserving with silicates is given below: 30 ~ 83 

^Nowotuy, E., Poly. J., 143, 238 (1857). 
31 Stead, Brit. Pat. 4,910 (1882). 

^Ladd, E., N. D. Exp. Sta., Bull. (1897) ; also U. S. Dept. Agri. Bull, 103, 
(1897). 

^Strauch, R., Milchwirtschaft. Ztg., 26, 342 (1897). 

34 Thieriot, J. H., U. S. Consular Reports, 563-564 (Dec. 1897). 

35 Jarvis, L. G., Ontario Agri. College and Exp. Farm Report, 193-196 (1898) 

M Ladd, E., N. D. Expt. Stat. Bull, 35, 330-332 (1898). 

37 Jarvis, L. G., Ontario Agric. College and Exp. Farm Report, 130-134 (1899) 

38 Queensland Agric. J., 4, 418-419 (1899). 

^Schutt, F. T., Canada Expt. Farms Report 223 (1899). 

40 U. S. Agric. Dept. Bull, Farmer's Bull, No. 103, 32 (1899). 

41 Gilbert, A. G., Canada Expt. Farms Report, 251-277 (1900). 
43 Borntraeger, H., Oesterr. Chem. Ztg., 3, 295 (1900). 

43 Graham, W. R., Ontario Agri. & Exp. Union, Report, 31-3 (1901). 
"Brigham, A. A., Rhode Island State Exp. Stat., Report 304 6 (1901) 
^Rylander, J. A., Brit. Pat. 23,523 (1901) ; /. Soc. Chem. Ind., 21, 183. See 
also U. S. Pat. 696,495 (1902). 

46 Brown, E., /. Board Agric. (London), 9, 494-497 (1903). 

47 Guenther, Richard, U. S. Statistics Bureau, Dept. of Commerce & Labor 
Consular Reports, No. 276, 73, 66-67 (1903). 

^Irwell, L., Dietet. and Hyg. Gas., 20, 1096 (1904). 

40 Jeffrey, J. S., N. C. Exp. Stat. Bull, 191, 11-17 (1905). 

60 Langworthy, C. F., U. S. Dep. of Agric, Farmers' Bidl, No. 128, 34-35 
(1906). 

51 Thatcher, R. W., Wash. Stat. Bull, 71, 14 (1907). 

^Prall, F., Z. Nahr. Genussm., 14, 445 (1907). 

53 Bell, G. Arthur, U. S. Dept. of Agric, Farmers' Bull, No. 287, 41-42 (1907) 

"Hendrick, J., /. Agric Soc, 2, 100 (1907) ; Chem. Soc. Rept., 3, 292. 

^Vosseler, J., Der Planzer, 4, 129 (1908) ; Chem. Zentr., 19, 11, 1214. 

56 Pennsylvania Agric Exper. Stat., State College, Bull 87, 48 (1908). 

67 Lamson, G. H., Jr., Conn. Storrs Agric. Exper. Stat. Bull 55, 203-214 
(1909). 

58 Arizona Agric. Exp. Station, Tucson, Bull, 60, 398-464 ( 1909) 

^Berger, Richard, Z. Chem. Ind. Kolloide, 6, 172-174 (1910) 

60 Delaroquette, M., L'ind. beurre, 1, 600-603 (1910). 

"Berger, R., /. Ind. Eng. Chem., 3, 493-495 (1911). 

62 Lamson, G. H., Conn. Agric. Exper. Stat. Bull, 67, 269-274 (1911) ; abs in 
Chem. Zentr., 82, 11, 780. 



388 SOLUBLE SILICATES IN INDUSTRY 

Gels. 

Conditions Necessary for Formation. 

The diversity of conditions under which silica forms protective films 
invites the question of what the general conditions are under which we 
may expect their deposition to take place. The films are like gels 
which include the whole mass of reacting liquids except that they are 
laid down from systems which contain much more water and result 
from a condition at a surface. This may render colloidal silica un- 
stable by chemical reaction or its concentration may be increased locally 
by electrical forces. 

The conditions of gel formation are those which make colloidal silica 
unstable or permit the process of coalescence to proceed. The rate at 
which this occurs is greater in concentrated than in dilute solutions. 
It is accelerated by heat and retarded by cold. Like charges upon 
the colloidal particles increase their repulsion of each other and help 
keep them dispersed. Thus either strongly acid or strongly alkaline 
solutions are more stable than those near neutrality. Acids have less 
effect than alkalies, which, as we have seen, are able permanently to 
stabilize the solutions. 

Numerous data on the conditions of gel formation were obtained 
by Flemming. 84 He was not able to check the statements in the older 

63 Vanderleck, ]., American Food J., 6, No. 11, 13-14 (1911). 

** Bartlett, J. M., Maine Agric Exp. Station, 8th Inter. Cong. Appl. Chem., 18, 
51-56 (1912). 

•"Benjamin, Earl W., Cornell Reading Courses for the Farm Home, 1, 300 
(1912). 

"Evequoz, A., and E. P. Haussler, Zeit. Nahr.-Genuss., 25, 96-97 (1913). 

OT Flohr, Lewis B., U. S. Dept. of Agric., Farmers' Bull. 594, 4 (1914). 

08 Arizona Agri. Experiment Station Record, 32, 870 (1915). 

89 Wing, Annie L., /. Home Econ., 7, 257 (1915). 

70 Arnoux, Andre, Compt. rend., 163, 721-722 (1916). 

"Alder, Byron, Utah Agric. Exper. Stat., Logan, Circ. 25, 6 (1917). 

73 Heiduschka, A., Chem. Zentr., 88, ser. 5, 21, pt. 2A, 116-117 (1917). 
"Slocum, Rob R., U. S. Dept. of Agric, Farmers' Bull. 889, 21-22 (1917). 

74 Chem. Ztg., 41, 440, 477, 691-692, 848. 

75 Reinthaler, Chem. Ztg., 42, 195 (1918). 

76 Dvorachek, H. E., and S. R. Stout, Expt. Stat. Record, 39, 781 (1918). 
"Hasterlik, Alfred, Zeit. Nahr.-Genuss., 48, n.s., 36, 170 (1918); Pharm. 
Zentr., 58, 265-266. 

78 Olson, G. A., Wash. (State) Agric. Expt. Stat., Popular Bull. 114, 1-3 
(1918). 

79 Love, Fanny, National Stockman and Farmer, 43 (1919). 

80 U. S. Dept. of Agric, Weekly News Letter, 6, No. 46, 9 (1919). 

81 Jones, H. I., and R. Dubois, /. Ind. Eng. Chem., 12, 751-7 (1920). 

83 U. S. Dept. of Agric, Dept. Circ. No. 15, 3 (Boys' and Girls' Poultry Club 
Work). 

83 Dunbar, Ruth, Country Gentleman, 85, pt. 2, 46-47 (July 31, 1920). 

84 Flemming, W., Z. Phys. Chem., 41, 427-457 (1902). 



GELATINOUS FILMS AND GELS 389 

literature that stirring or the presence of graphite, taken as typical 
of foreign solids, affected the time of setting. His work leaves much 
to be desired because it charts a very limited set of conditions, but it 
was carefully carried out and can best be presented by a series of 
tables and graphs. He found that differences in the purity of silicate 
solutions such as those between commercial products and specially 
purified preparations were unimportant as far as time of gel forma- 
tion was concerned. Hydrochloric acid causes a slightly faster gela- 
tion than sulfuric acid though on the basis of normality the times are 
similar. A comparatively narrow range of concentrations was cov- 
ered and no consideration was given to the many other compounds 
which can be used to cause silica to gel. The presence of other elec- 
trolytes in the silicate, as well as the manner of mixing, is known to 
have a great effect on time and on physical character of the resultant 
gel. Flemming made all his gels by pouring silicate into acid, as he 
could in this way prevent immediate precipitation in many cases by 
providing for a local excess of acid in the mixing process. 

The process of coalescence may be interrupted, as by adding fresh 
silicate solution to one that has been neutralized but has not yet gelled. 
Such a solution when used as a vehicle for pigments and spread out 
as a paint becomes unstable on drying and is less soluble than a straight 
silicate film. 

Carter found that Na 2 0, 3.3Si0 2 , 1.38 specific gravity, can be made 
to form a uniform gel by stirring in hydrochloric acid diluted to 1.009 
(5 volumes concentrated hydrochloric acid to 100 volumes), and con- 
centrated hydrochloric acid (39.11 per cent, 1.20 specific gravity) 
may be stirred into the silicate solution at a concentration of 1.03 specific 
gravity (4.5°Baume) (1 part of silicate by weight to 10 parts of water 
by weight), in either case without instant precipitation. Of course 
vigorous stirring is necessary. 85 

Concentration. If the ratio of silica to water in a silicate solution 
is one to 300 mols or less, the whole solution, when partly or com- 
pletely neutralized, may set to a solid gel. 86 One mol of silica makes 
with 300 mols of water a gel which is soft and weak, and which 
soon squeezes out some of the liquid phase by syneresis, or upon stir- 
ring becomes a gelatinous precipitate at the bottom of its container 
with a relatively large volume of supernatant liquid. As the ratio of 
water to silica in the reacting liquids declines, firmer and firmer gels 

85 Unpublished data of the Philadelphia Quartz Company. 

83 Holmes, H. N., Colloid Symposium Monograph, 1, 25 (1923). 



390 



SOLUBLE SILICATES IN INDUSTRY 



are formed, first stiff friable jellies and finally hard strong grains 
having the superficial appearance of sand. The so-called silicate ce- 
ments used in dentistry are strong and durable. They depend upon 
the formation of a gel from hydrous silica dispersed with phosphoric 
acid in the presence of small amounts of water. 87 ' 88 The acid-resist- 
ing cements described in Chapter VII, made from silicate solution dried 
with inert filler and then treated with acid, also contain a hard gel 
formed in the presence of about 20 per cent of water which is quite 



2J 










/■s 

V 














V 
















^^^ 





Mols N* OH p«r I iter 

Fig. 178. — Turbidity and Gelation (Flemming). 



different in texture from gels which form in the presence of much 
water. The amount of water in the system at the time of setting de- 
termines the structural arrangement of the solid phase and such gels 
are therefore different from those from which the water is removed 

87 Weiser, Harry Boyer, "The Hydrous Oxides," 1st ed., New York : 
McGraw-Hill Book Co., 1926, 175 et seq. 

88 Crowell, Walter S., Am. Inst. Chem. Eng., Cleveland Meeting, May 31 to 
June 3, 1927. 



GELATINOUS FILMS AND GELS 



391 





1 










f 

i 








t . 












&/ 




< 








\*/° 




*; 1 


> 1 






/* i 










( 


•>/ / 




» T 












J 






°s 










<L^*^ 








/ 




1 


i 


1 


t 



CC £.(,$, ,f IIIKth 



Fig. 179. — Effect of Alkali on Setting Time (Flemming) 



m 
























X 












X 
SO 


< 


>\ 










\< 


) 























Cc. Etertj (kid 



Fig. 180. — Effect of Acid on Setting Time (Flemming) 



392 SOLUBLE SILICATES IN INDUSTRY 

after they have assumed the solid form. Concentration is therefor? 
a vital factor in determining the properties of a silicious gel. 

Temperature. Temperature is also important for it affects the rate 
of coalescence, and if we think of the gels as structures built up by 
the aggregation of colloidal particles we should expect the most orderly 
and the strongest arrangement to occur where the transition was 
gradual. This is confirmed by experience. If conditions are so chosen 
that reaction is immediate no homogeneous gels can be had, but if the 
reaction rate can be reduced, as by cooling, the same solutions may yield 
a uniform translucent gel including the whole mass of the mixed solu- 
tions. 

Acidity and Alkalinity. Gels can be made in both acid and alka- 
line solutions although both acid and alkali tend eventually to stabilize 
the silica and make the gel form more slowly. 

Flemming 89 noted the appearance of turbidity on a curve substantially 
parallel to that which marks the passing from liquid to solid. A sharp 
rise of viscosity takes place very shortly previous to the actual setting. 

Table 118. Effect of Alkali and Acid on Gelation. 

125cc. total volume 
25cc. standard HC1 (1.83 N.) 
25cc. standard silicate containing 8.969% Si0 2 
Sol. contains 1.795% Si0 2 

Gelation Time, Minutes 

25°C. 
3.17 
1.50 
1.33 
1.45 
1.67 
1.83 
2.17 
2.67 
3.17 
4.08 



Excess Alkali,* 


C 


cc. 


18°C. 


0.0 


6.75 


0.5 


2.90 


1.0 


2.10 


1.5 


2.12 


2. 


2.22 


2.5 


2.67 


3. 


3.13 


3.5 


3.50 


4. 


4.08 


5. 


5.22 


Excess Acid, 




cc. 




11 


160 


12 


105 


13 


80 


14 


65 


15 


43 


20 


20 



* Excess alkali added as NaOH. 

89 Z. Phys. Chem., 41, 427-457 (1902). 



GELATINOUS FILMS AND GELS 393 

Table 119. Time of Gelation. 
(Flemming) 

Alkaline Sols 
Mols Si0 2 Time to Gel 

per Liter Minutes 

0.270 0.81 

0.2-22 2.92 

0.135 34.45 

Acid Sols 

0.663 21.12 

0.707 15.15 

0.757 10.00 

Table 120. Effect of Temperature. 

Alkaline Sols 
Temperature Time to Gel 

°C. 'Minutes 

35 14.05 

45 8.65 

55 4.82 

Acid Sols 

25 10.00 

30 7.25 

35 5.15 

40 4.12 

Table 121. Setting Time Related to Content of Acid and Alkali. 

(Flemming) 
Constant 

Total volume 40cc. 

Silicate volume lOcc. 

N F£C1 volume lOcc. 

Silicate contains 2.3 mols. Si0 2 

Mixture contains 0.575 " Si0 2 + xNaOH or HC1 

X60 





34.500 gm. per liter 




iols NaOH 


Mols HC1 


Average Setting 


per Liter 


per Liter 


Time in Minutes 


0.225 




26.00 


0.150 




10.25 


0.118 




3.25 


0.085 




2.75 


0.050 




2.25 


0.025 




1.00 


0.005 


# m 


5.00 


0.000 


0.000 


2300.00 




0.015 


7040.00 




0.025 


24540.00 




0.075 


29400.00 


.... 


0.138 


26640.00 




0.325 


16560.00 


.... 


0.890 


3580.00 


.... 


1.830 


1200.00 



394 SOLUBLE SILICATES IN INDUSTRY 

Table 122. 

1.625 per cent Si0 2 

Mols NaOH Setting Time 

per Liter Minutes 

0.0284 1.33 

0.0341 0.82 

0.0398 0.83 

0.0455 0.89 

0.0569 0.95 

0.0798 1.43 

0.1139 2.40 

4.57 per cent Si0 2 

Mols HC1 Setting Time 

per Liter Minutes 

4.07 23.6 

4.28 17.08 

4.49 14.33 

4.71 12.17 

4.92 11.57 

5.13 10.00 

Vinal 90 investigated the proportions of strong sulfuric acid and sili- 
cate solutions needed to form solid electrolytes in storage batteries. 

Time of setting before solidification takes place, and the stiffness 
of the jelly afterwards, are regulated by the proportions of the acid and 
silicate. When thickening of the mixture begins, the final setting 
process occurs within a very few minutes. An interesting time reaction 
is represented by this mixture, if it is made from dilute solutions, as 
for example, H 2 S0 4 specific gravity 1.275 and silicate of specific grav- 
ity 1.210; the greater the percentage of silicate in proportion to the 
acid, the more quickly the jelly sets and the more solid it becomes. The 
hard jellies are resonant. 91 ' 92 

Different acids give similar results on the basis of normality. Hy- 
drochloric acid is somewhat faster than sulfuric. 93 ' 94 

Jelly electrolytes may be made from mixtures of concentrated sul- 
furic acid and dilute solutions of silicate or from dilute solutions of 
the acid and somewhat more concentrated solutions of the silicate. Vinal 
shows that the time of setting is shortened by increasing the percentage 
of silicate and by using stronger acid. It is possible to prepare the 
jelly as a clear, translucent, bluish mass which varies in consistency 

90 Vinal, George Wood, "Storage Batteries." New York: John Wiley & Sons, 
1924, 121 et seq. 

"Williams, Albert H., U. S. Pat. 1,403,462 (Jan. 10, 1922). 

92 Thatcher, Charles J., U. S. Pat. 1,393,467 (Oct. 11, 1921), covers another 
application in storage batteries. 

93 Electro-Osmose Ges., Aus. Pat. 102,961. 

94 Poulsen, A., Brit. Pat. 491 (1909); U. S. Pat. 1,012,911; Fr. Pat. 410,716. 



GELATINOUS FILMS AND GELS 



395 



from a thick liquid to a fairly hard resonant solid. The time of setting 
for various combinations is shown in Figure 181. The curves are num- 
bered from 1 to 11 and represent different proportions of the silicate 
and acid solutions measured by volume, as follows : 

parts 1.275 acid to 1 part silicate 

parts 1.275 acid to 1 part silicate 

parts 1.275 acid to 1 part silicate 

parts 1.275 acid to 1 part silicate 

parts 1.400 acid to 1 part silicate 

parts 1.400 acid to 1 part silicate 

parts 1.400 acid to 1 part silicate 

parts 1.400 acid to 1 part silicate 

part 1.840 acid to 4 parts silicate 
part 1.840 acid to 3 parts silicate 
part 1.840 acid to 2 parts silicate 

Use in Storage Batteries. According to Vinal, batteries contain- 
ing jelly electrolytes do not have as good electrical properties as those 



Curve 


1, 


5 


<< 


2, 


4 


<( 


3, 


3 


a 


4, 


2 


« 


5, 


5 


<< 


6, 


4 


K 


7, 


3 


<( 


8, 


2 


<« 


9, 


1 


<< 


10, 


1 


it 


11, 


1 




J.ooo I.IOO /.zoo 

Sp>6. of Sodium S///eafe Solutions 

Fig. 181. — Preparation of lelly Electrolytes from Sulfuric Acid and Silicate 

of Soda. 



396 SOLUBLE SILICATES IN INDUSTRY 

with the ordinary electrolytes. The internal resistance is higher and 
the capacity lower. They do not last well in service. 

Since the jelly formed by the action of the silicate and the acid 
has a tendency to crack away from the plates of the storage battery, 
owing to shrinkage occurring because of the evaporation of water, 
Schoop has advocated the addition of paper stock, cellulose, or asbestos 
to the mixture to serve as a binder. In preparing this material for 
use, the silicate is poured into the acid and thoroughly mixed. The 
binding material is then added, and the mixture allowed to stand until 
thickening of the solutions is observable. When this point comes, it 
is necessary to pour the electrolyte into the cells immediately, as it is 
impossible to do so after solidification has actually taken place. When 
the electrolyte is prepared in this manner, it will not stick to the plates. 
Gas bubbles, which are formed at the plates during the process of the 
charging, will have an opportunity to escape between the plate and the 
solid electrolyte. A layer of fluid electrolyte is desirable between the 
solid electrolyte and surface of the plate. This facilitates the reactions 
within the storage battery and increases the capacity. Schoop 95 obtained 
a patent on jelly electrolytes in 1889. His experiments were further 
described in 1890. 

Resistance of a solid electrolyte of this character is approximately 
double that of the ordinary liquid electrolyte. Local action is con- 
siderably increased and the capacity of the cells reduced. The use of 
such electrolytes may be found desirable for special work, not for ordi- 
nary types of service. The use of sodium silicate for the preparation 
of solid electrolytes has been periodically rediscovered a number of 
times during recent years. 96-99 Its use, however, dates back probably 
thirty years. 100 A clear detailed description is given by Schoop. 

Batteries filled with hard grains of silica gels, which have been formed 
separately, dried, and washed, do not splash, and have better electrical 
properties than do those with gels formed in situ. 

Gels Formed by the Action of Salts of Heavy Metals. Gels have 
also been made by reaction between silicate solutions and salts of vari- 
ous metals. Organic compounds, such as phenols and aldehydes, which 

95 Electrotech. Z., 10, 473 (1889) ; Electrician, 25, 253 (1890). 
98 Winkler, C. R, U. S. Pat. 471,590 (March 29, 1892). 
"Hirsch, H. H., U. S. Pat. 1,183,009 (May 16, 1916). 
98 Williams, H. M., U. S. Pat. 1,417,007 (May 23, 1922). 
"Hacking, E., U. S. Pat. 1,421,217 (June 27, 1922). 

100 "Das Sekundar Element," Encyklop'ddie der Electro chemie, IV, Part 2, 140 
(1895). 



GELATINOUS FILMS AND GELS 397 

can react with sodium may also release silica to form gels. 101-103 Alka- 
line aluminates are also useful 101 - 106 — thus gels may be formed 
which contain colloids other than silica and which combine with the 
structural properties of the gel a specific chemical value which comes 
from the added material. Gels may thus be used as media of great 
surface to carry catalysts. Base exchange reactions used in softening 
water are also rendered more efficient by taking advantage of gel 
surfaces. 107-109 

To prepare gels for technical use, washing to remove reaction prod- 
ucts is usually the next step. In the case of ordinary silica gel, water 
alone is required, but the process is a slow one, as time is required to 
allow diffusion through the pore structure to take place. Holmes varies 
the porosity of the final product by using a salt of iron, nickel or 
other heavy metal as reagent to cause gelation and then dissolving 
it out with acid, thus leaving in addition to the natural porosity the space 
occupied by the metal. 

Drying and Rehydration. 

Van Bemmelen's Results. Drying and rehydration of silica gels 
has been studied by Van Bemmelen. 110 Shrinkage occurs with drying 
down to about two mols of water. Near this point the clear gel begins 
to show cloudiness and gradually becomes opaque only to become clear 
again in the region of one mol of water. Though these points are 
quite definite for a particular sample of gel, samples vary greatly ac- 
cording to the manner of their preparation and it must not be assumed 
that definite hydrates are involved. The range for the first point is 
about 1.5 to 3 and for the second 0.5 to 1. 

Molecular Rearrangements. The rearrangement of particles which 
results in gel formation does not cease at that point but continues with 
syneresis and drying shrinkage. Old samples of silica gel exhibit crystal- 
line structure as shown by the diffraction of X-rays and this may 
be looked upon as the result of continued action of the same forces 

101 Marcus, R., Ger. Pat. 279,075 ( 1914) . 

102 Michael, J. and Co., Ger. Pat. 348,769 (1922). 

103 Van Baerle, A., Swiss Pat. 93,268. 

104 Holmes, Harry N., and J. A. Anderson, hid. Eng. Chem., 17, 280 (1925). 
105 Behrman, Abraham S., U. S. Pats. 1,515,007 (Oct. 8, 1927); 1,584,716 (May 

18, 1926) ; Brit. Pat. 277,082 (Nov. 2, 1927). 

106 Wheaton, H. J., U. S. Pat. 1,586,764 (June 1, 1926). 

107 Patrick, Walter A., U. S. Pat. 1,577,186 (March 16, 1926); U. S. Pat. 
1,577,190 (March 16, 1926). 

108 Chemische Fabrik auf Aktien Vorm. E. Schering and W. Klaphake, Brit. 
Pat. 250,078 (July 20, 1925) ; C. A., 21, 995. 

109 Govers, Francis X., U. S. Pat. 1,504,549 (Aug. 12, 1924). 
110 Z. anorg. Chem., 13, 233 (1896). 



398 SOLUBLE SILICATES IN INDUSTRY 

which cause gelation. 111 Morey 112 has found that the treatment with 
steam at 4-5 atmospheres of a certain alumino-silicate gel which does 
not show crystal structure when dried helow 100° Centigrade, causes 
a rearrangement of the particles in such a way that an X-ray diffrac- 
tion pattern is obtained. 

Porosity of Silica Gel. The thermal history of silica gel makes 
great differences in its physical character. Holmes 113 proposes moist 
heat treatment to increase porosity by inducing set before the shrinkage 
of the usual drying process has reached its limit. In this way he was 
able to make gels with an increased capacity for the condensation o f 
vapors. The method is proposed as a general means of producing gels 
of the right porosity for any given use. 

The size of capillaries best adapted for the condensation of one liquid 
is not necessarily best for another. Also the conditions which deter- 
mine the properties of the gel are difficult to reproduce and different 
experimenters may easily obtain discordant results. The exact control 
of such factors — concentration, acidity or alkalinity, heat treatment and 
rate of drying — is a necessary basis of technical preparation of sili- 
cious gels. 

Absorption of Moisture. Dry silica gels absorb moisture with 
great avidity. They are much more efficient than calcium chloride for 
drying air for laboratory purposes. Two major industrial uses based 
on this property have been proposed. Plant designs have been drawn 
for drying air for blowing blast furnaces by exposing it to finely di- 
vided silica gel which is continuously removed from the system and 
re-activated by heat. The removal of moisture can be made quantita- 
tive and the advantages of dry air are great. 114 The problem is one 
of cost. 

Heat absorption by evaporation of water or other volatile liquid into 
an atmosphere the vapor pressure of which is reduced by condensation 
of the evaporating liquid in the pores of silica gel is used to produce 
artificial refrigeration. The gel requires only a source of heat to drive 
off the absorbed liquid and the cycle may be repeated indefinitely. 115 

Condensation due to the lowering of vapor pressure in a small open- 
ing does not alone account for the accumulation of vapors in silicious 
gels. Surface phenomena also come into play and water is specifically 
adsorbed on these surfaces, as may be shown by a study of volume 

^Scherrer, P., Nachr. Ges. Wiss., Gottingen, 96, 100 (1918). 

112 Morey, George W., personal communication. 

113 Holmes, Harry N., hid. Eng. Chem., 18, 386 (1926). 

114 Silica Gel Corporation, Baltimore, Md., Bulletin No. 2 (1921). 

115 Fulton, Chem. Age, 31, 521 (1923). 



GELATINOUS FILMS AND GELS 



399 



changes of supercooled systems. The adsorbed moisture does not 
freeze or increase in volume with falling- temperature. 110 



Adsorption. 

Other Vapors and Gases. Other gases may also be condensed but 
the great affinity of the gels for water is a serious limitation on ac- 
count of the difficulty of securing, industrially, gases which are free 
from water. 117 Condensation of petroleum vapors breathed from stor- 




Wafe, 



Content £nt*r, no the /j 



IZ 



hfe/f/jt of Get -/Oframs 
/fate i J~QQ tt/nttn 



10 



VOfier at Jg°C Ct.XU7aeSfr*) 






Set Ate /immerse* 1 '* fyO *f sot 



Water /r> e*/t f?* f cteterm/nea' 
ty r%& mettled 



fit pa< nt & jel 6acL attxartiett 



2/S-f* <S ,t* o*» #e/ 9 At- ~f ty 
Saturation ia/ve Pf<7 % 



/10 'to 2°° 

77m e im Mm u t~e s 



Fig. 182. — Adsorption of Aqueous Vapor by Silica Gel at 30° C. 

age tanks or the reclamation of lacquer solvents from air would be 
useful and easy of accomplishment were it not for the fact that the 
gel shows a preferential action toward water as compared with hydro- 
carbon or other organic vapors. 

Adsorption of S0 2 has been exhaustively studied by Patrick and his 
collaborators and a long list of condensible vapors has been experi- 
mented upon. This literature has been critically reviewed by Weiser 118 

lia Truog, Emil, Colloid Symposium Monograph, 111, 228-240 (1925). 

117 Teitsworth, Clark S., U. S. Pat. 1,570,537 (Jan. 19, 1926). 

118 Weiser, Harry B., "The Hydrous Oxides," 1st ed., New York: McGraw- 
Hill Book Co., Inc., 1926. 



400 



SOLUBLE SILICATES IN INDUSTRY 



Weight of Cef - /O grams 

Volume of flir • SOO cc/m/n 

nir Saturated ivif/i oajo/">e 
Vapor at f'~ /0 ° c 

Concert traf/on of f^a/oor 




fe/np. of ffa/sor^>f/on ~ 2S°C 

Saturation Va/ve (*'**% 

(2 -20- 4 %> 



20 30 40 SO 

Time /n Afsnutes 



60 



70 



Fig. 183. — Adsorption of Gasoline Vapor by Silica Gel. 

and is not extensively treated here as our principal concern is with 
the soluble silicates. 

Sulfur Compounds. Silica gel 119 - 129 i s also used for adsorption 



119 
120 



Ray, Arthur B., Chem. & Met. Eng., 29, 354-359 (1923) ; C. A., 17, 3390. 
Gas Accumulator Co., Brit. Pat. 234,462 (May 22, 1924) ; C. A., 20, 804. 

m Bradner, D. B., U. S. Pat. 1,457,493 (June 5, 1923) ; Chem. & Met. Eng., 29, 
72 (1923). 

^Miller, E. B., Am. Inst. Chem. Eng., 12th Semi-Annual Meeting, Montreal, 
Can. (June 28, 1928) ; Davison Chem. Co. Bull. (Baltimore, Md. : Aug. 1920). 

^Holden, E. C, Chem, & Met. Eng., 28, 801-804 (1923) ; C. A., 17, 2333. 

124 Anon., Chem. & Met. Eng., 29, 121 (1923). 

^Furness, Rex, Chem. Ind., 42, 850-854 (1923) ; C. A., 17, 3774-3775. 

126 Chaney, N. K., Arthur B. Ray, and A. St. John, Ind. Eng. Chem., 15, 
1244-1255 (1923). 

^Patrick, W.A., Chem. & Met. Eng., 22, 949-950 (1920). 

ia5 Behr, E., and W. Urban, Z. angew. Chem., 36, 57-60 (1923); C. A., 17, 
1741-1742. 

129 Silica Gel Corporation, Baltimore, Md., No. 2 (1921). 



GELATINOUS FILMS AND GELS 



401 



of sulfur compounds in refining petroleum and benzol, from which 
processes it may be regenerated by displacement of adsorbed material 
with water and by heating. This method has the great advantage of 
leaving unattacked the valuable unsaturated compounds which are re- 
moved in refining with sulfuric acid. 

References to the literature of preparation and use of silica gels in- 
cluding patents have been assembled by Kausch. 130 

Reactions in Gels. The physical form of silicious gels has been 
used to modify certain reactions by altering the rate at which the react- 




> O i / 2 J + ? 6 7 

Per Cent S0 2 /n fas /trirtvre 

Fig. 184.— Adsorption of S0 2 by Silica Gel. 

ing compounds come into contact. The beautiful experiments of Liese- 
gang 131 and Holmes 132 are of this character. If a soluble iodide is 
mixed with a silicate solution which is then caused to gel by the addition 
of acid, a solution of a lead or mercuric salt may then be poured upon 
the surface of the solid gel. A slow process of diffusion brings the 
heavy metal and iodine into contact without agitation and large crys- 

130 Kausch, Oscar, "Das Kieselsauregel und die Bleicherden," Berlin: Springer, 
1927. 

131 Liesegang, Z. anorg. Chem., 48, 364 (1906); Z. physik. Chem., 59, 444 
(1907). 

^Holmes, Harry N., "Laboratory Manual of Colloid Chemistry," New York: 
John Wiley & Sons, Inc., 1922, 93; /. Am. Chem. Soc, 40, 1187-1195 (1918). 



402 SOLUBLE SILICATES IN INDUSTRY 

tals are formed, very different from the finely divided product of 
mixing the solutions directly. This method has been applied to the 
formation of lead trees, gold crystals, and the rhythmic bands which 
simulate the banding of agate. It would appear to be applicable to any 
cases in which a solid is formed by the interaction of two aqueous 
liquids, one of which is miscible with a silicate solution or a silica sol. 
The following procedure from Holmes gives the technic for one case : 

"A 1.06 specific gravity waterglass — N acetic acid mixture, containing 
2 cc. of N lead acetate to every 25 cc. was poured into test tubes. After 
the silicic acid gel set firmly, it was covered with 2 N potassium iodide. 
A compact layer of lead iodide quickly formed on the surface, followed 
very soon by crystallization below the surface of the gel. In a few days 
fern-like fronds grew down into the gel, mixed with many hexagonal 
plates. These concentrations may be varied with interesting results, 
and the lead salt may be used above the gel with the potassium iodide 
in the gel. The first order is much better." 

Base for Catalysts. 

The great surface of silica gels makes them useful for reactions which 
take place on surfaces when it is possible to so activate the silica that 
it will function. 133 Platinized silica gel has been used for the catalytic 
conversion of S0 2 to S0 3 in the contact process for sulfuric acid. 
Other catalytic agents, as nickel for hydrogenating fatty oils, have 
been deposited on gel surfaces. 134-139 

Base Exchanging Gels. 

High Silica Silicates. Wheaton 140 found that by partly neutraliz- 
ing a silicate solution with an acid under such conditions that a gel was 
formed, and washing out the salt of the acid, part of the sodium re- 
mained adsorbed or combined in such a way that it did not give an 
alkaline reaction to indicators. This sodium could be partly displaced 

133 Silica Gel Corporation, Baltimore, Md., Bull. No. 2, 29 (1921). 

134 Van Arsdel, Wallace B., U. S. Pat. 1,497,815 (June 17, 1924). 

135 Bosch, Carl, Otto Schmidt and Alwin Mittasch, U. S. Pat. 1,391,666 (Sept. 
27, 1921). 

136 Patrick, Walter A., Brit. Pats. 212,034 and 212,035 (Jan. 17, 1923). 

"'Patrick, Walter A., U. S. Pats. 1,297,724 (March 18, 1919); 1,577,187, 
1,577,188, 1,577,189, 1,577,190 (March 16, 1926). 

138 Reyerson, L. H., and Thomas Kirk, Colloid Symposium Monograph, Vol. 3, 
1925, 1, p. 99-102. 

^Reyerson, L. H., and L. E. Swearingen, /. Phys. Chem., 31, 88-101 (1927) ; 
C A. 21 844 
" 140 Wheaton, H. J., U. S. Pat. 1,100,803 (June 23, 1914). 



GELATINOUS FILMS AND GELS 403 

by equivalent quantities of calcium or magnesium from hard water. 
The exchange would also proceed in the reverse direction when the 
exhausted gel was brought into contact with a sodium salt solution. 
Thus the material could be. used like a zeolite to soften water and 
could be regenerated with common salt. This gel did not reach great 
practical importance on account of relatively low capacity as compared 
with other available base-exchanging compounds. 

"Doucil." * A material of similar structure and much greater ca- 
pacity was obtained by forming a gel of the composition of Na 2 0, 
Al 2 3 ,5Si0 2 . With this an exchange of more than 6 per cent of 
its weight of CaO could be obtained, a higher capacity than either 
natural or prior synthetic materials would yield. It is known as 
Doucil. 141 - 145 

The porosity of this gel is such that the grains after centrifugal ex- 
traction contain approximately their own weight of water. When air 
dried, the grains become opaque. If they are then put into water a 
transparent area is seen to form at the outer surface and progress 
rapidly inward from all directions. The pressure of the rush of water 
through the capillaries is enough to disrupt the grains by the pressure 
of entrapped air, which may be seen to escape as bubbles when the 
grains burst. 

As grain size is an important consideration in water-softening plants 

* Doucil, manufactured by the American Doucil Company, 121 South Third 
Street, Philadelphia. 

141 Vail, James G., Trans. Am. Inst. Chem. Eng., 16, Pt. 2, 119-131 (1924); 
Silicate P's & Q's, 4, No. 5; 5, No. 7, Philadelphia: Philadelphia Quartz Co., 
1925; 6, No. 5, No. 10 (1926). 

143 Joseph Crosfield & Sons, Warrington, England, Booklet, "Water softening 
by means of Doucil." 

143 Hilditch, T. P., and H. J. Wheaton, Ghent. & hid., 44, No. 36, 885-887 (1925). 

144 Joseph Crosfield & Sons, and H. J. Wheaton, Brit. Pat. 142,974 (May 20, 
1920) ; Mex. Pat. 21,986 (Nov. 5, 1922) ; Brit. Pat. 196,646 (April 30, 1923) ; Fr. 
Pat. 565,006 (Nov. 2, 1923) ; Belg. Pat. 309,780 (May, 1923) ; Brit. Pat. 177,746 
(April 6, 1922) ; Belg. Pat. 301,994 (April 15, 1922) ; Fr. Pat. 549,051 (Mar. 
17, 1922) ; Mex. Pat. 21,987 (Nov. 5, 1922) ; Brit. Pat. 206,267 (Nov. 8, 1923) ; 
Belg. Pat. 312,583 (Sept. 8, 1923); Fr. Pat. 569,677 (Jan. 9, 1924); Mex. Pat. 
21,989 (Nov. 5, 1922) ; Ger. App. No. C. 33879 Class IV/12 i. 

145 Hilditch, Wheaton, and Crosfield, Brit. Pat. 206,268 (Nov. 8, 1923); Belg. 
Pat. 312,522 (Sept. 8, 1923); Fr. Pat. 569,725 (Jan. 9, 1924); Ger. App. 33,877 
(Class VIII/21); Brit. Pat. 203,158 (Sept. 6, 1923); Belg. Pat. 312,584 (Sept. 
8, 1923); Fr. Pat. 569,698 (Jan. 1924); Mex. Pat. 21,990 (Nov. 3, 1922); Ger. 
Appl. 33,878 (Class IV/12i) ; Brit. Pat. 206, 269 (Nov. 8, 1923) ; Belg. Pat. 
312,523 (Sept. 8, 1923) ; Fr. Pat. 569,726 (Jan. 1924) ; Ger. Appl. 33,876 (Class 
VIII/21) ; Brit. Pat. 203,497 (Sept. 13, 1923) ; Fr. Pat. 565,226 (Nov. 5, 1923) ; 
Belg. Pat. 309,963 (May 1923) ; Ger. App. C.33613 (Class IV/85 b2) ; Brit. Pat. 
212,453 (March 13, 1924) ; Brit. Pat. 224,656 (Nov. 20, 1924) ; Brit. Pat. Prov. 
Specification 28,773 (1924); U. S. Pat. 1,586,764 (June 1, 1926). 



404 



SOLUBLE SILICATES IN INDUSTRY 



it is convenient to bring the gel on the market with its pores full of 
water and to avoid allowing it to dry before it is put in service. 

It is neutral to indicators and capable of thousands of cycles of soften- 



4.00 






£3.00 

b 

1 2 

i 

^ i.oot 

I 

5 

















/ 1*1 
/ / 7 


1 








J 


•/ 




i i 





25 50 75 100 

L/T/?fS or WAT£tf PASSfP OY£f? 400 GFrlS or POUC/L (50%H 3 0)/N 50 cm. 

BEP. 

Fig. 185.— Water Softening by Doucil of Varying Grain Size. 

ing and regeneration. Its rated capacity is 12,500 grains CaCO a per 
cubic foot (1 cu. ft. = 50 lbs. containing 50% water) for a product 
graded between 8 and 30 mesh, producing water of zero hardness. 



Chapter XII. 
Additional Uses. 

Our earlier chapters have dealt with uses of soluble silicates in a 
sequence intended to illustrate the properties involved, and we arrive 
at the final group with many things unsaid. If the elements of this 
chapter seem rather miscellaneous, the reader is asked to view them 
as suggestions, for the examples have been chosen with a view toward 
helping him realize the diversity of properties of soluble silicates which 
stand at the service of industry. There can be little doubt that new 
uses will be found as new problems are presented and though many 
of these have little industrial importance, a patient cultivation of the 
field is sure to yield some good fruit. 

Purifying Water. 
Precipitation of Silicate Solution by Sodium Compounds. 

Since the introduction of fusion methods for making silicates which 
have the ability to exchange bases, as do zeolites, various workers 
have sought to reach the same results by wet methods. The most im- 
portant of these products are sodium aluminum silicates, for which 
the aluminum may be derived from various soluble compounds, but all 
the wet processes make use of a silicate solution. 1 ' 2 > 3 - 4 

Boehringer and Gessler 5 precipitated silicate solutions with sodium 
aluminates, plumbates, zincates and stannates, collected the flaky pre- 
cipitates, and by filtering and by drying made granular masses capable 
of removing alkaline earth metals as they occur in natural waters. 

Characteristics of These Precipitates. These could be regenerated 
by contact with salt solutions according to the equation : 

Ca(R 2 3 ) x . (Si0 2 ) y + 2NaCl = Na 2 (R 2 3 ) x . (Si0 2 ) y + CaCl 2 

'Killeffer, D. H., Ind. Eng. Chem., 15, 915-917 (1923) ; C. A., 17, 3393. 

2 Gans, R., Chemische Industrie, 32, 197-200 (1909); U. S. Pat. 943,535 
(1909) ; Can. Pat. 208,968 (March 1, 1921) ; C. A., 15, 1195; Ger. Pats. 423,224 
(Nov. 18, 1916) ; 426,083 (Oct. 12, 1919). 

3 Vogtherr, H., Z. angew. Chem., 33, 1, 241-243. 

4 Gutensohn, A., U. S. Pat. 773,494 (Oct. 25, 1904) ; /. Soc. Chem., 23, 1109. 

5 Boehringer, Rudolph, and Albert E. Gessler, U. S. Pat. 1,050,204 (Jan. 14, 
1913). 

405 



406 SOLUBLE SILICATES IN INDUSTRY 

in which the value of x and y might vary widely. Indeed, they could 
be used in general for all the purposes proposed by Gans, but with the 
advantage of higher rates of reaction, at least partly due to greater 
porosity and more surface of the insoluble silicate exposed to the water 
or salt solution. 

Bodies known to have properties similar to zeolites had been pre- 
viously made experimentally by precipitating silicate solutions. Thus 
Way, 6 studying the action of soils toward fertilizing materials, at- 
tempted the synthesis of compounds which might occur in the soil and 
observed the exchange of bases by double silicates made by precipitating 
silicate solutions but did not discover that the exchange reaction could 
be reversed; and Haushofer 7 described the preparation of sundry 
double silicates by the use of various salts for precipitation. Similar 
products were also encountered in trying to duplicate in the laboratory 
zeolitic minerals which occur in nature, 8, 9> 10 ' 1X but not until after the 
teachings of Gans did they assume any industrial importance. 

Bibliography of Zeolite Water Softening.* The technic of wet 
methods directed to economies and particularly to the development of 
silicates able to exchange increasing amounts of bases without losing 
their hard granular character on long exposure to water and adapting 
them to various reactions has claimed the attention of numerous in- 
ventors, of whom Wheaton, Hilditch, and Behrman, who made use of 
the peculiar characteristics of gel structure, have been mentioned in 
the foregoing chapter. 12-19 

Treatment of Greensand by Silicate Solutions. 

Silicate solutions have also been employed in preparing glauconite 
or natural greensand for use as a water softener. In its natural state 

"/. Roy. Agri. Soc, 13, 128-133 (1852). 

*/. prakt. Chem., 99, 241 (1866). 

8 Ammon, von, "Silikate der Alkalien u. Erden" (Gottingen, 1862), 37; Gmelin- 
Kraut, 3, 1,280 (1912). 

9 Heldt, /. prakt. Chem., 94, 143 (1865). 

10 Deville, Compt. rend., 54, 324-327 (1862). 

"Lemberg, Z. dent. geol. Ges., 35, 573 (1883). 

13 De Briinn, P., U. S. Pat. 1,161,200 (Nov. 23, 1915) ; Can. Pat. 204,243 (Sept. 
21, 1920) ; C. A., 14, 3290; Brit. Pat. 26,078 (Nov. 13, 1913) ; C. A., 16, 603. 

13 Kolb, A, U. S. Pat. 1,193,794 (Aug. 8, 1916). 

"Kriegsheim, H., U. S. Pat. 1,208,797 (Dec. 19, 1916). 

15 Rudorf, G., U. S. Pat. 1,304,206 (May 20, 1919). 

16 Massatsch, C., U. S. Pat. 1,343,927 (June 1, 1920). 

17 Willcox, O. W., U. S. Pat. 1,499,492 (July 1, 1924). 

18 Behrman, A. S., U. S. Pat. 1,515,007 (Nov. 11, 1924). 

10 Blumenthal, F., U. S. Pat. 531,836 (March 31, 1926). 

* A bibliography of the extensive literature of zeolite water softening pre- 
pared by Bartow and Baker has not been published, but a copy is in possession 
of the Philadelphia Quartz Company. 



ADDITIONAL USES 407 

it tends to undergo partial decomposition at surfaces long exposed to 
water, which is thus contaminated and discolored by iron compounds, 
a very objectionable characteristic in a device whose function is to 
provide a supply of clear soft water. To overcome this, Lee treated 
glauconite grains with A1 2 (S0 4 ) 3 in a 10°Baume solution, washed, 
treated with a 10°Baume silicate solution (presumably Na 2 0, 3.3Si0 2 ), 
washed again to neutral reaction and then baked at 500° C, which yielded 
a stable hard product in which iron at the surface was oxidized from its 
original green color to dark brown. 20 ' 21 

This procedure was simplified by Nordell, 22 who found it sufficient 
to exhaust the glauconite with hard water, that is, to replace the ex- 
changeable alkali metals with alkaline earth metals, and then to apply 
a hot silicate solution. The glauconite was thus stabilized without 
change of color and more cheaply. The finished product should be 
kept moist, for, in common with all wet-process base-exchange ma- 
terials, it undergoes some loss of exchange power if completely dehy- 
drated. 23 The capacity of greensand may be increased as much as 
50 per cent by soaking in hot dilute Na 2 0, 3.3Si0 2 without previous 
exchange of alkali metal for alkaline earth metal. During this treat- 
ment silica is deposited in the grains, 24 tending to harden them ; but the 
reason for increased exchange capacity is not fully understood. The 
effect has also been observed on base-exchange silicates made by sin- 
tering argillaceous materials with alkaline compounds. 

Miscellaneous Uses. 
Purifying Sugar Solutions. 

Colloidal compounds which contain silica have long been known to 
have value for separating gums and coloring matter from sugar solu- 
tions. Aluminum hydroxide and silicate of soda were used by Clough. 
Bachler 25 attributed the action to the fact that the gums are colloids of 
negative charge capable of precipitation by a positively charged colloid. 
Neutralization of acids is also necessary to satisfactory recovery of 

20 Lee, Yong K., U. S. Pat. 1,527,199 (Feb. 24, 1925). 

21 Brit. Pat. 228,380 (March 17, 1924). See also U. S. Pat. 1,472,011 (Oct. 
23, 1923). 

,23 U. S. Pat. 1,506,198 (Aug. 26, 1924). 

23 See also Permutit Company, Brit. Pat. 228,380 (March 17, 1924) ; C. A., 19, 
2866 (1926). 

24 Behrman, A. S., International Filter Co., Tech. Bulletin No. 3002, U. S. 
Pat. 1,624,711 (April 12, 1927). 

25 Bachler, F. R., Aus. Pat. 471,295 (1914); Cf. Wells, C. H., Louisiana 
Planter and Sugar Mfg., 71, 394 (1923). 



408 SOLUBLE SILICATES IN INDUSTRY 

sugar. 26-30 The silicious colloid may not always be produced from 
a silicate solution but such is a convenient starting point. 

Prevention of Fungus Growths. 

The fungi which cause blue stain on freshly cut lumber in hot, 
humid climates can be prevented by passing the freshly cut boards 
through a dilute silicate bath, which has the advantage over other 
alkaline salts that it penetrates the wood less deeply. It has been 
successfully used on a large scale. 

Experiments to use silicate solutions as sealing media in tree graft- 
ing gave a much lower percentage of success than when waxes were 
employed. This was to be expected. 

Insecticides. 

Insecticides in which silicate solutions exert a deflocculating or ad- 
hesive action have been used. 31 They are not of themselves used to 
destroy insect life without injury to plants, but are able to help the 
adherence of sulfur or other more active materials. Good dispersion 
of insecticides is also important to secure covering of plant surfaces, 
and here the deflocculating properties of silicates come into play. Sticky 
silicate solutions have been used to fill trenches for the prevention of 
the migration of corn borers. 

Leather Tanning. 

Processes for preparing leather are grouped into vegetable and 
mineral tannages. The deposition of basic chromium compounds is 
the most familiar of the second group, but it is well known that a 
great many inorganic compounds may be used to prepare skins in a 
non-putrescible condition more or less suited to the various uses of 
leather. Silica in colloidal dispersion has been studied in this con- 
nection and the development has reached a point where flexible white 
leathers made with its help are now in commercial use. Sols containing 
up to five per cent silica are stabilized with mineral acids at a pH of 
about 2.5, in which condition they may be mixed with various salts 
such as alum, barium chloride, magnesium sulfate, chromium sulfate, 
ferric chloride, etc., without gelling. 

^Clough, W., U. S. Pat. 87,759 (1869). 

m Wells, C. H., Louisiana Planter and Sugar Mfg., 71, No. 21, 394 (1923). 

^Deguide, C, U. S. Pat. 1,579,090 (March 30, 1926). 

^Kullgren, C. R, U. S. Pat. 1,616,131 (Feb. 1, 1927). 

30 Urban, Karel, U. S. Pat. 1,577,389 (Mar. 16, 1926). 

"Howard, H., U. S. Pat. 1,583,154 (May 4, 1926). 



ADDITIONAL USES 409 

Such a sol may be made by diluting a 40°Baume solution Na 2 0, 
3.3Si0 2 with 3 to 4 parts water and after thorough mixing, pouring it 
with constant stirring into an excess of hydrochloric or sulfuric acid 
so diluted that the residual acidity is about decinormal, with a pH of 
2.5. The silica sol alone, which would yield leathers containing up 
to 20 per cent silica, was of no use because the leather was too weak 
and brittle — the present commercial process involves the use of me- 
tallic salts with the sol and yields a white washable leather of good 
strength and great pliability. 32-36 

Silicate solutions can also be used as neutralizing agents in chrome 
tanning. The hides are treated after removal from the tanning baths 
to reduce the acidity of the salt adsorbed on the fiber and also to neu- 
tralize the residues of acid liquor held mechanically in the pores. The 
exact control of the process to prevent danger to the leather, which 
would result from any excess of a stronger alkali, is readily accom- 
plished with silicate solutions. 

Rayon. 

Rayon, formed by extruding viscous solutions of cellulose into a 
bath which coagulates the liquids to produce threads for a wide variety 
of textile uses, has of late years assumed great technical importance. 
The viscose process, which depends upon the formation of a xanthoge- 
nate by the action of sodium hydroxide and carbon disulfide upon 
cellulose, is one of the most important. The coagulating bath first used 
for this process was made from acid salts, notably bisulfites; but it 
was found that the threads after leaving such a bath could be passed 
through a silicate bath with the result that they had less tendency to 
stick together. 37 ' 38 It has also been proposed to add silicate solutions 
to the sodium hydroxide used in preparing the viscose colloid, the 
purpose being to obtain a stiffer fiber adapted to the imitation of horse- 
hair and other special uses, such as fabric for Welsbach mantles. 39 

Further study by Cross, however, revealed the fact that silicate solu- 
tions, particularly those of relatively high silica content, are well 
adapted to cause the original coagulation of the viscose. For example, 

32 Societe Genty, Hough et Cie., Ger. Pat. 322,166 (Aug. 8, 1918). 

33 Hough, A. T., personal communication. 

34 Le Cuir, "Le Tannage a la Silice" (Paris, Aug., Sept., Oct., 1919). 

35 See also Morin, H., U. S. Pat. 1,404,633 (Jan. 24, 1922). 

36 Rohm, O., U. S. Pat. 1,397,387 (Nov. 15, 1921) ; U. S. Pat. 1,569,578 (Jan. 
12, 1926). 

3T Howorth, T. E., Brit. Pat. 8,045 (1906). 

38 F. C. S., Fr. Pat. 361,319 (1906). 

^Huber, Joseph, and Paul Eckert, Ger. Pat. 405,601 (Nov. 8, 1924). 



410 SOLUBLE SILICATES IN INDUSTRY 

"the viscose is projected into a solution containing twenty per cent by 
weight of a silicate of soda of the composition 2Na 2 0,7Si0 2 , and main- 
tained at a temperature of from 40° to 50° C. This bath, although 
strongly alkaline in the ordinary sense, has the property of coagulating 
the viscose to the solid form, and this, after fixation (for instance, by 1 
per cent sulfuric acid) and after any other requisite, or desirable, 
manipulation, or treatment, results in lustrous threads, filaments and the 
like, of excellent quality." 40 ' 41 

Electrolyte in Storage Battery. 

It has been proposed to use a mixture of sodium metasilicate and 
sodium hydroxide as electrolyte in a storage battery with nickel and 
iron electrodes. This electrolyte has the advantage over sodium hy- 
droxide that it does not "creep," and is much cheaper than potassium 
hydroxide, which is ordinarily used to avoid this defect. Although 
the liquid is more viscous than the pure hydroxide solutions and hence 
less liable to splash, this process is not to be confused with the use of 
gels in acid electrolytes, as the silica remains in solution. By choosing 
silicates of high purity no detrimental compounds need be introduced 
into the alkaline electrolytes. 42 

Dehydrating Steatite. 

In the removal of water from steatite by electro-osmosis the addi- 
tion of soluble silicates favorably influences the process. This is 
probably a combined action of colloid and electrolyte, and the material 
is held dispersed and made amenable to the influence of the current. 43 

Straw Paper for Corrugating. 

It has been proposed to use the solvent action of silicate solutions 
for reducing straw to a pulp suitable for making the sort of paper re- 
quired by the maker of corrugated paper for shipping containers. The 
fibers are sufficiently separated by cooking in the silicate solution to 
permit preparing them for the paper machine by a short beating opera- 
tion, after which the silicate together with organic materials which it 
has dissolved are precipitated in the fiber with aluminum sulfate or 
other convenient precipitant. 44 ' 45 Thus the cooking reagent becomes 

40 Cross, C. F., U. S. Pat. 1,538,689 (May 19, 1925). 

41 Courtaulds, Ltd., London, Ger. Pat. 411,167 (March 24, 1925). 
"Freeth, F. A., and L. A. Munro, U. S. Pat. 1,541,699 (June 9, 1925). 
43 Schwerin, B., U. S. Pat. 1,266,330 (May 14, 1918). 

"Dixon, U. S. Pat. 52,545 (1866). 
45 Cobley, T. H., Brit. Pat. 13,096 (1896). 



ADDITIONAL USES 411 

a sizing material and the problem of the factory effluent, which is a 
serious one in making straw paper with lime, is simplified. The sili- 
cate could be used in combination with other alkaline reagents, and 
for kinds of fiber other than the straw which was investigated. 



46 



Clarification of Waste Waters. 

A similar double use of a silicate reagent has been suggested for 
controlling the character of a laundry effluent. Silicate used as a de- 
tergent can be precipitated in the waste waters which it helps to clarify 
for disposal. 

Removal of Fluorine from Phosphoric Acid. 

A special use of silicate solutions is for removing fluorine from 
phosphoric acid made by smelting natural phosphate rock with sand 
and coke. Fluorides are always present in the raw material but can 
be precipitated as sodium silico-fluorides. A silicious type of silicate 
is to be preferred for this use, but it should be used dilute to avoid 
gel formation. Na 2 0, 3.3Si0 2 is satisfactory. Ten thousand pounds of 
acid at 1.70 specific gravity are treated with 20 pounds of commercial 
1.38 specific gravity (40°Baume) silicate in 20 gallons of water, allowed 
to settle, and then filtered through sand. The fluorine is reduced from 
about 0.2 per cent to 0.02 per cent. 



47 



Extraction of Vanadium and Radium. 

Silicate solutions have been used to react with calcium fluoride and 
hydrochloric acid to make, with sodium nitrate, a reagent for the extrac- 
tion of vanadium and radium from carnotite ores. The vanadium and 
radium values can be extracted from 2000 pounds of dried residue of 
an alkaline digestion of carnotite ores by heating for one hour at not 
more than 3000° F., with the following reagents: 48 

Hydrochloric acid (12°Baume) 4000 pounds 

Calcium fluoride (fluorspar) 200 " 

Sodium silicate 25 " 

Sodium nitrate 42 " 

Physiological Effects of Silicate Solutions. 

Therapeutic Uses. 

Effect in Potable Waters. In potable waters, silica is regarded 
as inert ; and silicate solutions used for the control of corrosion in public 

4a Dedrick, C. H., U. S. Pat. 1,682,834 (Sept. 4, 1928). 

47 Carothers, J. N., and A. B. Gerber, U. S. Pat. 1,487,205 (March 18, 1924). 

^Bleeker, W. F., U. S. Pat. 1,445,660 (Feb. 20, 1923). 



412 SOLUBLE SILICATES IN INDUSTRY 

supplies on a large scale, though not above a concentration of ten parts 
of silica per million, have produced no ill effects. 49 The suspicion that 
silica in water might have something to do with cancer was investigated 
by comparing the cancer death rates in communities served with high 
and low silica waters. The result was completely negative. The death 
rate from cancer was slightly lower in the communities supplied by 
waters high in silica, though the differences were too small to be of 
any significance. 50 

Treatment for Tuberculosis. Therapeutic use of silicate solutions 
and colloidal silica has been studied for the treatment of tuberculosis, 
arterio-sclerosis, asthma, and some other diseases. 51-65 Silica is regu- 
larly ingested as part of the mineral content of cereal and other foods. 
Plants alleged to be of use in the treatment of tuberculosis contain 
large amounts of silica ; animal experiments indicate that the silica 
content of the pancreas is subnormal with tuberculosis, and doses up 
to 10 mg. per day given intravenously are tolerated by man. Large 
doses are definitely harmful. By mouth 1 to 3 grams daily have been 
given in treating arterio-sclerosis. There is a lack of exact informa- 
tion as to ratios used, and the results are not known to be important. 

Buffer Solutions in the Treatment of Intestinal Diseases. More 
recently Hepburn and Eberhard 66 ' 67 have studied the use of buffer 
solutions in the treatment of intestinal diseases and found them useful. 
Sodium metasilicate exhibited a much greater alkali reserve than a 
citrate buffer of similar pH and was able to neutralize much larger 
amounts of certain organic acids which are products of fermentation. 
Four-tenths normal sodium metasilicate, pH 12.56, and citrate buffer, 

40 Thresh and Beale, "Examination of Waters and Water Supplies," 3rd ed., 
Philadelphia: Blakiston, 1925, p. 153. 

50 Thresh, The Medical Officer (Nov., 1923). 

51 Kiihn, A., Fortschritte Med., 41, 75-7 (1923) ; C. A., 17, 3369. 

52 Scheffler, L., A. Sartory, and P. Pellisaier, Compt. rend., 171, 416-8 (1920) ; 
C A 14 3725. 
' M Messner, j, Pharm. Monatshejte, 3, 82-3 (1922) ; C. A., 16, 3972. 

04 Luithlen, F., Wiener klin. Wochschr., 35, 349 (1922) ; C. A., 17, 434. 

55 Kuhn, A., Medis. Klin., 18, 9-11 (1922) ; C. A., 16, 2934. 

°°Kuhn, A., Z. Tuberk., 32, 320 (1922) ; C. A., 16, 2934. 

57 Kahle, Hanns, Beitr. klin. Tuberk., 47, 296-324 (1921); C. A., 16, 1616. 

^Schubauer, R, Biochem. Z., 108, 304-8 (1920) ; C. A., 15, 269. 

M Gye, W. E., and W. J. Purdy, Brit. J. Exptl. Pathol, 3, 75-85, 86-94 (1922). 

80 Peter, B., Pharm. Monatshejte, 4, 63-7 (1923) ; C. A., 17, 2629. 

61 Gaube, "Cours de mineralogie biologique" (1904). 

02 Olivier, Decene, "Les Silicates en Therapeutique" (1906). 

83 Scheffler, Arch. gen. mid. (June 1908). 

84 Robin, Albert, "Therapeutique usuelle traitement de la tuberculose" (1912). 
65 Rudsit, K., Folia Haematol, 33, 95-104 (1924) ; C. A., 21, 959. 

66 Hepburn, Joseph, and H. M. Eberhard, Am. J. Med. Sci., 166, 244 (1923). 

67 Hepburn, Joseph, /. Am. Dietetic Assoc, 1, 55-59 (1925). 



ADDITIONAL USES 413 

pH 12.36, were titrated with 0.2 normal acid with phenol red to a pH 
of 7, with the following results : 

Table 123. Cubic Centimeters of 0.2 Normal Acid Required to Produce a pH 

of 7.0. 

With 100 cc. of With 100 cc. of 

Sodium Metasilicate Citrate Buffer 
Acid Solution Solution 

Hydrochloric 174.44 7.09 

Acetic 179.80 7.34 

Butyric 180.84 7.29 

Lactic 182.87 7.51 

Silicate Solutions for Surgical Bandages. Silicate solutions for 
making light rigid surgical bandages have been long and favorably 
known. The fabric is saturated with an adhesive silicate, preferably 
Na 2 0, 3.3Si0 2 , diluted just enough to penetrate, and bound on over 
a cotton dressing. It dries in a few hours to a greater strength than 
gypsum plaster and it is lighter and less bulky. 

Accidental Doses. 

Silicate in the Eyes. The accident of splashing strong silicate so- 
lutions, such as are used for adhesive purposes, into a human eye is 
a painful experience. The effect is much less deleterious than that of 
caustic solutions of like alkali content. The discomfort is due not only 
to the alkali but to the precipitation of granular material in the eye. 
The presence of the silica, on the other hand, mitigates the action of 
the alkali on the tissue ; and in no known case has the injury caused 
by a silicate solution lasted more than a few days. 

Like other accidents, it should be dealt with before it takes place. 
The wearing of glasses is a simple and effective precaution. Emer- 
gency treatment consists in thorough washing with warm water, pref- 
erably holding the afflicted eye in a gentle stream and getting circulation 
under the lids till most of the silicate has been removed, remembering 
that more water is required than one would naturally expect. This 
should be followed by liberal application of boric acid solution and 
the inspection of a physician. In some plants it is the practice to put 
a drop of castor oil in the eye, but the other method has been observed 
in a large number of cases without a case of permanent injury, though 
in the worst cases two or three days of severe inflammation and dis- 
comfort are often experienced. 

Silicate on the Hands. Complaints sometimes arise from workers 
who get silicate more or less continuously on their hands. This can be 



414 SOLUBLE SILICATES IN INDUSTRY 

avoided by the use of rubber gloves. The effect on the skin of an 
adhesive silicate in concentrated form is first to cause chapping, as 
would be the case if the hands had a similar exposure to laundry soap 
or other materials of like alkalinity. 

Silicate like other alkalies tends to remove the natural oils which have 
an emollient effect on the skin, and if in addition a thick film is allowed 
to dry it adheres and shrinks, tending to tear the epidermis from the 
dermis. Another effect is mechanical irritation due to hard sharp- 
edged films of silicate which form on the hands as the solution dries. 
The combined effect of alkalinity and abrasion may become very un- 
pleasant. Greasing the hands and keeping them clean are useful meas- 
ures. Cases of infection are due to outside contamination, as the sili- 
cate solutions supplied by the makers are sterile ; they have indeed been 
recommended as antiseptics. 68 ' 69 

Silicate Taken by Mouth. Small amounts of silicate solutions 
which may be accidentally taken by mouth are negligible ; their rather 
unpleasant taste is usually sufficient to guard against such mishap. They 
have even been used internally to neutralize acidity in place of bicar- 
bonate of soda taken by mouth. Two hundred cubic centimeters of a 
strong solution for egg preserving when taken internally induced violent 
physical distress, but did not prove fatal. 70 

It is hoped that the foregoing pages have made plain that silicates 
of soda, rightly used, are capable of many services of substantial value, 
but just as plowshares and pruning hooks can be fashioned into imple- 
ments of destruction, so silicates of soda are capable of wrong use 
which a knowledge of their nature provides the means to avoid. 

•Picot, Compt, rend., 75, 1516-1519, 1124-1125 (1872); 76, 99-103 (1873); 
Abst. in Chem. News, 27, 46 (1873). 

69 Champouillon, Compt. rend., 76, 355-356 (1873) ; Abst. in Chem. Neivs, 27, 
94-96. 

70 Eichhorst, H., Schweh. med. Wochenshrift, 50, 1081 (1920); /. Am. Med. 
Assoc., 76, 275; C. A., 15, 1166. 



AUTHOR INDEX 



Abel, F. A., 260 
Acheson, Edward G., 18 
Adhesives Research Committee, 211 
Agricola (George Bauer), 12 
Air Service, 266 
Alder, Byron 388 
Alignum Asbestos Company, 191 
Allen, S. W., 251 
Altmann, P. E., 282, 290 
American Doucil Company, 403 
American Oil Chemists, 369 
American Rubber Company, 271 
Amies, Joseph Hay, 197 
Ammon, von, 406 
Anderson, Harry O., 178 
Anderson, J. A., 397 
Andes, Louis Edgar, 260, 360, 365 
Andrews, O. B., 223 
Anonymous, 173, 196, 199, 400 
Arizona Agricultural Experiment Sta- 
tion, 388 
Armstrong, Morgan K., 197 
Arnoux, Andre, 388 
Arsem, William, 119 
Arthur, Edwin P., 272 
Arthur, Walter, 119, 260 
Artus, Willibald, 255, 360, 365 
Ashenhurst, Harold S., 260 
Atkins, W. R. G., 379 
Aubert, 368 



Bach, Karl, 360 

Bachler, 407 

Bachman, 21 

Bailey, Broadus, 355 

Baillio, Gervais, 92 

Baker, C. E., 406 

Ball, H. Standish, 199 

Ballay, 189 

Bancroft, Wilder D., 322, 353, 379 

Barlocher, Otto, 356 

Barnickel, Wm. S., 325, 326 

Barringer, L. E., 190 

Barron, W. S., and G. S., 173 

Bartlett, Francis, 190, 193, 388 

Bartlett, J. M., 388 

Bartow, Edward, 406 

Basseches, J. L., 155 

Basset, Harry P., 181, 183 

Basset L. P. 72 

Bastian, H. Charlton, 17, 83, 84 

Batchelder, James H., 256 



Battersby, John W., 106, 118 

Bauer, Georg, 12, 

Bayer, 94 

Baylis, John R., 18 

Bazille, 92 

Beadle, George W., 197 

Beal, R. B., 243 

Beale, John F., 412 

Becquerel, 74 

Beecher, Milton F., 177 

Beedle, F. C, 367 

Behr, E., 282, 400 

Behrens, George E., 194 

Behrman, Abraham S., 397, 406, 407 

Beightler, Robert S., 206 

Bell, G. Arthur, 387 

Bellamy, Harry T., 302 

Beltzer, F. J. G., 354, 355 

Benford, David M., 274 

Benjamin, Earl W., 388 

Benner, Raymond C, 193, 197 

Bennett, A. N. C, 44, 48, 49 

Berge, 361 

Berger, R., 387 

Bernhard, L., 14 

Berry, E. R., 190 

Bersch, Josef, 272 

Bert, Henry, 279 

Berzelius, 339 

Besele, Lynaz, 250 

Bhatnazar, S. S., 325 

Bibikon, N. A., 278 

Bickley, A., 189 

Bingham, Eugene H., 56, 139 

Bird, Charles S., 227 

Bishop, 199 

Blaire, S. M., 315 

Blanc, 92 

Blanford, T., 199 

Blardone, George, 18, 91 

Blasweiler, Thomas E., 281, 282, 284, 

288, 290, 291, 292, 361 
Bleeker, W. F., 411 
Bleininger, A. V., 301 
Blombery, George F., 278 
Blumenthal, F., 406 
Boehringer, Rudolph, 405 
Bogue, Robert H., 33, 34, 36, 38, 147, 

245, 248, 335 
Bolam, T. R., 367 
Bolley, 297 

Bonney, Robert D., 156 
Boorne, William H., 275 



415 



416 



AUTHOR INDEX 



Borcherdt, W. O., 306, 307 

Borntrager, H. f 198, 387 

Bosart, L. W„ 368 

Bosch, Carl, 402 

Bottler, Max, 249 

Bourcet, P., 275 

Bowen, N. L, 68, 101, 111 

Boxer, Frederic Nepheau, 197 

Bradfield, Richard, 305 

Bradner, D. B., 400 

Brannt, William T., 360 

Braun, K., 367 

Breuer, Carl, 167, 251 

Breyer, F. G., 373 

Briggs, T. Roland, 314, 323, 353 

Brigham, A. A., 387 

Bristow, John J. Rucker, 278 

British Thomson Houston Co., 270 

Britton, R. P. L., 78, 79, 197, 269 

Broadbridge, W., 306 

Brown, E., 387 

Browne, F. L., 245 

Bruni, 19 

Briining, 298 

B runner Mond and Co., 198, 206 

Buchner, A., 94 

Buffon, 12 

Burke, J. T., 198 

Butterfield, John Cope, 196 

Butterman, S. S., 244, 246 



Caldana and Santambrogio, 196 

Calvert, 339 

Cameron, James, 360 

Campbell, James R., 384 

Cann, Jessie Y., 45, 49, 138 

Capitaine, F., 90 

Carleton, F. W., 322 

Carothers, J. N., 411 

Carpenter, William, 360 

Carter, John D., 70, 78, 121, 127, 139, 

151, 178, 181, 195, 242, 253, 268, 280, 

282, 344, 349, 389 
Cavanaugh, A. J., 255 
Caven, R. M., 91, 94, 118 
Champouillon, 414 
Chance, 195 
Chaney, N. K., 400 
Chapin, Robert M., 328, 367 
Chappell, E. L, 379, 382, 383 
Cheek, Dorothy L., 45, 138 
Chemische Fabrik auf Aktien, 397 
Chevreul, 339 
Chisholm, Jessie C, 321 
Clapp, Albert L., 290 
Clapp, Harry Baker, 183 
Clark, G. L., 313 
Clark, K. A., 314 
Clark, L. H., 320 
Clark, T. S., 181 
Clarke, F. W., 17 



Classen, Alexander, 267 
Clayton, William, 120, 322 
Clews, Francis Herbert, 72 
Clough, W., 407, 408 
Clowes, 326 
Coblentz, W. W., 273 
Cobley, T. H., 330, 410 
Codd, Laurence, Wm., 91, 138 
Coffignier, C, 278 
Cole, George Warren, Jr., 296 
Colgrove, Charles E., 227 
Collins, N"., 91 

Collins, William Frederick, 179 
Connolly, J. P., 278 
Cook, A. A., 297 
Cook, Frank J., 190 
Cooperider, C. K., 246 
Courtaulds, Ltd., 410 
Covell, Bradford, 190 
Cowles, Edwin, 356 
Cremer, 273 
Creuzberg, H., 268 
Crispo, D M 90 
Crosby, P. A., 326 
Crosfield, Joseph & Sons, 403 
Cross, C. F., 409, 410 ^ 
Crowell, Charles H., 227, 256 
Crowell, Walter S., 390 



Dahse, W., 250 

Dake, Charles Lawrence, 21 

Dance, Edward L., 249 

Daniels, S., 373 

Danley, Mary, 342 

Davidsohn, J., 339 

Davidson, Frank B., 95, 237 

Davies, J., 264 

Davis, Watson, 198 

De Brunn, P., 406 

Deckert R. 94 

Dedrick, Charles H., 143, 148, 331, 411 

Deguide, Camille, 90, 408 

Deite, Carl, 360, 367 

Delaroquette, M., 387 

Deutsche Gold und Silber Scheidean- 

stalt, 345 
Deville, 406 

Diamond Decorative Leaf Co., 256 
Dickerson, Walter H., 120 
Dickins, E. J., 189 
Diedecks Sohn, A. C, 13 
Dienert, 53 

Dinsmoor, Paul A., 227 
Dixon, 330, 410 
Dixson, H. O., 199 
Dixson, James Q., 269 
Dodd, H. V., 326 
Doll f us, Robert, 81 
Donnan, F. A., 326 
Dorr, G., 298 
Dougal, John Wilson, 197 



AUTHOR INDEX 



417 



Dralle, 14 

Drefahl, Louis, 271, 310 

Droux, M. S., 360 

Drushel, W. A., 249 

Dubois, R., 388 

Dulac, A., 206 

Dunbar, Ruth, 388 

Dunham, Andrew A., 120, 245 

Dunnington, F. P., 202 

Dunstan, William, 197 

Dvorachek, H. E., 388 



Ebbesen, Poulsen Mads, 197 

Ebell, Paul, 96 

Eberhard, H. M., 412 

Eberlin, L. W., 270 

Eckert, Paul, 409 

Edeler, A., 343, 364, 366 

Edgerton, L. B., 120 

Edser, Edwin,_ 305, 306, 311, 313, 326 

Edwards, Junius D., 273 

Egloff, Gustav, 315 

Eichhorst, H., 414 

Ekstrom, P. G., 201 

Electro-Osmose Gesellschaft, 91, 306, 

394 
Elledge, 314 
Ellery, James B., 260 
Ellingworth, 314 
Ellis, C, 255 
Elmendorf, Armin, 251 
Emery, W., 184 
Emmons, 347 
Engelhardt, Alwin, 360 
English, 114 

Erdenbrecher, Alfred H., 59, 60, 67 
Eschenbacher, August, 260 
Euler, F., 339 
Evans, W. G., 17, 83 
Evequoz, A., 388 
Ewe, George, 356 



F. C. S., 409 

Fahrenw'ald, A. W., 306 

Fairchild, Walter H., 224 

Fall, P. H., 307, 310, 344 

Faragher, W. F., 368 

Farrel, 337 

Favre, Camille, 297 

Feary, N. A., 298 

Federal Trade Commission, 359, 365 

Feichtinger, G., 272 

Feldenheimer, William, 302 

Felix, Charles, 263 

Fenaroli, Pietro, 275 

Fenner, C. N., 68, 113 

Ferrell, J. L., 263 

Ferres, J. T., 227 

Fewins, Frank W., 278 

Fink, 272 



Finkeldey, W. H., 373 

Fischer, Martin H., 326, 364 

Fisher, Harry C, 268 

Fiske, William Grant, 224 

Flemming, W., 388, 389, 391, 392, 393 

Flohr, Lewis B., 388 

Flowers, A. E., 319 

Fluckiger, F. A., 72, 84 

Foerster, F., 58 

Folding Box Manufacturers Assoc, 255 

Forbes, E., 351 

Forest Products Laboratory, 234, 244, 

246, 251 
Fort Worth Laboratories, 321 
Francois, A., 199 
Freeth, F. A., 410 
Freight Container Bureau, 224 
French Thomson-Houston Co., 269 
Freundlich, 326 
Fritzsche, J., 58, 92 
Frohberg, A., 282 
Fuchs, Johann Nepomuk von, 12, 13, 

14, 73, 86, 94, 195, 266 
Fues, 291 

Fulcher, G. S., 183 
Fulton, 398 

Furness, Rex, 240, 251, 286, 400 
Fyleman, M. E., 315 

G. E. J., 357 

Gadd, Lawrence W., 360 

Gaelle, M, 196 

Gailbourg, 189 

Gallenkamp, W., 269 

Ganguly, P. B., 51, 52 

Gans, R., 405, 406 

Gardner, Henry, 262 

Gas Accumulator Co., 400 

Gathmann, H., 358 

Gaube, 412 

Gaudry, Tanciede, 278 

Gauthier, L., 197 

Geisenheimer, G., 355 

Gerber, A. B., 411 

Gerloch, Oscar, 190 

Gesell, 14 

Gessler, A. E., 405 

Gessler, Otto, 353 

Gibson, William H., 140 

Gilbert, A. G., 387 

Gilmore, K. E., 45, 138 

Gilmore, Q. A., 193, 198, 203 

Gilpin, R., 271 

Glauber, 12 

Gobels, Albert, 297 

Goetschius, D. M., 120 

Goldsmith, 337 

Gordon, Neil, 23, 282 

Gossage, William & Sons, 13, 92 

Gottwald, W., 77 

Govers, Francis X., 397 

Graf, 290 



418 



AUTHOR INDEX 



Graham, Thomas, 19,. 40 
Graham, W. R., 387 
Green, Henry, 267 
Greenwood, W. W., 173 
Greig, R. B. G., 113 
Groschuff, E., 19 
Grote, L., 190 
Grothe, H., 344 
Griin, A., 339, 347 
Grundmann, W., 20, 21 
Griine, W., 297 
Griiner, V., 385 
Guenther, Richard, 387 
Guernsey, F. H., 356 
Guillin, R., 357 
Gutensohn, A., 405 
Gye, W. K, 412 



Haas, Nelson R., 190 

Hacker, Willy, 167 

Hacket, William, 250 

Hacking, E., 396 

Hagg, 79 

Hale, H. M., 234 

Hantzsch, 28 

Haon, H, J., 319 

Harborne, R. S., 367 

Harman, R. W., 23, 29, 30, 31, 36, 38, 

43, 44, 47, 49, 50, 51, 53, 54, 55, 66, 

67, 158 
Harris, James E., 260 
Harris, John, 250 
Hart, Gilbert, 173 
Hartman, F. E., 320 
Harvey, A., 298 
Haskell, 249 
Hassam, A., 199 
Hasterlik, Alfred, 388 
Haushofer, 406 
Haussler, E. P., 388 
Haywood, Harry R., 263 
Hecht, Max, 57, 384 
Heermann, P., 296, 337, 347 
Heiduschpa, A., 388 
Heijne, Otto, 201 
Heinrichs, Berg, 227 
Heldt, 406 
Hendrick, J., 387 
Henkel et Cie., 178 
Henkel, Hugo, 353 
Henning, S. B., 246 
Hennis, W., 73, 74 
Hepburn, Joseph, 412 
Herbert, Arthur, 197 
Herrera, A. L., 83 
Hess, Henry K., 260 
Heuser, Emil, 282, 288 
Hexamer, C. J., 260 
Hey, H., 321 
Heyer, R., 19, 20 
Hicks, O. H., 227 



Higgins, E. F., 143 

Hilditch, T. P., 403, 406 

Hill, Irving, 227 

Hillebrand, 157 

Hillyer, 313, 323, 367 

Hinde, 227 

Hirsch, H. H., 396 

Holbrook, George M., 321 

Holden, E. C., 400 

Holley, Earl, 183, 195 

Holmes, Harry N., 19, 22, 83, 389, 397, 

398, 401 
Holslag, Claude J., 275 
Hoover, Herbert C., 12 
Hoover, Lou Henry, 12 
Hopkins, D. G., 211, 219 
Hopkins, Nelvil Monroe, 260 
Horton, P. M., 18 
Hoss, Charles, 197 
Hough, A. T., 409 
Howard, Charles H., 224, 227 
Howard, H., 408 
Howe, Raymond M., 183 
Howorth, T. E„ 409 
Hoyt, L. F., 369 
Huber, Joseph, 409 
Hiibner, 298 
Hughes, C. W., 273 
Humphries, R., 347 
Hunt, 195 

Hurst, George H., 360 
Hussein, Ahmed, 367 
Hutchins, Nancy A., 353 
Hutchison, A., 278 
Huth, F., 205 



Iding, Mathew, 173 

Imison, G. S., 275 

Imschenetsky, Alexander, 191, 193 

International Correspondence Schools, 

360 
Interstate Commerce Commission, 224 
Irwell, L., 387 
Isaacs, M. R., 249, 278 
Isherwood, 314 
Isnard, E., 367 
Israel, Albert H., 227 
Iversen, M. M, 263 



Jackson, H., 340 

Jacobs, Laura M., 140 

Jacques, 56, 139 

Jaeger, F. M., 68, 70, 100, 113 

Jarvis, L. G., 387 

Jeffrey, J. S., 387 

Jeromins, 244 

Jespersen, Thomas, 353 

Joclet, Victor, 297 

Johanson, Pehr, 178 

Johnson, Otis, 248 



AUTHOR INDEX 



419 



Jones, A. L., 227 

Jones, D., 184 

Jones, F. B., 306 

Jones, H. E., 367 

Jones, H. I., 388 

Jones, W. L., 246 

Jordis, E., 57, 59, 73, 74, 76 

Joseph, 79 

Jungmann, 339, 347 

Justice, 119 



Kahle, Hanns, 412 

Kahlenberg, L., 27, 28, 40, 41, 43 

Kaiser, C. G., 260 

Kail, G. A., 302, 303 

Kallauner, O., 86, 195 

Kalle and Company, 361 

Kasuva, Saburo, 297 

Katz," Henry G., 218 

Kausch, 251 

Kausch, Oscar, 401 

Kayser, Adolf, 356 

Keedwell, C. A., 278 

Keener, Francis M., 197 

Keever, Paul, 178 

Keghel, M. de, 330 

Keilmeyer, 339 

Keiper, 296 

Keit, 369 

Kelly, G., 197 

Kelly, Thomas Daniel, 199 

Kersten, Julius, 93 

Killeffer, D. H., 405 

Kind, W., 337, 339, 340, 345, 347 

King, A. M., 367 ' 

King, Jesse C., 275 

Kingzett, Charles Thomas, 360 

Kirk, Thomas, 402 

Klason, 281 

Kleim, A., 272 

Klemm, 279 

Klooster, H. S., van, 70, 113 

Knecht, 297 

Knight, Maurice A., 181 

Knup, J., 290 

Kobel, 86 

Kohl, H., 305 

Kohlrausch, F., 24, 25, 29, 31, 36, 41, 

135, 306 
Kojima, Yonejiro, 256 
Kolb, A., 290, 406 
Koller, Theodor, 260 
Kramer, Joseph, 227 
Kraner, H. M., 275 
Kratzer, Hermann, 14, 260 
Kress, Otto, 236 
Kriegsheim, H., 406 
Kroger, 91 
Krogh, A. T., 275 
Krozer, 20 
Krug, George, 79 



Kuhl, H., 339, 355 

Kuhlmann, F., 86, 195, 202, 203 

Kiihn, A., 412 

Kuhn, H. A., 322 

Kuldkepp, 290 

Kullgren, C. F., 408 

Kunheim, L., 352 



Ladd, E., 387 

La Forge, F. B., 251 

Lamb, M. C, 298 

Lamborn, L. L., 329, 360 

Lamson, G. H., 387 

Langston, S. M., 227 

Langworthy, C. F., 387 

Lara, F., 361 

Lawton, C. F., 195 

Le Chatelier, 70 

Le Cuir, 409 

Lederer, E. L., 362 

Lee, W. B., 211 

Lee, Yong K., 407 

Lefebure, Victor, 197 

Leide, 21 

Leimd6rfer, J., 329, 337, 339, 358, 363 

Leitch, Harold P., 367 

Lemberg, J., 86, 406 

Lennig, Albert M., 197 

Leonard, 21 

Lewis, 49 

Ley, Hermann, 295, 347 

Liebig, J. von, 86, 88, 89 

Liesegang, R. E., 22, 76, 83, 370, 401 

Lihme, I. P., 120 

Lincke, P., 76 

Lincoln, A. T., 27, 28, 40, 41, 43 

Locke, J. A., 263 

LoffiVK., 340 

Loomis, 43 

Lorenz, R., 282 

Losenbeck, 23 

Lottermoser, 91 

Love, Fanny, 388 

Lowe, 190 

Lowenthal, 297 

Lucius, 298 

Luckenbach, Roger, 322 

Luckiesh, M., 269 

Luithlen, F., 412 

Lussac, Gay, 92 

Lutz, Alfred, 291 



McBain, J. W., 31, 50, 211, 216, 219, 243, 

363, 367 
McBerty, F. N., 319 
McCoy, James P. A., 198 
McDowell, Joseph Curry, 294 
McDowell, Samuel J., 303, 304, 305, 344 
McGavack, John, 22 
McKee, R. H., 18 



420 



AUTHOR INDEX 



McLaughlin, G. D., 362 
McLennan, Charles, J., 278 
McMullan, 188 



Maetz, O., 95 

Magelssen, N. f 243 

Alain, V. R., 133, 146 

Alalcolmson, J. D., 84, 152, 223, 227, 

234, 250 
Mallard, E., 96 
Mallock, A., 154 
Mandelbaum, R., 349 
Mann, W. A., 314 
Mantel, Frank A., 190, 197 
Marcus, Robert, 356, 397 
Marino, Pascal, 256 
Marquand, A. B., 307 
Marriott, Hugh F., 199 
Martin, Harry C, 177 
Massatsch, C, 406 
Maston, Edward, 227 
Mathews, R. R., 326 
Mawson, T. T., 199 
Mayer, Hermann, 14, 295, 296, 298, 355, 

357 
Mees, E. R, 278 
Mees, R. T. A., 323 
Meigs, Curtis C., 195 
Meister, 298 
Melch, H. B., 227 
Meloche, D. H., 185, 189, 190 
Menner, 68 

Menuez, Anthony E., 190 
Menzel, K. C, 256 
Messner, J., 412 
Meta, Sarason, 250 
Meyer, Albert, 183 
Meyer, R., 352 
Meyerburg, Paul, 256 
Michael, J. & Co., 397 
Michell, Henry Colbeck, 191, 193 
Michler, J. R., 320 
Miles, W. H., 264 
Millard, E. G., 314, 323, 400 
Miller, P. S., 316 
Miller, W. E., 197 
Milson, J. R., 344 
Minerals Separation Ltd., 306 
Mitchell, Ardon, 197 
Mitchell, Walter M., 189 
Mitchener, W. B., 272 
Mittasch, Alwin, 402 
Mitton, H. Eustace, 199 
Moldenke, Richard, 185 
Mols, A., 90 
Moore, Benjamin, 17, 83 
Moore, K. R., 345 
Morey, George W., 66, 68, 100, 101, 103, 

104, 111, 112, 113, 115, 116, 118, 398 
Morgan, F. L., 199 
Morin, H., 409 



Morley, Walter S., 307 
Morrell, Jacques C., 315 
Morrison, Freeland, 256, 278 
Morse, Waldo, G., 197 
Alorveau, Guyton de, 12 
Moses, D. V., 310 
Mosley, J. F., 290 
Moyer, Albert, 205 
Muller, 290 
Munro, L. A., 410 
Muspratt, James Sheridan, 360 
Mylius, 19, 85 



Natho, Ernst, 92 
Naylor, Isaac, 190 
Neff, J. W., 384 
Neuhaus, 296 
Nicksch, K. Z., 264 
Niggli, Paul, 67, 96, 99, 100 
Nimtz, William A., 173 
Nishizawa, K., 311 
Noda, 79 

Nordelle, Carl H., 407 
Norman, J. T., 190, 216 
Norton, J. I., 305 
Nowotuy, E., 387 
Nuttall, W. H., 312 



Oakley, 79 

O'Brien, David J., 224 

Oelhafen, John Walter, 197, 222 

O'Hara, 183 

Oka, 79 

Olfers, 203 

Olivier, Decene, 412 

Olney, George, 197 

Olson, G. A., 388 

Onslow, H., 83 

Ordway, J. M., 70, 81, 82, 86, 159 

Ormandy, 20 

Osgood, G. H., 248 

Osgood, Samuel W., 270 

Ostwald, W., 282 

Otto, O. T., 320 

Otzen, Robert, 208 



P. L., 357 

Palmer, A. J., 305 

Palmetto, 345 

Pappada, 19 

Parkyn, Herbert A., 217 

Parmelee, J. S., 305 

Parsons, L. W., 326 

Pater, Carl J., 197 

Paterson, E. A., 118, 120, 195, 196, 197 

Patrick, Walter A., 22, 397, 399, 400, 

402 
Patsch, Albert, 260, 262 
Peacock, Samuel, 90, 94 



AUTHOR INDEX 



421 



Pech, P. L. E., 361 

Peddle, C. J., 114 

Pennington, Harry B., 197 

Permutit Co., 407 

Peter, A., 196 

Peter, B., 412 

Peter, Julius, 360 

Peterson, Theodor, 58 

Pettenkofer, Max, 272 

Philadelphia Quartz Co., 13, 70, 78, 87, 

341 
Philipp, Ferdinand, 278 
Philips, John Francis, 90 
Pick, 244 

Pickard, R. H., 298 
Pickering, S. V., 324, 330 
Picot, 414 
Pitman, E. C, 143 
Plausons, L., 307 
Plenty, J., 193 
Pliny, 11 

Plonnis, Rudolf, 278 
Plowman, W. W., 302 
Polleyn, F., 298, 351 
Pope, 298 
Possanner, 290 
Potts, Harold Edwin, 199 
Poulsen, A., 298, 394 
Power, Henry Robert, 177 
Praetorius, M., 91 
Prall, F., 387 
Prestholdt, Henry L., 245 
Procter and Gamble, 341 
Pukall, W., 68 
Puscher, 267 
Puttaert, Francis J., 18 
Puttaert, Jean Francois, 18, 91 



Quincke, G., 80 



Raffel, T. K, 227 

Randall, Merle, 49 

Raney, Murray, 90 

Ransome, Frederick, 173 

Rasser, E. O., 327, 329 

Rawling, Francis George, 372 

Rawson, 297 

Ray, Arthur B.. 400 

Reamer, R., 319 

Regnault, H„ 275 

Reichard, F., 290 

Reichert, J. J., 347 

Reinfurth, N., 361 

Reinthaler, 388 

Remler, R. F., 206, 207 

Reyerson, L. H., 402 

Reynolds, R. W., 183 

Rhodes, F. H., 319, 353 

Richards, H. W., 120, 311 

Richardson, A. S., 313, 314, 323, 331 



Richardson, L. G., 298 

Richter, Oswald, 18 

Ridgeley, 322 

Ries, E. D., 326 

Ritchie, J. A., 190 

Rivirigton, 272 

Roberts, J. K., 379, 382, 383 

Robertson, E. H., 199 

Robertson, I., 199 

Robin, Albert, 412 

Rochow, William, 183 

Roessler, 345 

Rogers, 368 

Rohm, O., 409 

Rohrig, 372 

Romagnoli, A., 339 

Rontgen, A. J., 312 

Roscow, James, 294 

Rose, Edward J., 90 

Rose, H., 96 

Ross, W. J. C, 81 

Rossbach, Helmut, 295 

Rouse, Thomas, 119 

Rudorf, G., 406 

Rudsit, K., 412 

Russell, Robert P., 275, 381, 383, 384 

Rylander, J. A., 387 



Sabanejeff, 19 

Sadtler, Samuel S., 199 

St. D., 365 

St. John, A., 400 

St. Paul, Johns, 264 

Salmon, 31, 50 

Salmonson, H. W., 321 

Sanderval, de, 92 

Sandham, 260 

Sandor, Nikolaus, 237 

Schaidhauf, Alois, 345 

Schaltenbrand, 12 

Scharwath, John A., 260 

Scheerer, T., 96 

Schemer, 412 

Schelhass, 339 

Schenitza, Philipp, 384 

Scherer, 251 

Scherrer, P., 22, 96, 370, 398 

Schestakoff, 368 

Scheurer, Kestner A., 89, 95 

Schilling, 193 

Schleicher, 243 

Schlotterer, G. K., 197 

Schmidt, Hugo F., 314, 323 

Schmidt, Otto, 402 

Schmidt, R.,' 360 

Schnabel, 336, 337, 339, 340, 343, 344 

Schneider, Louis, 118, 120, 121, 125, 126 

Schnitzer, Guido, 360 

Schoop, 396 

Schrero, Morris, 14 

Schubauer, F., 412 



422 



AUTHOR INDEX 



Schuck, E., 360 

Schupp, A. F., 355 

Schutt, F. T., 387 

Schwalbe, K, 331, 340 

Schwarz, I. R., 21, 68 

Schwerin, B., 410 

Searle, A. B., 20 

Seger, Herman A., 188 

Seideman, Leon, 274 

Sekiya, Keiya, 256 

Seligman, Richard, 371, 372 

Sharp, Robert, 278 

Sheeley, M. B., 367 

Sheppard, S. E., 270 

Sheridan, Joseph Charles, 356 

Shields, F. W., 361 

Shorter, S. A., 301, 314, 329, 330 

Shukoff, 368 

Siebel, R., 365 

Silica Gel Corporation, 91, 398. 400, 402 

Silverstein, Philip, 236 

Simmons, William H., 356, 360, 363 

Sisley, 296 

Slepian, Joseph, 190 

Slocum, Rob. R., 388 

Smith, R. H„ 243 

Smolens, H. G., 346, 347, 348 

Snyder, George C, 240 

Societe Genty, Hough et Cie., 409 

Societe Generale des Nitrures, 184 

Sommer, George G., 290 

Somner, H., 337 

Soxhlet, V. H., 297 

Spaeder, L. J., 227 

Spear, 21 

Speller, F. N., 379, 381, 382 

Spensley, Jacob Wm, 106, 118 

Spezia, G., 18, 22 

Spring, W., 311 

Staley, H. F., 187, 188, 353 

Standage, H. C, 251 

Stanton, William H., 103, 107 

Stead, 387 

Steffan, M. O., 365 

Stericker, Wm., 23, 34, 54, 84, 135, 143, 
146, 147, 148, 152, 154, 155, 157, 231, 
279, 323, 326, 335, 340, 341, 352, 369 

Sterne, E. T., 200 

Stiepel, C, 360, 361 

Stone Preservation Committee, 204 

Storer, F., 360 

Stout, S. P., 388 

Stowell, Edward R., 178, 190, 197, 275 

Stowener, 21 

Strauch, R., 387 

Stroud, Ben K., 315 

Stubbs, Robert C, 206 

Stutzke, R. W. G., 353 

Stryker, George B., 190, 197 

Sulman, H. L., 306, 311 

Sulzberger, Nathan, 217, 278 

Surpass Chemical Co., 345 



Suss, Herman M., 197 
Sutermeister, Edwin, 245, 251 
Swearingen, L. E., 402 
Sweeney, O. R., 251 
Swift, George W., 227 



Taggart, William, 179 

Taylor, Alfred, 298 

Taylor, Edward A., 310 

Teague, M. C, 250, 271 

Teesdale, Clyde H., 257 

Teitsworth, Clark S., 399 

Telenga, Jan, 321 

Texter, C. R., 381 

Thatcher, Charles J, 387, 394 

Thenard, 92 

Thickens, J. H., 242, 243 

Thieriot, J. H, 387 

Thies, F., 344 

Thomas, 356 

Thomas, C, 88 

Thompson, Hugh Vernon, 92 

Thompson, Lincoln, 35, 36, 38, 42 

Thompson, R. H., 227 

Thorp, 354 

Thresh, John C, 373, 378, 379, 412 

Tillotson, E. W., 114 

Tilton, Clarence B., 177, 178 

Toch M., 200 

Tondani, Carlo, 296 

Tone, 186 

Traube, I., 311 

Treadwell, Richard, 92 

Tressler, D. K., 249 

Trotman, S. R., 295, 354 

Truax, 251 

Truog, Emil, 399 

Tsukoski, 249 

Tumminelli, Arcangelo, 260 

Turner, 114 

Tyler, W. S., 171 



Ubbelohde, Leo, 360 

Udale, Stanley, 189 

Ungerer, 92 

United States Bureau of Census, 14 

United States Bureau of Explosives, 224 

L^nited States Bureau of Standards, 366 

U. S. Department of Agriculture, 245, 

388 
U. S. Department of Commerce, 233 
Urban, Karel, 408 
Urban, W., 400 
Urtel, Henry, 177 



Vail, James G., 17, 92, 107, 121, 127, 
178, 197, 251, 253, 255, 268, 279, 287, 
302, 340, 403 

Valentine, Basil, 11, 12 



AUTHOR INDEX 



423 



Van Arsdel, Wallace B., 402 

Van Baerle, A., 344, 397 

Van Bemmelen, 397 

Van Brunt, Charles, 316, 318, 319 

Vanderleck, J., 388 

Van Helmont, 12 

Van Meter, James W., 255 

Varley, 307 

Veit, Josef, 194 

Vesterberg, K. A., 59, 70 

Vinal, George Wood, 394, 395 

Vincent, G. P., 300, 313, 324, 335, 344, 

351, 352 
Vivas, F. S., 263 
Vogtherr, H., 405 
Vohl, 339 
Vorlander, 193 
Vosseler, J., 387 



Wade, Harold, 345 

Wagner, H., 251, 268 

Wagner, Joshua, 227 

Wakefield, 355 

Wakem, F. J., 184 

Waldenbulcke, 53 

Walen, Ernest D., 298 

Wallace, R. C., 100 

Walsh, M. J., 278 

Wandel Kurt, 224 

Way, 406 

Webb, H. W., 195 

Weber, G. J., 95, 339, 345 

Weber, K. L., 364 

Wedge, Utley, 195 

Weed, W. H., 18 

Weidlein, E. R., 382 

Weidmann, 295 

Weinig, Arthur J., 305 

Weintrauh-Schnorr (Naum), 197 

Weiser, Harry Bover, 390, 399 

Welles, C. E., 263 

Wells, C. H., 407, 408 

Welter, A., 355 

Wenck, 244 

Wernekke, 197 

Werner, 20 

West, Clarence, J., 290 

West, Frank P., 202 



Wezel, Julius, 256 

Wheaton, H. J., 56, 397, 402, 403, 406 

Wheeler, James A., 190, 191, 199 

Whewell, W. H., 298 

Whinfrey, Charles G., 189 

Whitman, W. G., 379, 382 

Whitmore, James Bryant, 270 

Whyte, Samuel, 189 

Wilhelmy, Odin, 189 

Willcox, O. W., 406 

Willett, Walter E., 197 

Willetts, Paul G., 183 

Williams, 92 

Williams, Albert H., 394 

Williams, H. M., 396 

Williams, Percy, 371, 372 

Wilson, Charles, 199 

Wilson, R. E., 326 

Wiltner, F., 360 

Windsor-Richards, W. E., 181 

Wing, Annie L. J., 388 

Winkler, Charles F., 396 

Winkler, Kasper, 199 

Winship, William W., 169 

Wirth, J. K., 264 

Withrow, James R., 272 

Wittorf, N. M. von, 96 

Wolcott, E. R., 183 

Wolf, K., 91 

Wood, 188, 189 

Wood, L. A., 306 

Wood, W. W., 249 

Wortelman, C. A., 263 

Wrede, Hans, 291 

Wright, C. A., 305, 360 



Yorke, 96 

Young, Ira Benjamin, 263 
Young, W. T., 265 
Youngman, Robert H., 183, 197 



Zanker, 336, 337, 339, 340, 344 

Zimmerman, Arthur C, 373 

Zsiemondy, Richard, 19, 20, 21, 22, 23 

Ztakikawa, 199 

Zuskoski, 199 

Zwick, Hermann von, 12, 13, 14 



SUBJECT INDEX 



Abrasives, 173-178 

Absorption, moisture by silicate, 117 

See also Adsorption 
Acetone, 81-82 

Acid Proof Cements, 169, 171, 179-182, 
201-202 

application and use, 179-181, 202 

fillers for, 181-182 

gels in, 390-392 
Acid resistant brickwork, 201-202 
Acid resistant concrete, 209 
Acids, reactions with silicate, 72, 389 
Activity, sodium ion, 50, 51 

coefficients, 47-50 
Adhesives, 12-13, 165-166, 210-251 

airplanes, for, 244-245 

alkalinity, 231 

asbestos products, for, 217-219 

blood, 249 

buttermilk in, 248 

calcium carbonate-silicate, 243 

carbohydrates-silicate mixes, 244, 250 

casein, 244-249 

china, for, 216 

clay-silicate, 242-243 

contrasted with cements, 165-166 

contrasted with sizes, 298 

corrugated board, 224-226, 230 

cottonseed meal in, 248 

definition, 165-166, 210 

dextrin in, 244 

felt paper, for, 241 

filler for, 166, 243 

flexibility of, 250 

four B formula, 245 

glass, for, 215-216 

glue-silicate mixes, 249 

glycerin in, 249 

gum arabic in, 248 

historical, 12-13 

humidity effect, 215 

insecticides, in, 408 

labels, for, 240 

laminated board, for, 235-237 

lime mixtures, 244-245, 248 

mica, for, 216-217 

mixtures, 241-251 

paper tubes, for, 239-240 

peanut meal with silicate, 248 

plywood, for, 220-222, 243-249 

pressure effect, 213 

references, 251 

rubber latex in, 249, 250 



Adhesives, salt brine-viscosity changes, 
152-154 

sealing boxes, for, 237, 238 

set and viscosity relation, 213-215 

shellac in, 249 

silicate removing from machinery, 
234 

silicate, unmodified, 215-241 

solubility of dried, 215 

soya-beans, from, 248 

specification for paper box sealing, 
233-234 

starch-silicate mixes, 244 

strength, 216, 219, 220, 243, 244 

surface porosity effect, 213 

sugar in, 250 

tackiness of, 154-156, 244 

temperature-drying relationship, 234 

testing, 236, 251 

theory, 210 

tin, for, 240 

veneer, for, 243 

verminproof, 239 

viscosity, 56, 211, 213-215, 243 

vulcanized fiber, for, 222-223 

wallboard, for, 237, 239, 241-242 

waterproof, 244-245, 249, 250 

whiting and silicate, 243 

wood^ for, 219-222, 243. See also, 
Sizing, Coating 
Adsorption by gels, 22, 400 

sodium ions on silica, 56, 57 

See also Absorption 
Agate, 22, 83 
Air, action on silicate films, 259 

action on silicate glass, 117 

action on silicate powders, 162 

drying by silica gel, 398 
Airplane, adhesives for, 244-245 
Albumin, solution of, 330 
Alcohol, reaction with silicate, 73, 81, 82, 

365 
Aldehydes, reaction with silicate, 396- 

397 
Alignum cements, 191-193 
Alkali, free, determination in soap, 366- 
367 

lubricating effect, 329-330 

maximum in silicate, 127 

metal silicates, 15 
Alkalinity, silicate, controlled, 335-336 

viscosity curve, 213 
Alloying, cast metals, 189 



425 



426 



SUBJECT INDEX 



Alum, paper size, for, 279 

precipitate, 280-281, 291 

reaction with rosin, 279-280 

reaction with silicate, 280, 283 

sizing, for, 283 
Aluminate gels, 397, 403-404 
Aluminates, reaction with silicate, 397, 

405 
Aluminum, bronze, greaseproofing, for, 
255 

castings, impregnating, 266-267 

cleaning, 371-373 

corrosion, 365, 371-377. See also Cor- 
rosion, aluminum 

metal cement, 202 

oxide in cements, 188, 189, 190 

oxide in detergents, 355-356 

paint, 268, 273-274 

reaction with silicate, 85, 273-274, 371. 
See also Corrosion, aluminum 

salts, reaction with silicate, 77, 78 

sulfate, fireproofing, for, 262 
Francois process, in, 199 
paper, in, 279 
silk weighting, in, 295 
Ammonia, reaction with silicate, 82 
Analysis, calcium carbonate by-product, 
typical, of, 218 

cements, 87 

detergents, of, method, 365-367 

free alkali in soap, method, 366-367 

sand, typical of, 108 

scale from water pipe, of, typical, 382 

silica determination, 19, 157-158 

silicate glass, method, 39, 40, 156-159 

silicates, typical, 35, 160 

soda ash, typical, 109 
Anhydrous silicates, solid, 68, 110-117 
Anti-dimming compounds, 321, 322 
Antiseptic, silicate as, 264-265, 414 
Arc furnaces, preparation of silicates, 

for, 103 
Arterio-sclerosis treatment, 412 
Asbestos, board, 217-218 

cements, 87, 188-189, 191-193 

electrode coating, 275 

paper, 217-219 

pipe covering, for, 219 

reaction with silicate, 87, 193 

waterproofing, 218 

wetting, 264 
Ash, paper, in, table, 285 

washing with silicate, from, 337-341, 
344 
Asphalt, acid-proof cement, in, 182 

water resistance, for, 237 
Automobile frames, fireproofing, 263 



Bakelite, paper sizing with, 290 
Bandages, surgical, 413 
Barium carbonate, 87 



Barium sulfate, cements, in, 181, 182, 

187-188 
Barrels, fiber, 240 

wooden, for silicate, 162 
Barrel sizing, 256, 260 
Barrel testing, 256-257 
Barytes, in paint, 268 
Base-exchange, gels, 55-56, 397, 402-404. 
See also Gels 

gels, dehydrating, effect, 407 

reactions, 405-407 

silicates, 405-407 
Baume, hydrometers, 127-128 

-specific gravity relation, 128 

-temperature tables, 133-134 

-total solids, tables, 128-130 

-viscosity curve, 214 
Bibliography, silicate literature, of, 14 
Bicarbonate, paint vehicle for, 269 
Binder, artificial stone, for, 12 

miscellaneous uses, 189-191 

roadways, for, 196-197 

vulcanized fibre, for, 222-223 
Bituminous cements, 197-198 
Bituminous matter, wetting, 315 
Bleaching, compounds, stabilizing with 
silicate, 345 

cotton, kier boiling, 354 

hypochlorite, 348-352 

peroxide, 344-348 

textiles, 344-352 
Blood adhesives, 249 
Bloom, films, of, 269 
Board, see Millboard, Wallboard, etc. 
Boiler compounds, 384 
Boiling-off silk, 299 

Boiling point elevations and constitu- 
tion, 45-47 < 
Boiling points, silicate solutions, of, 45- 

47, 138-139 
Borax, in paint, 272 
Bottles, washing, 335 
Boxes, paper, sealing, 225 
Brick, paints for, 271, 272, 275 
Brine corrosion, silicate for, 382-384 
Briquets, binder for, 178-179, 382 
Bristol, paper, 291 
Buffer, effect in bleach bath, 348 

effect in clay slips, 302 

effect of silicates, 297-298, 302, 348, 
412-413 

solutions, medicinal use, 412-413 
Buttermilk, adhesives, in, 248 



Calcium, acetate, for sizing jute, 264 
carbonate adhesives, 243 
cements, 86, 87, 195-197 
commercial, analysis of, typical, 

218 
reaction with silicate, 86, 87, 195 
waterproofing agent, 218 



SUBJECT INDEX 



427 



Calcium, hydroxide, cements in, 194 
reaction with silicate, 194, 200 
oxide, cements, for, 87 
phosphate, reaction with silicate, 87 
silicate, formation, 86 
water in, reaction with silicate, 331- 
332. See also Manganese in 
water 
Cancer, silica effect, 412 
Carbohydrate, silicate adhesives, 244 
Carbon, arcs, binder for, 191 
black, in paint, 268 
dioxide, fusion mixtures, in, 96, 98, 
99-100 
reaction with silicate, 72, 144, 146, 

244, 252 
silicates, in, 99, 144, 146 
reaction with silicate glass, 94-95, 103, 

188 
reaction with sodium sulfate, 94-95 
Carbonating, silicate glass, of, 117 
Carborundum, reaction with silicate, 92, 
178 
refractory paint, for, 275 
wheels, 178 
Carnotite ore extracting, 411 
Cartons, coating, 253-254 
Case-hardening, cement for, 188-189 
Casein-lime-silicate adhesives, 244-245 
paints, 272, 277 
paper sizing, 290, 292-293 
-silicate, adhesives, 244-249 
paper sizing, table, 292-293 
substitutes for, 248 
Casting, clay bodies, 302 
defective, coating, 266-267 
metals, 189 
Catalysis, gels for, 397, 402 
Cataphoresis, gelatinous films forma- 
tion, 370-371 
Caustic soda, see also Sodium hydroxide 
abrasive wheels, for, 178 
aluminum, action on, 371 
inhibiting effect of silicate, 371 
reaction with silicate, 298 
-silicate equilibrium, 358 
transport number, 32 
Cell structure, colloidal silicate, 83 
Cellulose, acetate dyeing, 298 
alkali, action on, 343 
bleached, effect on hypochlorite bleach, 

351 
silicate action on, 330-331 
wetting, 264 

See also Wood pulp, Paper, Straw 
Cement, acid effect, 179-182 
acid proof, 169, 180-182, 201-202,390, 

392 
acid proof masonry, for, 169 
acids in, for quick setting, 195 
adhesives, contrasted, 165-166 
alignum, 191-193 



Cement, aluminum oxide in, 188, 190 

analysis of, 87 

asbestos, 188, 191-193 

bituminous, 197-198 

briquets for, 178-179 

case hardening, 188-189 

chromite for high temperature, 183 

classification of, 166 

definition, 165-166 

dental, 390 

drying, 179, 185-187 

fillers for, 168-173 

fireclay analysis, typical, 183 

fireproof plastics, 197 

flexibility control, 179 

furnace, 183 

gastight, 183, 187, 202 

glass, high temperature, 183 

glycerin in, 179, 201-202 

heat effect on, 185-187 

high temperature, 183-185 

historical, 12 

insulating, 190, 197 

iron, 202 

kaolin, 187-189 

lime mortars, 193-194 

litharge-glycerin, 201-202 

magnesium oxychloride, 264 

mending saggers, for, 185 

metal, 202 

miscellaneous, 190-193, 197 

modifying materials for, 167 

patching, 200 

Portland, and silicate, 198, 201-202 

properties, 166-168, 179 

quick-setting, 179-180, 195, 200 

refractory, 183, 185, 186 

roadways, for, 196-197 

rubber latex in, 179 

sawdust in, 199 

setting accelerated, 179-180 

setting, causes, 166 

setting by chemical reaction, 193-209 

setting by moisture loss, 166-192 

setting time, silicate effect, 201-202 

shellac in, 179, 190 

silicate, 87, 165-209 

spark-plug, 187-188 

statuary, for, 195 

stove, 184-185 

strength of, 171-172, 179-180 

sugars in, 179 

sulfite liquors in, 179 

tanning extracts in, 179 

temperature effect, 183-187 

wallboard, for, 196 

water resistant, 138, 179, 195, 202 

wear, 206-209 

wood-fiber in, 199 
Cementation of water-bearing strata, 

198-199 
Census bureau report, 14, 15 



428 



SUBJECT INDEX 



Ceramics, clay casting with silicate, 302 

clay slips, 302. See also Clay slips 

glazes, 92, 275-277 

molding, binder for, 190 

molds, 302-303 
Chalk, hardening, 203-204 
Chinaware, adhesive for, 216 
Chipboard, 224, 234 
Chlorine, colors, silicated, effect on, 344 
Chrome tanning, silicate for, 409 
Chromite, high temperature cement, for, 

183 
Chromium salts in paint, 268 
Cinder, briquets, 179 
Cinnabar, paint, in, 268 
Citrate, buffer in medicine, 412-413 
Garication, by filtration, 127 

oil, of, 316 

waste waters, of, 411 
Clarity, silicate solutions, of, 127 
Classification of silicates, 14 
Clay, abrasive wheels, in, 173 

acid proof cements, for, 181 

adhesive, with silicate, 242-243 

casting, 302 

cement filler, for, 172 

heat-resistant effect, 184 

paper, in^ 284-285, 288-289, 292-293 

paper sizing, in, table, 284-285, 292- 
293 

reaction with silicate, 87 

sedimentation rate, 300-301 

-silicate mixture, lathering effect, 
326 

slips, silicate for, 302-305 

soap, in, 302 

suspension, viscosity effect, 301-303 
Cleaning metal, 335, 353 
Clearness of silicate solutions, 127 
Cloth, fireproofing, 204 
Coal briquets, binder for, 179 
Coalescence, see Gels, gelation 
Coating, 252-299 

castings, 266-267 

electrodes, 275 

glass, 269-271 

half-tone cuts, 264 

hot metals, 275 

light diffusion, 269-271 

lumber, 265-266 

metal, 263-264, 266-267 

paint, 267-278. See also Paint 

paper, 253-256 

paraffin and silicate, 255 

patent literature, 278 

plaster walls, 264 

silicate, material for overlaying sili- 
cate, 253 

thermionic valves, electrodes, 275 

tree wounds, 264-265 

walls, 264 

welding electrodes, 275 



Coating, whitewash, 272 

wood, 265-266, 271-272 

See also Adhesives, Sizing, Paint, 
Films 
Coefficient of expansion of silicate solu- 
tions, 114, 133 
Coherence, adhesion, relation to, 210 
Colloid mill, 307 

Colloidal, properties of silicate, 364 
Colloidal silica, gels, and, 388 

leather tanning, for, 408-409 

natural occurrence, 17-19 

rancidity of fats, for, 365 

silicate solutions, in, 52, 55, 57 
Colloids, sugar solution purifying, for, 

407-408 
Color, glass, of, 110-111. See also 
Glass, properties 

paints, in, 267-268 

retention in paper, 283 

silicate solutions, for, 85 

silk, weighted, 296 

stripping, 347 

textile, silicate effects, 297, 343-344. 
351, 352 
sodium carbonate effect, 369 
Commercial forms, 108-164 
Composition, dissolving effect, 104 

refractive index tables, 136-137 

silicate, 58, 104, 109, 159-161 

specific-gravity relation, 128-133 

viscosity relation, 143-151 
Concentration, acid-proof cement, for, 
169, 171 

cement, effect in, 166, 202 

conductivity graph, and, 25 

-hydrolysis relation, 38 

maximum, 127, 160 

silicates, of, 56 

specific-gravity relation, 133 

-viscosity graph, 148 
Concentrated silicates, 56 
Concrete, acid resistant, 209 

curing, 206-209 

free lime in, 205 

hardening, 206-209 

oil proofing, 204-206 

paint for, 271 

penetration of silicate in, 204-206 

reinforcing bars, corrosion of, 200 

repairing, 200 

setting, theory of, 204 

storage tanks, 164 

strength, silicate effect, 205 

waterproofing, 204-206 

water-resisting, formulas, 200 

wear, 206-209 
Conductivity, concentration, and, graph, 
25 

constitution relation, 24-31 

electrical, of silicate glass, 114 

equilibrium time, 27 



SUBJECT INDEX 



429 



Conductivity, equivalent of silicate solu- 
tions, 28-31 

high silica silicates, of, 25 

hydrolysis effect, 29 

metasilicate, of, 24 

mobility of silicate ions, 31 

potassium silicate, of, 27 

ratio effect, 26, 27 

silicate solutions, of, 29, 335, 370-371 

soap solution, of, 23 

sodium chloride, of, 24 

temperature effects, 25, 26 

theory of, 30, 31, 39, 335 

thermal, of intumescent silicate, 119 

thermal, of poplox, 119 
Constitution, 17-57 

activity-coefficient relation, 47-50 

boiling point relation, 45-47 

chemical evidence of, 53-55 

conductivity, relation, 24-31 

dialysis, evidence from, 51-53 

electrical evidence of, 23-40 

electrometric titrations, from, 54 

freezing point, relation, 40-44 

H-ion concentration, and, 33-39 

metasilicate of, 47, 48 

particle-number effect, 40-53 

refractive index relation, 135 

sodium-ion activity, 50, 51 

vapor-pressure effects, 44, 45 

viscosity relationship, 139 
Container board, 224-225, 230 
Containers, oil, 205 

silicate, for, 161-164 
Copper, metasilicate reaction, 74, 75 

paint, in, 268 

silicate cement, 189 
Corn borers, 408 
Corrosion, aluminum, 365, 371-377 

boilers, 57 

condenser systems, 382-384 

electrolytic baths, 385 

inhibiting by silicate, 371-384 

iron, 379-382 

iron reinforcing bars, 200 

lead pipe, 86, 373, 378-379 

prevention, films for, 164, 263-264, 371- 
384 

refrigeration machinery, 382-384 

theory, 379-380 

tin, of, 335 

water pipes, 380-382 

water, silicate in, 411-412 

zinc plates in batteries, 373 
Corrugated box, fireproofing, 262-263 

boxes, sealing, 231-234 
Corrugated paper, 224-234 

adhesive for, 224-226, 231 

asbestos, 217-218 

liners, 224 

manufacture of, 225-228 

moisture effect, 230 



Corrugated paper, patents, 227 

silicate for, 226, 231 

specifications, 224-225 

straw pulp for, 224, 410-411 

water resistance of, 230-232 
Cosmetics, silicate in, 365 
Cost of silicate solutions, 281 
Cotton, bleaching, 347, 349. See also 
Bleaching 

detergents, action of, 342-343 

dyeing, 297, 298 

fiber, cleaning, 331 

kier boiling, 354 

mercerizing, 298 

strength, effect of silicate, table, 336- 
339 

waste, washing, 352 

weighting of, 294 
Cottonseed, meal adhesive, 248 

oil refining, 321. See also Oil refining 

oil in soap, 361 
Cristobalite, melting point, 113 
Crystal growth in gels, 402 
Crystallization of silicate, 21, 222 
Crystalloidal nature of silicates, 52 
Crystalloidal silica, 53-54, 55 
Curing concrete, 206-209 



Dammar varnish for coating silicate, 269 
Definite soluble silicates, 58-71 
Deflocculation, 271, 300-311 

alkali comparisons, table, 310 

bleaching, effect in, 347 

boiler treatment, 384 

clay, 300-304, 306, 310 

concentration of reagents, 307-310 

deinking paper, 353-354 

detergency measuring, for, 307-311, 
367, 368 

flotation technic, 306 

hydraulic separation, in, 307 

insecticides, 408 

iron rust, of, 379 

lithopone, of, 310 

manganese dioxide suspension, 308- 
310 

minerals, of, 300-301, 305 

ratio effect, 303-305 

saponification of fatty acids, 330 

sedimentation of clay, 300-301 

selective, 306 

silicate for, 306, 308 

soap action, 307-311, 324 

sodium chloride for, 354-355 

temperature effect, 308, 310 

theory of, 300-301, 305 

ultramarine, of, 310 

use of, 311 

viscosity effects, 301-303 

wetting relation, 311 

See also Detergency, Washing 



430 



SUBJECT INDEX 



Degumming silk, silicate for, 299 
Dehydrated floe in dissolver, 138-139 
Dehydration, 118-120, 122-125 
Deinking paper, 353-354 
Density vs. ratio, table, 133 
Dental cement, silicate, 390 
Dental mirrors, anti-fog, 321 
Deoxidizing agent, 382 
Detergency, alkali action in, 310, 342- 
343, 367 

alkalinity, controlled, 335-336 

aluminum cleaning, 371-373 

analysis of silicated products, 365- 
367 

ash increase with silicate, 337-340 

color, effect, 297, 343-344, 369 

comparisons for deinking, 353-354 

deflocculation in, 300, 307-311, 367, 
368 

deinking paper, 353-354 

dirt, 368 

drop number, 313-314, 323, 367 

emulsification, see Emulsification 

fabric, effect on, 335-344. See also 
Textiles 

fatty acids, saponification of, 330 

film effect, 314 

free alkali in soaps, 367 

glassware cleaning, 335 

historical, 13 

lathering, 326-329, 367. See also 
Lathering 

lubrication, 329-330 

manganese dioxide tests, 307-310 

measuring, 307-310, 328-329, 353-355, 
367-369 

metal cleaning, 353 

pH of reagents, 344 

practice, 352-369 

rinsing, 340-341 

rosin, substitute in soap, 13 

salt effect, 355 

saponification of fatty acids, 330 

silicate action, 300, 331-340 

silicate mixtures, 324-325, 355-356 

soap builder, 327-328 

soap-silicate, 309, 324-325 

soap-sparing action of silicate, 331- 
335 

soaps, see Soaps 

solution effect, 330-331 

starch, 330, 368 

suspension tables, 308-310 

testing, 367-369 

viscosity effect, 314 

washing overalls, 352, 355 

washing tests,. 367-368 

water-softening effects, 331-335 

wetting in, 311-324. See also Wetting 

See also Deflocculation, Washing 
Dew-point lowerings, 45 
Dextrin, in adhesives, 244 



Dialysis of metasilicate-copper, 74, 75 

silica-sol formation, 20 

solutions, of, 51-53 

wallboard, in, 242 
Diatomaceous earth, 18 
Dichromate, corrosion prevention, for, 

382-383 
Diffusion, light, of, 269-271 

silicate solutions, of, 80-81 
Digester linings, acid-proof cements for, 

201-202 
Diluting silicate in paint, 271 
Dilution charts, 132 
Dirt, in detergency, 368 
Disilicate, anhydrous, 66-68 

concentration of, 127 

constitution, 47, 48, 135 

crystallization, 103 

dissolving, 105 

ennehydrate, 67 

evidence of, 100-103 

formation of, 100 

hydrolysis, 48 

melting-point studies, 112-113, 115 

mixtures, in, 112 

-quartz eutectic temperatures, 115 

solubility, 115, 116-117 

solution, in, 29, 36, 55 

stability, 116-117 

viscosity, 148 
Disinfectant, tree wounds, for, 264-265 
Dispersion, 105, 272. See also Emulsi- 
fication 
Dissolving, apparatus for, 106-107 

composition variation effect, 104 

hydrous solids, 121 

silicate glasses, 94, 104-107, 115, 156 

temperature effect, 121 

troubles, 138-139 

water for, amount, 121 
Dolomite, reaction with silicate, 87 
Doucil, base-exchanging gel, 403-404 
Drop number, 313-314, 323, 367 
Dry cells, zinc corrosion in, 373 
Dry cleaning, reclaiming solvents, 321 
Dryers, for silicate, 119-120 
Dye, paper coloring, for, 283 

reaction with silicate, 85, 283, 297, 344 

silicate, for, see Color 
Dyeing, textiles, 297-298 



Earth, silicate formation in, 17 
Economic factors in production, 15 
Efflorescence, silicate films, of, 87, 117, 
252, 269 

soap, silicated of, 363-364 
Egg preserving, 164, 385-387 
Eggs, freshness test, 387 
Electric batteries, jelly electrolytes, 395- 
396 

lamp bulbs, 269-270 



SUBJECT INDEX 



431 



Electrical conductivity, silicate glass, of, 
114 

insulation, cements for, 190 
mica sheets for, 216-217 
Electrode carbon arc, 191 

coatings, 275, 385 

wire, cement effect on, 187 
Electrodes, catophoresis of silicate, in, 

371 
Electrolysis of silicate solutions, 23, 91, 

370-371 
Electrolytes, electro-osmosis, in, 410 

gels, for storage batteries, 394-396, 
410 

reaction with silicate, 84, 85 

silica gel, of, 395-396 
Electrolytic baths, corrosion in, 385 

effect, aluminum and silicate, 371 
Electrometric titration of silicate, 23, 

54, 78, 79 ( _ 
Electroplating, 267, 353, 355 
Emulsification, 322-326 

bituminous bodies, of, 197-198 

breaking emulsions, 325-326 

drop number relation, 323 

film formation on, 272, 314 

kier boiling, cotton, 354 

mixture for, 325 

oil, of, 319, 320, 324 

paints, 274-275 

silicate for, 323-325 

soaps, in, 323, 324, 325, 330, 364 

sodium carbonate power, 323 

types of emulsion, 322 

viscosity effect on, 314 

washing in, 324 

water hardness, effect of, 325-326 

wetting, relation of, 314, 324 
Enameling metals, 263-264, 353 
Equivalent conductivity, 28-31 
Eutectic silicate mixtures, 112-113, 115 
Expansion, thermal, of silicate, 114, 133 
Eyes, physiological effect of silicate, 413 



Fabric, ash, 337-340 

bleaching, 344-352. See also Bleaching 

microscopical examination, 369 

silicate effect on, 335-352 

See also Textiles 
Factory floors, oil penetration preven- 
tion, 205-206 

locations, economics of, 160 
Fats, containers for, 256 

purification of, 321 

rancidity, 365 
Fatty acids, rancidity, 365 

reaction with silicate, 259 

saponification of, 330 
Fatty acid soap, paper sizing, for, 290 
Felt paper, splicing, 241 



Ferric (-ous) salts, reaction with sili- 
cate, 75-77 
Ferrous sulfate, paper sizing, in, 282 
Fertilizer bags, sizing, 264 
Fertilizer, silicate use in, 13 
Fiber barrels, 240 
Fiber board, 223-239 
Filler, cements, for, 166, 168-173, 181 
Films, acid action, by, 11 
adhesives, 210 
analysis of, 382 
bloom on, 269 

carbide-caustic reaction, 178 
chalky, 271 

coating paper, for, 253-256 
condenser systems, in, 382-384 
detergent, 314 
drying retardant, 250 
efflorescence of, 269 
emulsions, 272 

flexibility, 244, 249-250, 271-272 
gelatinous, 370-389 
appearance, 17, 384 
corrosion prevention by, 371-384 
egg preserving, 385. See also Egg 

preserving 
electrolytic baths, in, 385 
formation of, 370-371 
galvanized iron, on, 385 
gels, and, 388 
lead solution retarding, 313, 378- 

379 
lubricating effect, 329-330 
permeability of, 380 
strength of, 381 
thermal conductivity, 384 
zinc plates in dry cells, 313 
incombustible, 260 
insoluble, 268-270 
memo pads, for, 256 
metal, on, 266-267 
metallic on silicate, 256 
miscellaneous uses, 264-266 
moisture in dried, 252 
paint, requirements, 267 
pigments, without, 253-267 
protective, 86. 344 
silicate, 57, 215, 252, 253, 259 
solubility, 253 
water resistant, 250 
uses, miscellaneous, 264-266 
See also Sizings, Coating 
Filtration, 18, 127 
Fireclay, 172, 183 
Firedoors, alignum, 191 
Fireproofing, 12, 197, 204, 260-263 
Flannel, detergent action on, 342-344 
Flexibility of films, 244, 250, 271-272 
Flocculation, suspended matter in solu- 
tions, of, 127, 271, 305. See also 
Deflocculation 



432 



SUBJECT INDEX 



Floors, acid resistance of, 209 

fireproofing, 262 

oil penetration prevention, 205-206 
Flotation, 300-301, 305-307, 311, 326 

deflocculation for, 311 

frothing, 326 

ores, of, 305-307 

silicate for, 305-307 

surface tension, 326 

technic, 306 

theory of, 300-301 
Fluorides, reaction with silicate, 411 
Fluorspar, cement in, 182 
Flux, welding, first use in, 13 
Foam, 326-327, 329 
Foil, metal, on silicate, 256 
Foreign production, 15 
Formation of silicates, 17, 24 
Forms, anhydrous, 108, 110-117 

classification, 108 

commercial, 108-164 

hydrous solids, 108, 117-126. See also 
Hydrous solids 

solutions, 108, 126-156 
Francois process, 198-199 
Free alkali, analysis, 39 

silicated soaps, in, 366-367 

silicate solutions, in, 30, 35, 36 
Freezing point depression, silicate solu- 
tions of, 40, 41-44, 47-50 
Freezing points, constitution relation, 

40-44 
Freezing, silicate solutions, of, 36, 137- 

138, 164 
Frosting lamp bulbs, 269-270 
Froth, see Foam, Lathering 
Fungus growths on wood, preventing, 

408 
Furnace, brick, color after use, 188 

cements, 183 

lining glazes, 275 

silicate, 103, 104, 111 

temperatures, 109 
Fusion, silica and soda ash, 97, 103-104 



Galvanized iron, painting, 385 
Galvanized metal, reaction with silicate, 

85, 163 
Garden, silicate, 77, 79, 80 
Gas, adsorption by gels, 399-401 

container for generating, 255 

-tight cements, 183 
Gay-Lussac tower, 180-181 
Gelatinous films, see Films, gelatinous; 

see also Gels 
Gelation, 82-85, 268, 370 
Gels, 380, 388-404. See also Colloids, 
Films, Gelation 

acid-resistant cements, in 390, 392 

adsorption, 22, 398-401 

aluminate, 403-404 



Gels, base-exchange, 55-56, 397, 402-407 

catalysis, for, 397 

concrete, in, 204 

condensation of gases, 398-401 

crystal growth in, 82, 83 

density, 82 

Doucil, 403-404 

drying, 397-399 

egg preserving, 386, 387 

electrolysis of silicates, from, 91 

electrolytes, 395-396 

films, in, 253 

formation, 370, 388-397 
aluminates, from, 397 
conditions for, 370, 388-397 
H-ion effect, 390-395 
metal salts, from, 396-397 
particle charge effect, 388 
ratio effect, 389-392 
setting time, tables, 395 
temperature effect, 392-393 
theory, 20 

gas adsorption, for, 398-401 

gelatinous films, and, 388 

gelation rate, 370, 390-395 

high silica silicates, 402-403 

moisture absorption, 398 

natural, 22 

porosity of, 82, 397, 398, 403 

preparation of, 397, 398 

properties, 370 

reactions in, 401-402 

rehydrating, 397-399, 403. See also 
Gels, drying 

resonant, 394 

rhythmic banding in, 82, 83, 402 

setting time, 370, 390-395 

silica, 394-402 

silica, formation from sol, 19 

silica, occurrence, natural, 18 

silica, silica concentration in, 371 

silica, solubility, 90 

silica structure, 22 

sodium oleate, from, 332 

sols, from, 19 

steam treatment effect, 398 

storage batteries, for, 394-396 

structure, 22, 83, 370, 392-393, 397- 
398 

syneresis, 22, 389, 397 

turbidity-alkali curve, 390, 392 

vapor adsorption, for, 398-401 

water in, 390, 392 

X-ray examination, 22, 397-398 
Glass, adhesives for, 215-216 

anti-dimming compounds, 321-322 

coatings for, 269-271 

colored with silicates, 72 

containers for silicates, 162 

detergent for, 335 

high temperature cement for, 183 

opal, manufacture, 269-270 



SUBJECT INDEX 



433 



Glass, pot, glazes, 275 
reaction with silicate, 215-216 
removing silicate from, 216 
silicate alkaline, 111 
silicate analysis, method, 156-159 
silicate, carbon action with, 188 
silicate, containers for, 161 
silicate for corrosion treatment, 381 
silicate dissolving, 94, 104-107, 115, 

156 
silicate, eutectic, 112 
silicate, hydration of, 118-119 
silicate, moisture absorption of, 117 
silicate, neutral, 110-111, 160 
silicate, properties, 110-117 
silicate, from sulfate, 111 

Glassine paper, 283, 291 

Glazes, 92, 275-277 

Glover tower, 180-181 

Glucose, in silicate, 250 

Glue, characteristics of, 211-213 
hydrolyzed with silicate, 249 
paper sizing, for, 290, 292-293 
-silicate adhesives, 249 
sizing barrels, for, 256, 259, 260 
See also Adhesives 

Glycerin in adhesives, 249 
cement, in, 179, 201-202 
films, flexible, for, 249 
reaction with silicate, 73, 250 

Gravity, see Specific gravity 
— viscosity curve, 214 

Greaseproof paper, 254-255, 291 

Greensand, treating with silicate, 406- 
407 

Grinding wheels, see Abrasives 

Gum arabic, reaction with silicate, 73, 
248 



Half tone cuts, films, 264 

Hands, action of silicate on, 413-414 

Hardening agent, historical, 12 

present use, 86, 203-204, 206-209, 407 
Haskell's glue, 249 
Health, physiological effects of silicate, 

411-414 
Heating, effect on viscosity, 60, 151-152 
High temperature cement, 183-185, 187- 

188 
History, 11-16 

Horn shavings, paper sizing, for, 256 
Horticulture, tree grafting results, 408 
Hot surfaces, paint for, 273-275 
Humidity, adhesion effect, 215 

hydrous silicates, effect of, 122-125 
Hydrated silicates, resilience of, 194 
Hydrates, of metasilicate, 58-64, 125-126. 

See also Metasilicate 
Hydration, and dehydration, contrasted, 

118 
paper fiber, of, 279, 283 



Hydration, silicate glass, of, 105-106, 
115, 118-119, 122-125, 156 
soaps, in, 364 
Hydraulic separation of mineral, 307 
Hydrogen ion, brine-silicate effect, 152- 
154 _ 
constitution relation, 33-39 
hydrolysis relation, 55 
Hydrogen, manufacture, silicate by-prod- 
uct, 90 
peroxide, bleaching, 344-348 
sulfide, reaction with silicate, 72 
Hydrogenating oils, gel catalyst for, 

402 
Hydrolysis, concentration relation, 38, 
39 
conductivity effect, 29 
disilicate, 48 

pH measurements, and, 55 
products of, 73 
vs. ratio, 39 
silicates of, 32, 33, 34, 37, 38, 53, 104- 

105 
starch of, 330 
Hydrometers, 107, 127-128. See also 

Baume 
Hydrous solids, 117-126, 277 
Hydroxyl-ion concentration control in 

silicate, 335 
Hypochlorite bleaching, 348-352. See 
also Bleaching, hypochlorite 



Impregnating metal castings, 266-267 
Impurities, in silicate solutions, 72 
Indicator, silicate titrations, for, 157 
Indigo discharging, 297 
Induration, metal castings, of, 266-267 
Industrial uses, early, 12, 13 

value, census bureau report, 14, 15 
Infusorial earth, preparation of silicate 

from, 88, 89 
Inhibiting corrosion, 200, 371-384 
Inhibitor, silicate as, 85, 86, 178 
Ink, printers, thickening, 274-275 
Ink resistance, silicate paper, of, 286- 

287 
Insecticides, silicate in, 408 
Insoluble materials, silicate, from, 87, 

270 
Insulated wire, fireproofing, 262 
Insulating cement, 190, 197 
Insulation, mica sheets, 216-217 

thermal, 18, 217-218, 260-261 
Intraveneous injections of silica, 412 
Interfacial tension, 311-313 
Internal resistance of solutions, 148, 154 
Intumescence, cements of, 185 

fire protection from, 260-261. See also 
Poplox 

pigment effects in silicate for, 261 

silicate, 119 



434 



SUBJECT INDEX 



Iron, bleaching, action in, 346-347 

cement, 202 

galvanized, painting, 385 

oxide in paint, 268 

reinforcing bars, corrosion prevention, 
200 

rusting, 202, 263-264, 379-382. See 
also Corrosion, iron 

salts, reaction with silicate, 75-77 

water, in, silicate for, 335 
Isotherms of potash-silicate system, 98 

soda-carbonate-silicate system, in, 100 

Jute, paper, 224 
sacks, sizing, 264 

Kaolin cements, 187-189 
Kier boiling, cotton, 354 
Kraft paper, 224, 291 

Labels, adhesive for, 240 

Laminated board, 234-239 

Lamp bulbs, frosting, 269-270 

Latex, see Rubber latex 

Lathering, 326-329, 367 

Laundry, silicate use in, 411 

Lead, acetate in paper sizing, 256 
flotation, 305-307 
paint, in, 268 
reaction with silicate, 268 
salts, reaction with silicate, 405 
solution, inhibiting, 86, 373, 378-379 
water, in, physiological effect, 378 

Leather tanning, 408-409 

Liesegang rings, 82, 83, 402 

Life origin, theory of, 17, 83 

Light diffusion, 269-271 

Lime, adhesives in, 244-245, 248 
cement for roadways, 196-197 
fireproofing, in, 262 
mortar, strength effect of silicate, 193- 

194 
reaction with silicate, 194, 200, 277 
water, reaction with silicate, 88 

Linen, 337-338, 343 

Liquidus studies, 101, 112-113, 115-117 

Literature, early, 11-15 

Litharge, in cements, 87, 182, 201-202 

Lithium carbonate, decomposition, 99 
silicates, 70, 113 

Lithopone, 268, 271, 310 

Lubrication, in detergency. 329-330 

Lumber, 223, 265-266, 408 

Magnesium, carbonate, cements, for, 87 
oxychloride cement, 264 
sulfate, for paper size, 282 
water, in, reactions with silicate, 331- 
332 



Manganese dioxide, deflocculation tables, 

308-310 
Alanufacture, census bureau report, 14, 
15 

early, 13 

furnace reactions, 109 

soda ash and silica, from, 103-104 
Marble, imitation from calcium carbo- 
nate, 195 
Medicine, silicate in, 411-412 
Melting scrap metal, 266 

temperatures, 115 
Memorandum pads, 256 
Mercerizing cotton, 298 
Metal, casting, 189 

cement, 202 

cleaning, 335, 353, 355, 371-373 

coating, 266-267 

containers, for silicates, 163-164 

foil on silicate, 256 

oxidation prevention, 263-264, 266 

plating, 267 

porous, impregnating, 266-267 

salts, reaction with silicate, 396-397 

scrap, remelting, 266 

silicate action on, 164 

surfaces, size for, 264 
Metallic paints, 273-274 

silicates, preparation, 73 
Metasilicate, anhydrous, solubility, 66- 
68 

buffer solution for medicinal use, 412- 
413 

conductivity, 24 

constitution, 47-48 

copper, of, 74 

definite salt, a, 55 

dehydration of, 126 

dew point lowering, 45 

dissolving, 104, 125 

electrolyte for storage battery, in, 410 

formation of, 99-100. See also Meta- 
silicate, anhydrous, -hydrates, -hy- 
drous 

freezing point depression, 41 

fusion mixtures, in, 100-101 

humidity effect, 126 

hydrates, 62-65, 125-126 

hvdrous, 58-67, 121 

melting point, 99-100, 112-113 

metal cleaning, for, 353 

paper sizing, table, 284-285 

preparation, 41, 90, 91, 93 

reactions, 74-78 

rosin, saponified, 288-289 

saturation curve, 116 

silicate solutions, in, 36 

solubility studies, 116-117 

stability, 126 

storage battery electrolyte, in, 410 

structure, 32 

therapeutic use, for, 412 



SUBJECT INDEX 



435 



Metasilicates, vapor pressure lowering, 
44-45 

viscosity, 148 
Metasilicic acid, 55 
Mica, acid-proof cement, in, 182 

adhesive for, 216-217 

greaseproofing, for, 255 
Micelles, conductivity effect, 31 

existence of, 50 

multi-charged, 31, 335 

silicate solutions, in, 55 
Millboard, asbestos, 218. See also Wall- 
board 
Mineral, separation of ores, 306-307 
Mining, sealing shafts, 198-199 
Miscellaneous uses, 407-411 
Miscible materials in silicate, 250, 298 
Moisture, absorption by silicate, 117 

penetration of coated paper, 255, 264 
Molded articles, binder for, 190 
Molds, lining, for metal casting, 189 
Montan wax, paper sizing, for, 290 
Mordants, silicate for, 297 
Motion picture screens, 270 
Mouth, silicate taken by, effect, 414 
Mural painting, stereochromic, 272- 
273 



Naphtha soaps, 330 

Neutral glass, see Glass, silicate, neutral 

Neutral silicate solution, 268 

Neutralizing silicate solutions, 408-409 

Nomenclature, 14 

Normality, silicate solutions, of, 36 



Ocher, in paint, 268 

Oil, clarification by silicate, 316 

containers for, 205, 256 

cottonseed, in soap, 361 

emulsions, 322-325. See also Emulsifi- 
cation 

fires, fireproofing against, 262-263 

hydrogenating, catalyst for, 402 

paint, silicate in, 274-275 

-proofing concrete with silicate, 204- 
206 

rancidity, 365 

reclaiming, 316-320 

refining, 320-321 

wetting with silicate, 312-313, 315 
Oily cotton waste, washing, 352 
Opal glass manufacture, 269-270 
Opals, 17, 22 
Optical constants of anhydrous silicates, 

68 
Ore flotation, 300-301, 305-307, 311, 

322, 326. See also Flotation 
Organic compounds, reaction with sili- 
cate, 73, 396-397 
Orthosilicate, 53-54, 76, 100 



Osmosis, electro, silicate electrolyte for, 

410 
silicate solutions, of, 40, 41, 51-53, 77, 

79, 80 
Overalls, washing, 352, 355 

Paint, aluminum, 273-274 
analysis of, 278 
brick, 271-272 
casein, 272 

characteristics, 267-268 
colorimetric apparatus, for, 267-268 
colors for, 268 
concrete, 271 
diluting, effect of, 271 
dry mixtures, 277 
galvanized iron, 385 
historical, 12 
hot surfaces, 273-275 
lithopone, 268, 271, 310 
metallic, 273-274, 385 
oil, silicate in, 274-275 
patent literature, 278 
pigments for, 268 
refractory, 273-275 
rubber latex in, 271-272 
silicate, 267-278, 389 _ 
silicate, fire protection by, 261-262, 

263 
stereochromic, 272-273 
stone, 271 

vehicle, 267-269, 389 
wallboard, 274 
weathering effect, 268-269 
whiting, in, 268, 271 
wood, 271-272 

See also Coatings, Films, Sizing 
Paper, asbestos, adhesive for, 217-219 
ash in silicated, 286, 287, 289 
bleaching, 348-352 
board, 225, 235, 236, 287 
book, 291 
box, fireproofing, 225, 227, 239, 262- 

263 
bristol, 291 
coating, 253-256 
color, 279, 283 
corrugated, 224-234, 410-411. See also 

Corrugated paper 
deinking, 353, 354 
dyes for, 283 
envelope, 291 

felt, splicing with silicate, 241 
filler, retention, 282 
finish, 279, 286 
flexibility of sized, 290 
fuzz, reducing, 283 
glassine, 283, 291 
greaseproofing, 254-255, 291 
hardening, 279, 286 
hydration of fiber, 279, 283 
ink resistance, 286-287 



436 



SUBJECT INDEX 



Paper, jute, 224 
kraft, 291 

manufacture of, 230 
Mullen test, silicate effect, 286 
printing, 294 
silica in, 18, 281, 284 
sizing, 278-294 

alum for, 279-283 

asbestos paper, 217-218 

Bakelite for, 290 

capillary rise test, 289 

casein, 290, 292-293 

clay in, 284-289, 292-293 

fatty acid soap for, 290 

ferrous sulfate as precipitant, 282 

glue, 290, 292-293 

magnesium sulfate, 282 

metasilicate in, 284-285 

method, 283-287 

minerals, table, 284-285 

Mullen test, 286 

particle charges, 282 

pH desired, 280 

precipitating, 279-282, 284, 286, 291 

ratio of silicate, effect, 282 

retention, 286-289 

rosin in, 278-280, 287-290 

silicate combinations, 287-291 

silicate, effects, 279, 281, 286-287, 
291 

silicate, grade for, 283 

soap and silicate, 290, 292-293 

soya bean oil, in, table, 292-293 

starch and silicate, 290-293 

straw paper, 410-411 

tables, 284-285, 292-293 

theory of, 279 

time required, 287 

wax, 290 

writing paper, 283 
straw, 224, 291, 330-331,410-411 
strength test table, 279, 283-285, 288- 

290, 352 
tests, 284-285, 288-290 
trimmings reused, 287 
tubes, 239-240, 244 
unbleached, silicate effect, 240 
washing in manufacturing, 331 
water-resistance of, 279, 287, 290 
writing, 283, 291 
Paraffin, silicate action with, 254, 255 

sizing jute, for, 264 
Particle charge, gel formation effect, 388 
sizing, in, 282 
sodium-ion activity, 50, 51 
wetting carbon, in, 320 
Particle number, activity coefficient, 47- 
50 
boiling point effects, 45-47 
constitution effect, 40-53 
freezing point effects, 40-44 
vapor-pressure effects, 44, 45 



Parting films, for rubber, 266 
Peanut-meal adhesive, 248 
Penetration, concrete, in, silicate, 204- 
206 
dense materials, of, 202-204 
paper, of, 255 
wood, of, 257 
Permanganates, carborundum wheels, in, 

178 
Peroxide bleaching, 344-348. See also 

Bleaching, peroxide 
Petroleum refining, with silica gel, 400- 

401 
pH, detergent solutions, of, 344 
paper sizing solutions, of, 280 
silicate, salt effect, of, 85, 152-154 
silicate solutions, of, 33-38, 335 
Phenols, reaction with silicate, 73, 396- 

397 
Phosphate, silk weighting, for, 294 
Phosphoric acid, 348, 411 
Physiological effects, 336, 411-414 
Pigment, 261-263, 268 
Plaster, coating with silicate, 203-204, 
264 
painting on, stereochromic, 272-273 
Plastic, silicate with fillers, 166, 190, 194, 
195 
solids vs. viscous liquids, 139-140 
Plating metal, 267, 353 
Plumbates, reaction with silicate, 405 
Plywood, 220-222, 243 
Poplox, see Intumescent silicate 
Portland cement, asbestos millboard, for, 
218 
cements, for, 87 
mixtures, 198-202 
reaction with silicate, 198, 201-202 
See also Cement 
Potable waters, silicate in, 411-412 
Potassium bromide, reaction with sili- 
cate 84 
carbonate, 95-99, 361 
di- and metasilicate, 68-70, 99, 116- 

117 
silicate, for carbon-arc pencils, 191 
characteristics, 69, 70 
crystal forms, 69, 70 
efflorescence of, 87, 269 
equilibria studies, 68-70 
eutectic mixtures, 113 
glass, water in, 118 
historical, 12 
liquidus studies, 113 
paint vehicle, for, 269 
preparation, 89 
stability, 105 

stereochromic painting, for, 272- 
273 
Potassium oleate, reaction with silicate, 

362-363 
Pottery glazes, 275-277 



SUBJECT INDEX 



437 



Powdered silicate, abrasive wheels, in, 
178 
containers for, 162 
moisture absorption, 117 
preparation of, 120 
reaction with air, 117, 162 
See also Hydrous solids 
Precipitation, silicate, of, 72-82, 405- 
406 
character of precipitate, 57, 75-77 
compounds causing, 72, 73, 405-406 
fractional, 81, 82 
Preparation, 88-107 
carbon and sodium sulfate, from, 94- 

95 
commercial method, 103-104 
dry method, 94-104 
electrolytic, 91 
furnace reactions, 109 
hydrogen by-product, 90-91 
infusorial earth, from, 88-89 
miscellaneous materials, from, 89, 90, 

91, 92, 94 
potassium carbonate, from, 95-99 
silica for, 89-90 

soda ash and silica, from, 103-104 
sodium carbonate and silica, from, 95- 

99 
sodium chloride, from, 92-93 
sodium hydroxide, from, 27, 28, 94 
sodium sulfate and carbon, from, 94- 

95 
wet method, 88-93 
Printer's ink, thickening, 274-275 
Printing textiles, 297-298 
Production, economics, 15 
Projection screens, 270 
Properties of silicate, 108-164 
anhydrous solids, of, 111-117 
glass, neutral silicate, 110 
hydrous solids, of, 121-125. See also 

Hydrous solids 
melting temperatures, 115 
solutions, 127-156 
boiling, 138-139 
freezing effects, 137-138 
refractive index, 135-137 
specific gravity, 127-134 
tackiness, 154-156 
viscosity, 139-154 
Protective action of silicate, 349, 352 
Pruning wounds, coating, 265 
Pulley, dressings, 274 
Pulp, bleaching, 350-351 
deinking paper, 353-354 
digester lining, 201-202 
Pulpstones, 173 
Pumps for silicate, 164 
Purification of oils, see Oil reclaiming, 

Oil refining 
Purifying sugar solutions, 407-408 
Purifying water, 405-407 



Quartz, cristobalite, 113 

crystals from sols, 22 

formation of, 17 
Quick-setting cement formulas, 200 



Radium from carnotite, 411 
Ratio, calcium carbonate-silicate reac- 
tion, effect, 195 

cement, effect in, 167 

deinking paper, effect in, 353-354 

-density, table, 133 

determination by chart, 130 

dissolving effect, 104-105 

film, effect, 252-253 

hydrolysis, 39 

paper sizing, effect in, 282 

range of solution, 14, 126-127 

refractive index graph, 135 

solubility effect, 117 

specific gravity— total solids, 128-133 

tackiness effect, 155, 156 

total solids vs. specific gravity, 128-133 

variation in preparation, 89 

-viscosity graph, 142, 145, 149 

water-softening, effect in, 332 
Raw materials, 108-109 
Rayon, 343, 409-410 
Reactions, 72-87 

acids and acid salts, with, 72 

alcohols, 73, 81, 82 

aldehydes, 396-397 

alum, with, 280, 283 

aluminates, 77, 78, 199, 397, 405 

aluminum, with, 85, 273-274, 311 

ammonia, with, 82 

ammonia salts, with, 72 

asbestos, with, 87, 193 

barium carbonate, with, 87 

brine, with, 383-384 

bromine, with, 72 

calcium carbonate, with, 86, 87 

calcium hard water, with, 333 

calcium hydroxide, with, 194, 200 

calcium oxide, 87 

calcium phosphate, with, 87 

carbon dioxide, 72 

carborundum, with, 92, 178 

caustic, with, 298 

chlorine, with, 72 

clay, with, 87 

coloring materials, with, 85 

concentrated solutions, in, 79, 80 

concrete, with, 200 

dolomite, with, 87 

dyes, with, 283 

electrolytes, with, 84, 85 

fatty acid, with, 259 

ferric and ferrous salts, with, 75-77 

fluorides, with, 411 

fluorine, with, 72 

furnace, 109 



438 



SUBJECT INDEX 



Reactions, galvanized metal, with, 85 

glass, with, 215-216 

glycerin, with, 73, 179 

gum arabic, with, 73 

halogens, with, 72 

hydrochloric acid, with, 77 

hydrogen sulfide, with, 72 

iodine, with, 72 

iron salts, with, 75-77 

lead, with, 268 

lead salts, with, 405 

lime, with, 194, 200, 277 

lime water, with, 88 

litharge, with, 87 

magnesium carbonate, with, 87 

magnesium hard water, with, 333 

metallic salts, with, 72-79, 396-397 

metals, with, 164 

organic compounds, with, 73, 396- 
397 

phenols, 73, 396-397 

plastics, with, 194 

plumbates, with, 405 

Portland cement, with, 87, 198, 200 

potassium bromide, with, 84 

potassium oleate, with, 362-363 

rubber latex, with, 179 

sap, with, 264 

shellac, with, 179 

silica, with, 87, 193 

silicon carbide, with, 178 

sodium chloride, with, 84, 85 

sodium compounds, with, 405 

sodium nitrate, with, 84 

sodium oleate, with, 362-363 

sodium sulfate, with, 84 

sodium sulfide, with, 90 

solder, with, 164 

stannates, with, 405 

starch, with, 290-291 

strontium carbonate, with, 87 

sugars, with, 73, 179 

sulfite liquors, with, 179 

tannic acid, with, 73 

tanning extracts, with, 179 

tin, with, 164 

tin plate, with, 335 

tin salts, with, 405 

turpentine, with, 259 

tree sap, with, 264 

uranium salts, with, 81 

viscose, with, 409-410 

water, hard, with, 331-332 

zincates, with, 405 

zinc powder, with, 85 

zinc oxide, with, 87 
Reclaiming oil, see Oil refining, Oil 

reclaiming 
Red water, see Corrosion, iron rust 
Refining oil, see Oil refining, Oil re- 
claiming 
Refractive index, 114, 135-137 



Refractories, furnace, 103-104 

reaction with silicate fusion mixtures, 
95, 110-111 
Refractory, brick, color after use, 188 

cements, 183 

linings, 186 

paints, 275 

surfaces, repairing, 185 

silicate, action on, 95, 110-111, 184 
Refrigeration brines, silicate in, 382-384 
Refrigeration, silica gel method, 398 
Resonant gels, 394 
Rice hulls, 18, 91 

Rinsing, silicate detergents, 340-341 
Roads, binder for, 195-197 

concrete, 206-209 

frostproof, 310 
Rosin, paper sizing, in, 230, 278-280, 
288-289 

soap, in, 356, 364 

substitute for, 13 
Rubber latex, adhesive, in, 249 

cements, in, 179 

paint, in, 271-272 

silicate, in, 249-250 
Rubber, parting films for, 266 
Rubidium silicates, 70, 71 
Rusting of iron, 91-92, 202, 263-264. See 

also Corrosion 
Rhythmic bands, in gels, 22, 402 



Saggers, cement, 185 

Salt, brine, viscosity effect, 152-154 

cake, commercial manufacture of sili- 
cate, for, 103 

-silicate mixture, 152-154 

See also Sodium chloride 
Sand, 108-110, 315 
Sap, reaction with silicate, 264 
Saponification, 274-275, 330, 361 
Sawdust, cement, in, 199 
Screens, light projection, for, 270 
Sealing paper boxes, 225, 231-234, 237, 

238 _ 
Sedimentation rate, effect of silicate, 

300-301. See also Deflocculaton 
Setting of cement, 166, 179-180 
Setting time, control of silicate adhe- 

sives, 242-243 
Shaving cream, silicate in, 365 
Shellac, 179, 190, 249, 250 
Shipping case veneers, adhesive for, 243 
Silica, abrasive wheels, in, 173 

adhesives, in, 243 

adsorbed sodium on, 56, 57, 335 

analysis, 19, 157-158 

bleaching deposit on fiber, 352 

buffer action, 297 

cements, in, 169-173, 190 

colloidal, adsorption of sodium ion on, 
57 



SUBJECT INDEX 



439 



Silica, colloidal, alkalinity control, 335- 
336 
lead solution, in, 373, 378 
life origin, in, 17, 83 
occurrence, 17-19 
particle charge, 23, 282 
properties, 19 
rancidity of oils, 365 
solutions, in, 24, 55 
stability, 345, 388 
tanning leather, for, 408-409 
therapeutic uses, 412 
tuberculosis treatment, in, 412 
copper-metasilicate mixtures, in, 74, 

75 
crystalloidal solutions, in, 55 
crystals, 21 
determination in silicate, 19, 130, 157- 

158 
distance carried by water, 381 
earth, in, 17 

fabric, effect on, 337-340 
fiber after bleaching, on, 352 
foods, in, 412 

forms, for preparation of silicate, 89 
. gel formation, in, 389-392 
gels, in, importance of, 370 
gels, see Gels, silica 
hydrous, occurrence, 17, 18 
hydrous, in sodium silicate solution of, 

90 
impure, silicate from, 89, 90 
infusorial earth, from, 88, 89 
metasilicate-copper mixtures, in, 74, 

75 
mordant, a, 297 
oral ingestion of, 412 
paint vehicle, in, 389 
paper size, in, 18, 281, 284 
plants, in, 18 
reactions with alkali metal hydroxides, 

88 
reaction with potassium carbonate, 95- 

99 
reaction products, in 74, 75, 78, 79, 82 
reaction with silicate, 87, 193 
reaction with soda ash, 96, 99, 103-104 
reaction with sodium carbonate, 95-99 
* reaction with sodium chloride, 92-93 
reaction with sodium nitrate, 94 
reaction with sodium sulfate and car- 
bon, 94-95 
screen analysis for filler, 171 
sodium adsorbed on, 335 
solutions of, 55, 127 
stability of, in silicate, 280 
utilization of, 18, 19 
vegetation, in, 18 
water in, 17, 411-412 
Silicate garden, 77, 79-81 

ion, constitution, 32, 33, 48, 49, 50 
Silicates, natural, formation, 17 



Silicatization, process of, 202-204 
Silicic acid, conductivity, 20 

dialysis, 52 

electrometric titration, 23 

formation, 19, 52 

free, in solutions, 36 

historical, 12 

molecular weight changes, 20 

paint vehicles, for, 269 

properties, 19, 20 

strength, 23 
Silicon, 90-91 
Silicon carbide, 92, 178 
Silk, bleaching with peroxide, 347-348 

boiling off, 299 

degumming, 299, 344 

detergent action on, 342-343 

tendering, 296 

weighting, 57, 294-297 
Simplon tunnel, silica gel occurrence, 18 
Sizing, 252-299 

barrels, 256, 260 

calcium acetate for, 264 

fertilizer bags, 264 

glue for, 260 

jute sacks, 264 

metal surfaces, 264 

paper, see Paper sizing 

paraffin for, 264 

plaster, 264 

textile, see Textile sizing 

tubs, 259 

walls, 264 

Wallboard, 274 

See also Coatings, Films, Paints 
Skin, human, silicate action on, 413-414 
Slate pencils, silicate in, 191 
Smalt, in paint, 268 
Soap, alkalinity of silicate in, 364 

analysis of silicated, method, 365-367 

boiled, 357-360 

builder, 327-328, 364 

chip, silicate in, 365 

clay in, 302 

cold process, 360-362 

colloid, relation, 364 

conductivity of solutions, 23 

cosmetics, silicate in, 365 

deflocculating agent, as, 311, 324 

drop number, table, 314 

efflorescence of, 363-364 

emulsifying power of, 324 

filler, 364 

free alkali in, 343, 366-367 

graininess, prevention, 357-358 

hardness, 362 

history, 13, 356 

hydration in, 364 

iron water, for, 335 

lathering, silicate effect, 327 

lubricating effect, 329-330 

naphtha, 330 



440 



SUBJECT INDEX 



Soap, oil in, 330 
oil reclaiming, in, use in, 319 
oleate-silicate mixtures, 362-363 
paper sizing, use in, 290, 292-293 
powders, silicate in, 365 
rancidity of, 365 
ratio of silicate for, 364 
reaction with alcohol, 365 
rosin in, 13, 356, 364 
shaving creams, silicate in, 365 
silicate in, 300, 330, 332-335, 356-366 
silicate mixtures, detergent power of, 

325 
sizing paper, for, 256 
-sodium carbonate mixture, 335 
solubility, 362 
solvent effect, 330 
sparing action of silicate, 331-335 
structure, 364 

textile, sodium carbonate effect, 369 
toilet, silicate for, 365 
translucency, 364 

See also Detergency, Deflocculation 
Soapstone in cements, 190, 202 
Soda ash, 99, 103-104, 109, 355. See also 

Sodium carbonate 
Sodium acid silicate, in solution, 48, 55 
carbonate, aluminum, action on, 371- 
373 
emulsifying power, 323 
iron waters, for, 335 
melting point, 99 
preparation of silicate from, 95-99 
reaction with silica, 95-99 
soap, in, 327-328, 361 
chloride, preparation of silicate from, 
92-93 
raw materials, in, 103 
reaction with fuel gases, 103 
reaction with silicate, 84, 85, 354- 

355 
textile process, in, 297-298 
washing, in, 355 
compounds, reaction with silicate, 405 
dichromate for corrosion prevention, 

382-383 
hydroxide, 35, 36, 94. See also Caustic 

soda 
-ion activity, 50, 51 
nitrate, 84, 94 
oleate, 332, 362-363 
oxide, determination of, 156-157 
peroxide, see Bleaching, peroxide 
sulfate, in hydrous solids, 121 

preparation of silicate from, 94-95, 

103 
reaction with silica and carbon, 84, 

94-95 
textile processes, 297-298 
Solder, reaction with silicate, 164 
Solid box board, specifications for, 234- 
235 



Sols, silica, 19-23, 72, 88 

Sols, silicate, for leather tanning, 408- 

409 
Solubility, silicate glass, of, 110, 115-117 
Solutions, detergency, in, 330-331 
silicate analysis, method, 157-159 
boiling, 138-139 
clarity of, 127 

concentration, specific gravity rela- 
tion, 133 
density-ratio relation, 133 
dilution charts, 132 
filtration of, 127 
freezing, 137-138 
properties of, 127-156 
ratio-density, 133 
ratio range, 126-127 
refractive index, 135-137 
specific gravity, 127-134 
specific gravity vs. concentration, 

133 
specific gravity vs. temperature, 133- 

134 
tackiness, 154-156 
temperature-specific gravity varia- 
tion, 133-134 
viscosity, 139-154, 212-215 
volume change-concentration rela- 
tion, 133 
Solvent, in detergency, 330 
Solvents, reclaiming with silicate, 321 
Soya-bean adhesives, 248 
Soya-bean oil, paper sizing in, 292-293 
Spark plug cements, 187-188 
Specific gravity, Baume relation, and, 
128 _ 
composition relation, 128-133 
concentration relation, 133 
sand, 109 

silicate glass, of, 114-115 
silicate solutions, of, 127-134 
soda ash, of, 109 
temperature relation, 133-134 
total solids, relation, 128-133 
-viscosity, 214 
Spiral tubes, adhesive for, 244. Sec also 

Paper tubes 
Spontaneous generation of life, 17, 83 
Spray drying, of silicates, 120 
Stability, silicate solutions, of, 138-139, 

216, 408-409 
Stability test of silicate, 139, 296 
Stabilizing, bleach baths, 349 

greensands, 406-407 
Staining, wallboard, in, 242 
Stainproofing wood, 223, 265-266, 408 
Stains (paints), 267 
Stannates, reaction with silicate, 405 
Stannic chloride, for silk weighting, 294 
Starch, hydrolysis of, 330 
paper sizing, for, 290-293 
reaction with silicate, 290-291 



SUBJECT INDEX 



441 



Starch, -silicate mixtures, 244 

washing, in, 330, 368 
Statuary, cement for, 195 
Steam, silicate glass, action on, 104, 118 
Steatite, dehydrating, 410 
Steel, case-hardening cement for, 188- 

189 
Stereochromic painting, 272-273 
Stickiness, silicate solutions, of, 154-156 
Stokes law, 301 
Stone, artificial, historical, 12 

hardening with silicate, 202-204 

paint for, 271 
Storage batteries, electrolyte, 394-396, 
410 

tanks, silicate, for, 164 
Stormer viscometer, 141-143 
Stove cements, 184-185 
Straw paper, silicate in, 291, 330-331 
Straw pulp, corrugated paper, for, 410- 
411. See also Cellulose, paper pulp 
Strength, of cements, 171-172, 179-180 
Strength tests, glass-silicate joints, of, 
216 

wood joints, of, 220, 222 
Strontium carbonate, reaction with sili- 
cate, 87 
Structural stone, hardening, 202-204 
Structure, gels, of, 397-398 

micelle, multi-charged, 335 

silicate, of, 23, 55-56, 133 
Sugars, cement, in, 179 

reaction with silicate, 73, 250 
Sugar solutions, purifying, 407-408 
Sulfate glass, see Glass 
Sulfite liquors, cements, in, 179 

silicate, in, 251 

wood pulp, bleaching, 349, 351 
Sulfur compounds, adsorption by silica 

gel, 399-401 
Sulfuric acid, quick setting cement, for, 

179-180 
Surface tension, foam of, 329 

tackiness, effect on, 154 

wetting relation, 311-313 
Surgical bandages, first use in, 13 
Suspended matter, silicate solutions, in, 

127 
Suspension, see Deflocculation, Deter- 
gency 



Tackiness, 154-156, 244 

Talc, 182, 410 

Tallow, in soap, 357, 361 

Tank cars, 164 

Tannic acid, reaction with silicate, 73 

Tanning, extracts in silicate, 179, 251 

leather, 408-409 
Taste of silicate, 239, 414 
Temperature, abrasive wheels, for, 174 

boiling point of silicate solutions, 138 



Temperature, carbonate-silica reaction, 
effect on, 96 

cement effects, 183-187 

dissolving effect, 121 

freezing of silicate solutions, 138 

furnace, of, 103, 109 

fusion of carbon, sulfate, silica, 94-95 

gel formation, in, 392-393 

glaze firing, for, 277 

melting of glass, 111-114 

solubility effect, 117 

specific gravity relation, 133-134 

tackiness effect, 155, 156 

viscosity relation, 146-152, 212 
Tensile strength, abrasive wheel, of, 
176-178 

silicate cement, of, 171-172 
Ternary diagram of definite silicates, 67 
Testing, adhesives, 251 

barrels, 256-257. See also Barrel siz- 
ing, Barrel testing 
Textile, ash, effect of, 337-341, 344 

bleaching, 344-352. See also Bleaching 

boiling-off silk, 299 

colors, silicate effect on, 297, 343-344, 
352, 369 

color stripping, 347 

cotton, bleaching, 344-352 

detergent action on, 337-339, 342- 

343 
kier boiling, 354 
rust stains prevention, 354 

degumming silk, 299 

dyeing and printing, 297-298 

dyes, solubility in silicate, 344 

fabric, silicate effect, 335-352 

fabric strength, 336-338, 355-356 

flannel, detergent action on, 342-344 

historical, 13 

kier boiling cotton, 354 

linen, effect of detergents on, 337-338 

mercerizing cotton, 298 

microscopical examination, 369 

printing, 298 

rayon, 343, 409-410 

rinsing silicate detergents, 340-341 

rust stains, 354, 355, 384 

silicate action on, 297, 335-352 

silk, detergent action on, 342-343 

silk weighting, 57 

sizing, 298 

sodium chloride use, 297-298 

sodium sulfate in, 297-298 

stripping colors, 347 

washing, 355 

wool, detergent action on, 342-343 
Thawing frozen silicate, 164 
Theatrical scenery, fireproofing, 260 
Theory, adhesion, of, 210. See also Ad- 
hesive characteristics 

concrete setting, of, 204 

corrosion, of, 379-380 



442 



SUBJECT INDEX 



Theory, deflocculation, of, 300-301, 305 

gel formation, of, 20 

inhibition, of, 379-380 

life origin, of, 17, 83 

paper sizing, of, 279 

silk weighting, of, 294 

structure, of, 23, 56 

viscosity changes, of, 243 
Therapeutic uses, 12, 411-413 
Thermal, conductivity of gelatinous 
films, 384 

conductivity of intumescent silicate, 
119 

expansion of silicate glass, 114 

insulation, 18, 217-218, 260-261 
Thermionic valves, 275 
Timber, fireproofing, 262 
Tin, adhesive for, 240 

chloride, for silk weighting, 294 

plate, reaction with silicate, 335 

reaction with silicate, 164 

salts, reaction with silicate, 405 
Tissue, human, action of silicate on, 

413-414 
Titration, silicates, of, 157 
Total solids, ratio relation, 128-133 

-refractive index tables, 136-137 

-specific gravity relation, 128-133 

-viscosity, graph, 145 
Transport numbers, silicate, ions, of, 31- 

33 
Tree, sap, reaction with silicate, 264 

surgery, silicate coating, 264-265, 408 
Triaxial, composition diagram, 159 

potash-silicate diagrams, 98 

soda-silicate diagrams, 100 

solubility, diagram, 116 

viscosity diagram, 161 
Trisilicate, anhydrous, 68 
Trunks, board for, 222-223 
Trydymite, eutectic mixtures, 112-113 
Tuberculosis treatment, silicate in, 412 
Tubes, spiral paper, adhesive for, 244 
Tubs, sizing, 259 

Turpentine, reaction with silicate, 259 
Twaddell, hydrometer, 127 



Ultramarine, 268, 310 

Umber in paints, 268 

Uranium, reaction with silicate, 81 

Uses, miscellaneous, 12, 13, 405-414 



Vanadium, carnotite, from, 411 
Vapor, adsorption by gels, 399-401 

pressure, 44, 45, 47-50 
Varnish, coating over silicate, 269 

silicate as, 252 
Vehicle, paint, 267-269 
Veneer, adhesive for, 243, 244 
Vermin-proofing packages, 239 



Viscometers, 139-143, 146-147 

Viscose, coagulating in silicate, 409-410 

Viscosity, adjusting, 242-243 

alkalinity curve, 213 

carbon dioxide effect, 144, 146 

clay mixtures, of, 243, 301-305 

comparative, 139 

composition, relation, 143-151 

concentration graph, 148 

constitution relationship, 139 

detergency, effects in, 314 

dilution effect, 128 

di- and meta-silicate, of, 148 

formulas, 140-143 

-gravity curve, 214 

measuring, 139-144 

meta- and di-silicate, 148 

range of, 139 

-ratio graph, 142, 145, 149 

salt brine effect, 152-154 

setting of adhesives, and, 213-215 

silicate solutions, 56, 126-127, 139-154 

temperature, variations, 146-152, 212 

-total solids, graph, 145 

triaxial diagram, 161 

wooden containers effect, 162 
Viscous liquids vs. plastic solids, 139- 

140 
Volume, brine in silicate, effect of, 84, 

85, 152-154 
Vulcanized fibre, manufacture of, 222- 
223 



Wallboard, adhesive for, 237, 239, 241- 
243 

asbestos, 217 

cement, 196 

dialysis of silicate in, 242 

paint for, 274 

staining, 242 
Walls, sizing, 264 
Washing, alkali control by silicate, 336 

bottles, with silicate, 335 

color, silicate effect, 297, 343-344 

cotton waste, 352 

deflocculation in, 310-311 

emulsification in, 322, 324. See also 
Emulsification 

fabric strength, silicate effect, 336-338 

glassware, with silicate, 335 

historical, 13 

lathering, 326-329. See also Lathering 

lubricating effect, 329-330 

measure of, 354-355 

overalls, 352, 355 

paper pulp, 331 

rinsing silicate detergents, 340-341 

silicate-soap mixture, 325 

soap, see Soap 

solution effect, 330-331 

starch effect, 330, 368 



SUBJECT INDEX 



443 



Washing, surface tension, 311-313 

tests, 367-368 

wetting, relation, 311, 314-315 

See also Detergency, Deflocculation 
Water, determination, in silicate, 158- 
159 

-glass, early use of name, 12 

hard, reaction of silicate with, 331-332 

iron rust in, 379-382 

lead in, 86, 376, 378-379 

potable, silicate in, 411-412 

-proof adhesive, 244-245 
Waterproofing concrete, 204-206 

paper, 256 
Water purifying, 405-407 

-resistant, abrasive wheels, 174 

-resistant adhesive, 246, 249, 250 

-resistant cement, 179, 194, 195, 200 

-resistant paper, 230-232, 237, 279, 287, 
290 

rust control technic, 380-382 

silica in, 17 

silicate in, effect, 378 

soft, corrosion prevention, 381 
Water-softening, see also Zeolites, Gels, 
base-exchanging 

base-exchange method, 397, 402-407 

Doucil for, 403-404 

iron in water, 335 

silicate for, 330-335 

zeolites for, 405-407 
Water, waste, clarification of, 411 
Watch screws, polishing, 241 
Wax, Montan, for paper sizing, 290 
Weather, effect on coating paper, 254 
Weathering, of paint, 268, 269 
Weighting of silk, see Silk weighting 
Welding, electrodes, coating, 275, 385 

flux, historical, 13 
Wetting, adhesives, 210, 213, 221 

asbestos, 264 

bituminous matter from sand, 315 

carbon in oil, of 319-320 

cellulose fiber, 264 

charge on particle, effect, 320 

conditions necessary for, 311 

deflocculation relation to, 311 

detergency, relation to, 311-322 

differential, of mineral, 322 

emulsification, relation of, 314, 324 

fats and fatty oils, 321 



Wetting, oil, 312-313, 315, 319-320 

oily surfaces, 198 

particle charge effect, 320 

particles of, 243 

power, foams, of, 329 
measuring, 313-314 

surface tension relation, 311-313 

washing, 311, 314-315, 324 
White lead, reaction with silicate, 268 
Whitewash, coating for, 272 
Whiting, paints, in 268, 271 
-silicate adhesive, 243 
Willemite glazes, silicate for, 277 
Windshields, anti-fog, 321-322 
Wire, insulated, fireproofing, 262 
Wire web, abrasive wheels, 173 
Wood, adhesive for, 219-220, 243 

coating, 263, 265-266, 271-272 

fireproofing, 204, 262-263 

-fiber, cement in, 199 

joints, strength of, 219, 220 

moulding, of, prevention, 265-266 

paints, 271-272 

penetration, in 257 

plywood, 220-222 

pulp, bleaching, 349-351 
deinking paper, 353-354 

See also Cellulose, paper pulp 

-stained, 223 

stainproofing, 265-266 
Wood's glue, 249 
Wool, 342-344 

X-ray, examination of gels, 22, 397-398 

Zeolites, 402-407 

Sec also Gels, base-exchanging, Base- 
exchange materials 
Zinc, cement, in 202 

corrosion, in dry cells, 373 

flotation, 305-307 

loss, oxidation, by 266 

paint, in 268 

reaction with silicate, 85 
Zinc chloride, wood penetration, 257 
Zinc oxide, abrasive wheels, in 174 

sizing paper, in 256 
Zinc salts, reaction with silicate, 87, 405 
Zinc-silicate glazes, 275-277 



American Chemical Society 

MONOGRAPH SERIES 
PUBLISHED 

No. 

1. The Chemistry of Enzyme Actions (Revised Edition) 

By K. George Falk. Price $5.00 

2. The Chemical Effects of Alpha Particles and Electrons 

(Revised Edition) 
By Samuel C. Lind. Price $5.00 

3. Organic Compounds of Mercury 

By Frank C. Whitmore. Price $7.50 

4. Industrial Hydrogen 

By Hugh S. Taylor. Price $4.50 

5. Zirconium and Its Compounds 

By Francis P. Venable. Price $4.00 

6. The Vitamins 

By H. C. Sherman and S. L. Smith. (Out of print.) 

7. The Properties of Electrically Conducting Systems 

By Charles A. Kraus. Price $6.50 

8. The Origin of Spectra 

By Paul D. Foote and F. L. Mohler. (Out of print.) 

9. Carotinoids and Related Pigments 

By Leroy S. Palmer. Price $6.00 

10. The Analysis of Rubber 

By John B. Tuttle. Price $3.50 

11. Glue and Gelatin 

By Jerome Alexander. Price $4.50 

12. The Chemistry of Leather Manufacture (Revised Edition) 

By John A. Wilson. Vol. I. Price $10.00 

13. Wood Distillation 

By L. F. Hawley. Price $4.00 

14. Valence and the Structure of Atoms and Molecules 

By Gilbert N. Lewis. Price $3.75 

15. Organic Arsenical Compounds 

By George W. Raiziss and Jos. L. Gavron. Price $9.00 

16. Colloid Chemistry (Revised Edition) 

By The Svedberg. Price $5.50 

17. Solubility 

By Joel H. Hildebrand. Price $4.00 

18. Coal Carbonization 

By Horace C. Porter. Price $8.00 

19. The Structure of Crystals 

By Ralph W. G. Wyckoff. Price $7.50 

20. The Recovery of Gasoline from Natural Gas 

By George A. Burrell. Price $10.00 

[Continued] 



American Chemical Society 

MONOGRAPH SERIES 
PUBLISHED 

No. 

21. The Chemical Aspects of Immunity 

By H. Gideon Wells. Price $5.50 

22. Molybdenum, Cerium and Related Alloy Steels 

By H. W. Gillett and E. L. Mack. Price $5.50 

23. The Animal as a Converter of Matter and Energy 

By H. P. Armsby and C. Robert Moulton. Price $4.50 

24. Organic Derivatives of Antimony 

By Walter G. Christiansen. Price $4.50 

25. Shale Oil 

By Ralph H. McKee. Price $6.00 

26. The Chemistry of Wheat Flour 

By C. H. Bailey. Price $6.00 

27. Surface Equilibria of Biological and Organic Colloids 

By P. Lecomte du Noiiy. Price $4.50 

28. The Chemistry of Wood 

By L. F. Hawley and Louis E. Wise. Price $6.00 

29. Photosynthesis 

By H. A. Spoehr. Price $6.50 

30. Casein and Its Industrial Applications 

By Edwin Sutermeister. Price $5.00 

31. Equilibria in Saturated Salt Solutions 

By Walter C. Blasdale. Price $4.50 

32. Statistical Mechanics as Applied to Physics and Chemistry 

By Richard C. Tolman. Price $7.00 

33. Titanium 

By William M. Thornton, Jr. Price $5.00 

34. Phosphoric Acid, Phosphates and Phosphatic Fertilizers 

By W. H. Waggaman. Price $7.50 

35. Noxious Gases 

By Yandell Henderson and H. W. Haggard. Price $4.50 

36. Hydrochloric Acid and Sodium Sulfate 

By N. A. Laury. Price $4.00 

37. The Properties of Silica 

By Robert B. Sosman. Price $12.50 

38. The Chemistry of Water and Sewage Treatment 

By Arthur M. Buswell. Price $7.00 

39. The Mechanism of Homogeneous Organic Reactions 

By Francis O. Rice. Price $5.00 

40. Protective Metallic Coatings 

By Henry S. Rawdon. Price $5.50 

[Continued] 



American Chemical Society 

MONOGRAPH SERIES 

PUBLISHED 

No. 

41. Fundamentals of Dairy Science 

By Associates of Rogers. Price $5.50 

42. The Modern Calorimeter 

By Walter P. White. Price $4.00 

43. Photochemical Processes 

By George B. Kistiakowsky. Price $5.50 

44. Glycerol and the Glycols 

Bv James W. Lawrie. Price $9.50 

45. Molecular Rearrangements 

By C. W. Porter. Price $4.00 



IN PREPARATION 



Piezo-Chemistry 
By L. H. Adams. 

Biochemistry of the Fats and Related Substances 
By W. R. Bloor. 

Refining of Petroleum 

By George A. Burrell, et al. 

Diatomaceous Earth 

By Robert Calvert. 

Absorptive Carbon 

By N. K. Chaney. 

Bearing Metals and Bearings 

By William M. Corse. 

The Activated Sludge Process of Sewage Disposal 

By Robert Cramer and John Arthur Wilson. 

Fixed Nitrogen 

By Harry A. Curtis. 

The Manufacture of Sulfuric Acid 

By Andrew M. Fairlie. 

The Corrosion of Alloys 

By C. G. Fink and Robert J. McKay. 

Liquid Ammonia as a Solvent 
By E. C. Franklin. 

Surface Energy and Colloidal Systems 
By W. D. Harkins and T. F. Young. 

[Continued] 



American Chemical Society 

MONOGRAPH SERIES 
IN PREPARATION 

The Structure of Rubber 
By Ernst A. Hauser. 

Absorption Spectra 

By Victor Henri and Emma P. Carr. 

The Pyrolysis of Organic Compounds 
By Charles D. Hurd. 

The Rare Earths 

By Charles James and H. C. Fogg. 

Thyroxine 

By E. C. Kendall. 

The Properties of Metallic Substances 
By Charles A. Kraus. 

Nucleic Acids 
By P. A. Levene. 

Aromatic Coal Products 
By Alexander Lowy. 

Tin 

By Charles L. Mantell. 

The Biochemistry of the Amino Acids 
By H. H. Mitchell and T. S. Hamilton. 

The Rare Gases of the Atmosphere 
By Richard B. Moore. 

Physical and Chemical Properties of Glass 
By Geo. W. Morey. 

Carbon Dioxide 

By Elton L. Quinn and Charles L. Jones. 

The Chemistry of Intermediary Metabolism 
By Wm. C. Rose. 

Dielectric Constants and Molecular Structure 
By Charles P. Smyth. 

The Industrial Development of Searles Lake Brines 
By John E. Teeple, et al. 

Organic Medicinals 
By E. H. Volweiler. 

Vapor Phase Catalytic Oxidation of Organic Compounds and 
Ammonia 
By J. M. Weiss, C. R. Downs and Dorothy A. Hahn. 

Measurement of Particle Size and Its Application 
By L. T. Work. 



Date Due 



lUft^ 






IL 






29Sep 4 4 



JUL 2 8 



1945 



Oct 22 '49 ^qv7 , A9 



Oct 14 5 



1 15 Oct 



IIAB « sppft^T 










-— =r 



fa 7 



.3 L4: 



ltt6 13 71 



APR 13 1981 FEB jy 



JIJ^JJ^^^^^L 



3 1262 04014 7497 



CHEMISTRY 

UBRARY 



t* 



t 



*9><*4