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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 


v9.4) 


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.  Wtilson, 

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. 

3lZ.  Oesterr.  Ingenieurer,  14,  229  (1862). 
4Zwick,  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). 
10Zwick,  Hermann,  "Das  Wasserglas,"  1877,  p.  10. 


14  SOLUBLE  SILICATES  IN  INDUSTRY 

Fuchs  published  his  researches  in  1825.  A  forty-six  page  pamphlet 
by  Zwick11  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  Mayer14  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  Na20.2Si02, 
while  a  system  of  the  same  ultimate  composition  in  which  the  state  of 
chemical  combination  is  not  known  will  be  represented  as  Na20,  2Si02. 

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- 

1Bull.  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). 

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

9McKee,  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). 
19Bruni  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  H2Si03  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). 
30Krozer,  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). 

32Schwarz  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. 

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

3GBachman,  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  H2Si03 
with  salts  NaHSi03  and  Na2Si03.50  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. 

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

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

wHarman,  /.  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,  Na2Si03,  and  systems  with  more  silica  up  to 
Na20,  3.4Si02  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  Na2Si03 

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  Si02  per  mol  Na20.  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 

P1Z.  phys.  Chem.,  12s  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 
Na20,  3.4Si02 

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  Na2Si03,  1055  X  10~8  at  3.2  mols  per  liter  concen- 
tration or  17  per  cent;  and  the  Na20,  3.4Si02,  300  X  10"8  at  2.5  mols 


C  0  *  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  Na2Si03  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  Na20,  2Si02  was  reached  Values  for  the 
higher  <rajtios  were  only,  slightly  smaller.  Conversely,  the  second  series 
showed  no  real  change  until  Na20,  25i02  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  Na2Si03,  the  definite  substance 
from  which  the  study  began.  The  change  of  behavior  corresponded  to 
Na2Si205  and  the  curve  broke  sharply  at  this  point.  The  temperature 
coefficient  which  increased  from  0  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. 


Si02per 

Cone.  Na 

Temp. 

klol  Na20 

Mols  per  Liter 

Conductivity 

Coefficient 

0 

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 

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 
(Na20)  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 

0 

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 

Na2Si03 

NaHSiOa 

Na20,  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  NaHSi03. 

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  Na20: 

SiOa 

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,  Na2Si03,  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  Nw.    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  Na20*2Si02  in  solution  and 
similar  deviations  suggest  but  do  not  prove  that  2Na2OSi02  and 
Na2Si03  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  Na20.  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  Si03  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 

Na20  :  Si02  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  nNa  is  0.31,  of  nSi03,  0.16,  and 
n0H  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 
HSi03  ions  or  of  more  complex  ions  containing  more  than  one  mol  of  Si02, 
e.g.  Si03.2Si02. 

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  nNa  is  0.2,  and  n0H  is  0.8;  therefore  the  present 
result,  where  n0H  is  not  even  double  nNa,  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  Si03"~,  nor  in  fact 
should  we  expect  it  to  be." 

He  concludes  that : 

"Ratio  1:  1  evidently  ionizes  to  Na+,  OH~  and  Si03~~  ions;  nSio3  is 
small,  n0H,  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(Si02)  per  divalent  charge; 
the  average  number  of  mols  Si02  per  divalent  charge  being  equal  to  the 
ratio. 

'The  mobility  of  the  Si03  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 
Si03~"  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  Na20,  4Si02.  His  results  are 
given  in  Table  10. 

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


Silicate  No.  1. 

Na20,  3.97Si02 

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. 

Na20,  3.48Si02 

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. 

Na20, 2.93Si02 

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.     Na20,  2.48Si02 


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 

Na20,2.11Si02 

54.8 
32.0 
18.0 

8.8 

6.0 

Na20, 1.63Si02 

155.0 
90.0 
53.5 
26.8 
17.6 

Na20,  l.HSi02 

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  300  C. 

\e    in    Sc 

dium    Silicate 

Solution 

Na20,  l.HSi02 
Silicate        NaOH 

Na20, 1.63Si02 
Silicate       NaOH 

Na20,2.11Si02 
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 

Na20,  2.48Si02 
Silicate                 NaOH 

Na20, 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 

Na20,  3.48Si02 
Silicate                 NaOH 

Na20,  3.97Si02 
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 


Si02    

Na20    

R203    

C02     

S03 

CI    

H20    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  Na20, 2Si02.     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  Na20,Si02  ratios  as  abscissae,  he  found,  as  Kohlrausch 
had  for  conductivity,  a  sharp  break  in  the  curve  at  Na20,  2Si02.  From 
this  he  postulated  that  sodium  silicate  solutions  of  less  sodium  content 
than  is  indicated  by  the  ratio  NasO,  2Si03  are  composed  of  Na2Si205 
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 

Na20,  3.3Si02 

Na20,  2.25Si02 

Na20,2.21Si02 

Na2O,2.01SiO2 

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.  Na20, 2Si02 

Approx.  N"; 

i20,  2Si02 

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  HTU 

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  iVw,  Na2Si03 
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  Na2Si409  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  Na20,  2Si02.  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  Na3Si03,  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  Na20,  2Si02  and 
Na20,  5Si02.  Expressing  the  former  as  NaHSi03,  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  Na2Si50ii  =  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 

Na2O,2.01SiO2 

Na20,2.21Si02 

Na20,2.25Si02 

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  Na20  to  Si02  in  Silicates 


M1 

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  Na20  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. 


Na20, 

1.68Si02 

Na20,  2.06SiO2 

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 

Na30,2.55Si02 
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) . 


Na20, 

2.96Si02 

Na20, 

3.25  SjO. 

Na2( 

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 


0  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  Na2Si03  under- 
going both  hydrolytic  and  ionic  dissociation  giving  rise  to  Na+,  OH" 


48 


SOLUBLE  SILICATES  IN  INDUSTRY 


and  Si03""  ions  and  H2Si03,  most  of  the  latter  being  crystalloidal. 
Na2Si03  is  practically  completely  dissociated  in  dilute  solution,  but  only 
27.8  per  cent  hydrolytically.  Ratio  1 : 2  is  the  definite  salt  NaHSi03, 
behaving  like  Na2Si03  and  giving  rise  to  Na+,  OH-  and  HSi03"  ions 


10  r 


Activity  Coefficient  against  Ratio. 


and  H2Si03.  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  Si03 
wSi02aq.)m~  where  m  +  n/m  =  ratio ;  the  following  equilibrium  also 
existing : 

Si03~~  +  (Colloid  Si02  aq.)    (mSiOs.n  Si02  aq)m" 
(Colloid   Si02  aq.)    crystalloid  H2Si03  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  Na20 

to  Si02  in  the  range  covered.     Randall  and  Cann  71  point  out  that 

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

reaction 

Na2Si03  (Aq.)  +  H20  (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» 


Na2Si03 

*  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) 


0 


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  Na20  to  Si02  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  : 

Na2Si03     (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). 


Na2Si03 

Na20, 2Si02 

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  Si205""  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  H20  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  Na2Si03  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  Nw,  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  Nw  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  Nw  1 : 4  and  about  1/3  in  1.0  N/w  H2SiOs  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 

Si02  Gms. 

Na20  Gms. 

Si02  Gms.    Na20  Gms. 

Molar 

per  100 

per  100 

per  100          per  100 

Difference 

Ratio 

cc. 

cc. 

cc.                 cc. 

Si02 

Na20 

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 

Si02  Gms. 

Na20  Gms. 

Si02Gms.    Na20  Gms. 

Si02 

per  100 

per  100 

per  100          per  100 

Difference 

Na20 

cc. 

cc. 

cc.                  cc. 

Si02 

Na20 

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 

Na20 

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  NaoSi205  and  Na3Si03.  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). 
8V.  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  Na20 :  Si02,  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.,  Na2Si03, 
i.e.,  ratio  1:1,  and  NaHSiOs,  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  3Si02, 
Na20  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 
Na20,  3Si02  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  Na20  and  Si02 
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, 
Na2Si03.  6H20  in  monoclinic  crystals,  and  Na2Si03.  9H20  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). 

3Yorke,  Phil.  Trans.  Roy.  Soc,  147,  533  (1857). 
4Mylius,  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). 
6Jordis,  Z.  anorg.  Chem.,  56,  305  (1907). 

58 


DEFINITE  SOLUBLE  SILICATES 


59 


Vesterberg 7  prepared  the  ennehydrate  Na2Si03. 9H20  by  crystal- 
lizing from  solutions  containing  alcohol  and  also  reported  the  exist- 
ence of  a  compound  with  6H20  from  observations  of  the  dehydra- 
tion of  the  salt  with  9H20  over  concentrated  sulfuric  acid  and 
rehydrating  over  sodium  hydroxide  at  specific  gravity  1.26.  Dehydra- 
tion of  9H20  over  50  per  cent  potassium  hydroxide  led  him  to  believe 


Fig.  18. — Sodium  Metasilicate. 
Na2Si03.4H20 


there  is  a  hydrate  with  3H20  but  later  workers  have  not  confirmed 
this. 

In  an  effort  to  produce  a  silicate  analogous  to  NaHC03,  Jordis  s  ob- 
tained after  long  standing  of  the  solution  a  crystalline  mass  which 
proved  to  be  Na2SiOs.  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. 
Na2Si03.6H20 


Fig.  20. — Sodium  Metasilicate. 
Na2Si03.9H20 


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  Na2Si03,  the  manipulation  was 


Fig.  22. — Cooling  Curves  of  Sodium  Metasilicate. 
Na2Si03.6H20 


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 


Na2Si03 .  9H20  melts  at  47°,  crystals  rhombic. 
Na2SiO;.  .  6H20  melts  at  62.5°,  crystals  monoclinic. 
Na2Si03 .  4H20  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  ufes 


JO 


Fig.  23. — Cooling  Curves  of  Sodium  Metasilicate. 
Na2Si03.9H20 

which  is  thought  to  be  the  melting  point  of  Na2Si03. 14H20,  but  this 
salt  has  not  been  isolated. 

The  ennehydrate  is  the  most  easily  prepared.  Commercial  metasili- 
cate was  found  to  contain  10H2O,  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,  Na2Si03.9H20  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  Na2Si03.4H20. 

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  Na2Si03.6H20 
crystals  were  dissolved  while  Na2Si03.9H20  crystals  formed.  The 
change  from  Na2Si03.4H20  to  Na2Si03.6H20  was  similarly  observed. 
By  putting  Na2Si03.9H20  into  a  mother  liquor  of  Na2Si03.6H20,  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,  Na2Si03,  and  sodium  disili- 
cate, Na2Si205,  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  Na20,Si02  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  Na20 — Si02 — H20  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 

Na20 

Si02 

H20 

Na20 

SiOa 

H20 

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 

Na2Si03 

.9H20 

26.93 

26.18 

46.89 

Na2SiOs 

.6H20 

37.06 

36.04 

26.89 

Na2Si03 

.2.5H20 

50.69 

49.31 

•  •  •  • 

Na2Si03 

17.99 

34.98 

47.00 

Na20.2Si02.9H20 

53.45 

.... 

46.55 

NaOH.: 

IH20 

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


DEFINITE  SOLUBLE  SILICATES 


67 


He  confirmed  the  existence  of  Na2Si03.6H20  and  Na2Si03.9H20 — ■ 
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;03.<l  H»0. 

B.  Na^S.03.  6  Hz0 

C.  NazSiOz   2  5H<Q 

D.  WOjSi'Oj. 

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


Ternary    Systen 

Na*0  -   $.C\  -  Hx0. 


N'^Q 


Na.0H.l4ty 


Fig.  27.— Ternary  System.     Na20  =  SiQ2  =  H20. 


with  less  water  than  Na2Si03.6H20,  which  he  believed  to  be 
Na2Si03.4H20,  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  Na20,2Si02.9H20  was  indicated.  This 
has  never  been  isolated  at  ordinary  temperatures  though  there  are 
many  evidences  of  its  existence. 

Anhydrous  Systems. 

Sodium  metasilicate,  Na2Si03,  and  sodium  disilicate,  Na2Si205,  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,  Na20.  3Si02  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 

Na2Si03— 1088°,  Jaeger 
1086°,  Morey 
Na2Si205— 874°,  Jaeger  and  Morey 

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

(Morey  and  Bowen) 

Na2Si03  Na2Sb03 

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  K2SiOs  and 
K2Si205.  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  K2Si03— Si02— HaO  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. 

KHSi205 — decomposed  by  H20  below  420°.  As  observed  under  the 
microscope  the  action  is  so  slow  that  it  appears  to  be  practically  unat- 
tacked  by  H20. 

K2Si205 — melts  at  1041°  and  is  not  decomposed  by  H20.  The  crys- 
tals break  up  irregularly  in  water  under  the  microscope  showing  char- 
acteristic shred-like  forms  as  they  go  into  solution. 

K2Si205.H20 — rapidly  decomposed  by  water  at  ordinary  tempera- 
tures.   Crystals  dissolve  completely. 


70  SOLUBLE  SILICATES  IN  INDUSTRY 

K2Si03 — melts  at  about  966°.  It  is  very  hygroscopic  and  crystals 
dissolve  rapidly  and  uniformly. 

K2Si03.^2H20 — completely  soluble  in  water. 

K2Si03.H20 — decomposed  by  H20  at  temperatures  below  200°.  It 
breaks  down  at  370°  into  K2Si03.^H20  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  Li20  in  the  cake.  Finally  a  solution  was  obtained  containing 
2(Li20,4Si02),  Na20,4Si02.  A  solution  containing  8.5  per  cent 
Li2Si03  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  Si02  for  each  Li20  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  Li20, 
2Si02  could  be  prepared  from  the  carbonate  by  fusion  with  silica  at 
1300°  and  dissolved  with  some  decomposition  to  a  solution  containing 
6  per  cent  Li20,  3.2Si02  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  Li2Si03-Si02  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  Rb20  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  Rb2Si03  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  Si02  con- 
tent up  to  Rb20,  4Si02,  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  Na20,3Si02  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"X2  +  Me'SiOs  =  Me"Si03  +  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). 

4Jordis  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  Si02  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  CuS04  and  N  silicate  of  soda  of  composition 
Na20,2Si02,  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). 

Si02  Fe203  Na20                      CI                        H20 

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  FeCl3  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  Na2S04,  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:lSi02  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  Si02  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  Na20,3Si02)  and  ferric  chloride  led  Liesegang  9 

8Jordis  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  S04  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  SiOa  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                        Si02                    Al                        S04  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  Na20,  2.16Si02 

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  Na20,  2.16Si02  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 :  Na20, 
2.16Si02  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  —  ZrCl4    3.98  35.0  1.86 

0.01  M  —  ThCh     3.50  30.0  3.50 

0.0067  M  — A12(S04) 3  4.04  5.0  4.14 

0.02  M  — BeS04    5.31  20.0  5.69 

0.02  M  —  ZnS04    5.25  1.0  5.20 

0.02  M  — MnCU    7.35  1.0  8.41 

0.02  M  —  MgS04    9.50  1.0  10.49 

0.02  M  —  CaCl2    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  2Na20,3Si02  and  found  the  setting  time  to  be  as  follows : 

0.3  to  0.5  second    with  FeCl3  and  NiCh 
15    to  20    seconds  with  MnCh 
1      to  30    seconds  with  CuS04 
120  seconds  with  CuCl2 

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  Na20,2Si02  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  Na20,4Si02.  Uranium 
salts  will  produce  fungoid  forms  of  brilliant  yellow  color  and  great 
beauty  in  a  silicate  of  the  composition  Na20,2Si02.19 

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  Na20, 
1.7Si02  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 

18Proc.  Row  Soc.  N.  S.  Wales,  44,  583-592  (1910). 
19Dollfus,  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  Na20  in  the  supernatant  liquid 
and  correspondingly  the  more  silicious  the  precipitate.  Ordway  ob- 
tained precipitates  as  silicious  as  Na20, 4.78Si02,  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  Na20,  3.66Si02  yielded  a  precipitate  containing  43  per  cent 
of  Na20,  3.4Si02.  The  same  amount  of  ammonia  added  to  50  grams 
of  a  21  per  cent  solution  of  Na20,  3.8Si02,  gave  a  ratio  of  Na20,4Si02 
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, 
Holmes22  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  Na20,3Si02)  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   Na20,  3.5SiOz,  but  this  may  be  dis- 

28Chem.  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,2Si02, 
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  Na20,2Si02  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  Na20  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 : 


Na20 

8.40 

Si02 

27.96 

Fe203  +  A1203 

.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  C02.  Extraction  with  water  at  ordinary  tem- 
perature showed  less  Na20,  not  accounted  for  as  Na2C03,  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  Na20, 
4Si02  at  atmospheric  temperatures.   Suspensions  of  the  most  reactive 

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

33Liebig'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  CaC03  may  be  kept  in  closed  vessels  for  days  without  thick- 
ening, but  Na20,2Si02  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  NaaO,  2Si02  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  Na20,2Si02  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  Na20,  2.75 Si02  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,  Si02 72.9  74.39 

Sodium  oxide,  Na20   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,  Si02  64.1  68.98 

Potassium  oxide,   K20 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  Na20,3Si02  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  Al/2  to  6  atmospheres  pressure  to  give  a  ratio  Na20,2Si02. 

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  SiQ2  and  31.3  Na20 — a  molecu- 

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


90  SOLUBLE  SILICATES  IN  INDUSTRY 

lar  ratio  of  Na20,  2.12Si02.  Longer  boiling  brought  the  composition 
to  67.98  per  cent  SiO.  and  24  Na20,  i.e.,  Na20,  2.74Si02.  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  SiF4  by  water,  may,  when 
washed  nearly  free  of  electrolytes,  be  dissolved  in  silicate  of  soda  solu- 
tions of  ratio  Na20,  3.3Si02  at  100°C.  until  the  ratio  exceeds  Na20, 
4Si02.6' 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  +  H20  =  Na2O.Si02  +  2H2. 

4  Peacock,  Samuel,  U.  S.  Pat.  1,231,423  (June  26,  1917). 
5Deguide,  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  Na20,  3.3Si02 
which  is  easily  prepared  may  be  converted  to  Na20,  4.2Si02  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  +  2H20  =  Na2Si03  +  Na2COs  +  4H2. 

This  reaction  may  take  place  at  50° C.  when  a  50  per  cent  solution  of 
Na20,2Si02  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  Cl2  produced  as  follows : 

(a)  4x  NaCl  +  y  Si02  +  x  02  =  2xNa,0,ySiOa  +  2xCl2 

(b)  2x  NaCl  +  y  SiO,  +  x  H20  =  xNa20,ySi02  +  2xHCl 

(c)  4HC1  +  02  =  2H20  +  2C12 

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 

22Treadwell,  "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). 

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

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

27Fritzsche,  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). 

31Sanderval,  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  Na20,  3.25Si02  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  Na2S04  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  2Na2S04  +  C  =  2Na20  +  2SOa  +  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  Na2S04  and  8  of  coal  to 
100  of  Si02  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  3Na2S04  +  6Si02  +  5C  =  3S  +  4C02  +  CO  + 
3(Na20,2Si02).  (Six  atoms  of  oxygen  which  would  yield  3S02  are 
omitted  from  the  right  side  of  the  equation.)  His  suggestion  that  S03 
is  liberated,  then  breaks  down  into  S02  +  O  which  reacts  with  C  to 
form  C02,  CO  -f-  S,  does  not  seem  tenable  in  view  of  the  fact  that 
there  is  no  reaction  between  Na2S04  and  Si02  in  the  absence  of  a  re- 
ducing agent.    Some  soda  is  lost  by  volatilizing,  probably  as  Na2S. 

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  C02  from  both  sodium  and  potassium 
carbonates  with  the  same  amount  of  silica  and  also  that  as  the  amount 
of  silica  increased  the  C02  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  C02  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  C02  dis- 
placed per  mol  of  Si02  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  Si02  and  C02. 

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  C02,  take  up  some  of  the  gas 
which  would  be  again  released  when,  at  the  original  temperature,  air 
was  substituted  for  the  atmosphere  of  C02.  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  C02. 

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  C02. 

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  C02  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  C02  displaced  per  mol 

4aYorke,   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 


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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 
K20 :  Si02 


KoO—  Si02  —  C02   (Pressure  1  Atmosphere  C02) 

898°  956° 

Mol  Per  Cent  in  Melt  Mol  Per  Cent  in  Melt 

K20  Si02  C02  K2Q  Si02  C02 


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*'Os 


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  K2C03,  K2SiOa,  K2Si2Os. 


of  Si02  is  greater  the  less  the  concentration  of  Si02  in  the  melt,  but  in 
no  case  did  the  C02  liberated  from  K2C03  by  silica  reach  a  figure  as 
high  as  the  molecular  equivalent.  In  a  fusion  of  K20,2Si02  only  half 
this  amount  is  set  free  at  1000°.  Higher  temperatures  and  lower  partial 
pressures  of  C02  would  increase  the  amount  of  C02  expelled. 


PREPARATION  99 

Potassium  carbonate  melts  at  891°  and  forms  with  2Si02  a  crystal- 
line mass  of  KoSio05  with  a  melting  point  of  1015°  ±  10°.  The  melt- 
ing point  of  K2Si03  could  not  be  determined  because  it  could  not  be 
prepared  free  from  carbonate  and  disilicate  and  melts  of  the  compo- 
sition K2Si03  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  C02  were  found  in  melts  of  K2C03  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  C02,  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  Si02  gave  up  all  its  C02  at  1000°  yielding  a  crystalline  meta- 

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

(Niggli). 

Na20  —  SiOo—  C02  (Pressure  1  Atmosphere  CO.) 

Molecular  898°  956° 

Ratio  Mol  Per  Cent  in  Melt  Mol  Per  Cent  in  Melt 

Na20 :  Si02         Na30  Si02  C02  Na20  Si02  C02 

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  Na20  than  the  metasilicate  the  equi- 
librium relations  indicated   an  orthosilicate,    formed   according  to  the 

equation : 

Na2C03  +  Na2Si03  z±  Na4SiC>4  +  COa 

in  which  lSi02  displaces  2C02. 

Disilicate. 

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

/Va,C03 


Fig.  33. — Isotherms  in  the  System  Na2C03,  NatSiCX,  Na2Si03. 

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  Si02  for  each  mol  Na20. 
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  Na2Si03— Si02  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  Na20  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  Na20  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 

Na20 

Si02 

Na2Si03 

SiO. 

Point 

Phase 

21S4A 

50.40 

49.44 

99.23 

0.77 

1086.5 

Na2Si03 

2330A 

45.88 

54.03 

82.32 

17.68 

1031.0 

Na2Si03 

2 142  A 

44.92 

54.93 

79.27 

20.73 

1001. 

Na2Si03 

2115A 

39.55 

63.42 

36.58 

863. 

Na2Si03 

25 12  A 

37.83 

60.85 

39.15 

847. 

Na2Si205 

2144A 

37.59 

62.29 

58.48 

41.52 

859. 

Na2Si205 

2510A 

35.90 



54.29 

45.71 

871. 

Na2Si205 

2518A 

34.04 

50.03 

49.97 

873.5 

Na2Si205 

2414A 

33.99 

49.91 

50.09 

873.0 

Na2Si203 

2034A 

33.26 

48.44 

51.69 

872.5 

Na2Si205 

2411A 

32.83 

67.25 

47.32 

52.68 

868. 

NaaSiaO., 

2530A 

29.20 

39.97 

60.03 

831. 

Na2Si205 

2530B 

27.32 

36.44 

63.56 

802. 

Na2Si205 

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  Na2Si205  and  Si02  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  (Na2S04),  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  Si02  for  each  Na20  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 Na20,3Si02  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  Na20,3Si02  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,  Na2Si03  on  the  side  of  maximum  alkalinity,  and  the  highest 
silica  is  found  in  a  sodium  silicate  solution  having  the  composition 
Na20,  4.2Si02,  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 

Si02 99.14 

A1203    0.29 

Fe203    0.07 

CaO    0.28 

MgO    0.09 

Ti02    0.01 

Ignited  Loss   0.14 

108 


COMMERCIAL  FORMS  AND  PROPERTIES  109 

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

Per  Cent 

Na2C03    99.20 

NaHC03     None 

NaCl    0.42 

Na2S04  0.016 

Si02    0.003 

Fe203    0.0011 

A1203  0.0041 

CaCO.    0.025 

MgCOa   0.006 

NHS     None 

H20  0.32 

Total 99.99 

Na20  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  Na20  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. 

Na20,  3.265Si02 

Per  Cent 

Na20   23.24 

Si02     75.89 

Fe203    0.043 

A1203   0.195 

CaO   * 0.069 

MgO    0.069 

Ti02   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  Na20,  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 

Si02  75.31 

A1203  0.38 

Fe2Op  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. 

Na20,  2.06SiO2 

Per  Cent 

Na20    33.10 

Si02     66.27 

Fe2Os     0.036 

A1203  0.199 

CaO   0.098 

MgO    0.071 

Ti02     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  Na2SiOs — Si02.     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  Na2Si03  remained  the  primary  phase  until  the  mix- 
ture containing  39.15  per  cent  Si02  was  reached,  when  the  disilicate, 
Na20,2Si02,  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  Si02. 

The  melting  point  curve  of  sodium  disilicate  is  unusually  flat,  espe- 
cially on  the  side  toward  Na2Si03,  4.3  per  cent  excess  of  the  latter,  low- 
ering the  melting  point  only  2.5  degrees.  When  an  excess  of  Si02  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 
Si02  melts  at  802.7° C.  and  the  primary  phase  is  Na20,2Si02;  the  mix- 
ture containing  66.73  per  cent  Si02  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  Na2Si03,  65  per  cent  Si02,  or  26.5  per  cent  Na20,  73.5  per 
cent  Si02. 

Morey  found  that  the  addition  of  Na20  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 
Na20,  giving  a  mixture  containing  5.12  per  cent  Na2Si03  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 

Li2Si03  1201°  LhSioOs    1032°  (incongruent) 

Na2Si03   1088°  Na2Si205 875° 

K2Si03    976°  K2Si205 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  K2Si205  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  Na20.2Si02.  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  Si02.  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 

Si02 

Na20 

Ab03+Fe,03 

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"  (Na20,  3.3Si02)  be  powdered  to  pass  100  mesh  screen  and  ex- 
posed to  ten  times  its  weight  of  water  for  12  hours,  the  ratio  of  Na20 
to  Si02  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  H20  with  20     Heated  at  90°  with  20  Parts  H,0 

Na20:Si02    20°  C.  in  10  Poured  Parts 

in  Glass        Parts  H20  through  H20           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  Na20,  2.8Si02  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  H20-Na20 .  Si02,  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  Na20 :  Si02  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 

9Henkel  &  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,  Na20,  3.3Si02,  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  Na20,  3.8Si02.  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.?  Up  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. 

Na20,3.3Si02  Na20,2S.i02  Na20,3.3Si02  Na20, 2Si02 

At  100°C Anhydrous  Anhydrous  17.5%  H20  17.5%  H20 

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/  ffaffo     /*%  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 

t0  5,0i'/:£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  0  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- 


4U92  J9d 


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


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,   Na2Si03.9H20,  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  Na20,  1.5SiO,2  to  Na20,  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  Na20  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 

Na20 

SiC>2 

Total  Solids 

Baume        Specific  Gravity 

Na20, 

3.9Si02 

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 

Na20, 

1.0190 
3.36Si02 

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 

Na20, 

1.0183 
2.44Si02 

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 

Na20: 

1.2866 
,2.40SiO2 

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 

Na20,  2.06SiO2 

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 

Na20 

Si02 

Total  Solids 

Baume 

Specific  Gravity 

Na20, 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»/    0f    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 
Na20  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 

Si02:  NdiO. 

Molecular 

Ratio 

Cone.         Density 

Conc. 

Density 

Cone. 

Density 

Si02 :  Na20 

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. 
0 
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 


Na20,  3.34Si02,  dil. 

Temp.  °C. 

0  

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 

Na20,  3.34Si02,  41°  Baume 

Degrees 
Temp.  °C.                                 Baume 
0.0    42.0 

with  Temperature —  ( Continued) . 

Na20,2.61Si02,  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,  2.47Si02,  52° Baume 
0  52.06 

Na.0, 2.06SiO2,  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 

Na20, 2.06SiO2,  dil.  to  approx. 

40°  Baume 
17                                          39 1 

Na20,  2.06SiO2,  59.1°Baume 
35  00    59.80 

21                                           39  0 

45  00    59.20 

30                                         38  5 

50.50    59.00 

40                                         38  5 

55.50    58.80 

50                 .                        38  0 

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  0 

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/    fa20 


Fig.  54.— Variation  of  Refractive  Index  with  Ratio  at  Constant  Na20   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 
Na20  Si02  H20*  Index 


Na20,  3.9Si02 

7.01% 

26.599 

0                       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 
Na20,  3.36Si02 

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 
Na20, 2.44Si02 

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 
Na20,  2.40SiO2 

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 
Na20  Si02  H20*  Index 


Na2O,.2.06SiO2 

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 

Na20, 

1.69Si02 

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). 
33Codd,  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  Na20,  1.5Si02  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. 

„_2far\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 

0 

Jo 

3 

\ 

0 

< 

^          i 

< 

» 

i 

i 

• 

S     A 

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

%     NaeO 

Fig.  57. — Variation  of  Absolute  Viscosity  with  Na20. 

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,o2 

Fig.  58. — Variation  of  Viscosity  with  Si02. 

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 

MHiggins,  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  C02  from  the  air  and  as  far  as  viscosity  is 
concerned  the  conversion  of  NaaO  to  NaXO.  in  a  silicate  solution  is 


Table  55.    Vis 

Na20 

Si02          ' 
Na20,  3.9SiQ2 

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 
Na20,  3.36Si02 

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,  2.44Si02 

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. 


Na20 

Si02          Centipoises 

Na20,  2.40SiO2 

4.99% 

11.66% 

6.7 

3.02 

7.06 

5.1 

1.03 

2.41 

3.6 

.52 

1.21 
Na20,  2.06SiO2 

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 
Na20,  1.69SiOa 

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 

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146 


SOLUBLE  SILICATES  IN  INDUSTRY 


equivalent  to  removing  it.  At  a  point  where  0.1  per  cent  Na20  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  Na20 :  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 


0  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  5/02:/Vc7Z0 


Fig.  65. — Change  of  Viscosity  with  Ratio. 


150 


SOLUBLE  SILICATES  IN  INDUSTRY 


Table  56.    Changes  in  Viscosity  with  Changes  in  Temperature. 


Temp.  °C.  Centipoises 

Na20, 1.58Si02 

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 

Na20,  3.25Si02.     °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 


Na20,  3.86Si02 

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 


Na20,  3.86Si02 

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 

Na20, 2Si02 

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 

Na20,  3.25Si02.     °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,  3.86Si02.     °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 

Na20,  3.25Si02.     °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 

Na20,  3.25Si02.     °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. 

Stericker45  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  Na20,  3.32Si02 ;    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   Na20, 3.46Si02;   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  Na20, 2.1  Si02  diluted 124.5            11             ....  

3  Viscous  oil 2704.4           21.5           2.1  

4  Na20,  2.1  Si02  diluted 2548.9           44.4          11.3  4.5             2.6 

5  Dextrin     137.              69. 

6  Na20,2.1Si02    124.5           171. 

7  Na20, 1.24Si02 3.8 

8  Na20, 2.84Si02    969.0           ....            6.3  1.2 

9  Na20,3.41Si02 522.0           ....            1.5  1.0 

10  Na20, 3.47Si02   247.5  ....  1.3  0.7 

11  Na20, 3.32Si02    167.2  ....  0.6  0.6 

12  Na20, 3.92Si02 1723. 

13  Na20, 3.47Si02   (control)    ..     247.5  ....  0.8  0.7 

14  Na20  +  sodium  acetate  ... .     281.7  ....  1.0  0.7 

15  Na20  +  urea    261.2  ....  1.0  0.8 

16  Na20, 3.92Si02  +  20%  H20 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 Na20,  3.92Si02  at  the  high  viscosity  appears  tacky,  yet  the 
fact  that  at  higher  speeds  the  threads  of  this  liquid  break  off  short 
while  those  of  Na20,  2.1Si02  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  Na20,  3.3Si02,  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  Si02  per  Per  Cent  Total  Na20  Found 

Mol  Na20  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 
Si02  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  Na20-Si02-H20. 

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  Na20  and  Si02 
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  Na20,  3.3Si02,  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 

0 

O 

CO 

CO 

CO 

CM 

CM 

1— 1 

d 

d 

d 

d 

O 

Constituents 

OS 

c3 

03 

OS 

Sodium  oxide,  Na20 

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,  Fe203... 

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,   Ti02    

0.006 

0  007 

Lime,    CaO    

0.013 

0.04 

Magnesium,  MgO   . . 

0.044 

0.024 

0.006 

0.02 

0.01 

English  Neutral  Silicate, 

English  Silicate, 

Na20,  3.19Si02, 

39.8°Baume 

Na.0, 3.02SiO2, 

45°Baume 

Na20     

8.76 

Na2U     

SiOa     

10.42 

30.62 

0.01 

0.09 

0.05 

Si02    

27.21 

Fe2Os    

0.006 

Fe-»03    

A1203    

0.08 

A1,03    

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 
C02.  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° 
Na20,2Si02  containing  46  per  cent  water,  but  for  40°  Na20,  3.3Si02 
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  Na20,  3.11Si02  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 :    ■ 


Si02 

Na20 

AI2O3 

Fe2Os 

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.  Na20,3Si02  and  more  silicious  silicates  at  con- 
centrations above  38  per  cent  leave  the  metal  perfectly  bright  in  most 
cases.  Na20,2Si02,  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  Na20,2Si02  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  Na20,3Si02,  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  Na20,  3.9Si02  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"/-'     fl'l      ■   *                                       W-?r 

to                                                                                                                             ""■'■■-                                 ■        .  .-^  ' 

Fig.  78. — Silicate  Cement  in  an  Oil-Fired  Acid  Concentrator  for  H2S04. 


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  Na20,  3.3Si02  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  Na20,2Si02.  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 

vSee  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). 

10Iding,  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  Na20  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  A1203    0.22                   0.29  0.21 

"  "  Fe203    0.18                  0.18  0.17 

"  "  CaO    None                None  None 

"  "  MgO    None                None  None 

"  "  CI    0.07                  0.07  0.09 

"  "  S03    0.02  0.02  0.02 

"  "  H20    45.83  45.83  45.31 

"  "  Si02     35.58  35.50  36.29 

"  "  Na30    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  Na20,  3.3SiOs,  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  +  2H20  =  Na2Si03  +  Na2C03  +  4H2.  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, 

15Johanson,  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). 

17Henkel  &  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). 

20Stowell,  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 

MTaggart,  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  Na20,  3.96Si02 


Ground  Quartz  Rock 

340  parts  20-100  mesh 
220  parts  100  mesh  and 
finer 

146  parts  Na20,  3.3Si02 


Treatment 
Cone.  H2SO4 
Dil.      H2SC>4 
Cone.  HC1 
Dil.      HC1 
Cone.  HNO3 
Dil.      HNO3 

Cone.  H2S04 

Dil.      H2S04 
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  Na20,  3.3SiQ2 


500  parts  sand 
50  parts  BaS04 
137  parts  Na20,  3.3Si02 


500  parts  sand 

100  parts  talc 

150  parts  Na2Q,  3.3SiQ2 


500  parts  sand 
50  parts  litharge 
185  parts  Na20,  3.3Si02 

600  parts  sand 

200  parts  powdered  mica 

240  parts  Na2Q,  3.3Si02 


600  parts  sand 
200  parts  fluorspar 

242  parts  Na20,  3.3Si02 


600  parts  sand 
60  parts  blown  petroleum 
pitch,  asphalt  base 


650  parts  anhydrous 

Na20,  3.3Si02 
230  parts  Na2Q,  3.3Si02 


Treatment 

Cone.  H2S04 

Dil.  H2S04 

Cone.  HC1 

Dil.  HC1 

Cone.  HN03 

Dil.  HNO3 

Cone.  H2SO4 

Dil.  H2S04 

Cone.  HC1 

Dil.  HC1 

Cone.  HN03 

Dil.  HN03 


Cone. 

Dil. 

Cone. 

Dil. 

Cone. 

Dil. 


H2SO< 

H2S04 

HC1 

HC1 

HNO3 

HNO3 


Cone.  H2S04 
Cone.  HC1 


Cone.  H2S04 
Dil.  H2SC»4 
Cone.  HC1 

Dil.      HC1 
Cone.  HNO3 
Dil.      HNOs 

Cone.  H2SO4 
Dil.      H2S04 

Cone.  HC1 
Dil.      HC1 

Cone.  HNO3 
Dil.      HNO3 


Cone.  H2SO4 
Dil.      H2SC>4 
Cone.  HC1 
Dil.      HC1 
Cone.  HNO3 
Dil.      HN03 

Cone.  H2S04 

Dil.  H2S04 

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 

30Willetts,  Paul  G.,  U.  S.  Pat.  1,573,888  (Feb.  23,  1926). 
31Youngman,  Robert  H.,  U.  S.  Pat.  1,564,394  (Dec.  8,  1925). 
MYoungman,  Robert  H.,  Brit.  Pat.  250,480   (Oct.  24,   1925);   C.  A.,  21,   1172. 
33Rochow,    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). 
37Wolcott,  E.  R.,  U.  S.  Pat.  1,617,696  (Feb.  15,  1927). 
38  Reynolds,  R.  W.,  U.  S.  Pat.  1,422,130  (July  11,  1922). 
390'Hara,  C.  M,  U.  S.  Pat.  148,972  (Aug.  9,  1873). 

40Fulcher,  G.  S.,  Can.  Pat.  248,315  (March  31,  1925)  ;  Ceram.  Abstracts,  4,  347. 
41Holley,  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 


^f3^ 


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 

43Societe  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 

Na20,  2.5Si02  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). 

47Moldenke,  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,  Na20,  3.3Si02,  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  Na20,  3.3Si02)  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). 
53Bickley,  A.,  U.  S.  Pat.  1,432,523  (Oct.  17,  1922). 
"Whyte,  Samuel,  U.  S.  Pat.  1,366,305  (Jan.  18,  1921). 
65Gailbourg  and  Ballay,  Rev.  Metal.,  19,  222-226  (1922). 
59 For  example:  Whinfrey,  Charles  G.,  U.  S.  Pat.  1,567,632  (Dec.  29,  1925). 
67Wilhelmy,  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). 

65Bartlett,  Francis  A.,  U.  S.  Pat.  1,484,370  (Feb.  19,  1924). 

6aLowe,  U.  S.  Pat.  1,532,908  (April  7,  1925). 

6TStryker,  G.  B.,  and  Frank  A.  Mantel,  U.  S.  Pat.  1,436,061    (Nov.  21,  1922). 

68Stowell,  E.  R.,  U.  S.  Pat.  1,524,676  (Feb.  3,  1925). 

68  Berry,  E.  R.,  U.  S.  Pat.  1,131,463   (March  9,  1915). 

70Gerloch,  Oscar,  U.  S.  Pat.  1,468,149  (Sept.  18,  1923). 

71Slepian,  Joseph,  U.  S.  Pat.  1,638,888  (Aug.  16,  1927). 

73  Cook,  Frank  J.,  U.  S.  Pat.  1,393,346  (Oct.  11,  1921). 

73Stowell,  E.  R.,  U.  S.  Pat.  1,382,329  (July  14,  1921). 

74Covell,  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. 

76Menuez,  Anthony  E.,  U.  S.  Pat.  438,698  (Feb.  24,  1890). 

77Barringer,  L.  E.,  U.  S.  Pat.  1,423,985  (July  25,  1922). 

78Grote,  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  K20,  3.25Si02,  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 
Na20,  3.3Si02.  If  slow  setting  is  desired  in  this  type  of  mixture, 
Na20,2Si02  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.  Na20,  3.3Si02  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). 
83Michell,  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 0 

200 125 

300 500 

0 .0 

350 75  failed  by  cracking 

Test  No.  2. 

2"  X  10"  slab. 

Supports  46"  apart. 

100 0 

200 0 

400 032 

500 032 

600 063 

700 063 

800 094 

900 125 

1000 125 

0 0      no  set 

1100 157 

1200 157 

1300 188 

1400 188 

1500 313 

0 0      no  set 

1700 313 

1900 313 

2000 313 

0 0      no  set 

2500 438 

0 031  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  107 

3.21  X  10e 

30 

3.16  X  107 

1.20  X  106 

60 

9.20  X  107 

91 

3.07  X  108 

112 

1.00  X  10° 

1.74  X  106 

11:55 

140 

1.01  X  1010 

4.23  X  107 

2:13  P.M. 

107 

4.77  X  1010 

1.50  X  109 

3:37 

45 

1.38  X  HP 

9.70  X  10u 

5:00 

30 

1.07  X  1012 

8.21  X  1010 

Oct. 

13,  10:00  A.M. 

18 

1.48  X  10" 

2.30  X  1010 

Oct. 

23,    2:00  P.M. 

25 

6.68  X  109 

7.91  X  108 

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 

84Michell,  Henry  Colbeck,  U.  S.  Pat.  714,947  (Nov.  15,  1904). 
83Bartlett,  Francis  A.,  U.  S.  Pat.  1,598,636  (Sept.  7,  1926). 
86  Imschenetzky,  Alexander,  U.  S.  Pat.  631,719   (Aug.  22,  1899). 
87Vorlander  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 


3L°       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. 

91Behrens,  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.  Na20,  3.3Si02  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  Na20,2Si02  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. 
MCompt.  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  Na20  and  Si02  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 
Na20,  3.3Si02  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). 
114Dunstan,  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). 
117Oelhafen,  John  Walter,  U.  S.  Pat.  1,564,706   (Dec.  8,  1925). 
118Stryker,  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). 
120Lefebure,  Victor,  Brit.  Pat.  268,851   (April  17,  1927). 
mLennig,  Albert  M.,  U.  S.  Pat.  653,101   (July  3,  1900). 

132  Weintraub-Schnorr,  Naum,  U.  S.  Pat.  606,751    (July  5,  1898). 
12301ney,  George,  U.  S.  Pat.  627,008  (June  13,  1899). 
124Benner,  Raymond  C,  U.  S.  Pat.  1,573,369  (Feb.  16,  1926). 
^Ffoss,  Charles,  U.  S.  Pat.  1,111,021   (Sept.  22,  1914). 
126Stowell,  E.  R.,  U.  S.  Pat.  819,467  (May  1,  1906). 

127  Willett,  Walter  E.,  U.  S.  Pat.  1,454,780  (May  8,  1923). 
128Ebbesen,  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). 
lslGauthier,  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). 
138Britton,  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). 

140Paterson,  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,  3.3Si02,  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.  H20  "      6      " 

1451/'    "        "  Began  in  5       "       (approximately) 

1421/,    "        "  "       "    4      " 

136       "       "  "       "   3      " 

Pretty  firmly  set  in  A1/*  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 

0 

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  Francois153,  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). 

1MAnon.,  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<aBall,  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). 
16aMitton,  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  Na20,  3.3Si02,  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  Na20,  1.5Si02  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  Na20,  2.06SiO2 
30  parts  Portland  cement 
10  parts  water 


29  parts  graphite 
29  parts  Na20,  2.06SiO2 
28  parts  Portland  cement 
14  parts  water 

72  parts  talc 
7  parts  Na20,  2.06SiO2 
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,  3.3Si02,  Na20,2Si02.  and  Na20,  2.5Si02  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 
Na20,  2.5Si02  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. 

Na20,2.5Si02  Glycerin                     PbO 

at30°Baume  Parts  by                   Parts  by 

Parts  by  Weight  Weight                    Weight 

4  0                                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  Na2Os  3.3Si02  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). 
L8101fers,  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 
Na20,  3.25 Si02.  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 

184Moyer,  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) 
1S8Huth,  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 


pIG    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 

189Dulac,  A.,  Brit.  Pat.  250,439  (July  14,  1925)  ;  C.  A.,  21,  1174. 
190Stubbs,  Robert  C,  U.  S.  Pat.  1,315,749  (Sept.  9,  1919). 
191Brunner,  Mond  &  Co.,  D\cr,  Calico  Printer  (Aug.  15,  1924). 
192Remler,  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-  soc/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 
McBain5  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  Na20,  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   NaaO,  3.34SiOa    (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  Na20,  3.34Si02  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  Na20,  3.3Si02  (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,  Na20,  and  Si02  on  sundry  surfaces. 

Glass. 

Bottles  on  which  syrupy  silicate  solutions  between  Na20,2Si02  and 
Na20,4Si02  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  Na20,  2.7Si02  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  Na20,  2.7Si02  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.    Na20,  2.4Si02  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  Na20,  3.3Si02.  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.   Katz9  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  Na20,2Si02,  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 

A1203  and   Fe,03 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  Na20,  3.3Si02  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£0 

Fig.   98. — Shear   Tests.    Silicate   of    Soda   between   Walnut    Surfaces. 


to  the  square  inch)  with  a  1.41  specific  gravity  (42°Baume)  solution  of 
Na20,  3.3Si02  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   Na20, 3.34Si02  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 

lsFiske,  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). 

19Fairchild,  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 

Na20,  3.3Si02  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). 
MMelch,  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). 
27Ferres,  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). 
30Raffel,  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). 
33Langston,  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). 

39Heinrichs,  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). 

46Crowell,  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  Lsorrorr  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 ;  ■ 

0 

Br^p" 

'    |    | 

\-1n 

Jp  tii._iL»i— 

BssSKLlss 

aafa    »- 

^_^ 

,♦       1 

J*-    !*' 

°:XM 

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%  Na20  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%  Na20. 


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  Na20,  3.3Si02  and  Na20,  2.9Si02.  Translated  into  the  con- 
ditions of  a  box  in  a  rainstorm,  the  difference,  which  corresponds  to 
but  2  per  cent  Na20,  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%  Na20    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%  NaaO. 


Alkalinity.  The  lowest  practical  alkalinity  for  adhesive  use  is  near 
Na20,4Si02.48  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  Na20,  3.3SiOo  and  Na20,4Si02.  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,  2.9Si03  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  Na20,  3.3Si02,  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  Na20,  3.9Si02  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). 
MSandor,  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  Na20,  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.  Na20, 
3.3Si02  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  Na20,2Si02,  but  this  use  has  not  developed  to  the  extent  that  would 
be  possible  with  a  power-driven  spreading  device.  Na20,2Si02  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  Na20,4Si02,  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  Na20,  3.3Si02  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.  Na20,  2.9SiQ2  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  Na20  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.  Na20,  3.3Si02 
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  Na20,  3.3Si02  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  Na20,2Si02  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  Na20,  3.3Si02  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 

Na20,2Si02,  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.  Na20,  3.34Si02  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   Na20, 3.34Si02    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). 

87Jeromins,  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). 

70Bogue,  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     fer     /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 

75Butterman,  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)  Na20,  3.3Si02  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). 
slChem.  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 

Na20,3.3Si02  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  Na20, 
2.9Si02,  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). 

MDrushel,  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). 

91Dahse,  W.,  Ger.  Pat.  318,516  (Aug.  23,  1918). 

92 /.  Soc.  Chem.  Ind.,  39,  517A. 

93Meta,  Sarason,  Ger.  Pat.  316,080  (Nov.  13,  1919). 

^Besele,  Lynaz,  Ger.  Pat.  61,703   (1892). 

93  "Silicate  PJs  &  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  Na20,4Si02,  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  (Na20,  1.5Si02)  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.  Na20,  3.3Si02  or  Na20,4Si02  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  Na20,  3.3Si02 
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,  Na20,4Si02 
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. 

5Artus,  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). 
8Cavanaugh,  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  Na20,  3.3Si02  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         0         12        3 

rtaaflaf-  .  ....-lii'MiH  O.iHiiitiAli^llf 


9       10 


Fig.    128. — Comparative  Penetration  of   ZnCl2  and   Na20,  3.3Si02  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  ZnCl2  and  Na20,  3.3Si02.19  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 
Na20,  3.3Si02  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.  Na20,4Si02  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). 
25Hexamer,  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. 

28Sandham  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). 

MEllery,  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  Na20,  3.3SiQ2,  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  Na20, 3.3Si02  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  Na20,  3.3 Si02,  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). 
45Iversen,  M.  M.,  Nor.  Pat.  33,924  (Jan.  30,  1922). 

46  Locke,  J.  A.,  Brit.  Pat.  160,801   (March  24,  1921). 
47Ferrell,  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  Na20,  3.3SiQ2,  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.  Na20,  3.3Si02,  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. 

60Nicksch,  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 
Na20,  3.3Si02,  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  Na20,  3.3Si02. 

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  Na20,  2.9Si02  or  even  Na20,2Si0.2,  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  Na20,4Si02  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.  Na20,  3.3Si02  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). 
57Puscher,  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,  Na20, 3.3Si02  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  Na20,  4.2Si02,  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 : 

MU.  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). 

67Luckiesh,  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  Na20,  3.3Si02  . .  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  Na20, 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). 

72Eberlin,  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    Na20,2Si02  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. 

74Drefahl,  Louis,  and  Edward  Taylor,  U.  S.  Pat.  1,486,077   (March  4,   1924). 
75Teague,  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  Na20,  3.3Si02  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  Na20,4Si02,  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  Na20,  4.2Si02, 
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  280Baume  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  Na20,  3.9Si02  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). 
eoBenford,  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  Na20,4Si02.  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. 

94Stowell,  E.  R.,  U.  S.  Pat.  774,003  (Nov.  1,  1904). 

BSChcm.  &  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). 

98Boorne,  William  Hanson,  Brit.  Pat.  185,580   (Sept.  14,  1922). 

"Holslag,  Claude  J.,  U.  S.  Pat.  1,451,392  (April  10,  1923). 

100Keram.  Rundschau,  28,  239   (1920). 

101Fenaroli,  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%  Na20,  32.9%  SiOo,  and 
53.4%  H20)  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    (Ti02) 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 
Na20  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 


103Philipp,  Ferdinand,  U.  S.  Pat.  300,890  (June  24,  1884). 
°*Fewins,  Frank  N.,  U.  S.  Pat.  443,361   (Dec.  23,  1890) 


105Bibikon,  N.  A.,  U.  S.  Pat.  421,229  (Feb.  11,  1890), 
109McLennon,  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). 
mMees,  E.  F.,  U.  S.  Pat.  1,396,970  (Nov.  15,  1921). 

113  Walsh,  M.  J.,  U.  S.  Pat.  1,415,282  (May  9,  1922). 

114Keedwell,  C.  A.,  U.  S.  Pat.  1,476,016  (Dec.  4,  1923). 

113  Sulzberger,  N.,  U.  S.  Pat.  1,518,944  (Dec.  9,  1924). 

1,flP16nnis,  Rudolf,  U.  S.  Pat.  1,487,471   (March  18,  1924). 

117  Blombery,  George  Frederick,  U.  S.  Pat.  1,582,117  (April  27,  1926), 

1,sGaudry,  Tanciede,  U.  S.  Pat.  1,604,904  (Oct.  26,  1926). 

119Bristow,  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). 

126JVochbl.  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  Na20,4Si02  is  less  stable  in  solution 
than  that  in  Na20,2Si02. 

Table  86.     Precipitation  of  Silicate  by  Alum. 
Solutions  Used 

Amount  of  Amt.  Alum 

Concentration  Silicate  .00169 

Silicate  Composition  Per  Cent  Solution,  cc.  A1203  per  cc. 

Na20,  3.86Si02 1.56  51  65 

Na20,3.3Si02 0.13  401  47 

Na20,2.45Si02 1.25  36  51 

Precipitate 

Per  Cent 
Per  Cent  Na20  +       Per  Cent        Per  Cent 

Si02  in  Ppt.     Per  Cent      Undeter-        Total  of  Total 

Silicate  Composition     Dry  Basis         A1203  mined        Si02  Ppt.      A1203  Ppt. 

Na20, 3.86Si02 81.1  14.5  4.5  89.4  83.3 

Na20,3.3Si02 68.0  36.3  5.4  43.9  80.5 

Na20, 2.45Si02 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  Na20,3Si02. 

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  Xa20,4Si02 
are  too  costly  (cf.  Chapter  VI).  Xa20,  3.3Si02  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  Xa20,- 
3.3Si02  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). 
133Klason,  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  Na20,4Si02,  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. 

1360stwald,  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.     ,. 

13aBrit.  Pat.  177,137  (Nov.  24,  1921)  ;  Fr.  Pat.  543,763;  and  Paper,  31,  No.  20 
(1920). 

™Papeteric,  41,  634  (1919). 

141Altmann,  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. 

Na20,  3.86SiOv,   1.3  sp.  gr.,  requires  about  25  lbs.  papermaker's 

alum  (18%  AL>03)  for  100  pounds  silicate. 
Na-O,  3.3Si02,  1.4  sp.  gr,,  requires  about  33  lbs.  of  alum  per  100 

pounds  silicate. 

142Heuser  and  Behr,  Papierjabr.,  1-6   (1923);  Paper,  31,  No.  18,  7-12   (1923). 
143Heuser,  Paper  Maker,  64,  433  (1922). 


284 


SOLUBLE  SILICATES  IN  INDUSTRY 


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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 
Al2Os  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- 

lwVail,  James  G.,  Fibre  Containers,  6,  No.  8,  16  (1921). 


288 


SOLUBLE  SILICATES  IN  INDUSTRY 


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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  Na20,  3.3Si02 

146Kuldkepp  and  Graf,  Ger.  Pat.  245,975  (Oct.  20,  1909). 
147Clapp,  Albert  L.,  U.  S.  Pat.  1,345,317  (June  29,  1920). 
^Sommer,  George  G.,  Ger.  Pat.  257,816  (Aug.  20,  1911). 
149Kolb,  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). 
154Clapp,  Albert  L.,  U.  S.  Pat.  1,592,294  (July  13,  1926). 
155Muller,  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). 
1MMosley,  J.  F.,  Brit.  Pat.  226,850  (Aug.  24,  1923). 

160Reichard,  F.,  Brit.  Pat.  177,137  (Nov.  24,  1921). 

161  See  also  Fr.  Pat.  543,763:  Paper,  31,  No.  20  (1920). 

lfl2Altmann,  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). 
163Fues,  Wochbl.  Papierfabr.,  44,  835-841,  1223   (1913). 

188Wrede,  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). 


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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). 
171Roscow,  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, 

172Knup,  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  Na20,  2.4Si02  to  Na20,  3.3Si02,  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. 

179Neuhaus,  Ger.  Pat.  75,896  (Jan.  25,  1893)  ;  305,275,  305,770. 
180Keiper,  Melliands  Textileberichte,  3,  181   (1922). 
181Heermann,  Chem.  Ztg.,  35,  829  (1911). 
182Sisley,  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). 

18aTondani,  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). 
202Posselt'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 

1J.  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 : 
2r2  g 


V 


in  which   V  =  velocity  of   settling,  r  =  radius   of 


9K  (d-d1)' 

particles,  K  =  viscosity,  d1  =  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 


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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  Na20  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) 

Na2C03 

Silicate 

Na2C03 

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  (Na20,2Si02)  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 


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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  Na2COa  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 


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(McDowell). 


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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  Na20  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 

87.  Am.  Chem.  Soc,  44,  965-74  (1922). 

9Kohl,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  Na20, 
2Si02  and  NaoO,  3.3Si02. 

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  Na20,  3.3Si02  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. 
wEdser,  E.,  and  L.  A.  Wood,  Brit.  Pat.  168,927  (March  20,  1920)  ;  C.  A.,  16, 

405. 

20Edser,  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  showT  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. 

23Borcherdt,  W.  O.,  U.  S.  Pat.  1,448,514  (March  13,  1923);  1,448,515  (March 
13,  1923). 

'26Plauson,  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  Mn02  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  Na20,  3.97Si02,  specific  gravity  1.30. 
0  "K"  Brand  is  Na20, 2.92Si02,  specific  gravity  1.48. 
t"BW"  Brand  is  Na,0,  1.62Si02,  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 
3C 

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  Mn02  ground  in  colloid  mill  (No.  2). 

50  cc.  portions  of  alkaline  solutions. 

Values  given  represent  centigrams  of  Mn02  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 

Na2C03 

Na3P04 

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  Na20,  3.97Si02,   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). 

33Ind.  Eng.  Chem.,  15,  241-3  (1923). 

34Edser,  Edwin,  Fourth  Colloid  Report,  Sci.  &  Ind.  Research,  London:  His 
Majesty's  Stationery  Office.  1922,  p.  169. 

35Traube,  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,   T3  must  be 
>  Ti  +  V  where 

Ti  =  surface  tension  liquid/air. 
T2  =  surface  tension  solid/air. 
T12  =  surface  tension  liquid/solid. 

Owing  to  the  difficulty  of  measur- 
ing either  T2   or  T12  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  Na20,  3.3Si02  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  Na30,  2.61Si02,  Specific  Gravity  1.41. 
"BW"  Silicate  is  Na.O,  1.62Si02,  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. 

40Hillyer,  /.  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  Na20, 2.83Si02  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, 

i3Ind.  Eng.  Chcm.,  15,  810-811   (1923). 

44  Shorter  and  Ellingworth,  Proe.  Roy.  Soc.  (London),  A,  92,  231-247   (1916). 

45Elledge  and  Isherwood,  /.  hid,  Eng.  Chem.,  8,  793-794  (1916). 

46Briggs  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) 
Na20,  3.9Si02  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  Na20,  3.3Si02,  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. 

Na20,  3.3Si02  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,  Na20,  3.3Si02  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  Na20,  3.3Si02,  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,— Na20,  1.6Si02,  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 
Na20,  3.3Si02  and  NaOH,  the  other  using  Na20,  1.6Si02  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 
Na20,  3.3Si02,  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  Na20,  1.6Si02,  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. 

60Hartman,  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.  Na20,  3.3Si02  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). 

6aHey,  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  Na2C03, 

5  parts  paraffin  oil, 

5  parts  Na20,  3.3Si02,  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 

OTCarleton,  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 
Na20,  3.9Si02  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  Na20,  3.3Si02,  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  Na20,  3.3Si02  or  Na20,  3.9Si02. 

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,  Na20,  3.9Si02 
at  0.6  per  cent  and  Na20,  3.3Si02  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,  (Na20)2,(Si02)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  Mn02  value  of  "S"  Brand  silicate 
(Na20,  3.97Si02,  specific  gravity  1.30),  (Na20)2,(Si02)3.9r,  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  Mn02  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  Na20,  3.3Si02.  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  Na20,  3.3Si02  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  Na20, 3.34Si02,  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 

92Rasser,  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  Na20,  3.34Si02,  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  H20.  .015  g.  Na2COs 
equivalent  to  .008  g.  Na20. 

Third  tube  .055  g.  Na  oleate  1000 
cc.  distilled  H20.  .03  g.  Na20,  3.25Si02 
equivalent  to  .007  g.  Na20. 


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.  LM  "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.  CaCl2  +  2Na(Ci8H3302)  =  CaCGaH^O*)*  +  2NaCl 

2.  CaCl2  +  Na20,  3Si02  =  CaO,  3Si02  +  2NaCl 

He  found  that  the  calcium  silicate  precipitate  could  react  with  calcium 
soap  in  reversible  fashion,  of  which  the  following  is  typical : 

3.  Ca(C18H3302)2  +  Na20,3Si02^  CaO,3Si02  +  2Na(Ci8H3302). 

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 : 

103Dedrick,  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  Na20  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  Na20, 
2.83Si02. 

"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  CaC03  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  (CaC03)  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  MgCl2  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  CaCl2  MgCl2  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  CaCl2  MgCl2  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  reduce1  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  Na20, 
3.3Si02  containing  the  same  percentage  of  Na20  leaves  the  tin  bright. 

109Bogue,  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  Na20,  3.3Si02  is  a  trifling  annoyance.  A  like 
amount  of  Na20  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,  Na20,  3.3Si02  and 

5  per  cent  NaOH  solution,  presumably  enough  to  produce  Na20, 2Si02. 

3.  Washing  powder,  30  per  cent  fatty  acid,  containing  soap  and  Na2C03  only. 

4.  The  same,  plus  20  per  cent  1.38  specific  gravity,  NaaO,  3.3Si02  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  Na20  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  Na20, 
3Si02   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 

0 100.00  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 


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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. 
115Zanker  and  Schnabel,  loc.  cit. 
11<5Vohl,  Berliner  Musterzeitung  (1872). 

117  Calvert,  /.  Chem.  Soc,  18,  70-77  (1865). 

118  Schelhass,  Bayerisches  Gewerbeblatt,  203  (1872). 

119Euler,  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. 

mGriin,  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.) 

133Kiihl,  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 

0 

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 

0 

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  Na20, 
3.9Si02  to  NaoO,  1.6SiOz  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.    Na20,2SiOo  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 

Na20,  3.34Si02   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  Na20, 
3.34Si02  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  Na20,  2.47Si02,  Na20,  3.34Si02,  and  Na20, 
3.96Si02,  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  Na20,  2.47Si02  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  Na20, 
1.62Si02  and  Na20,  2.03SiO2  did  not  injure  samples  of  silk,  but  3  hours 
at  63° C.  was  sufficient  to  damage  them.  With  Na20,  1.62Si02,  the  woof 
threads  were  thinned  to  about  half  their  normal  size.  With  Na20, 
1.23Si02  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  Na20,  3.34Si02  and  Na20,  3.96Si02.     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.  Na20,  1.62Si02,  Na20, 2.03SiO2,  and 
Na20,  2.47Si02,  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  Na20,  1.62SiOo  as  well  had  dis- 
solved all  the  wool.  Na20,  2.03 Si02  had  left  spots  of  wool  and  Na20, 
2.47Si02  about  half  of  the  original  amount.  Soda  ash  had  dissolved 
enough  to  be  perceptible  but  Na20,  3.34Si02  and  Na20,  3.96Si02  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  Na20,  3.34Si02  and  Na20,  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 

iaZanker  and  Schnabel,  loc.  cit. 

142Edeler,  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 

143Thies,  F.,  Z.  angew.  Chem.,  36,  312-314  (1923)  ;  C.  A.,  17,  3424. 

144Milson,  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).' 

147Grothe,  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 

152Grothe,  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  Na20, 
2Si02.  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 


£()..  NHfO" 


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 

1MSmolens,  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  (Na02,  10.5%;  Si02,  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, 

165Heermann,  P.,  Z.  angew.  Chem.,  36,  107  (1923)  ;  Z.  dent.  61-  Fett-Ind.,  41, 
No.  22,  338-341   (1921). 

16flGriin  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). 
170Reichert,  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 
173Smolens,  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. 

Na20 

Si02 

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 

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  49c 

C.  for  3  hours 

Gram 

Per  Cent 

0 

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 

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 

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 

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 

0.03290 

0.03115 

0.00175 

5.3 

1 

0.03290 

38°C. 

0.03115 

for  2.5  hours 

0.00175 

5.3 

0 

0.11575 

0.11257 

0.00318 

2.7 

1 

0.11575 

Stood 

0.11257 
open  2.5  days 

0.00318 

2.7 

0 

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 

0.19822 

0.19043 

10 

0.00779 

3.9 

0 

0.19822 

0.18866 

30 

0.00956 

4.8 

0 

0.19822 

0.18406 

60 

0.01416 

7.1 

0 

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 

0.06830 

0.05166 

10 

0.01664 

24.3 

0 

0.06830 

0.05166 

10 

0.01664 

24.3 

0 

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  Na20,  3.3 Si02 
to  Na20,4Si02  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). 

183Kunheim,  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 
(Na3P04)  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  Na20,  3.3Si02  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. 

187Stutzke,  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 

0.795 

100 

10  grams  per  liter 

0.764 

95 

OAN 

0.72! 

84 

5  grams  per  liter 

0.717 

83 

0.1N 

0.715 

82 

0.02N 

0.70o 

78 

OAN 

0.693 

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 

0.644 

55 

OAN 

0.628 

46 

O.6O3 

30 

10  grams  per  liter 

0.597 

26 

0.01JV 

0.56, 

0 

O.OliV 

0.56o 

0 

O.OliV 

0.550 

0 

(Saturated) 

0.55a 

0 

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,"  Na20  3.3Si20, 

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  Na20  "S"  Brand  "O"  Brand  "C"  Brand 

per  Liter  Si02 :  Na20=3.89     Si02:  Na20=3.23  Si02 :  Na2O=2.0 

0.2  0.69e  ....  0.630 

0.1  0.730  0.723  0.70o 

0.05  0.7L.  0.71a 

0.02  0.69„  0.690  0.690 

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  Na20,  3.3Si02,  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  Na20,  3.4Si02,  1.35  specific  gravity  (38°  Baume) 
57  per  cent  Na2CO3.10H2O 
20  per  cent  Na2C03 

Aluminum  Oxide.  Since  colloidal  properties  are  recognized  as  help- 
ful in  detergent  operations,  the  idea  that  the  ability  to  act  as  a  mordant 

193Wakefield,  citation  in  Silicate  P's  &  Q's,  5,  No.  6  (1925),  Philadelphia,  Pa.: 
Philadelphia  Quartz  Company. 

194Schupp,  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. 

mBeltzer,  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). 

203Cowles,  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.    Na20,2Si02  in  solution  mixes  freely 

210  G.  E.  J.,  Seifenfabr.,  39,  253-256  (1919)  ;  C.  A.,  13,  2770. 
mGuillin,  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  Na20,  3.3Si02  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  Na20,2Si02.     The  relatively  stable 


Fig.    163. — Drawing    Hot    Silicated    Soap    from    Crutchers    into    Frames.    Same 

apparatus  as  foregoing  picture. 

behavior  of  Na20,2Si02  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 

a5Gathmann,   H.,    "American    Soaps,"    Chicago:    Gathmann,    1893,   p.   72,    187, 
214,  236. 

aeLeimdorfer,  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; 
Na20,2Si02  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. 

23aStiepel,  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. 

MSchuck,  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,  3.34Si02,  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       "       )  Na20,3.34Si02,  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). 

253Berge,  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.  H20  +  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.   H20    (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.  H20  -    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.  H20  (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  Na20,2Si02  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  Na20  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,  Na20,  3.3Si02,  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<HEdeler,  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). 

2mBur.  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  Na20,  3.3Si02  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. 

270Steffan,  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  Na20 
and  Si02  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  Na20  in 

Soap  Before 

Adding 

Silicate, 

Per  Cent 

0.0 
1.21 

2.32 
5.02 


Resulting 

Ratio 
Na20,  Si02 
(Molecular) 

1 :  3.22 
1 : 2.54 
1:2.12 
1 :  1.52 


Cc.  N  H2S04  to 

Neutralize  Alcoholic 

Filtrate  * 


0.05 
0.30 
0.50 
2.40 


0.05 
0.40 
0.50 
2.60 


Apparent  Free 

Na20  in  Silicated 

Soap, 

Per  Cent 

0.01 

0.07 

0.10 

0.52 


*  Each  analysis  was  made  in  duplicate  on  separate  samples. 


Table  113. 


Na02 
Per  Cent 

9.18 
11.37 
13.48 
17.72 
23.97 


Titrations  of  Alcoholic  Filtrate  from  Sodium  Silicates  of   Varying 
Composition. 


Si02 
Per  Cent 

29.71 
28.18 
26.13 
26.50 
23.48 


Ratio 
NaO :  Si02 
(Molecular) 


3.33 
2.55 
1.99 
1.54 
1.01 


Cc.  N  H2S04 
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). 

279Isnard,  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  Na2C03. 10H2O,  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  Na20,  3.3Si02  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  NaoCO3.10H2O  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  Na20,  2.2Si02 
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. 

zChem.  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  Na20,  3.3Si02  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 

4U.  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 

Si02    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 


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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  Na20,  3.3Si02  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  Si02  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 
Na20,  3.3Si02  is  best  on  account  of  its  slow  rate  of  solution.  Na20, 
2Si02  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  Na20  and  Si02  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). 

15Texter,  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  m3  (15.6  pounds  per  1000  cubic  feet,  about  76  parts 
per  million  of  Si02)  of  a  1.4  specific  gravity  solution  of  Na20,  3.3Si02 
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 

0                   3 

O                 4 

0             4 

0                £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. 
BNeff,  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  Na20,  3.3Si02  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.  Na20,2Si02  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  Na20. 

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). 

34Thieriot,  J.  H.,  U.  S.  Consular  Reports,  563-564  (Dec.  1897). 

35Jarvis,  L.  G.,  Ontario  Agri.  College  and  Exp.  Farm  Report,  193-196  (1898) 

MLadd,  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). 

67Lamson,  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). 

62Lamson,  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). 

OTFlohr,  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). 

70Arnoux,  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). 

76Dvorachek,  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  Na20,  3.3Si02,  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 

0     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%  Si02 
Sol.  contains  1.795%  Si02 

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  Si02  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.  Si02 

Mixture  contains  0.575     "      Si02  +  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  Si02 

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  Si02 

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 

Vinal90  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,  H2S04  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. 

94Poulsen,  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). 
105Behrman,  Abraham  S.,  U.  S.  Pats.  1,515,007  (Oct.  8,  1927);  1,584,716  (May 

18,  1926)  ;  Brit.  Pat.  277,082  (Nov.  2,  1927). 

106Wheaton,  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. 

109Govers,  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  of 
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/9At- ~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  S02  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 

liaTruog,  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  is  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. 

mBradner,  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. 

126Chaney,   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). 

ia5Behr,   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    S02    /n    fas      /trirtvre 

Fig.   184.— Adsorption  of  S02  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  S02  to  S03  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  Na20, 
Al203,5Si02.  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." 

143Hilditch,  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. 

145Hilditch,  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 

0  25  50  75  100 

L/T/?fS  or  WAT£tf  PASSfP  OY£f?  400  GFrlS  or  POUC/L  (50%H30)/N  50  cm. 

BEP. 

Fig.  185.— Water  Softening  by  Doucil  of  Varying  Grain  Size. 

ing  and  regeneration.  Its  rated  capacity  is  12,500  grains  CaCOa  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(R203)x.  (Si02)y  +  2NaCl  =  Na2(R203)x.  (Si02)y  +  CaCl2 

'Killeffer,  D.  H.,  Ind.  Eng.  Chem.,  15,  915-917  (1923)  ;  C.  A.,  17,  3393. 

2Gans,  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). 

3Vogtherr,  H.,  Z.  angew.  Chem.,  33,  1,  241-243. 

4Gutensohn,  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). 

9Heldt,  /.  prakt.  Chem.,  94,  143   (1865). 

10Deville,  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. 

13Kolb,  A,  U.  S.  Pat.  1,193,794  (Aug.  8,  1916). 

"Kriegsheim,  H.,  U.  S.  Pat.  1,208,797   (Dec.  19,  1916). 

15Rudorf,  G.,  U.  S.  Pat.  1,304,206  (May  20,  1919). 

16Massatsch,  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  A12(S04)3  in  a  10°Baume  solution,  washed, 
treated  with  a  10°Baume  silicate  solution  (presumably  Na20,  3.3Si02), 
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  Na20,  3.3Si02  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). 

,23U.  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). 

24Behrman,  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  Na20, 
3.3Si02  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, 

32Societe  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). 

3THoworth,  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  2Na20,7Si02,  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). 
43Schwerin,  B.,  U.  S.  Pat.  1,266,330  (May  14,  1918). 

"Dixon,  U.  S.  Pat.  52,545  (1866). 
45Cobley,  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.  Na20,  3.3Si02  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 

4aDedrick,  C.  H.,  U.  S.  Pat.  1,682,834  (Sept.  4,  1928). 

47Carothers,  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). 

51Kiihn,  A.,  Fortschritte  Med.,  41,  75-7  (1923)  ;  C.  A.,  17,  3369. 

52Scheffler,  L.,  A.  Sartory,  and  P.  Pellisaier,  Compt.  rend.,  171,  416-8  (1920)  ; 
C   A     14   3725. 
'  MMessner,  j,  Pharm.  Monatshejte,  3,  82-3  (1922)  ;  C.  A.,  16,  3972. 

04Luithlen,  F.,  Wiener  klin.  Wochschr.,  35,  349  (1922)  ;  C.  A.,  17,  434. 

55Kuhn,  A.,  Medis.  Klin.,  18,  9-11  (1922)  ;  C.  A.,  16,  2934. 

°°Kuhn,  A.,  Z.  Tuberk.,  32,  320  (1922)  ;  C.  A.,  16,  2934. 

57Kahle,   Hanns,  Beitr.  klin.   Tuberk.,  47,  296-324    (1921);    C.   A.,   16,    1616. 

^Schubauer,  R,  Biochem.  Z.,  108,  304-8  (1920)  ;  C.  A.,  15,  269. 

MGye,  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). 
65Rudsit,  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 
Na20,  3.3Si02,  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. 

70Eichhorst,  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,  DM  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 


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Date  Due 


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29Sep  4  4 


JUL  2  8 


1945 


Oct  22  '49  ^qv7,A9 


Oct  14  5 


1     15  Oct 


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APR  13  1981  FEB  jy 


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3  1262  04014  7497 


CHEMISTRY 

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