518 
Solubility  of  Glass  in  Water. 
Am.  Jour.  Pharm. 
Oct.,  1889. 
SOLUBILITY  OF  GLASS  EST  WATER.1 
By  F.  Mylius  and  F.  Foeestee. 
The  authors  have  very  carefully  examined  the  solubility  in  hot 
and  cold  water  of  a  large  variety  of  glasses  of  very  varying  compo- 
sition. The  glass  experimented  on  was  roughly  powdered  and  then 
sifted  by  means  of  two  sieves  of  72  and  121  meshes  respectively  to  the 
square  centimeter.  The  portions  passing  through  the  coarser  sieve,  but 
retained  by  the  finer,  were  tolerably  equal  in  size  of  grain,  and  it  was 
safe  to  assume  that  in  equal  volumes  of  the  different  glasses  thus  pre- 
pared the  total  surface  was  approximately  equal.  The  minimum 
surfaces  for  the  quantities  taken  (18  to  20  grann)  was  763  square 
centimeters. 
The  results  show  that  glass  as  such  is  not  soluble,  the  solution  always 
being  accompanied  by  decomposition,  and  the  ratio  of  the  various  con- 
stituents in  solution  is  quite  different  to  that  in  the  original  glass. 
The  action  is  essentially  a  chemical  one.  For  instance,  in  an  experi- 
ment where  2*5  grams  of  so-called  soda  water-glass  was  treated  with 
water  and  the  solution  separated  into  fractions,  the  result  was: 
Original  glass,  Na20  :  Si02  =  34-07  :  65*93  :  Fraction  I,  88*13  :  11*87; 
fraction  II,  41*64  :  58*33;  fraction  III,  30*31  :  69  69;  fraction  IV, 
3*1  :  96*7.  Fraction  I  was  obtained  by  the  treatment  of  the  powdered 
glass  with  cold  water  for  five  minutes;  II,  by  washing  with  hot 
water;  III,  by  15  minutes'  boiling;  IV  was  the  insoluble  residue 
left. 
The  principal  conclusions  deducible  from  the  experiments  are : — 
(i.)  Water-glass  is  decomposed  by  water  into  free  alkali  and  silicic 
acid,  a  certain  proportion  (varying  with  the  time  of  action,  concen- 
tration and  temperature)  of  the  latter  becoming  hydrated  and  dis- 
solved. 
(ii.)  Potash-glasses  are  far  less  soluble  than  soda-glasses,  but  the 
difference  decreases  with  increase  of  the  proportion  of  lime  present. 
(iii.)  Soda  and  potash  are  united  in  glass  both  to  the  silica  and  the 
lime.  The  resistance  of  glass  towards  the  action  of  water  is  dependent 
on  the  presence  of  double  silicates  of  soda  or  potash  and  lime. 
(iv.)  Of  all  sorts  of  glass,  the  plumbiferous  flint-glasses  are  least 
soluble  in  boiling  water. 
(v.)  The  relative  resistance  of  glasses  is  different  towards  hot  and 
cold  water. 
1Berichte,  xxii.  1092-1112;  reprinted  from  Jour.  Chem.  Soc,  Sept.,  1889,  p.  828. 
