66 
ACTION  OF  WATER  UPON  GLASS. 
cent,  of  lime,  we  may  conclude  that  the  water  had  decomposed 
about  10  per  cent,  of  the  glass. 
2.  Another  white  glass,  also  of  the  finest  quality,  composed 
of— 
Silica  77-3 
Soda  16-3 
Lime   64 
Alumina  and  oxide  of  iron  .  .  traces. 
5-180  grins,  of  glass  were  operated  upon  in  precisely  the  same 
way  as  the  last.  The  residue  of  the  aqueous  solution  was  0-945 
grm.  ;  the  weight  of  the  sulphate  of  lime,  0-250,  representing 
0-103  of  lime,  or  two  per  cent,  of  the  weight  of  glass.  The 
glass  containg  6-4  per  cent,  of  lime,  32  per  cent,  of  the  glass 
must  have  been  destroyed.  The  residue  of  the  aqueous  solution 
contained  0-281  grm.  of  soda,  or  5«6  per  cent,  of  the  weight  of 
the  glass  :  the  remainder  was  silica.  The  glass  containing  16-3 
per  cent,  of  soda,  34  per  cent,  of  glass  had  been  attacked. 
The  composition  of  the  silicate  of  soda  dissolved  in  the  water 
was  3(Si03)2NaO ;  at  302*  F.  it  retained  2  equivs.  of  water. 
3.  The  two  kinds  of  glass  just  mentioned  were  agitated  for  a 
few  minutes  with  cold  water,  a  few  drops  of  weak  muriatic  acid 
were  added  to  the  mixture,  which  was  filtered  immediately.  The 
loss  of  weight  of  the  glass  and  the  amount  of  lime  collected 
showed  that  the  glass  had  lost  2  to  3  per  cent,  by  this  simple 
contact  with  cold  water. 
By  boiling  for  a  few  minutes,  the  same  glass  lost  nearly  double, 
or  between  5  and  6  per  cent. 
4.  All  sorts  of  commercial  glass,  when  finely  powdered  and 
exposed  to  the  air,  are  slowly  decomposed,  absorb  carbonic  acid 
by  degrees,  and  after  some  time  effervesce  briskly  with  acids. 
The  same  effervescence  takes  place  with  acids  in  a  mixture  of 
powdered  glass  and  water  which  has  been  left  in  the  air  for  a 
few  days.  The  acid  water  contains  a  large  quantity  of  soda  and 
lime. 
Sulphuric  acid  also  is  almost  always  found  ;  as  most  glasses 
contain  sulphate  of  soda,  varying  in  weight  from  one  or  two- 
thousandths  to  two-hundredths. 
5.  Finely-powdered  glass,  boiled  with  water  into  which  a  cur- 
