514  Freezing  of  Colloidal  Solutions.  \Am-oct!!;i89o.arm" 
phate  such  a  quantity  of  free  phosphoric  acid  as  would  be  formed 
by  the  decomposition  of  the  salt,  no  decomposition  takes  place ;  for 
example,  for  I  salt  :  I  water,  this  quantity  will  be  7-5  per  cent.,  as 
seen  from  the  result  stated  above.  If  Erlenmeyer  finds  the  solu- 
bility of  the  salt  1  :  100,  it  follows  that  the  presence  of  0  4  per  cent, 
of  free  phosphoric  acid  in  his  salt  had  prevented  the  decomposition 
and  increased  the  solubility. 
The  author's  conclusions  as  regards  the  solubility  of  superphos- 
phates and  disuperphosphates  in  water,  are  of  technical  interest. 
FREEZING  OF  COLLQIDAL  SOLUTIONS.1 
By  N.  Lubavin. 
The  investigations  of  Pfaff,  Geiger  and  Payen^on  the  freezing  of 
colloidal  solutions  have  been  overlooked  by  subsequent  investiga- 
tors of  colloidal  solutions,  especially  Graham  and  Van  Bemmelen. 
The  author  finds  that  from  some  of  such  solutions  the  substance 
dissolved  is  completely  or  partly  separated  after  freezing,  whereas 
in  the  case  of  others  the  precipitate  again  passes  into  solution  A 
solution  of  colloidal  silicic  acid,  obtained  by  mixing  soluble  glass 
with  hydrochloric  acid  in  aqueous  solution,  was  divided  into  two 
parts,  one  of  which  was  exposed  to  a  temperature  of  7-100  for 
two  days  after  which  it  was  exposed  to  the  temperature  of  the  lab- 
oratory (-J--  1 50)  for  two  days.  From  the  frozen  solution  as  much 
as  96-96  per  cent,  of  the  silica  was  separated  by  filtration,  whereas 
the  original  /unfrozen  solution  yielded  only  o  72  per  cent,  of  insol- 
uble silicic  acid.  This  is  not  in  contradiction  with  Graham's  state- 
ment, that  the  stability  of  a  colloidal  solution  of  silicic  acid 
increases  with  decreasing  temperature,  for,  according  to  Graham, 
more  concentrated  solutions  are  more  easily  coagulated.  Indeed, 
on  freezing,  gradual  concentration  takes  place,  owing  to  the  sepa- 
ration of  1  ice,  so  that  the  coagulation  is  accelerated.  A  colloidal 
solution  of  antimony  trisulphide  was  prepared  by  Schulze's  method, 
namely,  saturating  a  solution  of  one  part  of  tartar-emetic  in  200 
parts  of  water  with  hydrogen  sulphide.  Nothing  separated  from 
the  original  solution,  even  when  it  was  allowed  to '  remain  for 
months  at  the  ordinary  temperature;  whereas  from  the,  same  solu- 
tion, after  exposure  to  a  temperature  of  —  6°  for  .29„hpurs  and 
1  /.  Russ.  Chem.  Soc,  21,  397-406.  Reprinted  From  Jour.  Oi^m^o^.y  July, 
1890,  p.  685.         '  i-  ' 
