Am.  Jour.  Pharm. 
Feb.,  1884. 
Solubility  of  Calcic  Hydrate. 
Ill 
730  (Wittstein) ;  500  (Ure),  and  450  (Davy).  At  100°C.  1  part  is 
dissolved  in  1,560  water,  according  to  Miller;  1,500  (Bineau) ;  1,350 
(Wittstein);  1,305  (Hager);  1,300  (United  States  Pharmacopoeia),  and 
1,270  (Dalton). 
According  to  the  German  Pharmacopoeia  aqua  calcarim  should  con- 
tain calcic  hydrate  equal  to  from  0*43  to  0*49  gr.  CaO  per  fluidounce ; 
the  United  States  Pharmacopoeia  gives  the  amount  in  solution  as  about 
\  grain,  while  the  British  Pharmacopoeia  requires  liq.  calcis  to  contain 
•56  gr.,  i.  e.,  to  be  as  nearly  as  possible  a  saturated  solution. 
According  to  Storer,  Dalton  disputes  the  correctness  of  the  state- 
ments of  observers  who  say  that  water  takes  up  -g-J-Q  or  -g-J-g-  its  weight 
of  lime,  the  fact  being,  he  says,  that  few  have  tried  the  experiment 
with  due  care. 
In  estimating  the  strength  of  solutions  of  calcic  hydrate  it  is  of  the 
utmost  importance  that  we  should  ascertain  correctly  the  temperature 
at  which  the  solutions  pass  through  the  filter.  This  is  a  matter  of 
considerable  difficulty.  I  have  found  that  different  methods  give  quite 
different  results,  and  there  is  not  the  slightest  doubt,  in  my  opinion, 
that  had  the  authorities  quoted  carefully  followed  an  uniform  system 
their  results  would  have  been  much  more  in  accord  than  they  are.  It 
is  sufficiently  obvious  that  out  of  the  eight  or  nine  different  solubili- 
ties quoted  not  more  than  one  can  be  absolutely  correct,  and  while  the 
question  is  not  one  of  crucial  importance  it  would  be  extremely  inter- 
esting if  by  some  means  or  another  the  real  figure  could  be  arrived  at. 
In  the  experiments  which  form  the  basis  of  this  communication  I 
adopted  the  following  method,  it  having  been  found  to  give  the  most 
constant  results. 
For  the  lowest  temperature  I  placed  a  glass  beaker  containing  calcic 
hydrate  and  distilled  water  in  a  freezing  mixture  till  the  thermometer 
fell  to  0°C,  and  ice  began  to  form.  The  liquid  was  then  filtered,  zero 
being  maintained  by  placing  the  funnel  also  in  a  freezing  mixture. 
The  temperatures  from  5°C.  to  15°C.  present  no  special  difficulty,  as 
they  are  easily  obtained  by  adding  hot  or  cold  water  to  the  beaker  till 
the  required  point  is  reached  and  filtering  in  the  usual  way.  Com- 
paratively little  variation  takes  place  when  the  surrounding  atmosphere 
indicates  from  10°C.  to  12°C.  From  15°C.  to  80°C.  I  made  use  of 
the  water-bath.  A  flask  containing  lime  and  water  was  placed  in  the 
bath,  and  as  soon  as  the  contents  reached  the  required  temperature,  the 
mixture  was  filtered  through  a  funnel  placed  in  the  ordinary  funnel 
