^'"yuiy^i^ys'!'"'-}     Solubility,  etc.,  of  Acid  Carbonates,  etc.  311 
should  be  dried  over  sulphuric  acid  in  an  atmosphere  of  carbonic  acid 
gas  ;  otherwise  they  become  covered  with  a  layer  of  neutral  carbonate, 
which  is  recognizable  in  the  analysis  of  the  salt  by  the  deficiency  of 
carbonic  acid. 
As  in  the  determinations  hitherto  made  of  the  solubilities  of  the 
potassium  and  sodium  acid  carbonates,  the  loss  of  carbonic  acid  fromi 
the  crystals  and  from  the  solutions  has  not  been  taken  into  account^, 
the  author  has  undertaken  these  determinations  afresh  with  samples  of 
the  pure  salts,  of  which  he  describes  the  preparation,  and  operating  in 
vessels  securely  corked,  in  which  the  decomposition  of  the  salt  in  solu- 
tion is  arrested  by  the  pressure  of  the  carbonic  acid  gas.  He  has  also- 
found  the  percentage  of  carbonic  acid  set  free  at  various  temperatures., 
and  has  determined  the  solubility  of  ammonium  acid  carbonate,  which 
decomposes  with  much  greater  readiness  than  the  other  two,  the  press- 
ure of  the  carbonic  acid  extricated  from  a  saturated  solution  at  30^ 
being  so  great  that  determinations  of  the  solubilities  at  higher  tempera- 
tures could  not  be  made,  while  in  the  case  of  the  other  two  salts  the 
determmations  were  carried  to  60°.  The  tensions  of  the  gas  liberated 
from  saturated  solutions  of  the  three  salts  at  15°,  roughly  measured  in 
millimeters  of  mercury  above  the  atmospheric  pressure,  were,  for  the 
sodium,  potassium  and  ammonium  acid  carbonates,  120,  461  and  720^ 
respectively.  The  ammonium  salt  was  prepared  by  the  author,  by 
placing  the  crystals,  after  pressure  in  bibulous  paper,  in  an  exsiccator 
filled  with  air,  over  sulphuric  acid  and  caustic  soda.  After  some  days- 
all  the  water,  free  ammonia  and  carbonic  acid  were  completely  absorbed,, 
and  the  pure  salt  remained  behind. 
The  following  table,  calculated  from  the  author's  determinations  of 
the  solubility  of  the  three  acid  salts  in  water,  exhibits  the  solubility  of 
the  potassium  and  sodium  salts  for  every  five  degrees  of  temperature 
from  0° 
to  60°, 
and  of  the 
ammonium  salt  from  0° 
to  30°  C 
Solubility 
in  100  Parts  of  Water. 
Temp. 
KHCO3. 
NaHC03. 
(NH4)HC03. 
1  Temp. 
KHCO3. 
NaHCOs 
0° 
22-45 
6-9 
11-9 
i  35" 
42-05 
11-9 
5 
25-0 
7'45 
13-7 
40 
45-25 
12-7 
10 
27-7 
8-15 
15-85  1 
45 
486 
13*55 
15 
30-4 
8-85 
i8-3 
50 
52'i5 
14-45 
20 
33-2 
9-6 
2 1  'O 
55 
55  9 
1 5 '4 
^5 
36-1 
10  35 
23'9 
60 
6o-o 
1 6'4 
30 
39-0 
1 1  •  I 
27-0  1 
— Journ.  of  Chem.  Soc.  \_Lond.~\,  May,  1875,  from  f.  pr.  Chem.  [2], 
417-443- 
