Am.  .Tour.  Pharm. 
Marcli,  1890. 
Sulphites. 
hydrated  sodium  sulphite,  then  the  double  sulphite,  and  lastly 
potassium  sulphate  ;  hence  it  would  seem  that  at  first  the  potassium 
sulphite  alone  undergoes  oxidation.  Heat  of  dissolution  of  the 
double  salt —  1-19  Cal. ;  heat  of  dissolution  of  hydrated  sodium 
sulphite  in  a  solution  of  potassium  sulphite  —  11  01  Cal.;  heat  of 
formation  of  the  double  sulphite  -j-  3-76  Cal. 
When  a  solution  containing  potassium  and  ammonium  sulphites 
in  equivalent  proportions  is  concentrated,  the  first  crystals  consist 
solely  of  potassium  anhydrosulphite.  These  are  followed  by  mono- 
hydrated  ammonium  sulphite,  in  which  part  of  the  base  is  replaced 
by  potassium.  In  presence  of  a  large  excess  of  ammonia,  hexagonal 
prisms  of  the  composition  ri4(NH4)20,  o-86K20,2S02  are  obtained, 
together  with  acicular  crystals  of  the  composition  K20,io(NH4)20,- 
1  iS02-f  1  iH20.  This  salt  dissociates  at  the  ordinary  temperature, 
and  if  it  is  enclosed  in  a  sealed  tube  containing  nitrogen,  ammonium 
sulphite  condenses  in  the  upper  part  of  the  tube. 
No  sodium  ammonium  sulphite  could  be  obtained. 
The  double  sulphite,  2Na20,K30,4S02-|-9H20,  is  obtained  by 
saturating  two  molecular  proportions  of  sodium  carbonate  with 
sulphurous  anhydride,  adding  one  molecular  proportion  of  potas- 
sium carbonate  and  concentrating.  It  separates  in  rounded  crystals 
which  cannot  be  dehydrated  without  decomposition.  At  900  the 
salt  undergoes  no  change,  and  at  100-no0  it  loses  water  and 
sulphurous  anhydride.  Heat  of  dissolution,  —  30-39  Cal. ;  heat 
developed  by  the  action  of  potassium  oxide  on  two  molecular  pro- 
portions of  sodium  anhydrosulphite,  -f  16-81  Cal.;  heat  of  forma- 
tion of  the  double  salt,  4-  25-88  Cal. 
The  salt  2Na20,(NH4)20,4S02-|-9H20  always  separates  from  mix- 
tures of  sodium  and  ammonium  sulphites.  It  can  readily  be  obtained 
in  a  crystalline  form  by  passing  ammonia  gas  into  a  saturated  solu- 
tion of  sodium  hydrogen  sulphite.  Its  heat  of  dissolution  is  —  30-72 
Cal.  The  action  of  ammonia  on  sodium  anhydrosulphite  develops 
-f-  15  68  Cal.;  the  formation  of  the  solid  salt  from  2Na.,SCK  sol  -f 
(NH4)2S205  sol  -f-  9H20  sol,  therefore,  develops  +  19  62  Cal. 
An  analogous  potassium  compound. also  exists. 
The  reaction  2Na2S205-f  (NH4)20  develops  +1568  Cal.  if  the 
solution  of  the  sodium  salt  is  freshly  prepared,  but  only  I  2  94  Cal. 
if  the  solution  has  been  kept  in  an  atmosphere  of  nitrogen  for  three 
months.    The  author  distinguishes  the  two  modifications  as  a-  and 
