202 E. DIVERS AND M. OGAWA : PEODUCTS OF HEATING 



ammonia, can be quite successfully made to deposit the salt by 

 cold evaporation in a potash desiccator, but to get such a solution 

 the moderately strong solution of ammonia, which must be used, 

 has to be kept very cold while passing in the sulphur dioxide. 

 Dilute solutions fail to yield the salt on evaporation because too 

 much of it suffers decomposition. Much better than evaporating 

 is to take advantage of the lessened solubility of the salt in 

 presence of much ammonia. Ammonia solution, sp. gr. 0.895, 

 containing therefore about 28 grm. ammonia in 100 c.c, is to be 

 treated in a flask with sulphur dioxide, while it is kept in mo- 

 tion in a mixture of ice and salt, and with the tube conveying 

 the sulphur dioxide not dipping into the solution. The formation 

 of a very little orange-coloured matter in the neck of the flask 

 cannot be avoided, but this can be easily removed afterwards. 

 When the solution has become thick with crystals, no more 

 sulphur dioxide is to be added, although very much ammonia 

 still remains. Even at the common temperature the crystals do 

 not sensibly dissolve in presence of this ammonia. The salt, 

 drained on a tile under close cover, can be dried either by 

 filter paper or by only short exposure in the desiccator over 

 potassium hydroxide or carbonate, salted just before with am- 

 monium chloride. It is equivalent in quantity to about one- 

 fourth of the ammonia taken. By long exposure in a dried 

 atmosphere the salt becomes anhydrous without loss of ammonia. 

 Exposed to the air, it is apparently deliquescent but in reality 

 it evolves ammonia and thus becomes the very deliquescent 

 pyrosulphite. 



Anhydrous aminonium sulphite is readily obtained from the 

 hydrated salt by long enough exposure in the desiccator ; it is 

 very hygroscopic. 



