AMMONIUM SULPHITES, TIIIOSULPHATE AND TRITHIONATE. 207 



considerable residue, more than one-tliird of the weight of the 

 salt taken, consisting of sulphate, trithionate, sulphur, and ap- 

 parently some tetrathionate. There was no sulphite or thiosul- 

 phate. The tetrathionate, the sulphur, and the sulphur dioxide 

 were very probably derived from decomposition of trithionate 

 by moisture. From a consideration of the results it seems almost 

 necessary to assume that perfectly dry pyrosulphite sublimes un- 

 changed (witli no doubt intermediate dissociation), and that the 

 presence of a little moisture causes it to decompose partly into 

 sulphate and trithionate. 



Anhydrous ammonium sulphite volatilises at about 150°, 

 yielding a sublimate of the same salt, or rather, a pseudosub- 

 limate, for the salt surely dissociates when heated. 



Hydrated ammonium sulphite. — According to Muspratt, this 

 salt all volatilises when heated, no sulphate being produced, and 

 yields water, then much ammonia, and finally a sublimate which, 

 judging, from its properties, is ammonium pyrosulphite. We 

 observed the following effects of gradually heating it in a very 

 slow current of dried nitrogen. At about 90°, the salt moistened 

 and escape of ammonia became quite evident, and at a little 

 above 100° distillation of water also took place ; both water and 

 ammonia continued to escape in noticeable quantities for 2Y2 hours 

 longer, when the temperature for some time had been 120°; up 

 to this, a very little sublimate only had formed and matters were 

 now almost at a standstill. The quantity of the salt heated was 

 about 4 grm., and this had now lost one-fifth of its weight, the 

 residue having the composition expressed by (]SrH3)io(SO..)G(OH2)7, 

 equivalent to a mixture or combination of the three salts, hydrat- 

 ed sulphite (39.49^), anhydrous sulphite (34.1^), and pyrosul- 

 phite (26.59^), dividing equally among themselves the sulphur 



