AMMONIUM SULPHITES, THIOSULPHATE AND TRITHIONATE. 209 



the other third of the original salt becomes converted into the 

 nearly anhydrous normal sulphite, between 120° and 150°, sul- 

 phur dioxide and water escaping. The presence of water is es- 

 sential to the occurrence of both changes ; dry ammonium 

 pyrosulphite partly sublimes as such at 150° and partly changes 

 into sulphate and trithionate, as already described. Heating in 

 the open tube, and more rapidly, Muspratt's results will be got, 

 for then weter is more quickly expelled, and some pyrosulphite 

 can deposit as a sublimate. 



