68 



DIVERS AND HA<-iA. 



tion with any crystalline precipitate (sulphate) is kept for some hours 

 at or about 0° and the mother-liquor decanted, while still at that 

 temperature, from the sodium sulphate. Evaporation, as already 

 described, then yields the disodium salt in good crystals, pure or 

 almost so. 



Disodium imidosulphonate crystallises readily in large rhombic 

 prisms. It is very soluble in water, slightly acid in reaction, and 

 devoid of sulphurous taste. Its crystals, which contain water, do not 

 effloresce, even in dry seasons, so that crystals of sodium sulphate 

 among them may be easily recognised. In air kept dry by sulphuric 

 acid, they slowly become opaque, but retain their shape, along with 

 much of their lustre and hardness ; while the rate of loss, even when 

 they have been crushed, is so slow as to make a water estimation in 

 this way almost impracticable. They can generally be kept for many 

 weeks in bottles, and apparently for any time in a sufficiently dry 

 atmosphere, but are liable to undergo hydrolysis into an acid mixture 

 of sulphate and amidosulphonate. The solution of the salt is also 

 unstable, but it may be heated for a short time to a moderate degree 

 and yet escape change. The crystals can hardly be heated to 100" 

 without some decomposition. 



The decomposition of disodium imidosulphonate that almost 

 unavoidably attends the process of removing the water of crystallisa- 

 tion, also complicates observation of the effects of a high temperature 

 upon it. For, having been to some extent converted by this water 

 into sulphate and amidosulphonate, it gives at first when heated only 

 ammonia, which comes from the reconversion of the amidosulphonnte 

 into imidosulphonate. But at a higher temperature, this is followed by 

 products the same as in the case of the dipotassium salt, namely, 

 nitrogen with more than double its volume of sulplnir dioxide, small 

 brown and white sublimates, and sodium sulphate. The sodium salt 



