IMIDOSULPHONATES. 69 



n.ppears to be much more fusible thun the potassium salt, bat then in 

 the state examiued the latter was practically pare while the former 

 was mixed with the products of its hydrolysis, which must have 

 affected its fusibility. 



Disodium imidosulphonate in aqueous solution gives, like the 

 much less soluble dipotassium salt (Berglund), no precipitates with 

 many of the usual metal salts. But it gives when in moderately con- 

 centrated solution a precipitate of dipotasssium imidosulphonate with 

 solutions of potassium salts ; of trisodium imidosulphonate with 

 sodium hydroxide; and of a barium sodium imidosulphonate with 

 barium hydroxide. Concentrated ammonia-solution also gives abun- 

 dant precipitation. The precipitate, when the disodium imidosulphonate 

 is unmixed with other salts, is a sodium ammonium salt (p. 75). 

 But when a httle sodium nitrate, chloride, or other sodium salt is 

 added before the ammonia, the latter, in concentrated solution, pre- 

 cipitates pure trisodium imidosulphonate. The two forms of pre- 

 cipitation are expressed by the respective equations : — 



5HN(S03Na)2 + 5NH, - 2NagAmN2(S03)4 + AmNCSOgAm)^ : 

 HN(S03Na)2 4- NHg -f-NaNO^ - NaNCSOsNa), + AmNOg. 



The precipitation by ammonia is in both cases greatly increased by 

 excess of the reagent, and with the disodium imidosulphonate added 

 in powder to strong ammonia-water, much of the triammonium salt 

 also precipitates. 



Hydroxy-lead acetates, it was known, give copious precipitates. 

 Normal lead acetate also gives scanty precipitation of a lead imidosul- 

 phonate, even when the acetate is truly normal as described, and the di- 

 sodium salt in solution faintly acid to litmus (pp. 86, 88). Lead nitrate 

 occasions no true precipitation, but, unlike the acetate, it rapidly 

 effects hydrolysis and consequent precipitation of a little lead sulphate. 



