IMIDOSULPHONATES. 73 



enonsrh to form the disodiniii salt, its iidditioii causes heating'. From 

 tlie neutralised solution sulphate and disodium imidosiilphonate can 

 be crystallised out. Carbon dioxide also decomposes the trisodium 

 salt in water, sodium acid-carbonate being precipitated, if the water 

 present is not too great. Concentrated ammonia-water precipitates 

 the trisodium salt free from ammonia, and with its usual water of 

 crystallisation. Ammonium salts suffer double decomposition with the 

 trisodium salt, ammonia then becoming free by the decomposing action 

 of water upon some of the triammonium salt. When concentrated solu- 

 tions of the trisodium salt and of a potassium salt, such as the nitrate, 

 are mixed, nothing is observable, but on neutralising with an acid, 

 there is precipitated the dipotassium salt in crystals. 



Trisodium imidosulphonate, unlike the disodium salt, precipitates 

 many metallic snlts, giving in some cases, however, onlv hydroxides. 

 Precijntates of imidosulphonates are ol)taiiied with silver nitrate, the 

 mercury nitrates, lead salts, and barium salts, while with calcium 

 chloride crystals may slowly form which are of characteristic appear- 

 ance. S])ecially noteworthy is tlie fact that silver nitrate added in 

 different j)roportions yields three precipitates distinct both in appear- 

 ance and in composition. The compounds formed by these reagents 

 are described later in this paper. Mercuric chloride has apparently no 

 action upon trisodium imidosulphonate, for nothing separates, and the 

 reaction with lituius remains alkaline. Mercuric oxide dissolves to a 

 limited extent in solutions <^f tlie trisodium imidosulphonate, the more 

 in cjuantity (in proportion to the trisodium salt) the weaker these 

 solutions are, and makes them somewhat caustic-alkaline (see, in this 

 connection, the reaction of mercuric sodium imidosulphonate with 

 alkali hydroxide, p. 104). 



It was not practicable to get the crystals of trisodium imidosul- 

 phonate exactly dry for analysis, because the thin plates adhering 



