AMIDOSULPHONIC ACID. 



243 



insoluble in excess of alkali. But when the alkali, iu excess, is rapidly 

 mixed with it, the salt all dissolves permanently. Mercuric chloride, 

 in presence of enough amidosulphonic acid, is not, therefore, precipitated 

 by potassium hydroxide in excess ; addition of more mercuric chloride, 

 or of a little acid, causes the white oxymercuric salt to precipitate, but 

 not mercuric oxide. 



The precipitation of the oxymercuric salt from an acid solution of 

 mercuric nitrate indicates its nature as a basic salt, while in degree of 

 basicity it agrees with the oxymercuric salts of sulphuric, sulphurous, 

 and imidosulphonic acids, that is, it possesses the bivalent group, 

 -OHgOHgO-. But the stability of the salt when heated (see later 

 on), its insolubility in dilute nitric acid, and its solubility in an alkali 

 suggest the possibility of its having another constitution, or of its 

 being subject to tautdmery. At least, in its alkaline solution, it must 

 almost certainly exist as a potassium salt with the following formula, 

 Hg" 3 N 2 (S0 3 Iv) 2 (OH) : ,, which exhibits it as a sulphonated mercurain- 

 monium hydroxide. Like other rncrcurainmonium salts, it does not 

 yield up its amine (amidosulphonic acid), when treated with alkalis. 

 It also behaves like a mercurammonium compound, in being com- 

 pletely resolved, in accordance with Pesci's reaction, into amidosul- 

 phonic acid (its amine) and mercuric bromide by a saturated solution 

 of ammonium bromide, ammonia being liberated, thus : — 



Hg s N 2 (S0 3 H) 2 (OH) 2 +12NH 4 Br=3iH g Br 2 (NH 4 Br) 2 ] 



+ 2NH 2 S0 3 NH 4 + 4NH 3 + 20H 2 . 

 The action of a dilute solution of ammonium chloride is to convert it 

 only into 'white precipitate' and a solution of mercury ammonium 

 chloride and ammonium amidosulphonate, without any ammonia 

 being liberated. 



The oxymercuric salt bears heat well ; its decomposition at a high 

 temperature will be described in the next section. 



