IMTDOSULPHOXATES. 



56 



air, fîivoni's the chang-e here described, and brings it still nearer to that 

 caused l^y heat in ammonium sulphate. 



Jacquelain found it fusible without decomposition and capable of 

 being kept in fusion without change in a current of dry ammonia, 

 and that, a little above its melting point, it decomposes into ammonia, 

 ammonium sulphite which sublimes, and ammonium acid-sulphate as 

 a residue. 



We have found matters otherwise. Diammonium imidosul- 

 phonate, heated in a vacuum, suffers no change (except that it yields 

 a very minute liquid sublimate at 190°) until very near to 357°, when 

 it melts and also effervesces or boils. Most of tlie vapours condense 

 as unchanged imidosulphonate just above the heated part of the tube, 

 but ammonia of very low tension is given off. At last, inconsiderable 

 sublimates, white and yellow, appear some distance up the tube, con- 

 sisting of compounds of ammonia with sul})hur dioxide, and then 

 with the formation of these, minute quantities of nitrogen escape. 

 Stopping the operation in an hour or two, when the evolution of gas 

 is hardly noticeable, the residue is found to be unchanged imidosul- 

 phonate, mixed with a little acid-sulphate. When the salt is subjected 

 to a stronger heat, so as to be kept in violent ebullition, most of the 

 unchanged salt condenses and flows back, and but little of it is got as 

 a sublimate. On the other hand, the sulphite-Jimmonia sublimates 

 are more considerable, though still not abundant, and nitrogen is now 

 given off more freely, l)ut also, as well as free ammonia, still in small 

 quantities, even though the heating be maintained for a long time. In 

 one experiment, after about an hour's violent ebullition, the residue was 

 found, by dissolving it in sodium-liydroxide volumetric solution in a 

 closed vessel and titrating with acid, to contain about one-fifth of its 

 weight of ammonium pyrosulphate. From what precedes it is evident 

 that diammonium imidosulphonate is a comparatively stable body. 



