4 ART. 8. DIVERS AND OGAWA : PREPARATION OF 



further production of sulphate by the decomposing salts present 

 in it. This does not matter, however, and to the turbid filtrate 

 silver nitrate is added, just so long as it continues to give a 

 precipitate. The barium hydroxide will have liberated much 

 ammonia, but a good deal of this will have evaporated during 

 the time taken up in filtration, especially if the precipitation has 

 been carried out in an open vessel. What remains of it inter- 

 feres only temporarily with the silver precipitation and does not 

 usually need external neutralisation. For, so much acid is formed 

 as the result of a very rapid decomposition of the precipitated 

 silver salts (in which they change from white to black), as to be 

 more than enough to neutralise the ammonia remaining in the 

 solution, and also to dissolve up any silver sulphamide that may 

 have been thrown down at first, When the mother-liquor has 

 become thoroughly acid or, exceptionally, has been made so by 

 adding nitric acid, and still holds silver in solution, it is filtered 

 from the black precipitate and just neutralised with ammonia. 

 Any slight precipitate then formed is also filtered off and rejected ; 

 it contains no trisulphimide. The filtrate holds little else than 

 sulphamide and ammonium amidosulphate, and if evaporated over 

 sulphuric acid, would yield both these substances in characteristic 

 crystals. But to isolate the sulphamide, it is to be precipitated 

 from this solution by silver nitrate and ammonia, that is, by 

 Traube's method. The silver sulphamide, thus obtained, is almost 

 pure, there being no such acid matter present as is met with 

 when the sulphamide has been prepared from sulphuryl chloride. 

 In that case, a viscid silver salt accompanies the silver sulphamide, 

 and, according to Hantzsch and Holl, can only be removed 

 from it by a process entailing the destruction of much of the 

 sulphamide. Even in the present case, however, the amido- 



