340 DR T. THOMSON on the Composition of Blende. 



various temperatures, but all these attempts were quite unsuc- 

 cessful. I always got a simple sulphuret of zinc, and nothing 

 else, in what way soever the process was varied. When anhy- 

 drous sulphate of zinc is decomposed by hydrogen gas, in a glass 

 tube, a portion of the sulphur is driven off, and there remains a 

 mixture of oxide of zinc and sulphuret of zinc, as was first ascer- 

 tained by ARFWEDSON *. If we substitute the acid sulphate of 

 zinc, which I have described elsewhere f, the result is the same. 



My attempts to form a super-sulphuret of zinc, by means of 

 sulphuretted hydrogen, were equally unsuccessful. But it may 

 be worth while to state one or two of the experiments somewhat 

 in detail, on account of the facts which they furnish. 



2 1 grains of pure anhydrous oxide of zinc were dissolved in 

 acetic acid, and a current of sulphuretted hydrogen gas was 

 passed through the solution (which was nearly neutral), as long 

 as any precipitate fell. The precipitate was white and flocky. 

 Being collected on a filter, washed (a tedious process), and dried, 

 it weighed 26 09 grains. The liquid from which this matter 

 had fallen, being evaporated to dryness, left 3.15 grains of a mat- 

 ter quite similar to the precipitate. Thus the whole substance 

 obtained, when a solution of 21 grains of oxide of zinc is treated 

 with sulphuretted hydrogen, amounted to 29.24 grains. 



This matter, when dry, assumed a dark green colour. It 

 was tasteless and insoluble in water, but dissolved in acid, with 

 the evolution of much sulphuretted hydrogen gas. When 

 heated to redness it emitted a white smoke, smelling strongly of 

 sulphur, and assumed a yellow colour ; but, on cooling, it 

 changed to white. The weight was now reduced to 23-86 

 grains. It dissolved in muriatic acid without effervescence, 



* KONGL. Vetens. Acad. Handl. 1822, p. 346. 

 f- First Principles of Chemistry, i. 55. 



