336 M. Arfioedson on the Decomposition of [May, 



obtained ; and an equally great, if not a greater deviation would 

 result if we suppose that the oxide and sulphuret are combined 

 in other atomic proportions. It was observed that a portion of 

 the zinc was reduced to the metallic state ; but the quantity 

 was so small that the amount of the change which it would 

 produce cannot come into calculation. Indeed if it were to 

 produce any change upon the result, the obvious consequence 

 would be to render the loss of weight a little too high ; whereas 

 in all the experiments that loss was too small. From the expe- 

 riment it is obvious, that the loss of weight is various in different 

 experiments, and that it becomes less when the quantity of salt 

 operated on is greater. 



These circumstances taken together might naturally lead to 

 the opinion that the sulphate of zinc was more or less completely 

 decomposed in the different processes. But as has been already 

 stated, a portion of the reduced mass was always dissolved in 

 muriatic acid, and tested with muriate of barytes, by which the 

 liquid was sometimes rendered slightly opalescent, but not the 

 least precipitate ever fell. There might, however, have been 

 some circumstance which occasioned the result to come out in- 

 accurate, but in what it consisted I cannot say. 



Meanwhile we may conclude from the preceding experiments, 

 that when sulphate of zinc is treated with hydrogen geus, the salt 

 is decomposed in such a way that somewhat more than the half 

 of it becomes sulphuret, and the remainder oxide of zinc ; 

 though at the same time the proportions of each of these bodies 

 do not correspond with any atomic numbers ; and experiments 

 which do not give corresponding results, are not worth the pains 

 of determining the relative proportions of the constituents 

 obtained. 



Examination of Native Sulphuret of Zinc, or Zinc-Blende. 



I employed for this analysis a portion of a large piece of crys- 

 tallized yellow transparent blende, as the purest variety of that 

 mineral met with in nature. 



a.- 1*758 gr. of pulverized blende were digested with an aqua 

 regia, which had been previously gently wanned, so that it began 

 to give out chlorine gas.* When the residual mass, coagulated 

 into a lump, seemed to be no longer acted on by the acid, it was 

 separated and washed. Dried on the stove in a platinum dish, 

 it weighed 0-393 gr. Being heated to redness in a crucible 

 much sulphur was driven off, but a portion remained which was 

 sulphuret of zinc. It was dissolved in aqua regia, without any 

 residue, and the diluted boiling-hot solution was precipitated by 



* I have found that this is the best solvent which can be employed ; for when we 

 dissolve blende in nitric acid or in an aqua regia in whicli no chlorine exists, as when a 

 dilute nitric acid is employed, there is always disengaged at first a little sulphuretted 

 hydrogen gas which may be made evident by holding a paper dipped in solution of lead 

 over the mouth of the vessel.. 



