588 PHILOSOPHICAL TRANSACTIONS. [aNNO I77C). 



the silver with much difficulty, and left a residuum. The solution being poured 

 ofF, and the residuum washed and exposed in a glass matrass to a red heat, there 

 was no sublimate of sulphur, nor any thing else obtained. The residuum, before 

 it was exposed to heat, did not appear to contain any sulphur; being of a blackish 

 colour after exposure to heat, it had a number of yellow particles mixed, which 

 easily dissolved in aqua regia. Tin being applied to the solution, made no pre- 

 cipitation, which it would have done if those particles had been gold; hence 

 they supposed they were iron. 



The silver was precipitated from the acid by co[)per: washed and dried it 

 weighed 4 grs. which, on coppelling with lead, lost J^. There were particles of 

 powdered quartz apparently mixed with the yellow particles left after the solution. 



Exp. 0. Being much disappointed in not finding any sulphur in the former 

 experiment, they took 300 grs. of the same ore. They freed it as well as 

 possible from heterogeneous matter: they mixed it with 4 times its weight of 

 mild fixed vegetable alkali, put them into an earthen body, to which was aflixed 

 a glass head, and exposed them to nearly a white heat in a naked tire for li hour; 

 but no sublimation took place, only a few drops of water distilling. They then 

 put the body into a melting furnace, and rendered the whole fluid ; as soon as it 

 was melted, it was removed from the fire. The mass, on concreting, was found 

 divided into 1; a black mass at top, and a metallic mass at bottom. The metal 

 being assayed by solution in nitrous acid and precipitation witli volatile alkali, 

 showed no sign either of gold or copper; lost nothing by coppellation with lead; 

 it weighed 213 grs., which were pure silver. 



The black mass at top, or scoriae, was boiled repeatedly in water, but did not 

 all dissolve. The insoluble part was unfortunately thrown away; but to the 

 solution they added muriatic acid: on the addition of the acid, there was a 

 strong smell of hepar sulphuris, and a copious precipitate, which, on being 

 examined by a microscope, appeared to consist of pellucid crystals, without the 

 smallest appearance of sulphur. This precipitation, being exposed to heat, did 

 not smell in the least like sulphur; nor was it in the least infiammable. 

 Excepting then the smell of hepar sulphuris, there did not appear any mark 

 of sulphur in this ore, and a very small particle of inflammable matter dropping 

 in by accident would give this smell. 



The foregoing experiments occasioning some doubt of sulphur being con- 

 tamed in vitreous silver ore, they endeavoured to investigate it by other means; 

 and after several experiments, they made the following one, which seems con- 

 clusive. Half an ounce of silver was precipitated from nitrous acid by copper, 

 in small flaky crystals, as usual ; being washed and dried, it was mixed with the 

 same weight of sulphur, and put into a crucible, over which another was placed 

 so as to cover it, and the 1 crucibles were luted together, leaving a small aper- 



