14 ON THE IMPURITIES OF COMMERCIAL ZINC. 
erated by this zinc through a solution of acetate of lead. But it must be remembered, 
first, that we have no evidence that Karsten’s acids were free from oxidizing agents, 
and secondly, that the reaction for sulphur on lead-paper is a more delicate test than 
any process of causing the gas generated to bubble through a liquid, even though the 
best form of apparatus be employed to secure as far as possible thorough contact of 
the gas with the fluid. Moreover, Karsten subsequently mentions that a delicate black 
precipitate is produced when the hydrogen from zinc is passed through nitrate of 
silver; this precipitate was probably sulphide of silver, and not metallic silver, as 
Karsten conjectured. 
Again, Jacquelain, in the memoir already referred to, concludes that sulphur was not 
contained in the specimen of French zinc which he examined, because a complete 
solution of the zinc-in aqua regia gives no precipitate with chloride of barium. But 
obviously the precipitation of sulphate of baryta in aqua regia is by no means a suffi- 
| ciently delicate test for an amount of sulphur at best exceedingly minute. In the same 
paper, Jacquelain, criticising the observation reported by Fordos and Gélis of the gen- 
eration of sulphuretted hydrogen from zinc and dilute sulphuric acid, implies that 
there is no sulphur in zinc by stating that the development of sulphuretted hydrogen 
from zinc may be avoided by using properly prepared acid. The acid which Jacque- 
lain used had been saturated with chlorine gas, in a process of which the principal 
object was the purification of the sulphuric acid from sulphurous acid. That this acid 
occasioned no development of sulphuretted hydrogen from the zinc is not to be won- 
dered at, but it is not to be argued from this fact, that there is no sulphur in zinc. 
With regard to sulphur in the zinc from New Jersey, Alger * has remarked that the 
New Jersey zinc ore is known to contain no sulphur; but, on the other hand, Jackson t 
observed the sulphuret of zinc in the mine of red oxide of zinc in Franklin, Sussex 
County, New Jersey, and a simple experiment demonstrated to us the existence of 
sulphur in that ore. 10 or 15 grammes of the red oxide of zinc, not entirely free from 
the gangue of carbonate of lime in which the ore occurs, were reduced to a fine powder, ` 
and treated with moderately dilute pure sulphuric acid. A vigorous evolution of sul- 
phuretted hydrogen was the immediate result. | : 
Arsenic. — The general opinion that arsenic is a very common impurity in commercial 
zinc may, we think, be traced back to the confident assertion of Proust, near the be- 
ginning of this century, afterwards extensively copied and generally believed. But it 
is quite clear that Proust, and probably many other of the early chemists, were led 
* Am. J. Sci, XLVIII. 253. + Proc. Am. Association, 1850, IV. 336. 
