86 ON THE IMPURITIES OF COMMERCIAL ZINC. 
To ascertain whether the Pennsylvanian and Vieille Montagne zincs were always 
free from arsenic, we procured and tested another sample of the zinc manufactured at 
the Pennsylvania and Lehigh zinc works, and a second sample of Vieille Montagne 
spelter. The Pennsylvanian zinc was, as before, remarkably free from lead, leaving no 
residue when dissolved in dilute sulphuric acid; but on testing 200 grammes of it in 
Otto's apparatus with purified acid, it gave in half an hour a slight deposit in the 
reduction-tube, which in an hour increased to a distinct brown coating. A similar 
result we obtained in testing the second sample of Vieille Montagne zinc; 200 grammes 
of it with pure acid yielded a deposit in the reduction-tube, fatal to its use in any 
delicate experiments. It should be stated, that the external appearance of this spelter 
indicated very clearly that its quality was inferior to that of the sample first examined. 
It is obvious from these results, that zinc manufactured in the same works, and from 
the same ore, may not always contain the same impurities, or rather that it never is to 
be expected to contain the same percentages of the same impurities. From the nature 
of the process of reduction, it would naturally be the case that the more volatile impuri- 
ties should be present in the zinc which distils first in greater quantities than in the 
zinc which is reduced from the last part of a given charge of ore. Thus it is easy to 
imagine that the zinc which comes over first should be contaminated with arsenic, while 
that which is last reduced might be perfectly free from that impurity. The same prin- 
ciple explains the variations in the amount of cadmium contained in different samples 
of the same spelter, and indeed accounts in great measure for the varying per cents 
of all the impurities found in different specimens of any zinc, though made by the 
same process from the same ore. 
which on solution in chlorhydric acid, and treatment with terchloride of gold, gave the reaction for tin. To 
the filtrate from the precipitate just mentioned, pure dilute sulphuric acid was added, and an abundant pre- 
cipitate separated at once; this precipitate, reduced on charcoal with carbonate of soda, gave a large bütton, 
which was dissolved in nitric acid, and tested with chromate of potassa, a voluminous precipitate of chro- 
mate of lead separated immediately. No traces of copper were detected. H 
About 250 grammes of the oxide of zinc had been placed in the retort in which the reduction was to be 
effected, but only about 50 grammes of zinc were obtained, because the experiment was prematurely ended by 
the melting of the retort, caused by a combination of the oxide of zinc with the silicates of which it was made. 
These 50 grammes were only a fourth of the quantity of zinc which 250 grammes of the oxide should yield, and 
it is interesting to observe that lead and tin, as well as arsenic, accompanied this early product of the distil- 
lation. The source of this lead is uncertain ; it is not inconceivable that the glaze of the retort should contain 
it, though to all appearances it was not a lead glaze; but the fact that lead was found in these first portions of 
the distilled zinc is perhaps none the less interesting, if it did come from the retort. The process of prepar- 
ing pure zinc by reduction from the oxide on a small scale, is at best very laborious and uncertain. (Compare 
Neumann in the Abridgment of his Chemical Works by Lewis, London, 1759, p. 116.) 
