94 ' ON THE IMPURITIES OF COMMERCIAL ZINC. 
The purest of all the zincs which we have analyzed is that manufactured at the 
Pennsylvania and Lehigh Zinc Works, Bethlehem, Pennsylvania. This spelter dis- 
solves in dilute sulphuric acid without leaving any appreciable residue, and therefore 
contains no lead; indeed, a trace of cadmium is the only impurity whose presence 
in the zinc we could confidently assert. The ore from: which this spelter is made 
is the hydrated silicate of zinc (electric calamine), and it is not surprising that this 
mineral should yield zinc of singular purity, if the ore be carefully selected. We 
have stated above that our first sample of this zinc was free from arsenic, but that 
the second sample was not pure in this respect. At these works the oxide of zinc is 
manufactured, as well as the metal, and we learn from a letter addressed to Professor 
Brush by Mr. Wharton, the director of the works, that the crust from the oxide fur- 
naces has now and then been worked into spelter, and that the ore used in making the 
oxide is less carefully selected than that which goes to the spelter-furnaces, and is 
much more likely than the latter to contain both blende and pyrites. This fact may 
account for the occurrence of arsenic in some specimens of this spelter, while the 
greater part of it, manufactured from carefully selected silicate of zinc, is perfectly free 
from that impurity. There seems to be no reason why zinc of uniform purity should 
not be obtained from this excellent ore. e 
Pure Zinc. — We have already referred to the difficulty of obtaining a pure zinc by 
reducing it from the oxide on a small scale; nothing but the direst necessity could induce 
us again to attempt the operation, although it has been recommended by many high 
authorities. Nevertheless it is by no means difficult to prepare a pure oxide of zinc, 
and manufacturers of pure chemicals, working on a larger scale than it is practicable 
for the chemist to do, might undoubtedly prepare from this oxide at moderate cost a 
really pure zinc. There are some processes of chemical analysis in which the contami- 
nation of zinc with metallic lead is a matter of importance, because it affects the accu- 
racy of the results; but in these cases the difficulty can generally be avoided by dis- 
carding zinc altogether, and resorting to other methods of analysis. But in order to 
use Marsh's process for the detection of arsenic, the chemist must procure zinc free 
from arsenic, and there is no escape from this necessity ` redistillation will not disem- - 
barrass zinc of its arsenic, and the process of reducing zinc from a pure oxide is very 
laborious and uncertain; how then can zinc free from arsenic be obtained? There is 
but one satisfactory answer to this question. Pure zinc might certainly be made from 
the oxide by the manufacturing chemist, but at present the zinc labelled “ pure” by 
those who sell chemicals is not to be relied upon, and the chemist must therefore test 
samples procured from the dealer in metals, until he finds a specimen of the pure zinc 
which is manufactured on a large scale, and is to be obtained in commerce. 
