f 
10 ON THE IMPURITIES OF COMMERCIAL ZINC. 
merest trace of carbonate of lime, — a little larger deposit, perhaps, than that obtained 
from the Silesian, Vieille Montagne, and other zincs first experimented upon, but not 
more than may easily have been derived from the invisible dust which undoubtedly 
collected on the residue. From none of these zincs could we obtain nearly as much 
carbonate of lime in the test-glass as we got from the smallest possible atom of carbon 
heated with chromate of lead; and it is quite clear that there is never anything more 
than an infinitesimal amount of carbon in the considerable residue which remains when 
thirty or forty grammes of commercial zinc are dissolved in dilute acids. 
Against the common opinion that carbon is one of the principal impurities of zinc, 
we would refer to the previously quoted statement of Wackenroder, who considered 
carbon only an accidental and mechanical impurity, and to the exact experiments of 
Karsten, who endeavored to determine the carbon in Silesian zinc by decomposing 
chloride of silver and chloride of copper by zinc, but * could find no trace of carbon in 
either the hard or the soft kinds of zinc." * 
Sulphur. — It has been frequently stated that sulphur is a common impurity of zinc, 
and that it even occurs in the insoluble residue in combination with lead. We first tested 
the insoluble residue from Silesian zinc for sulphur, by dissolving about 30 grammes 
of the zinc in pure chlorhydric acid, separating the black residue, and dissolving it in 
pure nitric acid. It dissolved without any appreciable residue (another evidence of the 
non-existence of tin in this spelter), and the diluted solution gave nó precipitate what- 
ever with nitrate of baryta. With 40 grammes of Vieille Montagne zinc, we obtained 
precisely the same result. 'The Pennsylvanian zinc leaves no residue when treated 
with dilute acids, and is therefore free from lead, and certainly contains no carbon or 
sulphur which manifest themselves as an insoluble residue. The New Jersey zinc 
gave an exceptional result. The blackish residue, from 32 grammes of this zinc, could 
not be completely dissolved in boiling nitric acid. The partial solution gave no pre- 
cipitate with nitrate of baryta; the undissolved portion was fused before the blow- 
pipe with carbonate of soda free from sulphur, and gave a distinct reaction, first. 
for sulphur, and secondly for tin. The presence of tin in this spelter has already 
been demonstrated, and a minute trace of ibd must also be counted Along 
its impurities. x 
In addition to this negative evidence, that no precipitation is produced by barium 
salts in the diluted nitric acid solution of the residues from the various zincs, we would 
* Archiv. f. Mineralogie, Karsten u. Dechen, 1842, XVI. 607. Karsten also says: «I have cemented 
sheet zine with coal for many days, and then melted it; but in the resulting mass of zinc I have found no trace 
of carbon." Ibid., 608. 
