ON THE IMPURITIES OF COMMERCIAL ZINC. 65 
used at the United States Mint, the results were negative. To confirm these re- 
sults, 25 gram. of Silesian zinc and 20 gram. of Mint zinc were separately dissolved 
in dilute chlorhydric acid, and the residues separated from the solutions just before the 
zinc had completely disappeared, in order to collect in the residues all the tin which the 
zines might contain. Each residue was then treated with strong chlorhydric acid; the 
chloride of lead formed was separated by decantation, and the solution tested with 
terchloride of gold. No trace of tin could be detected in either case. 
The precipitate produced in the solution of New Jersey zinc by sulphuretted hydrogen 
weighed after ignition 0.1285 gram. (see Table IV.), and gave evidence of containing 
copper. To determine whether it also contained tin, the precipitate was treated with 
nitric acid, and the matter insoluble in nitric acid was collected, and found to weigh 
0.0389 gram. When this insoluble residue was reduced on charcoal before the blow- 
pipe, it yielded metallic globules, the acid solution of which gave the characteristic 
reaction for tin with terchloride of gold. 
Copper. — No spelter except that from New Jersey gave the slightest evidence of 
. the presence of copper. We determined the per cent of copper with which that zinc 
was contaminated by the following method: 17.9452 gram. of the zinc were dissolved 
in pure chlorhydric acid, and the residue, having been treated with nitric acid, was 
added to the original solution, through which sulphuretted hydrogen was then passed. 
The precipitated sulphide of copper was filtered off, washed with sulphuretted hydrogen 
water, dried, and separated from the filter. The filter was then burned, and its ashes, 
wet with sulphide of ammonium, were added to the previously separated sulphide of 
copper; the whole was then ignited in a current of hydrogen, and the resulting disul- 
phide of copper weighed. 
` Weight of zinc taken . .  . 17.9452 grammes. 
* e disulphide of copper .  . 0.0292 “ 
*  * copper corresponding : 0.0233 * 
Per cent of copper E ma. 01298 
In what way copper was introduced into this zinc, we do not undertake to explain. 
We subsequently examined, in connection with our experiments on carbon in the 
residue from zinc dissolved in dilute acids, the precipitates produced by sulphuretted 
hydrogen in the chlorhydric-acid solutions of several different spelters. The experi- 
ments simply served to corroborate the results which have been already stated, as 
obtained with sulphuric-acid solutions of the different zincs, only one new fact being 
developed, the presence of a trace of cadmium in the Pennsylvanian zinc. From 
VOL. VIII. 9 
