ON THE IMPURITIES OF COMMERCIAL ZINC. 85 
^ 
arsenic obtained in the previous experiment. In two other similar examinations of 
the red oxide of zinc, we obtained the same strong evidence of the presence of arsenic 
in this ore, and the associated mineral, Franklinite, yielded, in the single careful test to 
which we subjected it, a mirror of arsenic sufficient to give the smell and all the other 
characteristic reactions for arsenic. To obtain satisfactory results, the solution of the 
oxide must never be heated above 100°, and the small quantity of nitric acid which is 
used to facilitate solution must be completely driven off before the liquid is introduced 
into the apparatus.* 
If any further evidence of the presence of arsenic in the New Jersey spelter and its 
ore were needed, it might be found in the following experiment with a zinc which we. 
ourselves prepared by reducing the New Jersey white oxide of zinc with charcoal, in 
a refractory retort such as are furnished by the dealers in chemical apparatus at Paris. 
20 grammes of this zinc, tested in Otto's apparatus with purified sulphuric acid, yielded 
in five minutes a distinct deposit of arsenic, and in half an hour a large mirror.t 
* We have also found arsenic in no inconsiderable quantity in the white zine oxide, prepared from this ore 
for use as white paint. Two different samples, bought of authorized dealers, yielded large mirrors of arsenic, 
many well-marked spots on porcelain, and other of the reactions for arsenic. Moreover, a large precipitate 
of sulphide of arsenic was produced by sulphuretted hydrogen in their solutions. The qualitative examina- 
tion of these two samples showed also the absence of lead and copper, and the presence of distinct traces of 
cadmium, iron, tin, and perhaps of antimony. It has been supposed that the superior quality of the French 
white zinc oxide was attributable to the presence of sulphur in the American article. To settle this question, 
we have determined, in two samples of New Jersey white oxide of zinc, the amount of matter insoluble in 
chlorhydric acid, and the per cent of sulphuric acid which they contained. 
I. d II. 
Matter insoluble in chlorhydric acid, . . 0.0006 percent. . +. 0.00033 per cent. 
OM ot oii oi 0536 « 
PE V eis “ sulphuric acid, . xod 
These impurities are obviously too insignificant to account for the difference between the American and the 
French zinc-white, a difference probably due to the different mechanical conditions in which the oxide is ob- 
tained by the different processes employed in this country and in France. In a letter from Mr. John M. 
Ordway, weshave the results of examinations of these paints made by this chemist in 1855: “The French 
oxide when dissolved in chlorhydric acid left a little coarse dirt; the colorless solution treated with ammo- 
nia in excess gave a very slight white precipitate, soluble in potash and in acids, haps alumina. There 
was also a very faint trace of iron and of sulphuric acid. The American oxide afforded a somewhat colored 
solution, a little fine soot remaining undissolved. The solution gave a brown precipitate of peroxide of iron 
when treated with ammonia, and also yielded a considerable precipitate with chloride of barium.” 
t A further qualitative examination was made of this zinc, as follows. About 10 grammes were dissolved in 
pure chlorhydrie acid; a considerable black residue remained, which was separated, dissolved in nitric acid, 
and the solution évaporated nearly to dryness. The flocculent precipitate which separated was filtered off and 
fused before the blowpipe with carbonate of soda which contained no metal. Ductile spangles were obtained, 
