82 ON THE IMPURITIES OF COMMERCIAL ZINC. 
* in American sulphuric acid, further than to suggest that its presence seems not unnatu- 
ral when we remember that the sulphides of arsenic are often associated mineralogically 
with the sulphur from which the acid is made. Long ago Pfaff,* in commenting upon 
the observation made by Martius of arsenic in sulphuric acid, said that the sample 
analyzed by Martius was probably made from sulphur containing orpiment or realgar, 
minerals which are found with sulphur in the solfataras. Stromeyer y detected arsenic 
in the mixture of salammoniac and sulphur, which is one of the many volcanic 
products of the Lipari Islands, and there seems to be no good reason for supposing ` 
that the sulphur, which is exported from the same locality, would escape contami- 
nation with arsenic. Daubrée ¢ has remarked that arsenic, as sulphide, occurs in the 
fissures of the lavas at Etna, at Vesuvius, and at the solfataras of Pouzzoles and of 
Guadeloupe. Scacchi§ also states, that among the subtances found in the fumaroles 
of the solfataras are pyrites, realgar, mispickel, and dimorphine. Orfila,|| and before 
him Vogel, of Munich, imply that the leaden chambers in which sulphuric acid is 
made communicate arsenic to the acid. 
Whatever we have said with regard to the American sulphuric acid, applies with 
still greater force to the commercial chlorhydric acids. "That common chlorhydric acid 
contains chloride of arsenic, is a fact which was long ago observed, and has been fully 
discussed by Wackenroder 9 Dupasquier,** Otto,t+ and many others. We have ex- 
‘amined two different samples of chlorhydric acid made in this country. Dilute chlor- 
hydric acid, instead of sulphuric, was used in Marsh's apparatus with 200 grammes of 
pure Vieille Montagne zinc, and before the hydrogen generated had been passing through 
the heated reduction-tube fifteen minutes, there appeared in the fine part of the tube 
a brown deposit, which in an hour increased to a,large and distinct mirror of arsenic, 
readily verified by other tests. Both samples of acid gave the same result, and we 
may add that, even on a small scale, we found great difficulty in preparing from salt 
and sulphuric acid a specimen of chlorhydric acid perfectly free from arsenic. The 
thorough purification of the acid by means of sulphuretted hydrogen, as recommended 
* Schweigger's Jour. f. Ch. u. Phys., 1816, XVIII. 283. 
t Ibid., 1825, XLIII. 452. E 
i Ann. des Mines, [4.] XIX. 680. 
$ Journal f. pr. Ch., 1852, LV. 54. 
| Ann. d'Hygiène Publique, XXII. 408. ` 
*| Ann. der Pharm., 1835, XIII. 241. 
** Comptes Rendus, 1841, XIII. 630. 
TT Ann. der Ch. u. Pharm., 1856, C. 39. 
11 See also Ure's Dictionary of Arts, &c., 4th edition, (Boston, 1853,) II. 248, Art. Muriatic Acid. 
