LÀ 
ON THE IMPURITIES OF COMMERCIAL ZINC. Ti 
the materials was desired. Not convinced that the zincs were the source of the arsenic, 
we desired to prepare a quantity of sulphuric acid in which the presence of arsenic 
could not.possibly be suspected. To attain this object, we subjected a specimen of 
American sulphuric acid to the following process. The acid was first boiled with a 
little flowers of sulphur, as proposed by Barruel,* in order to free it from the nitrous 
fumes which the common sulphuric acid almost always contains; a small quantity of 
pure chlorhydric acid was then stirred into the cooled acid, which had been carefully 
decanted from the free sulphur, and the whole again boiled; to the acid, again cooled, 
a second addition of chlorhydric acid was made, and again the acid was heated till 
dense white fumes had been escaping for upwards of half an hour. During this 
process, the volatile chloride of arsenic is completely driven off, the second addition of 
chlorhydric acid being made, as has been recommended by H. Rose,t in order to insure 
this result. Lastly, a portion of chlorine-water was added to the cooled acid to oxidize 
any sulphurous acid which might be contained in it, and after a third boiling, the 
acid, cooled and diluted with three parts of water, was ready for use. This method 
of purifying sulphuric acid is a combination and modification of several well-known 
processes. Buchner} has described in full the process of purifying sulphuric acid by 
means of chlorhydric acid, and the use of chlorine as above described was recom- 
mended by Jacquelain.§ The whole operation can be performed in a shallow evapo- 
rating-dish, and presents no serious difficulties of any kind. "With the acid thus pre- 
pared, we tested 200 grammes of Vieille Montagne zinc, and after passing during more 
than an hour a continuous, gentle stream of gas through the reduction-tube, of which 
about four centimetres were maintained at a bright red heat, we found that there was 
absolutely no deposit whatever in the cool and narrow part of the reduction-tube. 
With the same acid and apparatus, 200 grammes of Pennsylvanian zinc (which had been 
proved to be altogether the purest zinc in our possession) gave absolutely no deposit of 
any kind in the fine reduction-tube at the end of one hour, the time during which, in all 
our examinations for arsenic, we maintained a steady flow of hydrogen through the 
red-hot reduction-tube. We had now demonstrated that two different spelters, of 
which we were fortunate in possessing considerable quantities, were free from arsenic, 
or, more strictly, that in the given quantities of metal, and in the stated times, Marsh's 
infinitely delicate test could not detect arsenic in these two zincs. It was also rendered 
* Dingler’s Polyt. Jour., 1837, LXIV. 55; from Jour. de Ch. Médicale, 1836, No. 4. 
+ Pogg. Ann., 1858, CV. 571. 
1 Ann. der Ch. u. Pharm., 1855, XCIV. 241. 
§ Ann. de Ch. et Phys., 1843, [2.] VII. 191. 
