ON THE IMPURITIES OF COMMERCIAL ZINC. 18 
first prepared by dissolving carbonate of lime in chlorhydric acid, adding ammonia 
in excess to the boiling solution, filtering off the precipitated oxides of iron and alu- 
mina, adding to the filtrate chloride of barium, and evaporating to dryness. "The resi- 
due was dissolved in distilled water, and in this solution a slight excess of chloride of 
barium was present, as was proved by the precipitate produced by a solution of sulphate 
of lime. Oxalic acid free from sulphur was then prepared by the following process: a 
quantity of commercial oxalic acid was treated with enough cold water to dissolve about 
half of the acid taken, and the cold solution thus obtained was partially evaporated 
and crystallized ; the mass of crystals was washed with a saturated solution of a portion 
- of the crystals, and was finally dissolved in distilled water. In these two reagents, 
the chloride of calcium and the oxalic acid, so prepared, no sulphur could be detected, 
either by barium salts, Loewenthal's test, or by the blowpipe reaction on silver. 
We applied to every zinc in our possession the following test for sulphur. 10 or 15 
grammes of zinc were introduced into a small flask, and a portion of the solution of 
chloride of caleium and of oxalic acid added thereto; hydrogen gas was freely de- 
veloped, and was tested for any sulphuretted hydrogen which it might contain, by 
placing a slip of paper moistened with alkaline acetate of lead in the narrow neck 
of the flask. In every case the paper was immediately and strongly blackened, 
showing conclusively that every one of the following zincs contains sulphur in a 
quantity extremely minute, but distinctly appreciable if a sufficiently delicate test 
be applied : — 
Vieille Montagne zinc (in two distinct samples). 
Silesian zinc. 
'The United States Mint zinc. 
Pennsylvanian zinc. 
Rousseau Fréres zinc. 
Berlin sheet zinc. 
Silesian zinc (subjected to Meillet's * process for purification from arsenic). 
New Jersey zinc. 
Sg * (reduced by us from the New Jersey white zinc oxide). 
English zinc (in four distinct samples). 
These results are not in accordance with the statements of some previous observers. 
Thus Karsten, in the memoir previously cited, infers that sulphur is not contained 
in Silesian zinc, from the fact that he obtained no precipitate in passing the gas gen- 
Se oag mS mr 
EI 
* Dingler's Polyt. Jour., 1842, LXXXIII. 205, from Jour. de Pharmacie, 1841, 625. 
` got, VIII. 10 
VM 
4 
