364 
ON OXIDE OF ZINC. 
and hydrosulphuric acid, were added without producing any 
result. Possibly manganese might be present, which, in only 
slight traces, it is well known, is not easily detected. In the 
burnt oxide, manganese must be present in the state of oxydu- 
loxide : if, therefore, this be converted into a muriate, chlorine 
must be present, and this will exert a solvent action on gold-leaf 
simultaneously exposed to its influence ; faint traces of gold in 
solution may be indicated by chloride of tin, and the author 
trusts that in the cases of the presence of manganese that he 
may obtain a decisive reaction. At first the muriatic acid em- 
ployed, with a possible admixture of free chlorine, was tested by 
digestion with gold-leaf, but with negative results. In the next 
place, one loth (equal to half an ounce) of the burnt oxide of zinc 
was dissolved in the same hydrochloric acid which contained 
gold ; and the vessel being closed by a glass stopper was set on 
one side for twenty-four hours. Chloride of tin produced no 
change in the solution, even after several hours' exposure to the 
action of warmth. Dr. Wittstein employed also a very sensitive 
test for manganese, first proposed by Crum, and which he has 
himself frequently found useful, viz. a solution of the oxide in 
nitric acid, to which is added a small quantity of the brown bin- 
oxide of lead, heat being applied ; manganese being present, hy- 
permanganic acid is formed, and the fluid becomes reddened. 
By this test, however, no manganese was discovered, and the 
author therefore concluded that the oxide of zinc was free also 
from this impurity. 
Dr. Wittstein repeated his experiments for the detection of 
other metals, upon larger quantities of the oxide, as in his earlier 
researches. Half an ounce was dissolved in excess of hydro- 
chloric acid, and hydrosulphuric acid passed through the solution 
for a long time — it produced not the slightest disturbance. 
Again, half an ounce of the oxide was dissolved in hydrochloric 
acid, which had not shown any change on the addition of sul- 
phocyanuret of potassium, and on the then employment of this 
reagent, a faint red discoloration showed the presence of slight 
traces of iron. The extraneous admixture, which was shown to 
be present by the aid of the microscope, consists also of oxide of 
iron, but in such minute quantity, that of all its tests the sul- 
phocyanuret of potassium alone manifested its presence. 
