the Arseniates of Copper , and of Iron . 
heat, lost 12, which were pure water. Nitric acid was poured 
upon the residuum ; and, finding that it was dissolved with diffi- 
culty, the ebullition was continued during several hours. The 
liquor was then filtered. 60 parts, which shall presently be ex- 
amined, remained undissolved. Into this filtered liquor, nitrate 
of lead was poured, which occasioned a precipitate as usual ; 
but the operation was discontinued, until I should obtain ail the 
arseniate of copper which I imagined to be contained in the 
ore. For this purpose, I had recourse to the 60 parts men- 
tioned above. They were in the form of a greenish grey pow- 
der, very hard and gritty, which had every appearance of silica, 
contaminated by a small portion of copper interposed between 
the molecules of that earth. I resolved to treat it in the same 
manner as all siliceous stones, and proceeded to boil it with 
potash. 
In less than three minutes, it became of a very red brown, 
from the greenish grey which it originally was ; and seemed 
considerably attenuated in its particles. The liquor was de- 
canted, and examined. It was found to contain arsenic acid ; 
and the precipitate, which had resisted the action of the potash, 
was proved to be a mixture of iron and copper. 
These preliminary experiments were sufficient to indicate a 
ready method of analysis. 100 parts, boiled with potash, imme- 
diately became of a deep reddish brpwn. The liquor was sepa- 
rated from the residuum by filtration; and, after the usual 
satisfaction which that chymist generally affords. No doubt, the scarcity of the ore 
prevented his making every necessary research ; and I may deem myself fortunate in 
having been so near the spot in which it is found. My friend, Mr. Hatchett, very 
obligingly gave me a specimen of this ore which he had received from Dr. Pallas, 
who had brought it with him from Siberia, where it had been found. 
Ff 2 
