the Arseniates of Copper, and of Iron. 233 
similar, I shall mention that only which proved to be the most 
ample, and the most conclusive. 
One hundred parts of the pulverised ore were introduced 
into a small phial, and dilute phosphoric acid was poured in, so 
as to fill it. A ground stopper closed it completely ; and, in 
that state it was suffered to remain three days, during which 
time the bottle was frequently shaken. The acid became at first 
of a light blue, and increased in colour by remaining upon the 
ore. At the expiration of the above term, the liquor was de- 
canted ; the residuum was well washed and dried, and weighed 
42. The blue liquor contained merely common phosphate of 
copper, held in solution by an excess of acid. Upon the 42 
parts of residuum, strong muriatic acid was poured, which did 
not appear to produce the smallest change or effect. It was 
evident, therefore, that some previous alteration had been pro- 
duced; for, if it had remained in its original state, muriatic acid 
would have acted upon it, as in the case already mentioned. 
To operate more effectually, nitric acid was added, and the 
whole gently heated. A complete solution followed, during 
which, much nitrous gas was disengaged. The remainder of 
the nitric acid was expelled by evaporation ; and a plate of 
polished iron, immersed in this muriate of copper, afforded a 
precipitate of metallic copper, weighing within one part as much 
as the weight of the first residuum. It was evident, therefore, 
that a partial reduction of the ore had taken place; and, what 
is still more strange, had taken place by means of the presence 
of an acid. 
In many observations which have presented themselves, in 
the course of various analytic experiments, something similar 
had before occurred to me. I have known metallic oxides yield 
MDCCCI. H h 
