a mineral Substance from North America. 51 
and tincture of galls, when the excess of acid had been pre- 
viously saturated by an alkali, formed a precipitate of a rich 
purplish brown colour. 
Experiment 11. 
Another portion of the powder was, in like manner, digested 
with nitric acid; but, excepting some slight traces of iron, this 
acid afforded nothing worthy of notice ; the action of it upon 
the ore, was indeed scarcely perceptible. 
Experiment in. 
Some of the pulverized ore was digested with concentrated 
sulphuric acid, in a strongly-heated sand-bath, until nearly the 
whole of the acid was evaporated ; the edges of the mass then 
appeared bluish, and became white, when boiling distilled water 
was added. 
This acid certainly acted much more powerfully than those 
which have been mentioned ; but still only a small part of the 
ore was dissolved. It must however be observed, that a very 
copious blue precipitate was obtained by prussiate of potash ; a 
plentiful purplish brown precipitate was also produced by tinc- 
ture of galls, after the excess of acid had been saturated by an 
alkali; and, lastly, when the yellow ferruginous precipitate 
formed by ammonia was dissolved in diluted nitric acid, some 
white flocculi remained, which were completely insoluble in 
the acid, even when it was added so as to be in considerable 
excess. 
From these experiments it was evident, that the ore could 
not readily be decomposed by the direct application of the 
mineral acids; and I therefore had recourse to the following 
Ha 
