£14 Mr. Hatchett on an artificial tanning Substance. 
It therefore appeared to me, that the first or dark brown 
solution had been formed by the action of the nitric acid on 
the uncombined carbonaceous part of the bitumens, or that by 
which they are rendered black, and that the deep yellow 
portion which was separated, was that which constituted the 
real or essential part of these bituminous substances. This 
opinion was confirmed by some experiments which I purposely 
made upon amber, and having every reason therefore to 
believe, that the dark brown solution obtained from asphaltum 
and jet was in fact a solution of coal, I repeated the experi- 
ments on several varieties of the pit or mineral coal, from all 
which, I obtained the dark brown solution in great abundance ; 
but those coals, which contained little or no bitumen, did not 
yield the deep yellow substance which has been mentioned. 
In each experiment I employed 100 grains of the coal, 
which I digested in an open matrass with one ounce of nitric 
acid diluted with two ounces of water. (The specific gravity 
of the acid was 1.40.) 
After the vessel had been placed in a sand-bath, and as soon 
as it became warm, a considerable effervescence attended, with 
much nitrous gas was produced ; after about two days I com- 
monly added a second and sometimes a third ounce of the acid, 
and continued the digestion during five or six days, or until 
the whole, or nearly the whole, was dissolved, excepting in 
those cases when the deep yellow substance was formed ; for 
this I constantly separated. 
The next experiment was made upon charcoal, which was 
more readily dissolved than the preceding substances, without 
leaving any residuum ; the solution was perfect, and the colour 
was reddish-brown.* 
* The solubility of charcoal in nitric acid, and some of its properties when thus 
