On an artljlcial tanning Substance. 1 75 



' the solullons of the resins and those of many cf the bititmens, 

 such, for instance, as asphaltum and jet. The first effect 

 of nitric acid, during long digestion with these substances, 

 was to form a very dark brown solution, whilst a deep yel- 

 low or orange coloured mass was separated, which by sub- 

 sequent digestion in another portion of nitric acid was com- 

 pletely dissolved, and by evaporation was converted into a 

 yellow viscid substance, equally soluble in water and m 

 alcohol, so as to perfectly resemble that which by similar 

 ■ Jneans had been obtained from the resins, exceptino- that 

 when burned it emitted an odour somewhat resemblino- 

 that of the fat oils. ° 



ft therefore appeared to me that the first or dark brown 

 Solution had been formed bv the action of the nitric acid on 

 the vncojnhined carbonaceous part of the bitumens, or that 

 oy wluch they are rendered black, and that the deep yellow 

 portion which was separated was that which constituted 

 tlie real or essential part of these bituminous substances. 

 This opinion was confirmed by some experiments which I 

 purposely made upon amber ; and having everv reason there- 

 fore to believe that the dark brown solution'obtained from 

 asphaltum and jet was in fact a solution of coal, I repeated 

 the experiments 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 1 employed 100 grains of the coal, 

 which I digested in an open matrass with one ounce of 

 • nunc 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 cHcrvescence, at- 

 tended witti much nitrous gas, was produced : after about 

 two days I commonly added a second and sometimes a third 

 ounce of the acid, and continued the di.rcstion during five 

 or six days, or till the whole, or nearly the whole, was dis- 

 solved, excepting in those cases when the deep yellow sub- 

 Stance was formed ; for this I constantly separated. 



The next experiment was made upon cliarco<^l, which 

 was more readily dissolved than the preceding substances, 

 without leaving any residuum ; the solution°was perfect' 

 and the colour was reddish-brown*. 



Having 



* The solubility of charcoal in nitric acid, and rome of itr properties 

 when thus dissolved, have been noticed by proft-iscr Li'chtcnstein in CrcU's 



Chemit.'.l 



