20 TANNING MATTER, &C. 



ExDcriments "^^ orangevcolourcd mass still remained, which was 

 &c.on thcard- speedily dissolved by alcohol, and was precipitated from it 

 ficial substance by a large addition of water. 



ractcr of tan- ^^^^ substance in many of its properties resembled the 

 uing matter, resins, but in otlicrs, seemed to approach those which cha- 

 racterize the vegetable extractive matter. It appeared to 

 be similar to that which has been cursorily mentioned in 

 my first paper, and which was obtained from many of the 

 pit-coals and bitumens when treated with nitric acid. I 

 have since paid more attention to this substance during 

 the following experiments : 



Kilkenny coal was digested with nitric acid, and pro- 

 gressively, although with diificulty, was converted into 

 that variety of the tanning substance which has so often 

 been mentioned. Similar experiments were made on the 

 same sort of coal from Wales, which was given to me by 

 my friend Mr. Tennant, as well as upon a coal sent to 

 me by Professor Woodhouse, which was from Pensyl- 

 vania, and is there called Leigh high coal. All of these 

 were converted into the tanning substance, but they did 

 not yield any product similar to that obtained from the 

 elastic bitumon. 



The contrary however happened when the common pit- 

 coal, or Canncl coal, or asphaltum, were employed. For 

 when these were treated in the way which has been de- 

 scribed, and when the digestion was not too long con- 

 tinued, then I obtained from 100 grains of each of the 

 above substances (after the separation of the tanning mat- 

 ter) a residuum as follows : 

 From 100 grains of the common Newcastle coal 9 grains. 



From 100 grains of Cannel coal 36 grains. 



From 100 grains of pure asphaltum 37 grains. 



The substances thus obtained, were very similar in 

 their external characters, being of a pale brown, ap- 

 proaching to Spanish snuft' colour ; their internal frac- 

 ture was dark brown, with a considerable degree of re- 

 sinous lustre. When exposed to heat they did not easily 

 melt, but as soon as inflamed, they emitted a resinous 

 od(jifir mixed with that of fat oil, and produced a very light 

 coal, much exceeding the bulk of the original substance. ^ 

 Alcohol completely dissolved them, and if water in a 

 large proportion was added to a saturated solution, a 



precipitate 



