the cliaracterisiic Properties of Tannin. Qq 



r.ot so rapidly effect a change in the elastic bitumen as it 

 does when applied to the other bituminous substances. 



1. 100 grains of pure soft elastic bitumen were digested 

 during three weeks in one ounce of nitric acid, diluted with 

 an equal quantity of water; a tough and slightly elastic 

 orange-coloured mass then remained. Another ounce of 

 the acid, not diluted, was poured upon this mass, and the 

 digestion was continued until the whole was evaporated. 

 The residuum was tenacious, and of the colour above men- 

 tioned. Water partially dissolved it, and formed a deep 

 vellow liquid, which copiously precipitated gelatine, and 

 possessed the other properties of the tanning substance which 

 is produced from the resins, Sec. by nitric acid. 



An orange-coloured mass still remained, which was 

 speedily dissolved by alcohol, and was precipitated from it 

 by a large addition of water. 



This substance in many of its properties resembled the 

 resins, but in others, 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 vt'ith nitric acid. I have 

 since paid more attention to this substance during the fol- 

 lowing experiments : 



Kilkenny coal was digested with nitric acid, and pro- 

 gressively, although with difficulty, 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 Pennsylvania, and 

 is there called Leigh high coal. All of these were convert- 

 ed into the tanning substance, but they did not yield any 

 product similar to that obtained from the clastic bitumen. 



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 describ- 

 ed, and when the digestion was not too long continued, 

 then I obtained from 100 grains of each of the above sub- 

 K 3 stances 



