24 TANNING MATTER, &C. 



black state, a small portion of nitric acid was poured, and 



&c. on an arti- after being digested for about five hours, the whole was 



ficial substance evaporated to dryness. The residuum was of a brownish 



ractc?o/tau" <''**ng<^ colour, and yielded a similar coloured solution to 



ning matter, water when digested with it. This was filtrated, and upon 



the addition of solution of isinglass, became turbid, and 



deposited a tough precipitate, which was not dissolved b/ 



boiling water. 



3. 

 Another portion of the walnut peels was moderately 

 roasted, and was then digested in water ; the brown so)u> 

 tion was filtrated, and formed a slight precipitate with 

 gelatine. 



4. 

 ^ On the residuum of the last experiment, a small qnan* 



tity of nitric acid was poured, some water was then ad- 

 ded, the whole was digested during about five hours, and 

 until it became perfectly dry. 



Water formed with this a brown liquor, which yielded 

 a very abundant precipitate by the addition of dissolved 

 isinglass. 



Upon these experiments we may remark, that the solu- 

 tion in the first instance contained carbon in a state ap- 

 ]>roaching to coal, for when treated with nitric acid* in 

 the second experiment, a portion (although small) was 

 produced of the same tanning substance which is formed 

 from the diiferent kinds of coal by nitric acid. 



The third experiment appears to shew, that a small 

 quantity of a substance approaching to tannin was pro- 

 duced by the simple process of roasting; and the fourth 

 evpcriraent corroborates those already described, in which, 

 the artificial tanning matter was copiously produced, 

 whenever roasted vegetable substances were treated with 

 nitric acid. 



In respect to vegetable substances, especially those 

 which contain tannin, I shall here relate a few other ex- 

 periments. 



It has been remarked in my second Paper, (p. 288,) 

 that the tannin of galls was immediately destroyed by 

 nitric acid. Since that time, I have made the following 

 additional experiments : 



One 



