TANNING MATTER, &:C. §9 



coufained in the Iceland schistus.*) 1 am much inclined Experiments, 



to believe, that an extractive substance of secondary for- ?^* ?^' f " ^'''** 



' •' ficial substance 



mation,if I may be permitted to employ such a term, is hxvxngthecha- 



produced during the process of carbonization. If a sub- racters of tan- 

 stance, therefore, so compact and solid as oak timber can * ^- * 

 by long submersion, be deprived of its tannin, it naturally 

 follows that the same etlect must be more speedily pro- 

 duced by the action of water on the smaller vegetable bo- 

 dies, which present an extensive surface, and also on 

 porous and bibulous substances such as peat. 



But although peat, as I have already observed, does 

 not contain any tannin, yet the imperfect carbonization 

 which it has undergone, renders it like the roasted lig- 

 neous bodies, peculiarly susceptible of being converted 

 into the artificial tanning substance when exposed to the 

 action of nitric acid. It would be useless to enter into a 

 detail of tiie dilierent experiments which I have made 

 upon it, as they were similar to those already related, and 

 I slmll therefore only here state, that when seven ounces 

 of well dried peat had been twice moistened, and digested 

 with diluted nitric acid, (to the auiount of rather more 

 (han two ounces,) and subsequently dried, I obtained by 

 water a solution of the artificial tanning substance, which 

 when evaporated to dryness w'eighed tMo ounces. I am 

 convinced, that much more might have been obtained 

 from the residuum of the peat, had I thought proper to 

 have repeated the operation ; and I am also certain, that 

 less nitric acid would have been sufficient, had the process 

 been conducted in close vessels, and with other economi- 

 cal precautions, which at that time, were for the sake of 

 expedition and convenience omitted. 



§ VI. ^ 



It has been generally stated, even by modern chemists, 

 that the acids act but little, if at all, upon resinous sub- 

 stances. , 



The contrary has howeverbcen proved, not only in the 

 three Papers upon the present subject, but also in some 



hers which I have formerly had the honour to lay bc- 



re this learned society. 



In my experiments on lac, printed in the Phil. Trans. 



* Phil. Trans, for x8o6, p. 391. 



for 



