72 Expeidments on a Substance u.liicli possesses 



of tannin which the horse chestnut peels originally contained, 

 was destroyed by the process of roasting; that the brown 

 decoction subsequently obtained from the roasted peels and 

 from the horse chestnuts, did not act upon gelatine; but 

 that these were speedily converted into the artificial tanning 

 substance, by the addition of a small portion of nitric acid 

 and subsequent evaporation. 



The first preparations of the artificial 'tanning substance 

 which have been mentioned in the former papers, were made 

 from coal of different descriptions digested with nitric acid ; 

 and as similar products have been obtained by the same acid 

 from various decoctions of roasied vegetable substances, 

 there cannot be any doubt, that vegetable bodies when 

 roasted, yield solutions by digestion in water, which essen- 

 tially consist uf carbon approaching to the state of coal, al- 

 though not absolutely converted into it ; for, if so, all solubi- 

 lity in water would cease. 



But coal is apparently nothing more than carbon oxidized 

 to a certain degree, and may be formed by the humid as 

 well as by the dry way. 



Examples have been already stated respecting operations 

 in which sulphuric acid has produced this effect, but the 

 same likewise appears to be produced with some modifica- 

 tions, whenever vegetable matter undergoes the putrefactive 

 process; for when this lakes place, as in dunghills, &c. a 

 large proportion of the carbon of the original vegetable sub- 

 stances appears to be combined with oxygen sufficient to 

 communicate to it many of the properties of coal, whilst the 

 compound nevertheless is capable of being dissolved by water 

 with the most perfect facility. 



It must not however be understood that by this process all 

 the other elementary principles arc separated, so that only 

 the carbon remains combined with oxygen, but merely, that 

 the other principles are so far diminished, that these, namely 

 carbon and oxygen, predominate in a state approaching to 

 co^al, although soluble in water. 



Such solutions, 1 have every reason to believe, are nearly 

 similar to those afiorded by vegetable substances which have 

 been previously roasted j and although I have examined fcut 



a few 



