the characteristic Proper lies of Tannin. 103 



thus turpentine is almost iimnediately converted into resin, 

 then into the third variety of the tanning substance, and 

 lastly into coal. 



Without being under the necessity of adducing other ex- 

 anipleSj we may therefore state sulphuric acid to be a solvent 

 of the resinous substances, but which continues afterwards 

 to act on their principles so as to decompose them, coal 

 being the ultimate product. 



Nitric acid, as I have shown in the course of these papers, 

 and likewise on some former occasions, dissolves the resins, 

 but the progress of its effects seems to be conversely that of 

 sulphuric acid ; in the latter case, solution precedes decom- 

 position ; but when i>itric acid is employed, decomposition 

 to'a certain degree precedes solution ; for it at first converts 

 the resins into a pale orange-coloured brittle porous sub- 

 stance, then into a product which apparently possesses the 

 intermediate characters of vegetable extractive matter and of 

 resin ; and lastly, this is converted into the first variety of 

 the tanning substance, beyond which I have not been able 

 to cfiect any change. 



As coal, therefore, appears to be the ultimate effect pro- 

 duced by sulphuric acid upon the resinous bodies, so does 

 the first variety of the tanning substance seem to be the ter- 

 minating product afforded by the same when acted upon by 

 nitric acid. This effect of nitric acid has been already amply 

 discussed, neither does it appear necessary that 1 should here 

 repeat the remarks which have been made on some of the 

 simultaneous products, such as the vegetable acids; but, 

 amongst the effects produced by sulphuric acid, the coal 

 which is fonned seems to merit some attention. 



§ VII. 

 After the tanning substance and the other products had 

 been obtained from the resins, balsams, &c. which have 

 been mentioned in the beginning of this paper, the follow- 

 ing proportions of coal remained * : 



• Tlic wci;;ht of the ronl obtained from C'lrh of the .ibovc-mrntioncd ^iitj- 

 •tiinceii was c>>liiTiatfd after the complete separation of every other product, 

 .'.nd alur the r.i'jisturt; liad been c/pelled by red heat in close vessels. 



G 4 Coal. 



