180 On an artificial tanning Suhstancc. 



The eflects produced by sulphuric acid upon turpentine 

 and resin are manifestly caused by the union of the two 

 constituent principles of the latter (namely, hydrogen and 

 carbon) with part of the oxygen of the former, so that sul- 

 phureous acid, water, and coal are produced. I therefore 

 availed myself of this process, by which coal could be pro- 

 grcs.>ively formed, whilst the original substance was gradu- 

 ally decomposed, to make the following experiment. 



A quantity of common turpentine was treated with sul- 

 phuric acid in the way which has been described, and 

 different portions of the solution being poured at different 

 periods into water whilst the remainder was digested during 

 several days, I thus obtained, from the same original sub- 

 stance, yellow resin, brown resin, black resin, and coal. 

 I then digested a portion of each of these, as well as some 

 of the turpentine, in separate vessels with nitric acid until 

 they were completely dissolved, and afterwards reduced 

 them to dryness. 'J'he different residua varied in colour 

 from yellow to dark brown, corresponding to the substances 

 which had been employed. These were then dissolved in 

 distilled water, and were examined by solution of isinglass 

 and other rea2;cnts. 



1. The solution of the residuum of turpentine was pale 

 straw colour, and did not precipitate gelatine. 



i.'. That of yellow resin resembled the former in every 

 respect. 



3. That of the brown resin was of a deeper yellow, but 

 in other particulars resembled the above. 



4. That of the black resin, on the contrary, yielded a con- 

 siderable portion of the tanning substance, — and 



5. That, of the coal afforded it in great abundance. 

 Hence it appears, thai these different modifications of 



turpentine vielded the tanning substance only in proportioiv 

 to the quantity of their original carbon, which, bv oxidize- 

 ment, had been progressively converted into coal*. 



Other substances, when reduced into coal in the humid 

 w.ty, were in like manner forn>cd into the tanning sub- 

 stance by nitric acid. In fact I foimd this to be the con- 

 stant lesult, and amongst the nvany subst:uices which were 



is very corrsiderable ; we may take common resin as an example, for when 

 100 grains were exposed to suiiple distillation in a small glass retort placed 

 over an open charcoal lire, the residuum of coal only amounted to three- 

 fourths of n grain. 



; * Some laic experiments have however convinced me that carboti need 

 .aot be ab^-olutely coi;v( itid into coal in order to produce tlie artificial tan- 

 a'tig -lub^tuiiC".-: bur tixia v.iU be more fully explained in a subsequent 

 r,..--"r. 



e,Kaiiiined, 



