330 ARTIFICIAL TAN. 



fwt or fix hours, is completely black. When the digeftion b 

 continued for feveral days, until no more gas is given out, 

 the refin will be converted into a black porous coal, which 

 , <!oes not contain any refin, if the experiment has been pro- 



,p^r!y conducted. This coal was about 43 per cent of the 

 refin ufed, and after being expofed in a platina crucible loofely 

 covered to a red heat, ftill amounted to .SO per cent, and by 

 the flownefs of its combuftion, and other circumftances, ap- 

 proached nearly the character of fome mineral coals. 

 Produfls of this A portion of the coal, the black refin, brown refin, and 

 Svcd^uTnitric 3 fe ^ ow re * in obtained from the turpentine defcribed, and alfo 

 acid. fome of the turpentine itfelf, were each dilfolved in nitric 



acid, and reduced to drynefs; the refidua, which varied in 

 colour from yellow -to dark brown, according to the fubftance 

 employed, were dilfolved in water, and examined with 

 ifinglafs and other reagents. 

 Their refiducs The folution from the turpentine refiduum, thai of the 

 sftcr eva-ora yellow refin, and the brown refin, did not precipitate 



tion are tried J . , 



with gelaten, geiaten. 



& c ; That from the black refin yielded a confiderable portion of 



' the tanning fubftance, and that from the coal afforded it in 



great abundance. Hence it appears, that thefe fubftances 



yielded artificial tan only in proportion to their conversion 



into carbon. 



Various kinds of wood, copal, amber and wax, reduced 

 to coal by fulphuric acid, yielded limilar products on being 

 treated with nitric acid. '■ 

 Tan formed by Mr. Hatchett formed the artificial tan from the refins, and 

 alcohol. . g Um refins (fuch as common retin, elemi, affafoetida, &c.) 

 when reduced to the ftate of coal from long digeftion with 

 fulphuric acid, by means of alcohol, without ufing any nitric- 

 acid : In the carbonized ftate mentioned, tbey are digefted 

 in the alcohol, a portion is diflblved, a dark brown folution 

 is formed, which by evaporation yields a mafs foluble in 

 water as well as in alcohol, and which precipitates gelaten, 

 acelite of lead, and muriate of tin, but produces only a flight 

 effecl on oXy-fuIphate of iron. 

 Suppofiticn re- The author fuppofes, that the tanning matter known to be 

 lative to un ex^ved by peat in certain places, is effected by a procefs in 

 p " fome refpecls limilar to the above, fince if it was produced by- 



its mere digeftion in water, all peat would afford it, which is 

 contrary to experience, 



Mr. 



