water ; and the carbon being thus in fome meafure denuded, 

 is rendered capable of being acted on gradually by the nitric 

 acid, in a manner nearly (imilar to what takes place when it 

 has been previoufly converted into coal. 



The precipilales of this tanning fubflance from gelaten are 

 always pale or deep yellow, while thofe formed by the firft 

 fpecies are conftantly brown ; which induces the author to be- 

 lieve that the different colours of the precipitates depend on 

 the ftate of tiie carbon of the tannin. 



The quantity of artificial tan obtained from refin and other Quantity of ar- 

 bodies, was always lefs than that from coal, or even from the fro^^[efins'lhan 

 fame bodies previoufly converted to coal in the humid way by from coal, ac- 

 fulphuric acid. The caufe of this feems to be, that a number counted for. 

 of other produds are fimultaneoufly formed with the tanning 

 fubftance, all of which require more or lefs carbon as an in- 

 gredient; fo that, according to the affinities which prevail, 

 (bme bodies afford but little, and others none of it. 



The greatefl proportion of this fubftance was yielded by Its proportions 

 indigo, common ref.n, and flick lac. fSanSr' 



The quantity obtained from affafoetida and gum ammoniac 

 was lefs. 



Benzoin, balfam of Tolu, balfam of Peru, and dragon's 



blood, were inferior to the former in this refpeft ; fo that the Benzoic acid 



produdtion of benzoic acid feemed to counterafl the formation ^ nterafts^he 



•of the tanning fubftance. But oxalic acid, when formed in formation of the 



any confiderable quantity, feemed abfolutely to prevent the*^"' ,. ., 

 r ' r r.u- r V/i c l- . and oxalic acid, 



lormation of ttiis fubitance : tor gum arahic, tragacanih, man- when produced, 



na, and guiacum, which prx3(iuced oxalic acid in abundance, P/S^*"" *' *°* 



yielded no tanning matter. 



Common liquorice feems to be an exception ; but the author 

 fuppofes that the fmall quantity of tan produced by it, was 

 formed by the adion of the nitric acid on a portion of uncom- 

 bined carbon, which being in a ftate approaching to coal, ia 

 probably the caufe of the blacknefs of the common liquorice. 



The third variety of the tanning fubftance appears to be Third variety of 

 uniformly produced during a certain period of the procefs ; artificial tan. 

 but by a long continuance of the digeftion there is reafon to 

 think it is deftroycd, 



Subftances, fuch as gums, which yield my..ch oxalic acid, 

 io not apparenlljf afford any of this tanning matter. 



'C.{2 The 



