On an artificial tanning Substance. 177 



of isinglass to that state in a close vessel, and having rubbed 

 it into fine powder, I digested it with nitric acid in the 

 manner which has been described. At first the acid did 

 not appear to act upon it, but at length it was slowly dis- 

 solved excepting a small quantilv? which however was in 

 every respect unchanged ; and here we may remark, that as 

 animal coal is incinerated with much more difficulty than 

 vegetable coal or charcoal, so was the same difference 

 to be observed when oxygen was presented to these bodies 

 in the humid way. 



The solution resembled those which have been described, 

 excepting that the brown colour was more intense. It was 

 evaporated to dryness, and was then dissolved in distilled 

 water, after which the solution, being examined by the re- 

 agents which had been employed in the former experiments, 

 was found to produce similar effects, excepting some diffe- 

 rence in the colour of the precipitates. 



I next added some of the liquid to a solution of isinglass, 

 and obtained a copious precipitate. Thus it is evident, that 

 a tanning substance may be formed from animal as well as 

 from vegetable and mineral coal ; and it is not a little cu- 

 rious, that this enables us to assert as a matter of fact, al- 

 though not of oeconomy, that one portion of the skin of an 

 animal n)ay be employed to convert the other into leather. 



In the course of these experiments I also subjected coak 

 to, the action of nitric acid, and obtained a product which 

 resembled that which had been afforded by pit-coal ; but in 

 this case (as might be expected) there was not any appear- 

 ance of the deep yellow substance which has bo often been 

 mentioned. 



These experiments, therefore, prove, that a tanning sub- 

 stance may be artificially formed by exjjosing carbon to the 

 action of nitric acid ; and it also appears, that this is best 

 effected when the carbon is uncombined with any other 

 substance excepting oxygen. The following experiments 

 seem to corrol)orate this opinion. 



1. Apiece of Bovey coal, whicli had perfectly the ap- 

 pearance of half-charred wood, was reduced to powder, 

 and was digested with nitric acid until the whole was 

 dissolved. 



The colour of the solution was deep yellow ; and, by eva- 

 poration, a yellow viscid mass was obtained, wliich was 

 dissolved in distilled water. This solution was then ex- 

 amined by Various ri'agcnts, and particularly by gelatine, 

 hut not a:iy vestigt- (jf tanning matter could be discovered, 

 and the picilouiinant substance appeared to be oxalic acid. 

 Vol. 23. No. 90. XiH'. I'iOi. M 2, Another 



