36& ON ARTIFICIAL TANNIN". 



little or not at all changed? The colour of this substance 

 leads me to incline to the latter opinion : yet I do not con- 

 sider it as impossible, that, beside the acid and coloured 

 principle, it may contain a portion of aloes with its nature 

 changed ; for the pretty copious production of oxalic acid 

 in the treatment of aloes by nitric acid proves, that a part 

 of the aloes is completely decomposed. 

 Hypotheses. 13 p erna ps it may be thought, that the amers of brasil 



and aloes are only compounds of amer at a maximum, 

 nitric acid, and substances resulting from tfie more or less 

 advanced decomposition of the articles with which they 

 were formed. Without venturing to assert, that this opi- 

 nion is absolutely false, it appears to me more natural at 

 present, to consider these amers as two distinct species of 

 amer at a maximum. Hence it follows, that resinous sub- 

 stances treated with nitric acid do not aiford a homogeneous 

 principle, that may be considered as a kind of artificial 

 Different sub- tannin. Besides, the following experiments will prove, that 

 stances precipi- ^j ie f acu ity of precipitating gelatine belongs to substances 

 tate gelatine. ' \.„ , . , . , , 



of a very different nature, and in which the presence of 



amer at a maximum cannot be suspected. 



Tannin from Part II. Tanning matter formed with carbonaceous 

 pitcoal. substances. 



§ I. With pitcoal. 



Mr. Hatchett's 1. Mr. Hatchett asserts, that several bitumens, as jet and 



experiments on as | ia ] tum are formed of charcoal and a resinous matter: 



bitumens r 7 7 



and that, when nitric acid is digested on these compounds^ 



the carbonaceous part dissolves, and the resinous part sepa- 

 rates in the form of a yellow or orange-coloured mass. Mr. 

 and coal Hatchett applies this discovery to pitcoal ; and says, that 



when this contains no resinous substance, which is the most 

 common case according to him, it is completely di-solved by- 

 nitric acid, and converted into tannin ; and that, on the 

 contrary, when it contains a little resinous matter, this is 

 The author's not dissolved. The results I have obtained differ a little 

 results some- from those of Mr. Hatchett. Like him, by treating pit- 

 whatdifferent. ^^ ^^ concentra t e d nitric acid, and reducing the liquor 

 to a sirupy consistence, J. obtained a thick, brown homo- 

 geneous liquid ; but when this liquid was poured into water, 



a yeU 



