ON ARTIFICIAL TANNIN. 265 



to have a. greater tendency v to solidity than the latter; and 

 that the presence of a certain quantity of resin, with which 

 it may be united, favours this precipitation. 



§ III. Tanning substance formed with aloes. 



11. On treating aloes after the mode of Mr. Braconnot, Tannin from 

 I obtained the matter he called aloetic acid *. aloes * 



This acid substance has a yellow colour; an acid, astrin- 

 gent, and bitter taste : projected on a hot iron, it emits a 

 yellow smoke, is carbonized, and melts. Heated in the 

 glass bulb it yields, 1st, water; 2d, carbonic acid; 3d, 

 prussic acid ; 4th, an inflammable gas, which I believe to be 

 a mixture of oily hidrogen and gaseous oxide of carbon; 

 5th, nitrogen gas; 6th, charcoal. 



Hence it appears to me, that the aloetic acid is a com- A similar com- 

 pound of nitric acid analogous to those I have already P ound « 

 described. 



This substance is but little soluble in water ; and, though Its properties 

 it is yellow, its solution is of a fine purple. I imagine the 

 water acts in this case by weakening the action of the 

 nitric acid on the vegetable matter with which it is combined. 

 This purple solution becomes yellow on the addition of 

 nitric acid, muriatic acid, &c. 



It gives a purple colour to alcohol. 



I boiled some in nitric acid at 50° [sp. gr. j 1'5], and eva- not altered by 

 porated to dryness. On dissolving the'residue in water, I mtric acid " 

 obtained a red solution, inclining a little to fiery, because 

 probably there remained a little excess of acid. It seems 

 to me, therefore, that the nitric acid had not changed the 

 nature of this substance. 



With salifiable bases it forms purple compounds, which its compounds 

 are detonating, as Mr. Braconnot first observed. with the bases. 



I have found, that it precipitates gelatine very well ; and Precipitates ge- 

 even that several of its soluble compounds precipitate it latme * 

 without the addition of an acid, which Welther's amer 

 eombined with potash never does, when it contains no resin. 



12. Is the aloetic acid a compound of nitric acid and Itsnature 

 a substance arising from the decomposition of aloes? or a 

 compound of nitric acid and the coloured principle of aloes 



* Journal, vol. xxvii, p. 365. 



little 



