possessing Ihe Prcperties of Tannin, 323 



glasses, and one drachm, in measure, of the strong nitric 

 acid was added. 



The different infusions were then examined by solution 

 of isinglass, and I found that those of galls, sumach, and 

 oak wood, were not rendered turbid, whilst the contrary 

 happened to the infusions of oak bark, and of the artificial 

 substance ; for these continued to precipitate gelatine, until 

 four drachms, or half an ounce, ot the nitric acid had been 

 added to each half ounce of the infusion. 



When the results of these experiments are compared, 

 they seem to establish, that although the aitificial pro- 

 duct is by much the most indestructible of all the tan- 

 ning substances, yet there is some diflerence in this re- 

 spect even between the varieties of natural tannin ; and 

 that common catechu, and the tannin of oak bark, resist 

 the effects of nitric acid mucli longer than gails, sumach, 

 kascutti, and Pegu cutch. The last, , as I have observed, 

 is replete with mucilage, and by nitric acid yields a large 

 quantity of oxalic acid; it also appears to be the niost de- 

 structible of all the varieties of catechu ; and on this ac- 

 count I attempted, although without success, to promote 

 the destruction of the properties of the artificial substance 

 by adding gum arable in one case, and sugar in anollier, to 

 different portions, previous to exposing it to the action of 

 nitric acid. I am, however, convinced that the presence of 

 gum or mucilage in natural siibstances which conlaiii tan- 

 nin, renders this more speedily destructible by nitric acid ; 

 and I shall soon have occasion to notice some expcrin-.ents 

 which tend to prove that the presence of aum or mucilage 

 in certain bodies, also prevents, or impedes more or less, 

 the formation of ilie artificial tanning substance, 'i'he 

 cause of this difference, I am inchned to susp,ict, is, that 

 in those bodies tlie ^um or mucilage is not Siinply mixed, 

 but is present in a star^ of chemical combination, by which 

 certain modifications produced by the action of iiitric acid 

 upon the elementary principles of the origin;U substance 

 become facilitated. 



§ III. 



A. When sulphuric ac-id was added to a siiiution oi tlie 

 artificial tanning substance, the latter became turbid, and 

 a copious thrown precipitate subsided, which was st-lublc in 

 boihng distilled water, and then was caj>ab]e. ot precipi- 

 tating gelatine. 



B. 'I he same eflcct was produced by muriatic acid ; so 

 thai in lliesc particulars ihc artifieii! tnnniug substance was 



X 2 fuubd 



