ON VEGETABLE ASTRINGENTS. 24** 



be united. I confess that I am disposed to adopt the doc- 

 trine of Proust: for although Mr. Davy's remark be correct, 

 that in all vegetables, in which tan has been discovered, it 

 exists in a state of combination with other principles, and 

 that its action must necessarily be modified by these com- 

 binations ; yet I conceive, that, as far as we are able to Probably not 

 judge, the nature of the combinations will not account for 

 the difference of the effects. The extract of rhatany is co- 

 piously precipitated by jelly, and considerably so by the 

 oximuriate of tin; but as this reagent produces scarcely 

 any effect after the addition of jelly, we must conclude, ac- 

 cording to the generally received opinion, that the effect of 

 both these substances depends upon the tan which it con- 

 tains, so that we are led to regard it as consisting of tan, 

 combined with a little mucilage and a minute portion of 

 gallic acid. Yet we find, that tartarized antimony and the 

 carbonate of potash, which act so powerfully upon the tan 

 of the gall-nut, scarce!)' produce any precipitate with the 

 tan of rhatany. We must therefore conclude, either that 

 the action of the oxide of antimony and the caibonate of 

 potash depends upon the presence of some extraneous body, 

 or that there may be a substance, which forms an insoluble 

 compound with jelly, and which, on this account, is entit'ed 

 to the appellation of tan ; but which may be so modified, as 

 in some states to unite with the above reagents, and at other 

 times to hare no effect upon them. Considering the mag- 

 nitude of the effect produced, compared to the supposed 

 nature of these extraneous bodies, 1 cannot but think the 

 latter opinion the more probable. This, it is admitted, is 

 no more than a presumptive argument; but I apprehend, 

 that the same point is more firmly established by what I 

 have observed respecting Mr. Hatchett's artificial tan. This Artificial tan, 

 substance we may regard as homogeneous, and therefore not 

 liable to those objections, which apply to such experiments 

 as are performed upon any of the vegetable infusions; and;. 

 yet I have found it to act very differently upon other re- 

 agents, at the same time that it exercised the most power- 

 ful action upon jelly. I have now before me a solution of 

 the artificial tan, which copiously precipitates jelly, the oxi- 

 muriate 



