coristUncnt Parts of astringent Vegetables. 30i 



febrifuge properties. My experiments tend to confirm the 

 observation. None of the infusions of the strongly bitter 

 veg<;table substaners that I hav e examined give anv precipi- 

 tate to gelatine. And the infusions of quassia, of gen- 

 tian, ofhops, iind of camouiile, are scarcelv affected by 

 muriate of tin ; so tiiat they likewise contain very little ex- 

 tractive matter. 



In all substances possessed of the astringent taste, there 

 is great reason to ^uspect the presence of tannin ; it even 

 exists in substances whicb contain sugar and vegetable 

 acids. I have found it in abundance in the juice of sloes ; 

 and my friend xMr. Poole, of Stowey, has detected it in Port 

 wine. 



V. General Olservat'iowi. 



'Sir. Proust has supposed, in his Paper upon Tannin and 

 its Species *, that thei-e exist different species of the tanning 

 principle, possessed of different properties and different 

 powers of acting upon re-agents, but all precipitable by 

 gcUiline. This opinion is sufficiently conformable to the 

 facts generally known concerning the nature of tlie sub- 

 stances which are produced in organized matter ; but it 

 cannot be considered as proved, till the tannin in different , 

 vegetables has been examined in its pure or insulated state. 

 In all tlic vcgetiible infusions which have been subjected to 

 exj;eriment, it exists in a state of union with other princi- 

 ples ; and its properties must necessarily be modified by the 

 peculiar circumstances of its combination. 



From the experiments that have been detailed it appears 

 that the specific agencies of tannin in all the different astrin- 



fcent infusions are the same. In every instance it is capa- 

 )le of entering into union witb the acids, alkalis, and eartlis ; 

 and of forming insoluble compounds with gelatine and with 

 skill. The infusions of the barks affect the greater number 

 of re-ageiUs in a manner similar to the infusion of galls; 

 and that this last tluid is rendered green by the carbonated 

 alkalis, evidently depends upon the large proportion of gallic 

 acid it contains. The infusion of sumach owes its charac- 

 teristic property, of being precipitated by the caustic alkalis, 

 to tlie presence of sulphate of lime; and that the solutions 

 of catecliu do not copiously precipitate the carbonated al- 

 kalis, appears to depend upon their containing tannin in a 

 peculiar state of union with extractive matter, and uncom- 

 buied with gallic acid or earthy suits. 



• Annala dc CHmie, tome xl'. p \\x. 



In 



