ON VEGETABLE ASTRINGENTS. 



n 



this case we defer the addition of the j oily, until the fluid 

 shall have had time to deposit its contents in a solid form, 

 we shall find, that a fresh quantity will he precipitated. If 

 this operation be repeated, until the fluid no longer affords 

 any farther precipitate with jelly, the oximuriate of tin will 

 indeed still produce some effect, but not in general a very 

 considerable one. Nor indeed does it certainly follow, that 

 this small quantity of precipitate ought to be attributed to 

 the union of extract with the oxide of tin. Although the 

 infusion has ceased to precipitate upon the addition of jelly, 

 although the jelly was added in small quantities at once, 

 and no more added than what seemed necessary, yet I believe 

 that the fluid may still contain both jelly and tan. I found ray 

 opinion upon the circumstance, that in the successive addi- 

 tions of jelly to an astringent infusion, the first quantity 

 added unites with a large proportion of tan, and forms a 

 more insoluble compound, than any of the subsequent ones; 

 and that in proportion as we proceed, the jelly becomes in- 

 corporated with less and less tan, and forms a compound 

 less and less insoluble ; until at length a substance is Compound of 



formed, which remains in a state of half solution, and which ^. elIy and tan 



less and less 

 renders. the fluid opake, without ever producing a complete insoluble, 



precipitate. This kind of combination between jelly and 

 can maybe inferred from some of the experiments, which I 

 mentioned in my former paper, and will be farther support- 

 ed by the following considerations. The weight of the pre- 

 cipitate formed by the addition of jelly to an astringent in- and differs ac- 

 fusion is considerably influenced by the manner in which mod em ^hick 

 the jelly is added, whether all at once, or in successive por- the jelly is 

 tions. If we add together at one time the proportion of tan ac e " 

 and jelly which we suppose will mutually saturate each 

 other, we procure a dense precipitate, which separates im- 

 mediately, and leaves the fluid transparent; whereas if 

 jelly be added to tan in successive portions, a larger quan- 

 tity is necessary before the fluid exhibits an excess of jelly, 

 the precipitate separates more slowly, it is in larger quan- 

 tity, less dense in its consistence, the fluid retains a degree 

 of opacity, and continues for a considerable time to deposit 

 a sediment. The following comparative experiment bears 

 also upon the same point. An equal quantity of the ex- Experiments 

 tract of rhatany and of prepared jelly, each in solution, were with rhatany. 



added 



