£ ] J ON VEGETABLE ASTRINGENTS. 



to be referable to the other constituents. The circumstan- 

 ces, that have been adduced to prove the existence of extract 

 in the infusion of galls, may be referred to the following 

 heads. 1. When jelly has been added to the infusions, 

 until it no longer produces a precipitate, the fluid will still 

 be precipitated by the oximuriate of tin. 2. If an infusion 

 of galls be exposed for some time to the atmosphere, and 

 especially, if it be kept at an increased temperature, a part 

 of its contents will be rendered insoluble, and will separate 

 from the fluid. 3. If two portions of galls be infused in 

 water, one for a short space of time, and the other for a 

 longer period, they will be found to be differently affected by 

 the reagents; the quick infusion being proportionally more 

 acted upon by jelly, and the slow infusion by the oximu- 

 riate of tin. I shall consider each of these points indivi- 

 dually, and shall examine how they authorize our conclu- 

 sions in favour of the existence of extract. 



The first of them I do not propose to controvert, and yet 

 the precipitate 1 thing it presents some degree of ambiguity, of which those 

 by jelly should who have written or experimented upon the subject do not 

 before more' seem to have been perfectly aware. I am disposed to be- 

 jelly is added. ]jeve, that the effect has been a good deal exaggerated. 

 When we add jelly to the infusion of galls, it seldom hap- 

 pens, that the whole of the precipitate is separated at once; 

 a part of it remains suspended in the fluid, giving a greater 

 or less degree of opacity ; and if in this state more jelly be 

 added, it will appear to produce uo more effect, or even by 

 farther diluting the fluid, to render it more transparent, and 

 partially to redissolve the solid contents*. If however, in 



* Mr. Davy states, that in the addition of jelly to an infusion of 

 mn, if the jelly be added in excess, part of the precipitated compound 

 will be redissolved. In order to observe this effect the following experi- 

 ment was tried. A quantity of a weak infusion of galls had about 

 twice as much jelly added t* it as I supposed would form the most per- 

 fect compound ; a dense substance was precipitated, and the whole of 

 the fluid was jendered milky. Two equal quantities of this milky fluid 

 were put into separate glasses, to one an additional portion of jelly was 

 added, and to the other the same bulk of nine water, Both the fluids 

 were rendered more transparent from the effects of dilution, but I did 

 pot perceive that it was more so in one iase than in the other, al- 

 though the tan must now have had abotxt ten times its proper quantity 

 #f jelly added to it. 



this 



