constituent Parts of astringent Vcgetahles. 71 



astringent infusion, had formed two combinations ; one 

 containing chiefly galhc acid, which was easily soluble ia 

 water ; the other containing chiefly tannin, which was very 

 ditficultlv soluble. 



Alumine boiled with the infusion became yellowish-oray, 

 and gave a clear white fluid, which produced only a tin^e 

 of light purple in the solutions of iron. When the earth * 

 was employed in a very small quantity, however, it formed 

 an insoluble compound only with the tannin and the ex- 

 tract, and the residual liquor was found to contain a gaU 

 late of alumine with excess of acid. 



The oxides of tin and of zinc, obtained by nitric acid, 

 were boiled with separate portions of the infusion for two 

 hours. In both cases a clear fluid, which appeared to be 

 pure water, was obtained ; and the oxides gained a tint of 

 dull yellow. A part of each of them was dissolved in mu- 

 riatic acid. The solution obtained was yellow ; it copiously 

 precipitated gelatine, and gave a dense black with the salts 

 of iron. Mr. Proust f, who first observed the action of" 

 oxide of tin upon astringent infusions, supposes that por« 

 tions of tannin and gallic acid are decomposed in the pro- 

 cess, or converted, by the oxygen of the oxide, into new- 

 substances. These experiments do not, however, appeat 

 to confirm the supposition. 



M. Deycux observed that a copious precipitation was 

 occasioned in infusion of galls, by solutions of the alkalis 

 combined with carbonic acid. Mr. Proust has supposed 

 that the solid matter formed is pure tannin, separated from 

 its solution by the stronger affinity of the alkali for water; 

 and he reconnnends the process as a method of obtaining 

 tannin. 



In examining the precipitate obtained by carbonate of 

 potash fully combined with carbonic acid, and used to sa»- 

 turation, I have not been able to recognise in it the proper- 

 ties which are usually ascribed to tannin : it is not possessed 

 of the astringent taste, and it is but slightly soluble in cold 

 water or in alcohol. Its solution acts very little upon ge- 

 latine, till it is saturated with an acid j and it is not posses* 

 scd of the property of tanning skin. 



In various cases in which the greatest care was taken to 

 use no excess, either of the astringent infusion or of the 

 ulkarme sokition, I have found the solid matter obtained 

 possessed of analogous properties ; and it has always given, 



• Mr. Ficfller, I b-lievc, first observed the action of alumine upon 

 tannin, — Van Mimi's journal, vol. i. p S<.. 

 •J 4>i'taici </f Chivufi tome xlii. p. 69. 



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