on the constituent Parts of astringent Vegetables. 245 
obtained ; and the oxides gained a tint of dull yellow. A part of 
each of them was dissolved in muriatic acid. The solution ob- 
tained was yellow : it copiously precipitated gelatine ; and gave 
a dense black with the salts of iron. Mr. Proust,* who first 
observed the action of oxide of tin upon astringent infusions, 
supposes that portions of tannin and gallic acid are decomposed 
in the process, or converted, by the oxygen of the oxide, into 
new substances. These experiments do not, however, appear to 
confirm the supposition. 
M. Deyeux 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 so- 
lution by the stronger affinity of the alkali for water; and he 
recommends 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 saturation, I 
have not been able to recognise in it the properties 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 gelatine, till it is saturated with 
an acid; and it is not possessed 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 alkaline 
solution, I have found the solid matter obtained possessed of 
analogous properties ; and it has always given, by incineration, 
a considerable portion of carbonate of potash, and a small quan- 
tity of carbonate of lime. 
The fluid remaining after the separation of the precipitate, 
9 Annales de Cbimic, Tome XLII. p. 69. 
