26 o Mr. Davy’s Experiments and Observations 
and formed without much agitation ; in consequence of which, 
the constituent parts of it that are least soluble, being first pre- 
cipitated, appear in some measure distinct from the more soluble 
parts, which assume the solid form at a later period of the 
process. 
From the observations of Mr. Kerr,* it would appear, that 
the pale catechu is that most sought after in India ; and it is 
evidently that which contains most extractive matter. The ex- 
tractive matter seems to be the substance that gives to the 
catechu the peculiar sweetness of taste which follows the impres- 
sion of astringency ; and it is probably this sweetness of taste 
which renders it so agreeable to the Hindoos, for the purpose 
of chewing with the betle-nut. 
IV. EXPERIMENTS AND OBSERVATIONS ON THE ASTRINGENT IN- 
FUSIONS OF BARKS, AND OTHER VEGETABLE PRODUCTIONS. 
The barks that I examined were furnished me by my friend 
Samuel Purkis, Esq. of Brentford ; they had been collected in 
the proper season, and preserved with care. 
In making the infusions, I employed the barks in coarse 
powder; and, to expedite the solution, a heat of from too to 
120° Fahrenheit was applied. 
The strongest infusions of the barks of the oak, of the Lei- 
cester willow, and of the Spanish chesnut, were nearly of the 
same specific gravity, 1.05. Their tastes were alike, and strongly 
astringent ; they all reddened litmus-paper ; the infusion of the 
Spanish chesnut bark producing the highest tint; and that of 
the Leicester willow bark the feeblest tint. 
Two hundred grains of each of the infusions were submitted 
* Medical Observations, Vol. V. page 155. 
