44 Mr. Brande’s observations , &c. 
their infusion extremely brittle when dried. The same cir- 
cumstance however, namely, the absence of extractive prin- 
ciple, probably would materially contribute to their excellence 
as a source of the black dye, the intensity and perfection of 
which is, I conceive, often interfered with by the presence of 
extractive matter in the common gall nut and other vegetable 
astringents usually employed. These galls are likewise par- 
ticularly proper for the production of writing ink, the ten- 
dency of which to become thick and mouldy seems principally 
to be derived from extractive matter. 
