a 48 Mr. Davy’s Experiments and Observations 
some hours, they combined with the tannin contained in it, so 
as to form with it insoluble compounds ; and, in each case, a 
deep green fluid was obtained, which gave no precipitate to 
gelatine, even when an acid was added, but which produced a 
deep black colour in the solutions of the salts of iron. 
Sulphate of lime, when finely divided, whether natural or 
artificial, after having been long heated with a small quantity 
of the infusion, was found to have combined with the tannin of 
it, and to have gained a faint tinge of light brown. The liquid 
became of a blue-green colour, and acted upon the salts of iron, 
but not upon gelatine; and there is every reason to suppose, 
that it held in solution a triple compound, of gallic acid, sulphuric 
acid, and lime. 
We owe to Mr. Proust, the discovery that different solutions 
of the neutral salts precipitate the infusion of galls ; and he 
supposes, that the precipitation is owing to their combining with 
a portion of the water which held the vegetable matter in solu- 
tion. In examining the solid matters thrown down from the 
infusion, by sulphate of alumine, nitrate of potash, acetite of 
potash, muriate of soda, and muriate of barytes, I found them 
soluble, to a certain extent, in water, and possessed of the power 
of acting upon gelatine. From the products given by their inci- 
neration, and by their distillation, I am however inclined to 
believe that they contain, besides tannin, a portion of gallic acid 
and extractive matter, and a quantity of the salt employed in the 
primitive solution. 
It is well known, that many of the metallic solutions occasion 
dense precipitates in the infusion of galls ; and it has been gene- 
rally supposed that these precipitates are composed of tannin and 
extractive matter, or of those two substances and gallic acid, united 
