on a Substance possessing the Properties of Tannin. 301 
solution acted on the metallic salts like those which have 
already been noticed, but with gelatine it formed only a very 
slight precipitate, which was immediately dissolved by boiling 
water ; and the remainder of the solution being evaporated, 
yielded a very large quantity of crystallized oxalic acid ; so 
that in this respect guaiacum was found to resemble the gums, 
and to be totally unlike the resins.* 
§v. 
As many vegetable substances when roasted, yield by decoc- 
tion a liquid, which in appearance much resembles the artificial 
tanning matter when dissolved in water ; I roasted some of the 
common dried peas, horse-beans, barley, and wheat flour, the 
decoctions of which however did not afford any precipitate by 
solution of isinglass. 
Even the decoction of coffee did not yield any precipitate by 
this method, until several hours had elapsed, and I found that 
the precipitate so formed was permanently soluble in boiling 
water. But to explain this, we must recollect, it is extremely 
probable, that some peculiar nicety is required in the roasting of 
such bodies before the tanning substance can be developed ; 
and this seems to be corroborated by some experiments which 
I made on the decoction of a sort of coffee prepared from 
the chicoree ( I suppose endive ) root, which was given me by 
• The properties of guaiacum which have been described, as well as those which 
were previously known, appear to indicate, that it is a peculiar substance of a nature 
distinct from the resins, balsams, and even the gum resins. 
So remarkable indeed is this substance, that an accurate series of experiments on 
the whole of its propetties may justly be placed amongst the chemical desiderata. 
