£6 Memoir upon Coffee. 
This decoction, when filtered, turned into ig gtpen the aqueous 
tincture of turnsole, 4 
I mixed a part of this decoction with a solution of sul- 
phate of iron, and I obtained a precipitate of a very. deep 
blue, drawing towards black; I redissolved this precipitate 
by the oxymuriatic ecid, by weak and strong acetic acid, 
by the tartarous acid, the citric acid, and even by:the ben 
zoic acid, 
The muriatic acid changed, the Tiquor i into yellow ; aark it 
resumed its transparency on depositing a heayy precipitate of 
oxygenated extractive. . This. precipitate, redissolved by am- 
monia, gave a fine red brown colour to the liquor... 
The immediate precipitate of the sulphate. of iron, dis- 
solved by the acetic acid acted like the former, the 
colour only excepted, which was violet blue; it was, be- 
sides, redissolved by ammonia. The other acids yielded 
nearly the same precipitate as the muriatic acid. . Their ac 
tion, in general, followed the ratio of acidities, , 
I treated in the same manner some precipitate of sulphate 
of iron obtained by the gallic acid, and the results presented 
no differences from the Porabers 
T precipitated by the muriate of tin what remained of the 
coffee in decoction.. This salt occasioned a very abundant 
deposit in the liquor. I washed the pvecipitate until the 
washings no longer exhibited any signs of acidity; I after- 
wards put. this metallic compound in a Woolf’s bottle, and 
I poured plenty of distilled water on it. I placed the appa- 
tatus of Woolf so.as to cause sulphuretted hydrogen gas to 
pass over the precipitate. As soon as the first portions of 
gas began to pass, the mixture acquired a brown colour, © 
which became darker in proportion as the liquor was satu- 
rated with sulphuretted hydrogen gas. The precipitate was 
decomposed ; there was formed a. hydro-sulphuret. of tin, 
and the liberated acid passed into the liquor. . This liquor, 
fiitered, was evaporated at a gentle heat until it was reduced 
to one-eighth. This product, supposed by M, Payssé to 
be coffic acid, seemed to me to be nothing else than gallic 
acid. Not only did I submit it to the action of all the re- 
agents, comparatively with the acid drawn from. gall-nuts 
by 
