Memoir upon Coffee. 19 
befitnents more than twenty times, but the decoction never 
was acid. 
It decomposes sulphate of alumine and precipitates the 
earth from it, which it colours feebly. wag 
Dry Coffee treated by Alcohol.—An infusion of alcohol 
and dry coffee, even in the cold, becomes slightly coloured, 
and holds in solution a very abundant extracto-resinous prin- 
ciple. If water is poured in, the solution becomes milky, 
and the resin is precipitated of a dirty white. With a so- 
lution of sulphate of iron the precipitate is green; with the 
muriatic acid it is fawn-coloured. Coffee, when exhausted 
by alcohol and afterwards treated with water, still farnishes 
some extract and mucilage, 
It may be concluded from these first experiments that 
dried coffee contains, 1st, An aromatic principle soluble in 
water: 2d, A very small. quantity of essential oil: 3d, An 
abundant resin:' 4th, A gum in greater quantity: 5th, Gallic 
acid, but no tannin: 6th, Extractive matter: and, 7th, 
A little alumine. 
Observations. 
If the warm filtered decoction becomes turbid on cooling, 
it is because it holds in solution, on account of the heat, a 
little resin. |The alkalis make it brown; the usual effect of 
these re-agents upon vegetable decoctions. Lime water pre- 
cipitates it, because, on the one hand, gallate of lime is 
formed; and, on the other hand, the extracto-gummous 
matter unites itself to the earth and takes it down with it. 
There is even sulphate of alumine in it. Spirit of wine se- 
parates the mucilage from it, because the gums are not so« 
luble in alcohol; and water precipitates the alcoholic tinc- 
ture, because water does not dissolve resins. This precipi- 
tate becomes white when water is used, on account of its 
extrome minuteness ; green by the sulphate of iron, because 
it is mixed with the gallate of iron; fawn-coloured by the 
oxymuriatic acid, because oxygen acting on resin sets free a 
little carbon. The insoluble scum which is formed upon 
the decoction is a vegetable albumen coagulated by boiling 
water. To obtain this it is necessary that the water stand 
some time cold upon the coffee before heating it. 
. Be General 
