Memoir upon Coffee. 23 
Decoction—I boiled two ounces.of. ground coffee in, one 
pound of water for two hours. The decoction had.an infis 
nitely less agreeable and Jess aromatic smell than the infu- 
sion. It did not change the colour of blue papers did not 
precipitate the solution of gelatine; and became, black with 
the sulphate of iron. Alcohol separated much more mnuci- 
laze from it than is found in equal proportions of the infu; 
sion. The three kinds of coffee yielded the same results, ., 
If we boil, for a long time in the, open air, a filtered and 
Jimpid decoction of coffee, it becomes turbid-and depgsits a 
black powder, which has been sometimes: taken for resin, 
but it is only a highly oxygenated extract. Physicians and 
apothecaries have not yet sufficiently well ascertained. the 
action of the atmospheric air upon vegetable decoctions'; 
‘they might derive some experience of the greater or less 
energy of certain remedies from experiments on this subject. 
Extract of Coffee.—The decoction of coffee, filtered and 
evaporated to the consistence of an extract, has no longer 
the aromatic smell of the infusion; its taste is bitter; heated 
with alcohol the extract colours the liquor, but this colour is 
not precipitated by water. “From this we may conclude that. 
the decoction of coffee, when it is filtered or has rested some 
time, contains no resin, ' 
Alcoholic Tincture of roasted Coffee —Roasted coffee di- 
gested in alcohol yiclds a strong coloured tincture, which 
precipitates, by means of water, a greater quantity of resin 
as the coffee is dry or green. _ In green coffee the resinous 
matter is white; in the tincture of roasted. coffee it is fawne 
coloured, 
T. 
Observations,.. 
Tt results from these experiments that roasting deyelops 
jn coffee odorous and resinous principles, and forms tannin, 
which is only soluble in cold'water$ a very singular pheno- 
menon. The gallic acid manifests itself in cofice at allthe 
temperatures of the water-employed. to dissolve it, .. The 
gum and the colouring extractive matter are more abundant 
in decoctions than in infusions; but the aromatic principle 
is more sensible and more agreeable in the latter. 
Roasted Coffee distilled.—I distilled several litres of water 
B4 fron 
