18 Memoir upon Coffee. 
I shall perhaps be more fortunate in throwing light upor 
this substance, in a manner as yet new. 
Examination of drt y Coffee. 
ob Coffee treated with Water-—When boiling water is 
poured upon dry coffee, such as we meet with in the shops, 
the water becomes yellowish green *. . If the action of heat 
is continued, the decoction becomes brown, and a slight 
scum is formed, which remains insoluble; when filtered it 
passes very clear, and becomes turbid upon cooling. A 
little caustic potash poured into this decoction makes it 
more brown. Ammoniaproduces the same effect. Lime 
water produces an, abundant flaky precipitate ; sulphate of 
iron converts it into a black ink. Solution of gelatine does 
not become turbid upon being mixed with this decoction. 
The oxymuriatic acid only partly discolours it; arid if any 
alkali is added to the mixture it becomes red. 
Distillation.—I distilled eight pounds of water over a 
pound of dry coffee. I obtained a very aromatic water, on 
which floated’ some drops of a concrete oil like that of the 
myrica cerifera. The decoction remaining in the alembic 
_was viscous... I dilutedit a little with water, and poured 
alcohol into it; an abundant matter was precipitated, which 
being, collected on the. filter, was soluble in water; and had 
all the characters. of a mucilage. The coffee from which 
the water had been. distilled, dried in a stove, and digested 
in alcohol, furnished a tincture which precipitated by means 
of water. 
The watery decoction of dry coffee ee not redden the 
blue vegetable colours + it even gives a green colour to turn~+ 
sole tincture. Every chemist who has analysed coffee before 
my time has. said that.the decoction holds a free acid su- 
spended in, it, which reddens the blue) vegetable colours. 
Geoffroy has even gone the length of asserting that water 
distilled from epiee in B.M. became very acid. I have 
tried five different varieties of coffee, and repeated my ex- 
‘ When the coffee is newly gathered, its decoction is of a superb emerald. 
green. Alac may be then made of it. .M. Dupont de Nemours assured me 
that he made use of it as one of the tints for colouring maps. 
periments 
