I 
NOTE UPON COFFEE. 229 
separated by the acetate of lead, and caused to pass through 
it a current of hydro-sulphuric acid to decompose the excess 
of acetate. This liquid being heated and filtered, was finally 
evaporated to the consistence of an extract. This extract 
re-dissolved in alcohol, furnished two different products, one 
soluble in this vehicle and which yielded, upon evaporation, 
an abundant crystallization of caffein; the other soluble in 
water, left only extractive matter, tumefying by heat and giv- 
ing off*, when torrefied, an odour more analogous to that of 
burnt coffee, than any other product having the same origin — 
but yet far from identical with it. 
We pass rapidly over these facts, because none of them 
being capable of facilitating the solution of the problem 
sought for, it would be useless to insist upon them further. 
We have tried other measures in addition, but without 
greater success; these we shall mention for the benefit of our 
successors. It has been supposed that torrefaction developes 
new principles, and it has often been asserted that an essen- 
tial oil is driven over by heat, the true source of the odour 
of coffee. To be assured of this, we constructed a small 
condensing apparatus, composed of two matrasses fitted to 
each other, one the roaster, the other the receiver and con- 
denser. It was believed, from the arrangement we had made, 
that no product of torrefaction could escape, and yet only a 
small quantity of pure water, in the first instance, came over, 
then acetic acid coloured with a litle oil having an agreeable 
taste, but very sensibly empyreumatic, although the coffee 
had not attained the requisite degree of charring. Such were 
the only volatile products we obtained, water, acetic acid, 
and empyreumatic oil. In fact, this oil, when in very small 
amount, has an agreeable odour, and the acetic acid accompa- 
nying it, contributes not a little to bestow greater diffusibility 
upon it. It may, perhaps, be recollected that one of us has 
proved that acetic acid serves as an odoriferous vehicle to 
many perfumes. 
To return to our operation, we ought to add that the longer 
this torrefaction is prolonged, the more the acetic acid becomes 
VOL. III. NO. III. 29 
