Memoir upon Coffee. 27 
by the ordinary method; but, in order to leave no doubt on 
this subject, gall-nuts by the same process. The muriate 
of tin formed a more abundant precipitate in the latter than 
in coffee; this precipitate, decomposed, like the former, by 
the sulphuretted hydrogen gas, yielded mean acid of the 
same colour and the same taste, enjoying the same proper- 
ties, and presenting no difference except in the proportions, 
I then thought I might conclude that the coffic acid does 
not exist, but that coffee contains less gallic acid than gall- 
nuts. 
It is possible that this gallic acid may present, in its com 
binations and compounds, some slight shades which make 
it differ a little from the acid produced from oak-galls, but 
itis not the jess of the same nature. We know that the 
immediate materials of vegetables, although of the. same 
species and perfectly analogous, are not rigorously identi- 
cally the same; the gums and the saccharine matters pre- 
sent variations in their physical properties ; nevertheless the 
saccharine substance and mucilage are the same when ch¢- 
Phically considered *, 
Proust has proved that tannin, obtained from several ve- 
getables, presents differences, It is possible, therefore, that 
the gallic acid drawn from coffee is not absolutely the samg 
as that of galls; but it is by no means a distinct acid. 
Recapiiulation. 
It seems to be demonstrated by the above analysis that 
the coffee-berries (as known in commerce) contain muci+ 
Jage in abundance, a good deal of gallic acid, a resin, a con- 
crete essential oil, some albumen, and a volatile aromati¢e 
principle. ‘To these principles we may add those which are 
found in most vegetables, viz. lime, potash, charcoal, iron, 
&c.t Roasting develops the soluble principles ; but it ought 
to 
* The feculum of potatoes does not resemble that of wheat; the latter 
differs from that of sago, arum, maize, &c.; nevertheless, all the chemists 
tell us that it is an amylaceous substance, and they acknowledge the same 
principal characters in all of them. 
+ The presence of iron in a vegetable is a common thing, but the pre- 
sence of iron in a vegetable which contains plenty of gallic acid, without this 
5 acid 
