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SELECTED ARTICLES. 
the liquids were united and the neutral acetate of lead added 
in slight excess, and a magma obtained of a beautiful citrine 
yellow colour, which, when properly washed and suspended 
in a certain quantity of water, was submitted to a current of 
sulphuretted hydrogen. When the reaction had been suffici- 
ently prolonged, it was heated to boiling, in order to drive off 
the excess of gas and then thrown upon a filter. The liquid 
product was evaporated by means of a salt water bath, to a 
consistence almost syrupy, then allowed to remain a very 
long time, and yet no crystallization took place. It is very 
probable that this product was not pure, for the coffee evidently 
contained colouring matter, which alkalies rendered more 
apparent by deepening the shade and causing it to pass often 
from yellow to green, properties which are found in a marked 
degree in the product of the precipitate of lead, treated by 
sulphuretted hydrogen; but this product also contains an acid 
of some energy, judging by the taste which is very decided. 
These two principles, viz.: the colouring matter and the acid, 
are present in the greater number of combinations, so that it is 
difficult to establish with clearness the distinctive characters 
of each of them; and doubtless, from this cause, all the che- 
mists who have investigated them up to the present time, 
have disagreed as to the nature of the acid; — thus, while Cadet 
regards it as the gallic, Grindel confounds it with the kinic, 
Paysse makes it a peculiar acid, and Pfaff considers it as the 
cause of the aromatic odour of burnt coffee, which we may 
remark, en passant, appears to us to be very far from the 
truth, for we have observed nothing that can support this 
opinion. We would be more disposed to look upon it as the 
gallic acid, with Cadet, on account of its action upon the per- 
salts of iron, for which it is really a very sensible reagent. 
We conceive that in order to give a positive opinion with 
regard to it, it is necessary to separate it from the colouring 
matter; but this product does not possess sufficient interest 
to induce us to seek the means of overcoming this difficulty. 
To give connexion to our experiments, we took the decoc- 
tion from which the acid and colouring matter had been 
