-2d Memoir vpon Coffee. 



was not a crowd of other distinctions, which it would be 



superfluous to relate bene. 



As to the oraHic acid and that of coffee, the former preci- 

 pitates in black the suiphate of iron: it is very sokible 

 in water; it precipitates solutions of gold and silver in 

 brown, those of bismuth and mercury in yellow; and causes 

 no change in that of the green sulphate of iron; while the 

 acid of cofi'ee gives to this last a very sensible green tint, 

 and precipitates the iron from it in the same colour on ex- 

 posure to the air; it gives precipitates of a dirty while with 

 the nitrates of mercury and bismuth, without causing any 

 change in the solutions of gold and plalina. 



The existence of an acid in coiTee being once well demon- 

 strated, it only remains to know in what proporlions it does 

 exist, what are the combinations it is capable of forming ; 

 and, in one word, the order it follows in its chemical attrac- 

 tions. 



In order to attain these branches of knowledge I treated 

 2000 parts of coffee of the above species, and prepared as 

 above described, with a sufficient quantity of pure water, 

 by various decoctions and in close vessels. The extract, 

 brought to the consistence of honey, was 2Sa parts : I took 

 100 parts of this and dissolved them in six times their weight 

 of jture water; I afterwards proceeded, as already pointed 

 out, with muriate of tin, and decomposed the new com- 

 bination by sulphuretted hydrogen. This operation fur- 

 nished, after having suitably evaporated the liquor contain- 

 ing the acid of coffee, 0-55 of this matter. Wishing to know 

 the substances with which it was combined in the extract of 

 coffee, I look 100 fresh parts of' it, which I dissolved m an 

 equal quantity of water, upon which solution I poured as 

 much highly rectified alcohol ; at the same instant t*he li- 

 quor became a little milky, and a whitish flaky matter was 

 S'.qiaratcd from it, which I collectLfl on a filter: when dried 

 It weighed 0'05, and when examined it presented all the 

 characters which belong to vegetable albumen. Having 

 afterwards mixed a great quantity of water with the mixture 

 of alcohol and acid of coffee and extractive matter, the liquor 

 formed a second deposit, more coloured, collected at one 



sinole 



