32 Memoir vpoi Coffee. 



however, iloc? not act, in.on that of alumip.e. The nitric, 

 muriatic, and pho5i)horic acids decompose them also in a 

 srreat measure; it happens at the saiDe time that the acid of 

 colfee is it?elf changed into malic acid by the nitric, after 

 the latter has been isolated from its union with the bases, 

 in such a manner that a malate and nitrate is obtained, as I 

 was convinced by thus decomposing the caliate of lime. 



Coficlus'ion, 



1. It results From all that precedes, thai cofice contains a 

 particular acid, very distinctly characterized ; that it there 

 enjovs a sort of liberiv, :oi;ice the poivder of this grain sud- 

 denly reddens the blue vegetable tinctures ; and that infu- 

 sions in cold water, and even in alcohol, may be separated 

 from the acid in a state more or less pure. 



2. That the acid decoction of coffee decomposes with fa- 

 cility aln)03t. all the metallic solutions, particularly those of 

 lead, tin, iron, &c»* , 



3. That the precipitates obtained by the mixture of this 

 decoction and tv.etallic solutions, are more abundant and 

 more highly coloured than those formed by the same acid 

 in a pure state ; that this difference, I say, proceeds from 

 two causes, which must be considered: first, because the 

 decoction of coftee, besides the caffic acid it contains, con- 

 tains also extractive matter, colouiing matter, albumen, Sec; 

 that the colouring matter is partly precipitated by the affinity 

 it has with the compound formed of caiilc acid and the me- 

 tallic base ; that the albumen, on the other hand, isolated from 

 the acid body which favoured the solution in the liquid, is 

 deposited, and increases the volume of the precipitate; that 

 in order to be convinced of this fact, in cue word, it is only 

 necessary to boil a cafiate of tin, lead, or alumine, in a co- 

 loured vegetalile decoction, in order to obtain the result now 

 mentioned. 



4. That the acid of coffee may be obtained very pure by 

 mixing watery decoctions of coffee or alcohol macerations 

 of it, with muriate of tin or of lead, and afterwards decom- 



* Ryhiner [Journal df Phi/xi'jiip, tom. xiii. August 1778, p. 238.) has aecer- 

 fained that the infu.ions of the dilTerent ipecics of ihs cofiue of tTie Leviiut 

 and lis ishnds arc astringent. 



posing 



