Memoir vpon Coffee. 31 



a part of the acid of coffee existed in them free, merely en- 

 tangled in a little extractive matter and a good deal of char- 

 coal. 



It- remained, in order to render this analysis more com- 

 pletCj to consider the pure acid of coffee with respect to its 

 ihemical attractions for the different known bases. I ob- 

 served, after a multiplicity of experiments, that the metallic 

 oxides were the bodies which combined the most intimately; 

 those of tin, lead, mercury, iron, antimony, bismuth, and 

 copper, precipitated from their solutions or put in contact 

 with this acid, on aiding its action by heat, were there com- 

 bined, and formed saline comipounds, of an austere and me- 

 tallic taste in general, not crystallizable, pulverulent, and little 

 soluble in" water ; that of mercury was, however, dissolved 

 in about 160 parts of this liquid, combining itself with and 

 precipitating several colouring matters, which fix very so- 

 lidly, particularly when stuffs are impregnated and boiled 

 with the compourids so formed with tin, lead, antimony, 

 and alumine. The colouring particles of saffron, of yellow 

 wood, madder,, sorrel, and of some pharmaceutical extracts, 

 &c., are those which have proved to me that this new mor- 

 dant may become useful in the art of dyeing. All these sa- 

 line combinations are decomposable by fire; biit more easily 

 by sulphuric acid ; those of iron, tin, and antimony, ex- 

 cepted. The nitric acid decomposes only the combination 

 which the acid of coffee forms with copper. 



The earthy substances also form saline compounds with 

 the acid of coffee ; alumine is that which seemed to unite 

 most easily ; this combination, which is not very soluble, 

 has a slightly saccharine and astringent taste, always pulve- 

 rulent, and fixing some colours. Lime, barytes, strontian, 

 and magnetia, combine with it also : the last of these e.irths 

 adheres to it only very feebly. 



Putasli, soda, and ammonia, form compounds extremely 

 soluble, of a bitter taste, little crystalli/able, and decom- 

 pfjsable by a slight heat, of a colour always yellow, which 

 becomes brown upon heating it too long. 



The muriates of tin and lead dissolved in water, speedily 



dccouipose these salts, as does also sulphuric acid, which, 



4 however. 



