ON COFFEE. 127 



hidrogen, as Mr. Chenevix did ; or by decomposing coffat 

 of lead by the sulphuric acid. 



5. That this new acid is not crystallizable in the state in It is soluble in 

 which I obtained it ; but is completely soluble both in ^oho* 

 water and in alcohol. 



6. That it is capable of decomposing the prussiate of Decomposes 

 iron contained in the prussiate of potash, forming with this fro^'and forms 

 metal a green precipitate: and in this respect it may be of a green preci- 

 great service to chemists for obtaining prussiate of potash pi a e ' 

 perfectly pure, which hitherto they have been unable to 



deprive of a certain portion of iron, it retaining this with 

 so much obstinacy. 



7. That the colour it communicates to the oxigenized Its effects on 

 and green sulphate of iron appears altogether new*. *"on 



8. That the attraction of the compounds it forms with May be of use 

 tin, lead, antimony, and alumine, for the colouring part as a mordant - 

 of vegetable decoctions or infusions, may render it of use 



in the art of dyeing. 



9. That the diiferent kinds of coffee contain it in nearly in all kinds of 

 the same proportion ; and that it exists without alteration, coff e e > r *w or 

 though in smaller quantity, in the infusions and decoctions 



of coffee roasted in different degrees, as well as in the pro- 

 ducts of its distillation. 



10. That the comparison I made of the properties of Differs both 

 this acid with those of the gallic acid and tannin did not ^™J^/ id 

 show me any identity of nature between these three very 



different substances. 



11. That the peculiar principle obtained by Mr. Chenevix rtwas the pe- 



. , . ■• , • I- ,, , ., culiar principle 



was, no doubt, the acid substance in question ; though it obtained by 



was not examined with sufficient strictness by that learned Chenevix. 

 chemist. 



12. That, having examined the infusions and decoctions No tannin in 

 of different sorts of roasted coffee, th*.y did not afford me roasted coffee ' 

 any proof of the existence of tannin, by mixing them with 

 gelatine, as Mr. Chenevix asserts. 



* Cofnc acid, dissolved in six times its weight of water, added 

 to a solution of oxigenized sulphate of iron, immediately gava it 

 a fine green colour ; and after it had stood six hours, a precipitate 

 of the same colour fell down. To a solution of green sulphate it 

 gave at first a very light green tinge, but this grew deeper, after 

 it had been some time exposed to the air. 



13. That 



