Memoir u[jon Coffee.- 33 



jjosing these co'jibinations by sulphuretled hydrogen, as 

 practised by Mr. Cheiievix as well as by myself, or rather 

 on decomposing the cafiate of lead by the sulphuric acid. 



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

 which I obtained it, and that it is completely soluble in al- 

 cohol and water. 



6. That it is capable of decomposing the prussiate of 

 iron contained in the prussiate of potash (a common re-agent 

 in the laboratories) by forming with the metal a green com- 

 pound, which is precipitated ; and in this respect it may, 

 perhapSj be of great use to chemists, in order to obtain very 

 pure, prussiate of potash, which hitherto could not be de- 

 prived of some portions of iron which it obstinately retained. 



7. That the colour which it communicates to the solu- 

 tion of oxvgenaied and green sulphate of iron, seems to be 

 completely new. 



8. That the attraction of the compounds which it forms 

 with tin, lead, antimony, and alumine, and with the co- 

 louring matter of infusions or vegetable decoctions, may 

 render it very useful in the art of dyeing. 



g. That the different species of coffee contain it in pro- 

 portions little variable ; and that ii exists at the same time, 

 vithout alteration, in a smaller quantity, in the infusions 

 and decoctions of coffee roasted at different degrees, as well. 

 as in the products of the distillation of this crain. 



10. That-the comparison I have made of the properties of 

 this acid with the gallic acid and the tanning principle, showed 

 no kind of identity of nature among these three very dif- 

 ferent substances. 



11. That the particular principle obtained by Mr. Che- 

 tievix is nothing else than the acid iu question, but which 

 had not been subjected by this accurate chemist to a strict 

 enough examination. 



12. That, having examined the infusions and decoctions 

 of different kinds of roasted coffee, they gave me no evi- 

 dence of the existence of the tanning; principle on mixing 

 them with gelatine, as asserted by Mr. Chenevix. 



13. Th.at the acid of coffee is susceptible of being united 

 Vol. 27. Noi 105. Fid'. 1807. C with 



