Peculiar vegetable principle ifc coffee. 115 



of the quality of which I was wcllaffured. I then filtered the 



liquor, and reduced it nearly to drynefs, in a glafs evaporating 



dim, at a gentle heat. By this means I obtained a fmall quantity gave a clear ye 1 - 



of a clear yellow refuluum, like the moil tranfparent horn, and of low refi . due » 



the confidence of honey. This refiduum did not deliquefce, or 



feem to be fubjeft to change, by expofure to the atmofphere. 



It was foluble in alcohol. It did not manifeft either acid or 



alkaline properties. By fome experiments I perceived it to beeffentiallydifFer- 



a fubftance differing efientially from all the vegetable pr inci- entfro " lother 

 & J . t vegetable pro - 



pies with which I was acquainted; and, finding that I Could duels. 



obtain it pure by a method which Prouft ufed to procure tannin, 



I proceeded in the following manner: 



I poured a folution of muriate of tin into fome water whichit was precipi- 



had been made to boil upon coffee, and obtained a precipitate, tate^by muriate 



which I collected upon a filter, and warned. I then put it into and the tin 



water, and caufed a current of fulphurated hidrogen gas to ? 1 ro ^ n h ^ wn .^ r 



pafs flowly through the liquor. By this procefs the oxide of 



tin combined with the fulphurated hidrogen gas, and the fub- 



ftance originally contained in the coffee, but which, as I (hall 



immediately fhew, had combined with the metallic oxide, was 



difengaged, and remained in the liquor, while the hidrogen- 



ized fulphuret of tin was precipitated. It then remained only The difengaged 



to evaporate the liquor to obtain the vegetable principle. In new v e?jetable 



this flate it exhibited nearly the fame appearance as before it^ us obtained 



had been combined with the oxide of tin, but feemed of a purer. 



lighter colour, and more clear and tranfparent, being freed, as 



I fuppofe, from all extractive or other matter. 



Imagining it now to be fufhciently pure, I diflblved it in aitshabitudes.Sn- 

 very fmall proportion of water, and examined it chemically. lubie . in alcohol » 



The folution was of a bright horn colour ; had a bitter tali e, Dltter ta ft e . 

 though not unpleafant. It was neither acid nor alkaline. 



Solution of potafh, of foda, or of ammonia, poured into the Alkalies turn it 

 liquor, changed its colour to a bright garnet red. red » 



Nitric acid produced a fimilar effect. as Q ]d n i tr ie acid. 



Very concentrate folutions of the alkaline carbonates did not No precipitate 

 caufe a precipitate, as in a folution of tannin* Jj alkaline car- 



Sulphuric acid became of a dirty brown colour with the fo- Sulphuric acid, 

 lution, but no other change was apparent. * l£tle * nan g e » 



With muriatic, phofphoric, and the vegetable acids^ there Other acids, 

 was no change but what would naturally refult from a mix- noftc * 

 fure of the colours of both liquors, 



12 With 



