Vegetahle Principle contained in Coffee. 35 1 



porating difh, at a gentle heat. By this means I obtained a 

 fmall quantity of a clear yellow reficluum like the moft Iranf- 

 parent horn, and of the confiftence of honey. This refiduum 

 did not deliqiiefce, or feem to be fubjetl to chane;e, by expo- 

 Uirc to the atmofphere. It was foluble in alcohol. It did 

 not manifeft either acid or alkaline properties. Bv fome ex- 

 periments 1 perceived it to be a fubitance differing effentially 

 from all the vegetable principles with which I was acquaimed; 

 and, finding that I could obtain it pure by the method which 

 Proud iifed to procure tannin, I proceeded in the following 

 martner : 



I poured a folutlon of muriate of tin into fome water which 

 had been made to boil upon coffee, and obtained a precipi- 

 tate, which I colleAed upon a filter, and waflied. I then 

 put it into water, and caufed a current of fulphuretled hydro- 

 gen gas to pafs (lowly through the liquor. By this procefs the 

 oxide of tin combined with the fulphuretted hydrogen gas ; and 

 the fubftance originally contained in the coffee, but which, 

 as I (hall immediately Ihow, had combined with the metallic 

 oxide, was difcngaged, and remained in the liquor; while 

 the hydrogcnized fulphuret of tin was precipitated. It then 

 remained only to eyaporate the liquor to obtain the vegetable 

 principle. In this (late it exhibited nearly the fame appear- 

 ance as before it had been combined with the oxide of tin ; 

 but feemed of a lighter colour, and more clear and tranf- 

 parent; bring freed, as I fuppofe, from all extraftive or 

 other matter. 



Imagining it now to be fufficiently pure, I diffolved it in 

 a yrr)' fmall proportion of water, and examined it chemically. 



The Iblution was of a bright horn colour, and had a bitter 

 tafte, though not unpleafant. It was neither acid nor alka- 

 line. 



Solutions of potafi), offoda, or of ammonia, poured into 

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



Nitric acid produced a fimilar effect. 



Very concentrate folutions of the alkaline carbonates did 

 not caufc a precipitate, as in a folution of tannin. 



Sulphuric acid became of a dirty brown colour with the 

 fululion ; but no other chimgc vvas apparent. 



With muriatic, phofphoric, and the vegetable acids, there 

 vvas no change, even or colour. . ' 



With muriate of gold, of platina, of copper, there was 

 not any change, but what would naturally rcfult from a 

 mixture of the colours of both liquors. 



With any folution of iron, in which there was not excefs 



of 



