Hfj PECULIAR VEGETABLE PRINCIPLE IN COFFEE, 



Solution of iron; With any folution of iron in which there was not excefs of 



^TfuJT en '' acId ' the lic l uor P afl " ed to a beautiful green ; and, if it was con- 

 centrate, there was a green precipitate. Salts formed of the 

 red oxide of iron fucceeded the beit ; and the reciprocal action 

 of this principle and iron is almoitas delicate as that of either 

 gallic acid or tannin and iron. 

 Muriate of tin, With muriate of tin there was a very abundant yellowifh 

 pr p * precipitate, which was a combination of the new vegetable 

 principle with oxide of tin. Both this precipitate and that 

 with iron are foluble in all the acids, and the liquors lole their 

 colour. 

 Waters of lime, Lime-water did not caufe any precipitate in this liquor, nor 

 barytes, ftron- jjj ft r ontia-water. Baryles-water gave a fawn coloured pre- 

 cipitate. With lime-water tannin gave a bluifh-green precipi- 

 tate ; and nearly the fame with ftrontia- water, as alfo with ba- 

 rytes-water. 

 Gelatine gave no A folution of gelatine did not give any precipitate with this 

 precipitate. vegetable principle. The effect of tannin upon gelatine is well 



known. 

 Hence this prin- By thefe experiments it is proved that the principle bears 

 ciple is different f u ffi c ient charades to diftinguifh it from tannin, or any other 

 vegetable principle with which we are acquainted. The only 

 property which it pofTeffes in common with tannin, is its affinity 

 for oxide of tin, while it is clearly diftinct from tannin in every 

 other point* 

 Coffee does not It is evident that coffee, before it is roafled, does not con- 

 exhibit tannin tain tannin. A folution of gelatin poured into a decoction of 

 well roafled coffee, gives, however, an immediate precipitate ; 

 and the precipitate is the combination of tannin with gelatin. 

 MefFrs. Prouft, Seguin, and Davy, have obferved, that heat 

 "Whether this developes the tannin principle in many vegetables. In a 

 new principle, commercial point of view, it might be advantageous to exa- 



while intheve- . , , r , r , , , ° r . . ° r . 



getable, may not*™ 116 * whether thole vegetables are not tuch as, betore they arc 

 be converted in- heated, contain this new principle. Although I did not per- 

 inea*."" 111 ^ ceive that the principle, when infulated from the entire veget- 

 able, was converted by heat into tannin ; yet the prefence of 

 the other component parts of the vegetable may influence the 

 diftribution of elements in fuch a manner as to produce combi- 

 nations different from what the feparate principles will afford. 

 I have not had an opportunity of extending thefe refearches 

 any further in the vegetable kingdom. 



XII. Account 



