30 Memoir upon Coffee. 



The astringent liquid tried with turnsole tincture made it 

 quickly become red ; solution of sulphate of oxygenated 

 iron acquired a very siici't green colour : the muriates of tin 

 and lead were but vervi slightly psecipitfitcd : but in some 

 other trials 1 made comparatively with pyromucous acid 

 it presented the characters of the latter; from which I in- 

 ferred that a portion of the acid of coffee was disengaged 

 during the dislillalion without experiencing any alteration, 

 and that it was mixed with the pvromucous acid. After 

 having determined the proportion of the principles which 

 appeared to me to compose coffee, I thought it necessary to 

 examine if heat developed tannin in this grain, as Mr. Che- 

 ncvix asserted. In order to convince myself of this T roasted 

 some Martinique coffee until it was of a chestnut brown; 

 after having reduced it into powder, S portion was infused 

 in boiling distilled water, and a second was treated by the 

 same vehicle and bv decoction. These two liquors filtered 

 were tried each separately with gelatine, but they gave no 

 kind of precii)itate which could indicate the presence of the 

 tanning principle. 



The diflerence between these results and those of the 

 London chemist induced me to roast the coffee more 

 strongly. After it was treated, like the former, by infu- 

 sion, deco^jtion, and mixed with the solution of glue, there 

 did not even result any change in the transparency of the 

 liquor. Not confining myself to this second experiment, I 

 roasted some new coffee until it was of a brownish black, 

 and at the same time examined all the species known in 

 commerce under the names of Java, Bourbon, St. Domingo, 

 Martinique, Moka, &c.; but none of them gave me any 

 proofs of the existence of tannin treated as we have de- 

 scribed. Each of these infusions and decociions constantly 

 reddened the blue vegetable tinctures; it precipitated, in 

 fawn colour, the nmriates of tin and lead ; in green, the sul- 

 phate of oxygenaied iron ; in brown, the sulphate of copper; 

 and in chocolate colour, the nitrate of mercury. The pure 

 and carbonated alkalis, barytes, lime, and the hyurosulphu- 

 rets. communicated to theie infusions and decoctions a very 

 deep saffron-yellow colour; which led me to suppose that 



a part 



