22 Memoir tipon Coffee. 



presented phoenomena very analogous to those of the decoc- 

 tion ; 1 say analogous, because the decomposition of some 

 of them appeared to have taken place more slowly and less 

 completely ; which made me presume that the presence of 

 the greater quantity of extractive matter than the decoction 

 contains was one of the causes which facilitated these de- 

 compositions, and increased the quantity of the precipitates. 

 We shall return to this subject: this solution was moreover 

 mixed with certain other re-agcnts, of which it is interesting 

 to ascertain the action. 



With the prussiate of iron and crystallized potash dis- 

 solved, the mixture of the liquor gave a green colour; with 

 the prussiate of ammonia, a yellow colour; with the prussic 

 acid, a colour slightly gray. 



The preceding experiments only proving the existence of 

 an acid combined, or simply mixed with foreign matters, 

 Avhich might perhaps have occasioned some of the phseno- 

 incna observed, it became important to verify the processes 

 employed by Mr. Chenevix (who has not ascertained the pre- 

 sence of the acid I remarked) ; and, in short, to take away 

 every kind of uncertainty upon this matter by endeavouring 

 to obtain it by the processes of the Enrrlish chemist. 



I boiled, in a glass alembic in a sand bath, 489 grammes 146 

 milligrammes (l pound) of Martinique coffee, reduced into 

 powder, in three times its weight of distilled vi'ater for about 

 two hours : the water,when filtered, I replaced upon the husks 

 as they were condensed in the distillation, with an addition 

 of abuuf a kilogramme of the same liquid. The operation 

 being finished, I filtered and mixed the two liquors; 1 then 

 poured muriate of tin, crystallized and dissolved in pure 

 water, until no more precipit:;te was formed : f passed the 

 whole through a filter, washed the husks remaining upon the 

 paper in several waters, and afterwards introduced the whole 

 iuto a tlask with tw^o apertures, with six times its weight of 

 water: having carefully agitated the mixture, T introduced, 

 by means of a suitable apparatus, sulphuretted hydrogen gas, 

 which passed slowly through the liquor. The decomposi- 

 tion of the compound of tin and the acid of coffee was easily 

 effected : the new combination of the hydrosulphurct of tin 



was 



