\ 24 ON COFFEE. 



in their physical properties ; yet all mucilage, all saccha- 

 rine matter, is the same chemically considered*. Proust 

 has demons' rated, that tannin obtained from different vege- 

 tables displayed some differences : it is possible, therefore, 

 that gallic acid obtained from coffee may not be absolutely 

 the same as that from galls, but it is not a distinct acid. 



Recapitulation. 

 principles of It appears to be demonstrated from the analysis above 

 given, that the coffee berry contains abundance of muci- 

 lage, a great deal of gallic acid, a resin, a concrete es- 

 sential oil, albumen, and a volatile aromatic principle. 

 To these principles are added those found in many vegeta- 

 EfFects of roast- bles ; namely, lime, potash, iron +, carbon, &c. Torre- 

 mg " faction develops the soluble principles ; but it must be 



moderate, if we would retain the aroma, and not decom- 

 pose the acid, the gum, and the resin. 

 Tannin pro- The roasting adds anew principle, which is tannin, 



Treatec^with though in very small quantity. The cold infusion is very 

 water. aromatic; but it contains little mucilage or gallic acid. 



The hot infusion retains some of the aroma ; and the prin- 

 ciples dissolved in it are in such proportions, as to be agree- 

 able to the taste. The decoction has little aroma, and is 

 much loaded with gum and gallic acid, the resin too may 

 even be suspended in it, and it is less pleasant to the taste 

 than the infusion. 



Different sorts The coffees from the island of Bourbon and Martinico 



of coffee. 



*The fecula of potatoes does not resemble that of wheat, and 

 this again differs from the fecula of cassada, sago, salep, arum, 

 maize, &c. Yet chemists would say of all these, that it is an 

 amylaceous substance, and find in them the same leading cha- 

 racters. 

 Iron in coffee t The presence of iron in vegetables is very common ; but that 

 with gallic acid, of iron in a vegetable containing a great deal of gallic acid, with- 

 ted t> 0t "l ar out *^ s ac ^ oem S combined with it, and imparting a blue or 

 black colour to the vegetable, is a very remarkable phenomenon. 

 It appeared to me deserving of inquiry, and I made a comparative 

 analysis of the ashes of galls, in which also I found a sensible 

 quantity of iron. [It may be observed, however, that galls have 

 very often an evident blue tinge; so much so, that it is commonly 

 considered as an evidence of superior quality. T.] 



do 



