CAFFEIN. 91 1 



lion, the liquid is concentrated by evaporation ; the caffein 

 crystallizes on cooling, and is purified by a second crystalliza- 

 tion. It may be obtained by boiling tea-leaves in water, filtering 

 and proceeding precisely as with coffee, and also from guarana. 

 It is snow-white, and in fine needles, having a silky lustre, 

 which have a very weak bitter taste ; does not act upon vege- 

 table colours, and is sparingly soluble in cold water and alcohol. 

 It loses 8 per cent of water at 212, fuses at 352 (178 centig.), 

 and sublimes at 725 (385 centig.). From its solution it is 

 precipitated only by tannin. Boiled in a solution of caustic 

 potash, it is resolved into carbonic acid, formic acid and am- 

 monia. With sulphuric acid and hydrochloric acid, it forms 

 crystalline compounds. According to the analysis of Liebig, 

 crystallized caffein consists of C 8 H 5 N 2 O 2 -f HO. The quantity 

 of this substance in different kinds of coffee was found by 

 MM. Robiquet and Boutron to vary ; Martinique coffee con- 

 taining 6.4 per cent, and St. Domingo coffee only 3.2 per cent 

 of caffein. It is evidently not the principle upon which the 

 peculiar properties of either coffee or tea depend. 



Caffeic acid was discovered in coffee by Runge. It is a white 

 powder, which yields, when heated, the characteristic aromatic 

 odour of roasted coffee. 



Coumarin is a neutral substance, extracted from the Tonka 

 bean, the fruit of the Coumarouna odorata, and the flowers of 

 the melilot, Melilotus officmalis, which crystallizes in silky 

 needles, or short prisms. Its composition according to M. 

 Henry is C 10 H 3 O 2 . 



Hesperidin, a crystalline substance, obtained by M. Lebreton 

 from the skin of the unripe orange or lemon. 



Populin, found by Braconnot, in the bark of the Populus 

 tremula, where it is acompanied by salicin. It crystallizes in 

 snow-white silky needles, has a sweet taste, not unlike that of 

 liquorice, requires about 2000 times its weight of cold water to 

 dissolve it, but dissolves in about 70 times its weight of boiling 

 water.* 



Plumbagin, discovered in the root of the Plumbago europea. 



Daphnin, extracted by Gmelin and Baer from the bark of the 

 Daphne mezerium, or common mezerion. It is crystalline, 

 colourless, but little soluble in cold water, soluble in alcohol 



* Ann. de Chim. et de Phys. t. 44, p. 296. 



