CAFFEINE, kat-Win, THE'INE, or GUA RANINE, ( Brazil) (from Neo-Lat. coffee, coffee), C,}1.„N,O,± HO. An alkaloid found in tea, coffee, and other ve;etable products. It is a solid substance, in long, flex ible, colorless needles, which melt at 225° C. It combines with the strong mineral acids to form salts, such as the hydrochloride of caffeine—which are, however, very unstable. Pure caffeine is odor less. has a bitter taste, and is permanent in the air. If its solution in chlorine water is evaporated to dryness and the remaining residue redissolved in dilute ammonia water, a beautiful violet-red coloration is obtained. By this reaction the pres ence of caffeine may be detected in samples sub mitted for examination. Caffeine may be ex tracted from the tea by treatment with hot water and the subsequent addition of lime; the mixture thus obtained is evaporated to dryness, and the caffeine is dissolved out of the residue by chloroform. It may be prepared from coffee by the following process. The coffee is extracted with water: the solution is precipitated with lead acetate and filtered; sulphuretted hydrogen is passed into the filtrate to eliminate the excess of lead acetate added; the solution is then ren dered more concentrated by evaporation and is neutralized with ammonia: on cooling, crystals of caffeine separate out, which may be purified by recrystallization from water. The amount of caffeine found in tea and coffee varies with the product—coffee usually contains less than 1 per cent., while amounts varying between 2 and 4 per cent. have been found in different samples of tea.
The alkaloid is supposed to exist in these prod ucts in combination with tannic acid and potas sium. C'aff'eine has absolutely no nutritive value. If taken in moderate quantities, it has the effect of increasing the blood-pressure and of stimulat ing the cerebrum. thus increasing the reasoning power and the imagination; it is even believed to increase the powers of muscular endurance. Larger quantities. however, are liable to cause trembling of the muscles, and toxic doses have the effect of paralyzing the heart. The symp toms of caffeine-poisoning are buzzing in the ears. flashes of light, a heavy feeling in the head. restlessness, insomnia, a vapid and feeble pulse,' coldness of surface, and rise of central temperature. Even moderate quantities of tea and coffee are in some persons liable to cause irregularity of the heart. Therapeutically caf feine is used to combat certain forms of nervous and cardiac depression, certain headaches and neuralgias, gout, the insomnia of alcoholism, and opium narcosis. It is also used as a diuretic. Caffeine was discovered in coffee in 1820 and in tea in 1827 (theine) ; in 1838 Jobst proved the identity of caffeine and theine. and in recent years Emil Fischer succeeded in producing the sub stance artificially. Fischer determined the chemical constitution of caffeine, and showed that it is closely allied to uric acid, as well as to tile alkaloid theobromine.