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Bibliography Of Methods For The Estimation Of Caffeine - Allen, A. H. A thin dough is made of the powdered tea, caustic lime, and water and the whole allowed to stand several hours. It is now dried on the water-bath, extracted with benzole, the benzole evaporated and the caffeine re-crystallized from water. Chem. News, 29, 129, 140, 167, 189, 221; 30, 2.

Beekman. The material is extracted with water containing a little sodium carbonate. The aqueous extract is mixed with an alum solution, the excess of alum precipitated by sodium carbonate and the precipitate filtered off. The filtrate and washings are evaporated to a syrupy consistence, made alkaline with sodium carbonate, and the caffeine extracted with ether. Zeitsch. f. anal. Chem., 4, 206.

Blyth, A. W. This method is based on the ease with which caffeine sublimes. The author proceeds as follows: From one to two grams of finely powdered tea are boiled with water for an hour in a flask connected with an upright condenser. The whole is transferred to a porcelain dish, about its weight of magnesia added, and the mass evaporated nearly to dryness. It is now transferred to an iron subliming plate and covered with a tarred glass funnel, the edge of which is accurately ground and which has a neck several inches long. The mixture is first heated to 110° C., then slowly raised to 200° C. and finally to 220° C. The caffeine sublimate is collected and weighed. Analyst, 2, 39; also in Foods: Their Composition and Analysis, A. W. Blyth.

Canada, Dominion of. Ten grains of the finely ground sample are exhausted by repeated boiling with water, filtered, the filtrate made up to a definite vol" ume, and an aliquot part precipitated with basic acetate of lead. The filtrate without any concentration is shaken with successive portions of chloroform. The chloroform is removed by distillation and the caffeine is weighed. Report on Adulteration of Food, Supplement III, Report of the Dept. of Inland Revenue, 1886.

Cazeneuye-Caillol. Add to the tea four times its weight of boiling water and when the leaves become soft add an equal weight of slaked lime. Dry and extract with chloroform. Distill off the chloroform and dissolve the residue in boiling water. Filter and wash with boiling water. Evaporate the filtrate and washings carefully on the water bath to obtain the caffeine. Zeitsch. f. anal. Chem., 17, 221.

Claus, C. The material is extracted with ether and the extract evaporated to one-third its original volume. This is now mixed with one-tenth of its volume of very dilute sulphuric acid, shaken in a separator, and the acid solution run off, successive portions of dilute acid being added until the ether is no longer bitter. To the united acid solutions magnesium oxide in excess is added, its whole mass dried, pulverized, and extracted with ether. The ethereal solution is evaporated and the resulting caffeine weighed. Zeitsch. f. anal. Chem., 4, 205.