Commaille, A. Five grams of the powdered tea are mixed with 1 gram of calcined magnesia, dried twenty-four hours, and the caffeine extracted with three successive portions of chloroform. The chloroform extract is evaporated three times with boiling water. The aqueous extract is evaporated and the caffeine dried and weighed. Ber. d. chem. Ges., 8, 2, 1590.

Eder, J. M. Ten grams of tea are dried, powered, and mixed with 3 grams anhydrous sodium carbonate and 3 grams lead oxide. The mixture is moistened with 10 grams of water, dried, powdered, and extracted with chloroform. The chloroform is distilled off and the caffeine weighed. Zeitsch. f. anal. Chem., 19, 371.

Heijnsius, H. Separate the caffeine from tea by means of a subliming apparatus similar to that employed for benzoic acid. J. f. prakt. Chem., 49, 317; Jsb. d. Chem., 1849, 382; Pharm. Centralhalle, 1850, 73.

Iwanow. Extract with dilute sulphuric acid; add an excess of magnesia to the acid extract; evaporate and extract with ether. This method gives results uniformly lower than any other method. Zeitsch. f. anal. Chem., 4, 207.

Kremel, A. Estimation of caffeine in guarana. Ten grams of guarana are mixed with 100 cc 25 per cent alcohol in a flask and the whole weighed. After digesting for one to two hours on the waterbath, the loss in weight is made up with similar alcohol and 50 cc of the solution is (== 5 grams guarana) filtered off, mixed with calcium hydrate and dried. The finely powdered residue is extracted with chloroform, the chloroform distilled off, and the caffeine dried at 100° and weighed. Arch. Pharm. [3], 26, 318; Pharm. Post, 21,101.

Lieventhal, E. Extract the powdered tea with chloroform, filter, wash the residue with chloroform. Distill off the chloroform, extract the residue several times with boiling water, filter, and evaporate. The residue consists of caffeine. Zeitsch f. anal. Chem., 12, 104 (orig. Pharm. Zeit. f. Russland, 11, 369).

LoscH, A. Ten to 20 grams of tea are boiled twice with water, filtered, and the residue washed with boiling water until the filtrate runs colorless. The filtrate is mixed with magnesia equal to 1 1/2 times the weight of tea taken, and then evaporated to dryness on the waterbath. The residue is finely powdered and extracted with boiling chloroform. The chloroform is evaporated in a tared beaker, and the caffeine obtained dried at 100° and weighed. Arch. Pharm. [3], 25, 497; Jour. Chem. Soc, October, 1887, 1002.

Markownikoff, W. Ten grams of tea are extracted with 500 cc of water, after having been mixed with 30 grams of magnesia. The extract is filtered, the filter being washed with hot water and the filtrate and washings mixed with a little magnesia and sand, then evaporated to dryness. The residue is extracted with hot benzole, the benzole distilled off, and the caffeine weighed. Ber. d. chem. Ges., 9. G1313.

Paul, B. H. Author states that he has proved by experiment that chloroform can not be substituted for alcohol in determining caffeine in tea. By chloroform he obtained 1.3 per cent caffeine from a tea known to contain 3.78 per cent. Boiling alcohol was then used and the rest of the caffeine was obtained. Experiments were made to determine whether caustic lime decomposed caffeine. By experiment he determined that caustic lime does not decompose caffeine under the conditions obtaining in analysis, but that lime exerts a restraining influence on the extractive power with chloroform. Complete extraction of caffeine was obtained with boiling chloroform when magnesia was used. Pharm. J. Trans., March 1891, 882.

Paul and Cownley. Five grams of powdered tea are moistened with hot water, well mixed with 1 gram of calcicum hydrate, and the whole dried on the water bath. The dry residue is then transferred to a small percolating apparatus and extracted with strong alcohol. The clear liquor is evaporated to remove the alcohol and the remaining water solution, which amounts to about 50 cc, is mixed with dilute sulphuric acid which separates traces of lime and partially decolorizes the liquid. After filtering it is transferred to a separator and well shaken with chloroform, about 200 cc, in five to six successive portions. The united chloroform solutions are then placed in a separator and shaken with very dilute sodium hydrate. This renders the caffeine quite colorless. The chloroform is then distilled off and the caffeine weighed. Phar. J. Trans., [3], 908, 417.

Patrouillard, C. Fifteen grams tea are extracted with boiling water until completely exhausted. The liquid is filtered, evaporated to the consistence of an extract, mixed with 2 grams calcined magnesia and 5 grams powdered glass, and dried, The residue is ground to powder, extracted three or four times with 60 cc of ether and this solvent then distilled off. The crystals of caffeine obtained are redissolved in chloroform and recrystallized. Chem. Ztg. No. 9, Feb. 26, 1880; Chem. News, 42, 259.

Peligot. Make an aqueous extract of the tea, precipitate with lead acetate, add ammonium hydrate, and heat. Filter, pass hydrogen sulphide into the liquid, and filter again. Evaporate to a proper consistency and allow the caffeine to crystallize. This chemist determined the caffeine in exhausted tea leaves by means of a standard tannin solution, but does not give the details of his method. Zeitsch f. anal. Chem., 4, 207.

Schwarz, M. H. Exhaust the tea with boiling acidulated water, neutralize with lime, evaporate to dryness, and exhaust the residue with ether. Evaporate collect, and weigh the caffeine. Bull. Soc. Chim. de Paris Aug. 5, 1876, 3; Chem. News, 34, 94.

Smith, E. D. Coarsely powdered coffee (0.65 gram) is mixed with 0.13 gram magnesia, boiled 15 minutes with 150 cc water, filtered, and the fiitrate made up to 300 cc by percolation. The filtrate is evaporated to 20 cc and the residue treated with 120 cc strong alcohol, transferred to a filter, and washed with alcohol. The alcohol is then drawn off and the residue dissolved by gradual addition of small quantities of water. This water solution is extracted three times with 25 cc chloroform. The chloroform is distilled off and the caffeine dried and weighed. Chem. Centrbl. 1887,1270,1271; Zeit. oesterreich. Apoth., Ver., 41, 359.