Snyder, Harry. Author states that the albuminoids of tea are almost entirely insoluble in hot water. He extracts the powdered sample with four or five portions of hot water, collects the residue on a filter (S. & S. No. 589), and transfers filter and contents to a digestion flask, and determines the nitrogen by the Kjeldahl method. Total nitrogen in the sample (as determined by Kjeldahl method for alkaloids), less nitrogen of the insoluble portion, gives the alkaloidal nitrogen from which the caffeine may be determined. See Kozai's article on teas, which gives the distribution of the nitrogen, page 879, Journ. Anal. Chem., 4, 443.

Stahlschmidt. Extract the tea six hours with water; precipitate with basic lead acetate; decant and wash the precipitate by decantation. Remove excess of lead by H2S; filter off the PbS and evaporate the filtrate to a sirup. Extract this with hot benzole, which on evaporation will yield the caffeine. Poggendorf 's Annalen, 112, 441; Chem. centrbl., 1861,396.

Thompson. Exhaust the tea by boiling with water, remove the tannin by means of lead acetate, and free the filtrate from lead by means of hydrogen sulphide. The lead sulphide is filtered off and the caffeine precipitated in the filtrate by means of potassium carbonate. The caffeine is crystallized from an alcoholic, solution to purify it. Zeitsch. f. anal. Chem., 1872, 203; Jsb. d. Chem., 1872, 924.

Vite, F. The author has made a critical study of the methods for the estimation of caffeine in teas. He adopted a modification of Hilger's method. Extract 5 grams tea, 3 times, one hour each, with successive portions water of about 300 cc.; evaporate the united extracts to one-fourth the original volume, and while still hot add fresh lead hydrate and coarse sand. Dry on water bath and extract with chloroform. Collect the caffeine as usual and dry at a temperature not exceeding 100° C. - Mitth. Lab. ang. Chem. Erlangen, 3,131; Chem. Centrbl. (1890), 2, 274; Joum. Chem. Soc. 140, 372.

Waage. This chemist prefers Mulder's method modified as follows: Ten grams tea are exhausted by boiling four times with water, the exhaustion requiring about three hours. The decoction should amount to about two liters. It is evaporated to a syrupy consistence after filtering. The residue is mixed with 2 grams magnesia and 5 grams pure sand, dried, extracted in a Soxhlet appa-ratus with anhydrous chloroform, and this extract carefully evaporated. The caffeine is purified by dissolving in water, filtering, evaporating to dryness, drying two hours at 100c C, and weighing. - Archivd. Pharm, 225,443; Zeitsch. f. anal. Chem., 28, 257.

Weykich. This author has examined various methods of caffeine estimation and reports as follows:

Peligot's method is very unreliable and must be rejected, as the titration with tannin must of course be very uncertain and the tannin besides precipitates many other substances.

Zoller's method gives a very impure caffeine, and the long heating with a concentrated acid may cause decomposition of caffein. The method is also quite complicated.

Loewenthal's method is uncertain, as the chloroform is unable to penetrate the tea sufficiently to dissolve all the thein. Besides it dissolves other substances.

The author finally recommends Mulder's method as being simple and accurate. The magnesia in this method must be very finely pulverized, as the ether extraction may otherwise be incomplete. The mass previous to extraction must be pulverized in a warm mortar. Zeitsch f. anal. Chem., 12, 104.

Zoller. Extract the powdered leaves with quite concentrated sulphuric acidt dilute the extract with water, neutralize with lead hydrate, and evaporate to dryness. Extract the residue with 85 per cent alcohol, filter, and evaporate to dryness. Extract the caffeine from the residue by means of ether, distill off the ether, and weigh the caffeine. Zeitsch f. anal. Chem., 12,106.

Additional References To The Literature Of Caffeine - Aubert. Caffein, per cent of in coffee. Dingl. Polyt. Jour., 206, 500; Jsb. d. Chem., 1872, 805

Attfield, J. Caffeine in cola nuts. Jsb. d. Chem., 1865, 632. Pharm. J. Trans.

[2]) 6,457. Bottger, R. Caffeine;detectionof. Zeitsch, f. anal, Chem., 1873, 442; Jsb, d, Chem,; 1873, 960, Bottger, R. Caffein, reaction of. Pol. Notizblatter, 1873, 257; Zeitsch. f. anal.

Chem. (1873), 12, 442. Caffeine, influence of, on digestion. Journ. Chem. Soc, 1889, 534. Caffeine oxalate. Journ. Chem. Soc, 1889, 1018. Caffeine, oxidation of, with ozone. Journ. Chem. Soc, 1889, 1017. Caffeine in coffee. Pharm. Transactions, 1887, 565. Caffeine, synthesis of. Chem. News, 1889, June 28, 305.

Commaille, A. Caffeine, estimation of in coffee. Compt. Rend., 81, 817-819. Fisher, E. Caffeine, derivatives of. Jsb. d. Chem., 1881, 902; Ber. d. chem. Ges., 1881, 637, 1905 Fisher, E. Caffeine, constitution and derivatives. Ber. d. chem. Ges., 1882, 29, 453;

Monit. scien. [3], 12, 381,433. Greene, F. C. Caffeine, estimation of. in Guarana. Phar. J. Traus. [3], 8, 87. Grosschopff, C. Caffeine, preparation of. Jsb. d. Chem., 1866, 470; Arch. d. Pharm.

[2], 128, 206. Heckel and Schlagdenhauffen. Caffeine in cola nuts. Jsb. d. Chem., 1882,1162;

Compt. Rend., 94, 802. Hilger. Caffeine, determination of. Zeitsch. f. anal Chem., 28, 257 (orig. Arch. d.

Pharm., 223,828). Hinterberger. Caffeine, compound of, with mercuric chloride. Ann. Ch. Pharm.,

78, 201; Jsb., 1851,474. Kohl .and Swoboda. Caffeine, compound, with mercuric cyanide. Wien. Acad. Ber.,

9, 252; Ann. Chem. Pharm., 83, 339; Jsb. d. Chem., 1852, 549. Lafean, A. H. Caffeine, solubility in alcohol. Phar. J. Trans. [3], 11, 902; Jsb. d.

Chem., 1881,902. Lehmann, J. Caffein, physiological action of. Jsb. d. Chem., 1853, 751; Ann. Chem.

Pharm., 87, 205, 275; J. pr. Chem.,62, 104. Loesch. Caffeine, estimation of. Chem. News, 56, 47.

Luchin. Caffeine, reactions of. L'orosi, 8, 110; Arch. d. Pharm. [3] 23, 684; Zeitsch. f. anal. Chem., 25, 565. Malyand Hinteregger. Caffeine, constitution and derivatives. Monatsh. f. Chem., 1882, 85

Paul and Cownley. Caffeine, content of, in teas. Centrbl., 1890, 2, 491.

Paul and Cownley. Caffeine, estimation of, in tea. Journ. Chem. Soc, 106, 540.

Payen. Caffeine caffeo-tannate in coffee. Ann. chim. phys. [3], 26, 108; Jsb. d.

Chem., 1849, 486. Pelletier. Caffeine, isolation of pure. Jour. Pharm. [2], 12, 229. Petrik. Caffeine, per cent of, in tea. Dingl. polyt. Jour., 218, 220. Pfaff. Caffein, spec. grav. of. Ann. Chem. Pharm. 1, 17.

Polacci, E. Caffeine, preparation of. Jsb. d. Chem., 1857,412; Cimento, 5, 396. Puccetti, P. Caffeine, preparation from tea and coffee. Arch. d. Pharm. [2],

84, 198. Robiquet, Caventon, and Garot. Caffeine, isolation of pure. Jour. Pharm. [2], 2,

234. Rochleder. Caffeine, decomposition of. Ann. Chem. Pharm., 69,120; Jsb. d. Chem.,

1849, 382. Rochleder. Caffeine, decomposition of, by chlorine. Wien. Acad. Ber., 1850,96;

Pharm. Centrbl., 1851,41; Jour. pr. Chem., 51, 398. Rosengarten and Strecker. Caffeine, formula of. Ann. Chem. Pharm., 157, 1;

Bull. Soc. Chim. [2], 15, 66. Ritnge. Caffeine, discovery of. Schweigg. Jour. Chem. Phys., 31, 308. Schmidt, E. Caffeine, literature of. Ber. d. chem. Ges., 14, 814. Schmidt and Biedkmann. Caffeine, derivatives of. Ber. d. chem. Ges., 1881,813, Schultzen, O. Caffeine, decomposition products of. Bull, soc chim. [2], 9, 239;

Jsb, d. Chem., 1867,516.

Schwarzenbach. Caffeine, reaction of. Chem. Centralbl., 1861, 989; Zeitsch. f.

Anal. Chem. 1, 229. Spencer, G. L. Estimation of caffeine. Jour. Anal. Chem., 4, October, 1890. See this report, page 889. Strauch, A. Caffeine, properties of. Jsb. d. Chem., 1867,808, 770. Zeitsch. f. anal.

Chem., 6, 503. Strecker. Caffeine, preparation of, from Theobromine. Ann. Chem. Phar., 108,

151; Compt. Rend., 52, 1210. 1268. Tiemann, F. Caffeic and hydrocaffeic acids. Ber. d. chem. Ges., 1878, 659. Tilden, W. A. Caffein, iodine derivatives of. Ann. Chim. Phys. [4]) 5, 487; Chem.

Soc. Jour. [2], 3, 99; Jour. pr. Chem., 96, 371; 98, 245. Versmann, H. J. Caffeine, preparation from coffee. Arch. d. Pharm. [2], 68, 148;

Pharm. Centrbl., 1851, 889; Jsb. d. Chem., 1851, 474.

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