BIBLIOGRAPHY OF LITERATURE. 1007 



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 H 2 S ; filter off the PbS and evaporate the filtrate to a sirup. Ex- 

 tract this with hot benzole, which on evaporation will yield the caffeine. 

 Poggendorf 's Annalen, 112, 441; Cheiu. 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 alco- 

 holic solutiou 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 ehloroform. Collect the caffeine as usual and dry at a 

 temperature not exceeding 100 C. Mitth. Lab. ang. Chem. Erlaugen, 3, 131; 

 Chem. Centrbl. (1890), 2, 274; Journ. 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 100 C 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 

 Avith tannin must of course be very uncertain and the tannin besides precipi- 

 tates 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 sub- 

 stances. 



The author finally recommends Mulder's method as being simple and accu- 

 rate. 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 acid t 

 dilute the extract with water, neutralize with lead hydrate, and evaporate 

 to dryness. Extract the residue with 85 per cent alcohol, filter, and evapo- 

 rate 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 OP CAFFEINE. 



AUBERT. Caffein, per cent of in coffee. Dingl. Polyt. Jour., 206, 500; Jsb. d. Chem., 



1872, 805. 



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



[2]) 6, 457. 

 BOTTGER, R. Caffeine ; deteptionpf. Zeitsch. f. anal, Chein. ; 1873, 442 j Jsb, d, Chem, ; 



1873, 960, 



