186 ALKALOIDS. 



Hager^ and Hielbig- have both experimented on the estimation 

 of certain alkaloids by precipitation Avith picric acid. I have no 

 doubt that in many cases very satisfactory results might be 

 obtained by combining precipitation by picric acid with extraction 

 by agitation with solvents, and in this opinion I have recently 

 been confirmed by experiments published by Hager on the 

 quantitative determination of nicotine. Hager recommends 

 precipitation with picric acid at a temperature of 15°, washing 

 with an aqueous solution of the precipitant, and finally drying at 

 a temperature not exceeding 40° to 50°. He found the nicotine 

 precipitate to contain 27 per cent, of alkaloid. 



§ 176. Estimation of Caffeine. — I may supplement the method 

 given in § 66 for the estimation of this alkaloid by the following 

 remarks : Ether ^ extracts the alkaloid in a state of greater 

 purity than chloroform, and yields therefore a correspondingly 

 better result ; but the mass must be very finely powdered, and 

 the treatment with ether repeated several times to be certain 

 of dissolving the whole of the caffeine. I have also used a mixture 

 of 3 parts of ether Avith 1 of chloroform with success. 



In estimating the alkaloid in guarana it is not advisable to 

 extract with acidified water, nor is it necessary in determining the 

 theine in tea. 



Lieventhal* extracted the powdered tea directly with 

 chloroform, by which, however, far less than the total quantity of 

 theine was dissolved. I must make the same objection to Claus's 

 method,^ which consisted in extracting with ether, shaking the 

 ethereal extract with dilute sulphuric acid, neutralizing the 

 aqueous solution with magnesia, evaporating to dryness, and 

 again extracting with ether. Moreover, it would be difficult to 

 remove the whole of the theine from ethereal solution by shaking 

 with acidified water. *^ 



^ Pharm. Centralblatt, x. 137, 145, 1871. Comi)are also Medin and Almfen, 

 Jahresb. f. Pharm. 1871. 



" Loc. cit. 



3 Compare Wurthner's investigations, Pharm. Zeitschr. f. Russland, 711, 

 1872 ; and Weyrich, ' Ein Beitr. z. Chemie des Thees und Kaffees,' Diss. 

 Dorpat, 1872 (.Tourn. Cham. Soc. xxvi. 1235). 



^ Pharm. Zeitschr. f. llussland, 369, 1872 (Year-book of Pharm, 239, 

 1873). 



•' Pharm. Zeitschr. f. Eussland, 357, 565, 1862. 



" For the less recent methods of Peligot and Zöllner, see my ' Chem. 

 Werthbestimmung,' 59. For other methods see Comaille, Zeitschr. f, anal. 



