198 ALKALOIDS. 



The same course may be i^ursued when only traces of quinidine 

 are precipitated. 



§ 185. Beliaviour to Polarized Light. — Attempts have also been 

 made in examining barks to take advantage of the differences 

 the alkaloids show in their behaviour towards polarized light, but 

 the requisite accuracy does not seem to have been yet attained. ^ 

 In working with mixtures of the pure alkaloids, the results are, 

 it is true, very satisfactory ; but as soon as the mixed alkaloids 

 separated from barks are examined the errors increase, as even 

 small quantities of contaminating impurity can exercise a con- 

 siderable influence on their action on a ray of light. 



The most feasible is Oudemans' method of estimating quinine 

 and cinchonidine. The alkaloids are precipitated as tartrates, and 

 redissolved in hydrochloric acid (to 0-4 gram precipitate about 

 3 cc. normal acid, and water to 20 cc). Such a solution of quinine 

 shows a rotation [a]i, = - 215-8°; of cinchonidine [ajp = - 131-3°. 

 The calculations may therefore be made according to the formula : 



215-8.C-I- 131 -3(100 - .r) = 100(a)'" 



where z is the percentage of tartrate of quinine, and {a)'" the 

 specific rotatory power of the mixture. 



§ 186. Other Cinchona Alkaloids. — The following are some of the 

 cinchona alkaloids of less frequent occurrence : 



Aricinc,'^ the sulphate of which swells up to a jelly in chloro- 

 form. 



Cusconine,^ the neutral sulphate of which gelatinizes in aqueous 

 solution, and does not dissolve in more sulphuric acid. Acetate 

 of cusconine is also gelatinous. 



Quinamine.^ This alkaloid occurs notably in Cinchona succirubra, 

 and generally remains associated with the ' amorphous alkaloid ' 



^ Compare the papers quoted in § 172 by Oudemans, Hesse and Hielbig. 

 For the application of fluorescence, see Kerner, Zeitschr. f. anal. Chemie, ix. 

 135, 1870. 



- Compare Hesse, Anna!, d. Chera. und Pharm, clxxxi. 58, 1876 (Pharm. 

 Journ. and Trans. [3], vii. 331, 1876). 



=• See Hesse, Ber. d. d. chem. Ges. ix. 742, 1876 (Year-book Pharm. 226, 

 1880). 



* Compare Hesse, Ber. d. d. chem. Ges. x. 2152, 1877 (Year-book Pharm. 

 62, 1878) ; Annal. d. Chem. und Phami. cxcix. 333, 1880 (Year-book Pharm. 

 34, 1880) ; de Vrij, N. Tijdschr. voor de Pharm, en Nederl. 69, 1877. 

 Oudemans, Annal. d. Chem. und Pharm, cxcviii. 135, 1879 (Year-book 

 Pharm. 57, 1879; 34, 1880). 



