§ 184. ESTIMATION OF CINCHONA-ALKALOIDS. 197 



in hydrochloric acid, added to the aqueous filtrate containing 

 soda, etc., and removed from solution by shaking with chloroform. 

 The alkaloid thus isolated must be weighed and added to the 

 amount jDreviously found, from which sum, however, the cin- 

 chonidine and quinidine left in solution must be deducted if great 

 accuracy is required. 



Hielbig also describes a second process for determining quinidine, 

 cinchonine, and amorphous alkaloid, as follows : 



VII. The filtrate and washings from the precipitated tartrates 

 are evaporated to 20 cc, and for each gram of mixed alkaloids 

 0'5 gram of iodide of sodium, dissolved in 5 cc. of Avater and 15 

 of 90 per cent, spirit, is added, and the whole allowed to stand 

 for twenty-four hours in a cool place. The iodide of quinidine is 

 then collected on a tared filter, washed with a little water, dried at 

 100°, and weighed. (No correction is necessary for the alkaloid 

 left in solution.) 



VIII. The filtrate from the last operation is treated as in V., 

 but the precipitate produced by the soda solution is here filtered 

 off and the alkaloid still retained by the liquid extracted by 

 shaking with chloroform. Both portions are then transferred to 

 a beaker, and macerated with 40 per cent, spirit to remove 

 amorphous alkaloid. It is best to cool the mixture and agitate, 

 repeating the treatment as long as the spirit becomes coloured. 

 The cmchonine is finally filtered off, dried, and weighed, 0*000202 

 gram being added for each cc. of spirit used. 



IX. The alcoholic solutions are evaporated to dryness at 110°, 

 and from the weight of the residue the quinine, cinchonidine, and 

 cinchonine, previously reckoned as 'correction,' deducted. The 

 remainder is to be regarded as amorphous alkaloid. 



If the bark contain so little quinine and cinchonidine that 

 after the addition of tartrate only single crystals are deposited on 

 the sides of the beaker where touched by the glass rod, in quan- 

 tity too small to allow of their being weighed, it may be assumed 

 that the liquid contains at least the amount of alkaloid equal to 

 the correction to be made. The actual presence of quinine may 

 be detected by the thalleioquin reaction (§ 171) : if that yield a 

 positive result, the presence of cinchonidine must remain a matter 

 for conjecture ; but if the result be negative, the precipitate may 

 be assumed to consist of cinchonidine, and its quantity calculated 

 from the correction to be made. 



