§ 184. ESTIMATION OF CINCHONA-ALKALOIDS. 195 



of sulphuric acid ; the filter used in the previous operation is also 

 extracted with spirit of the same strength. One part of precipi- 

 tate should yield about 20 parts of solution; from this the quinine 

 is best precipitated by the reagent recommended by de Vrij/ 

 which is prepared as follows : To a solution of 2 parts of sul- 

 phate of quinoidine in 8 of 5 per cent, aqueous sulphuric acid, 

 a solution of 1 part of iodine and 2 of iodide of potassium in 100 

 of water is gradually added with constant stirring. The flocculent 

 precipitate thus produced is slightly warmed till it agglomerates 

 into a resinous mass, which is then washed with warm water, 

 dried, and dissolved with application of heat in 6 parts of 92 to 94 

 per cent, spirit. After cooling the liquid is filtered off and 

 evaporated to dryness, the residue redissolved in 5 parts of spirit, 

 again filtered, and the filtrate used as the reagent. During the 

 precipitation of the herapathite with this reagent, the liquid must 

 be vigorously stirred to prevent the partial separation of cinchoni- 

 dine in the form of orange flocks. If that has taken place the 

 mixture must be warmed until the precipitate disappears. Accord- 

 ing to de Vrij, sufficient of the reagent has been added when an 

 intense yellow colouration makes its appearance in place of a 

 green precipitate of herapathite ; the mixture is then heated to 

 incipient ebullition, cooled, and its weight ascertained to allow of 

 a correction for dissolved herapathite being subsequently made. 

 Finally, the precipitate is collected on the filter previously used 

 in separating the tartrates and washed with a saturated alcoholic 

 solution of quinine-herapathite. After draining, the funnel is 

 weighed with the filter, dried, and again weighed ; the diff'erence 

 is the amount of herapathite solution retained by it, for each 

 gram of which, as well as of mother liquor (not washings), a 

 correction must be made of 0-00125 gram of quinine. 100 parts 

 of herapathite dried at 100" indicate 58*22 of anhydrous quinine. 

 To ensure the success of the experiment, it is absolutely necessary 

 that the herapathite should separate in the form of green glitter- 

 ing crystals, as otherwise the solubility differs from that here 

 stated; amorphous herapathite, as well as some of the quinine 

 compounds richer in iodine prepared by Jörgensen, are far more 

 easily soluble. Unfortunately it sometimes happens, when work- 

 ing upon the mixed alkaloids separated from bark, that it is 

 impossible to obtain the precipitate in this crystalline condition even 



1 Loc. cit. 



13—2 



