§ 184. ESTIMATION OF CINCHONA-ALKALOIDS. 195 



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

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

 tate ehouid yield about 20 pairts of solution; from this the quinine 

 is best precipitated by the reagent recommended by de VrijV 

 which i.s prepared as follows : To a solution of 3 parts of sul- 

 ph.'tto 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 floccnlent 

 precipitate thus produced is slightly warmed till it agglomerates 

 into a resinous mass, wkioh 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 ofif and 

 evaporated to dryness, the residue redissolved in 6 parts of spirit, 

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

 precipitation of the herapathite with this reageat, the liquid must 

 be vigerously stirred to prevent the partial separation of cinchoni- 

 ditta in the form of orajige flocks. If that has taken place the 

 mixture must be warmed until, the precipitate disappears. Accord- 

 ing to de Viij, sufficient of the reagent has boan added when an 

 intense yello# 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 op. the filter previotisly 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 difference^ 

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

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

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

 of herapathite dried at 100° indicate 6S'22 of anhydrous quinine. 

 To ensure the success bf 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 Jorgensen, are far more 

 easily soluble. Unforttmately 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 



' Loc. cit. 



13—2 



