210 CAROTINOIDS AND RELATED PIGMENTS 



the course of two days the xanthophyll crystallized out at room tem- 

 perature as yellow to orange-red tablets with a brilliant steel-blue 

 reflection. Willstatter and Mieg secured a yield of 12 grams of crude 

 crystals from the 100 kgs. of dried nettle leaves. Further purification 

 was obtained by crystallization from boiling methyl alcohol, from 

 which the crystals come down with one molecule of alcohol of crystal- 

 lization, or by dissolving in the least possible amount of chloroform 

 and adding an excess of petroleum ether, in which the xanthophyll 

 is almost insoluble. 



Jorgensen and Stiles (1917) have described what appears to be a 

 more convenient method for isolating crystalline xanthophyll, which 

 also gives higher yields than the method of Willstatter and Mieg. 

 They prefer the dry, powdered nettle leaves because of their excellent 

 keeping quality, but in this respect spinach, which is richer in caro- 

 tinoids, should serve equally well as a source of pigment. 



In Jorgensen and Stiles' method the air dried, powdered leaves 

 are submitted to a final drying in vacuum, over H 2 S0 4 . About 500 

 grams of this powder are placed on a filter paper in a Biichner funnel 

 24 cm. in diameter and sucked to the paper with a strong water pump 

 or vacuum pump. To get the best results the powder must be thor- 

 oughly dry and be sucked in a coherent mass not more than 5 cm. 

 deep on the funnel. Half a liter of 80 per cent acetone is now al- 

 lowed to permeate the powder on the filter for 5 minutes without the 

 use of the pump. Then 250 cc. of solvent are added and slowly sucked 

 through with the pump. After 5 minutes another 250 cc. portion of 

 solvent is added and sucked through with the pump for 10 minutes. 

 This operation is repeated with two further 250 cc. portions of 80 per 

 cent acetone, and finally the pump is allowed to act as strongly as 

 possible until the powder is sucked dry. The 1,500 cc. of solvent 

 used give 800 to 900 cc. of extract. 



When the extract has been obtained from 2 kgs. of dry powder in 

 this manner, the fractions are combined and washed free from many 

 impurities and finally from acetone by the following procedure. The 

 acetone solution is added in two successive portions to 4 liters of 

 petroleum ether (sp. g. 0.64 to 0.66) in a separatory funnel of 7 liter 

 capacity. Water (0.5 liters) is added with each of these additions 

 while the funnel is being gently rotated, and after separation into 

 two layers the lower layer is drawn off and discarded before the 

 addition of the second portion. The petroleum ether layer is now 

 mixed with two successive liters of 80 per cent acetone solution, the 



