202 CAROTINOIDS AND RELATED PIGMENTS 



cipitation from carbon disulfide solution with absolute alcohol. In 

 this process the colorless impurities precipitate first and then the pure 

 carotin. By repeating the fractional precipitation pure carotin was 

 finally obtained. 



Green leaves. Arnaud (1885) was one of the first to show that 

 crystals of carotin may be secured by a gentle and rapid petroleum 

 ether extraction of vacuum dried, powdered leaves, e.g., spinach, fol- 

 lowed by spontaneous evaporation of the concentrated extract. 

 Arnaud found that the waxy substances^could be washed away with 

 a little cold ether and the pigment recrystallized from petroleum 

 ether. The interesting feature of this method is the fact that quick 

 extraction of the perfectly dry powdered leaves removes practically 

 no green pigment, and also no appreciable amount of xanthophylls. 



Willstiitter and Mieg (1907) applied the method of Arnaud to the 

 leaves of the stinging nettle, Urtica dioica, in order to isolate carotin 

 on a large scale. The nettle leaves are not so good a source of pig- 

 ment, however, as spinach, according to these investigators, but their 

 low yield of carotin may have been due to the fact that the leaves 

 were harvested in July when their carotin content, according to Arnaud 

 (1889), is quite low. The details of the operation should be useful 

 for the isolation of carotin from any green, leafy material containing 

 a relatively large quantity of the pigment. One hundred kgs. of pow- 

 dered nettle leaves (moisture 7.7 per cent) were allowed to stand in con- 

 tact with 120 liters of cold petroleum ether (b. p. 40-70 C.) in glass 

 flasks for two days. The petroleum ether was filtered off on a Biichner 

 funnel and the residue on the filter washed with 60 liters of petroleum 

 ether. It is stated that no xanthophyll was present in the greenish 

 yellow extract. The small amount of chlorophyll present was removed 

 first. This was done by shaking the extract gently with a little con- 

 centrated alcoholic potash, being careful to avoid an emulsion. The 

 alkali was removed by washing with water, but here again care had 

 to be taken to shake the mixtures very gently because the petroleum 

 ether solution still contained considerable fat-like material. In the 

 writer's experience these processes of removing the chlorophyll and 

 washing out the alkali are likely to be somewhat tedious. When they 

 are completed one can proceed to the evaporation of the extracts, 

 which must be carried out in vacuum. In Willstatter and Mieg's ex- 

 periments the 200 liters of petroleum ether were evaporated to about 

 three liters before setting aside for the carotin to crystallize out. It 



