224 CAROTINOIDS AND RELATED PIGMENTS 



and Lubimenko (1913b). The lycopin bands represent the general 

 impression which one obtains when viewing a solution containing 

 about 5 mg. per liter at a depth of about 20 mm. The relative posi- 

 tions of the lycopin and carotin bands are very characteristic, but 

 they at once introduce the difficulty that a mixture of the two pig- 

 ments would show an almost continuous absorption spectrum. It is 

 seen, therefore, that lycopin solutions should be nearly free from caro- 

 tin in order to identify lycopin by the position of its absorption bands. 

 No means have yet been devised for effecting such a separation when 

 the isomers are present together in solution. Fractional crystallization 

 must be resorted to, and this is made possible by the fact that lycopin 

 is much less soluble than carotin in almost all the carotin solvents. 

 The measurements of the absorption bands of lycopin in alcohol 

 and carbon disulfide are given by Willstatter and Escher as follows, 

 the bands in carbon disulfide being those shown by a standard solu- 

 tion containing 5 mg. per liter. 



Lycopin in Lycopin in carbon 



alcohol (mi) disulfide (mi) 



10 mm. 20 mm. 



Band I 510-499 554-540 561 -536 



Band II 480-468 514-499.5 517.5-498 



Band III 440- 479-472 481.5-468 



Xanthophylls. As pointed out in Chapter II, the chromatographic 

 evidence of Tswett seems to justify the assumption that several 

 isomeric xanthophylls exist in nature, in spite of the fact that only 

 one such pigment has so far been secured in definite crystalline form. 

 Willstatter has not yet agreed to an unqualified acceptance of this 

 assumption. However, if the fact that Tswett's observations can be 

 readily verified is sufficient grounds for accepting his view of the 

 situation, the existence of more than one xanthophyll can no longer 

 be doubted. At the same time it is recognized that we owe most of 

 our knowledge of the properties of xanthophyll solutions to the ob- 

 servations of Willstatter and Mieg (1907), who first isolated pure 

 xanthophyll crystals in sufficient quantity to determine their ele- 

 mentary composition. For the distinguishing characteristics of the 

 other xanthophylls which have not been crystallized it is necessary 

 to refer to the observations of Tswett (1911) . 



Xanthophylls give well-colored solutions in a large number of sol- 

 vents, including alcohol, ether, acetone, chloroform, benzene, carbon 

 tetrachloride, glacial acetic acid, petroleum ether, carbon disulfide 



