236 CAROTINOIDS AND RELATED PIGMENTS 



covered the red hydrocarbon, C 211 H 14 , m.p., 306 C., which he calls 

 rubicen, and which dissolves in CHC1 3 , giving solutions showing an 

 intense yellow fluorescence. It is not readily soluble in the other or- 

 ganic solvents. The chloroform solution shows one absorption band 

 with a maximum at 498iui. The spectroscopic properties of the other 

 colored hydrocarbons mentioned has apparently not been determined. 



Apparently color among hydrocarbons, although rare, is not con- 

 fined to yellow and red. Sherndal (1915) has isolated a blue hydro- 

 carbon oil, azulene, C 15 H ]S , from a number of essential oils. It is a 

 coincidence, perhaps worth mentioning, that this blue hydrocarbon 

 dissolves in 60 to 65 per cent sulfuric acid with a yellow color, 

 whereas carotin, a red hydrocarbon, dissolves in strong sulfuric acid 

 with a blue color. 



In addition to these substances Marchlewski (1903) called atten- 

 tion to the fact that pigmented compounds could be made start- 

 ing with methyl-ethyl maleic acid anhydride, which show a strong 

 resemblance to the lipochromes both with respect to spectroscopic 

 properties and color reactions. Marchlewski's note on the subject 

 was for the purpose of reserving the field of investigation, but so 

 far as the writer is aware no further results have ever been published. 



Xanthophyll. The crystals of xanthophyll obtained from plants 

 by Willstiitter and Mieg (1907) and from egg yolk by Willstatter 

 and Escher show complete correspondence in form, color, solubility, 

 oxidation products and halogen derivatives, but not in melting point. 

 The latter point was discussed in Chapter VI. 



Xanthophyll appears to crystallize best from alcohol, preferably 

 methyl alcohol, from which the forms are mostly quadratic, often 

 trapesium tablets, frequently showing indentations. Their general 

 appearance is shown in Plate 2, Figure 2. From ethyl alcohol the 

 crystals are lance- and wedge-shaped prisms. Sometimes the crystals 

 are rhombic, almost hexahedrons. In all cases the crystals contain a 

 molecule of the solvent from which crystallization occurred. A sin- 

 gle example is reported by Willstatter and Mieg in which crystals 

 from CS 2 contained 22 per cent sulphur. 



The color of the crystals varies with the thickness from a green- 

 ish-yellow to a rose, similar to the crystals of carotin but distin- 

 guished by a less red color. The crystals are even more strongly 

 pleochromatic than carotin, their brilliant steel blue reflection being 

 especially evident when suspended in the solvent. The powdered 

 crystals have a brick red to red-lead color. After removing the sol- 



