PROPERTIES AND METHODS OF IDENTIFICATION 237 



vent of crystallization by drying in vacuum over H 2 S0 4 or P 2 5 xan- 

 thophyll crystals from plants melt at 173.5-174.5 C. (corrected), 

 but according to Willstiitter and Ksrhcr xanthophyll from egg yolk 

 mi-Its at 195-196 C. (corrected). 



Xanthophyll crystals arc entirely insoluble in low boiling petro- 

 leum ether. The solubility in cold methyl alcohol is quite low, 1 gram 

 requiring about 5 liters, but is considerably greater in the boiling sol- 

 vent, 1 gram requiring 700 cc. to 1 liter. The solubility of the pure 

 pigment in ethyl alcohol is considerably greater. The crystals dis- 

 solve rather easily in warm CS 2 , 1 gram requiring about 400 cc. of 

 solvent. The solubility in ether is a little greater and in acetone and 

 chloroform quite rapid. Phenol also dissolves the crystals quickly 

 as does hot glacial acetic acid. A mixture of 3 parts phenol crystals 

 and 1 part glycerol also dissolve xanthophyll crystals very readily, 

 as van Wisselingh (1915) has shown. 



Xanthophyll crystals, like carotin, dissolve in con. H 2 S0 4 with a 

 deep blue color, from which green flakes are precipitated on dilution 

 with water. They also dissolve in warm ethyl alcohol containing 

 strong HC1 with a pure green color which soon changes to blue. This 

 reaction is apparently peculiar to xanthophyll in contrast with the 

 hydrocarbon carotinoids. According to van Wisselingh xanthophyll 

 crystals can be distinguished from carotin crystals by the fact that 

 the former are colored blue but are not dissolved by 65 to 75 per cent 

 H 2 S0 4 while the latter turn blue only after some lapse of time or when 

 stronger acid is used. With con. HN0 3 a colorless solution only is 

 obtained from which colorless flakes separate. This is Willstatter 

 and Mieg's finding, but van Wisselingh found that the blue color re- 

 action resulted with 50 per cent acid. This may also serve to dis- 

 tinguish the crystals of the two types of carotinoids. 



Xanthophyll, like carotin, is unsaturated and forms an iodide, 

 C 40 H 56 2 I 2 , which precipitates at once on addition of iodine to the 

 ethereal solution of the pigment. An excess of iodine prevents the 

 crystallization. The iodide has a dark violet color and consists of 

 tuft-like prisms, the form of which is shown in Plate 2, Figure 3. The 

 compound is not very stable and possesses no definite melting point. 

 It is fairly readily soluble in the xanthophyll solvents, excepting 

 ether, giving yellow to yellowish-red solutions. When xanthophyll 

 is brominated it loses its oxygen, since Willstiittcr and Escher (1910) 

 report a xanthophyll bromide with the constitution C 40 H 40 Br 22 . 



Xanthophyll crystals slowly oxidize in the air or in oxygen, with 



