232 CAROTIXOIDS AND RELATED PIGMENTS 



methyl alcohol KOH, and in this solvent the pigment is changed so 

 that on dilution with water and extraction with ether (the pigment 

 being liberated from its temporary alkali compound by water) it is 

 much more sensitive towards HC1. Ether solutions will now give 

 the blue color reaction on shaking with only 16 per cent HC1 solu- 

 tion, whereas 25 per cent HC1 solutions had scarcely any effect before 

 the treatment with alkali. Even 3 per cent HC1 now has a noticeable 

 effect, and in concentrated ether solution even 0.001 per cent HC1 

 will give the blue color. The hydrochlorides formed in these cases 

 apparently contain even more chlorine than the hydrochloride which 

 the original pigment forms. 



The ether solution of fucoxanthin which has been changed by the 

 concentrated methyl alcohol KOH has a greenish tinge and shows a 

 spectrum whose bands are shifted considerably towards the violet. 

 The ether solution of this pigment containing 5 mg. per liter shows 

 bands at 461-451(41 and 435-423[.iu. in 10 mm. layer. 



Properties of Crystalline Carotinoids 



Carotin. Carotin crystallizes from carbon disulfide on addition of 

 absolute alcohol, forming rhombic tablets or prisms, and from petro- 

 leum ether, forming almost quadratic leaflets, which are frequently 

 indented. Plate 2, figure 1, shows the form of crystals from carbon 

 disulfide-alcohol. The color of the crystals varies with their thick- 

 ness from bright yellow to deep rose or copper colored with a rich 

 velvety appearance. The crystals are highly pleochromatic and have 

 an intense blue to bright green metallic luster by reflected light. The 

 crystallography of carotin has been described in detail by Kohl 

 (1902b). Some investigators have ascribed a striking violet or crocus- 

 like odor to the pure crystals, but this has not been observed by 

 others, e.g., Willstatter. The crystals from alcohol usually contain 

 some alcohol of crystallization, which is given up in vacuum over 

 H 2 S0 4 or P 2 5 . 



Pure carotin crystals are almost insoluble in cold ethyl alcohol, 

 and even less so in methyl alcohol. They dissolve with difficulty in 

 the hot alcohols. About 1.5 liters of low boiling petroleum ether are 

 required to dissolve one gram, under a reflux condenser, but the solu- 

 bility is somewhat greater in the higher boiling gasoline fractions. 

 About 900 cc. of hot ether are required for one gram of crystals. 

 Acetone dissolves the crystals with difficulty, even hot acetone not 



