354 PHOTOSYNTHESIS 



similar in appearance the crystals can be distinguished by the fact that 

 xanthophyll crystals appear red when a number of them are super- 

 imposed, while the carotin crystals are yellow. The solubility of these 

 two yellow pigments differs considerably. When an alcoholic solution 

 of xanthophyll is mixed with petroleum ether and a small quantity of 

 water is added, most of the xanthophyll passes into the alcoholic layer. 

 Schertz ^'^ has reported the following solubilities determined at 25° in 

 1 liter of the solvents: 9.5 mg. in petroleum ether (50-55°), 201.5 mg. 

 in absolute alcohol, 134.9 mg. in absolute methyl alcohol, 952 mg. in pure 

 anhydrous ether. It is easily soluble in chloroform, but not very soluble 

 in carbon bisulfide. Its melting point is 173-174°, though this is not a 

 good criterion of its purity. 



There are two absorption bands in the blue and a faint band in the 

 violet (?i = 420 |.i[.i). In Table 45 are given the results of Willstatter 

 and Stoll's determination of the absorption of xanthophyll. 



TABLE 45 



Absorption Spectrum of 0.005 G. Xanthophyll in 1 Liter of Alcohol and of 

 Carbon Bisulfide. (Willstatter and Stoll.) 



Solvent Alcohol Carbon Bisulfide 



Thickness of layer ' " ^ 



in mm. 5 10 10 20 



Band I 484 472 488—471 515... 501 516 501 



Band II 454 441 454—440 482 — 469 483 — 467 



Band III ..,.., 



End absorption . . . 419— 420— — 447 . 441 



Fucoxanthin in the pure state is easily soluble in carbon bisulfide 

 and alcohol. In 100 cc. of methyl alcohol 1.66 grams dissolve at boil- 

 ing temperature and 0.41 gram at 0°. It can be crystallized from methyl 

 alcohol, in red-brown, long prisms. It melts at 159.5-160.5°. The ether 

 solution is orange-yellow, the alcohol and carbon bisulfide solutions appear 

 more red. The absorption spectrum is given in Table 46. 



TABLE 46 



Absorption Spectrum of 0.005 Gram Fucoxanthin in 1 Liter of Alcohol. 



(Willstatter and Stoll.) 



Thickness of layer in mm. 5 10 



Band I 486—469 493—469 



Band II 455—440 \ 454_ 



End absorption 440 — j 



c. The Chemical Properties of the Leaf Pigments. 



The early efforts to determine the chemical composition and the con- 

 stitution of chlorophyll met with some of the same obstacles which were 

 encountered in similar investigations on proteins and other complex sub- 



' Schertz, Jour. Agri. Rescar., 30, 253,. 575 (1925). 



M 



