366 PHOTOSYNTHESIS 



exposure to light for months. Wurmser considers that the protective 

 action of the colloidal substances mentioned is due to the fact that these 

 envelop the particles of chlorophyll and thus protect them against the 

 access of oxygen. He found that the initial rates of decolorization in light 

 of different w^ave length have the following relation : X > 560 |i[i = 45 ; 

 ?, = 580 — 460 \i\i = 125 ; ?. < 400 ^i = 30. 



Carotin is an unsaturated hydrocarbon of the formula C40H56. It is 

 easily oxidized by the oxygen of the air, thereby it loses its color and 

 increases in vi^eight by 35 per cent in dry air and by 41 |>er cent in moist 

 air. The crystals do not change form in this process. When perfectly 

 pure, carotin is not oxidized so readily by air. Carotin reacts with 

 halogens ; iodine is easily taken up with the formation of a dark violet 

 crystalline compound, CioHseK- Under anhydrous conditions carotin 

 forms a bromine compound, C4oH36Br22. In concentrated sulfuric acid, 

 carotin dissolves forming an indigo-blue solution.*^ 



Xanthophyll, C40H56O2, like carotin is unsaturated, it is oxidized in 

 the air with an increase of 36.5 per cent of its original weight, corre- 

 sponding to the absorption of 13 atoms of oxygen or the formula 

 C4oHg60i5. When the oxidized compound is recrystallized from ether a 

 compound having the formula C40H56O18, m.p. 140", is obtained. The 

 structure of xanthophyll has not been established. It has been suggested 

 that xanthophyll is an oxidation product of carotin ; this has. however, 

 not been found to be the case.*® It is probable that the oxygen in xan- 

 thophyll is present in an ether like combination, for it gives no reactions 

 for the carbonyl, alcohol or carboxyl groups. Xanthophyll, like carotin, 

 is also bleached on oxidation. Schertz ^" reports that it is unstable in 

 ether solution, slightly unstable in petroleum ether solution but very 

 stable in absolute ethyl alcohol solution. It adds iodine to form C40H56O2I2, 

 a dark violet colored substance. Xanthophyll crystals when dissolved in 

 concentrated sulphuric acid also form a deep blue solution ; on diluting 

 this with water, green flakes are precipitated. In warm ethyl alcohol 

 containing concentrated hydrochloric acid it dissolves with a green color 

 which changes to blue. This reaction has been used to distinguish xan- 

 thophyll from hydrocarbon carotinoids. Only strong alkalies seem to 

 affect xanthophyll. It is absorbed by dry calcium carbonate, by the 

 Tswett method, from petroleum ether solutions. However, even traces 

 of alcohol interfere greatly with the adsorption. 



** Kohl, "Untersuchungen (iber das Carotin und seine physiologische Bedeutung 

 in der Pflanze.," Leipzig, 1902. Willstatter and Mieg, Ann. Chem.. 355, 1 (1907). 

 Willstatter and Escher, Zeit. physiol. Chem., 64, 47 (1910). Escher, ibid., 83, 198 

 (1913). Palmer, "Caratinoids and Related Pigments," 1922. Schertz, Jour. Aqri. 

 Res., 30, 469 (1925). 



** Willstatter and Mieg, /. c. Willstatter and Escher, /. c. Wis eMngh, Flora 

 (7), 107, 371 (1915). 



"^Schertz, Journ. Agr. Res., 30, 575 (1925). Ewa t, Proc. Roy ■: I'ictork 

 30, 178 (1918). 



