10 



Prof. A. J. Ewart. 



cold absolute alcohol, filtered, again evaporated to dryness, and dissolved im 

 petrol ether, in which the xanthophyll is more soluble and keeps better than 

 in water or even in alcohol. 



Using 18 feet of tubing lined with - 38 grm. of xanthophyll, the bleaching 

 was completed after 12 hours' exposure to sunlight. The water in the- 

 collecting tube contained 0-155 grm. of formaldehyde. Some of the formal- 

 dehyde may escape solution, however, since the collecting tube always 

 smells stronger of formaldehyde than does a solution of equal strength as 

 indicated by colour tests. The colourless residue ki the tubes weighed 



037 grm., and the whole of it came away in water, forming a slightly turbid 

 liquid, which gave a dense white precipitate with a drop of sulphuric acid. 

 On boiling a pale yellow oily solid separated out on the sides of the tube, 

 the liquid filtering clear. It showed a doubtful feeble dextro-rotation 

 equivalent to O001 grm. of glucose (O'Ol per cent, in 10 c.c), and gave 

 a strong reduction with Fehling's equivalent to - 24 grm. of glucose. 



If these numbers are correct they would indicate an absorption of 



38 per cent, by weight of oxygen, or of oxygen and water vapour. Haas 

 and Hill quote (p. 238) an absorption value of oxygen of 36"55 per cent, for 

 xanthophyll. In my own experiments the weight and surface of the glass 

 was necessarily relatively so great as to preclude very exact weighing. 



The Photo-oxidation of Carotin. 



This, according to Arnaud, has the formula C26H38, and absorbs up to 

 21 per cent, by weight of oxygen, whereas Willstiitter gives it the formula 

 C40H513 and an absorption value for oxygen of 34 - 3 per cent.* Carotin 

 oxidises much more rapidly than either xanthophyll or chlorophyll. Thus, 

 using thin films of equal weight spread over the same area and exposed to- 

 full sunlight, carotin took one hour, xanthophyll 12 hours, and chlorophyll 

 20 hours to bleach completely. With very thin films, however, there is less 

 relative difference in the rate of bleaching, while with thick films the 

 difference in the relative rates increases. A thick film of chlorophyll may 

 take months to bleach fully. • This is largely a matter of the permeability 

 of the oxidised surface layers to oxygen. During the oxidation of chloro- 

 phyll the blue-green colour passes to green, then yellow (or brown if a thick 

 layer), then colourless. During the yellow stage xanthophyll appears to be 

 set free, and subsequently to be oxidised, but no carotin. 



In one experiment with carotin obtained during the purification of 

 chlorophyll, 0'3 grm. films of carotin were exposed in tubes to light in a 

 current of moist C0 2 -free air. The dry colourless transparent residue 



* For literature, see Haas and Hill, as well as Czapek's ' Biochemie.' 



