220 CAROTINOIDS AND RELATED PIGMENTS 



iron salt being at the same time reduced to the green FeCl 2 . Huse- 

 mann (1861) apparently discovered this reaction when adding 

 Fe 2 Cl 6 to an alcoholic solution of carotin, but it is doubtful whether 

 the reaction is applicable to alcoholic solutions of the pigment be- 

 cause of the fact that alcohol itself will reduce the red ferric salt to 

 the green ferrous compound. 



Gill (1917) has found that the so-called Crampton-Simons test 

 for palm oil, in which a bluish-green color reaction is given by an 

 acetic anhydride reagent, is due to carotinoids in the oil. Gill's idea 

 that carotin alone is involved is hardly justified, because the color 

 reactions of carotin are in general shared by the other carotinoids. 



Solutions of carotin in alcohol which has been diluted with water 

 to a concentration of 80 to 90 per cent alcohol are characterized by 

 giving up the pigment quantitatively to carbon disulfide and petro- 

 leum ether. Conversely, carotin in petroleum ether is unaffected by 

 shaking with 80 to 90 per cent alcohol, even 92 per cent methyl al- 

 cohol failing to extract any pigment from the petroleum ether solu- 

 tion. These properties of carotin, especially the relatively great solu- 

 bility in petroleum ether in comparison with diluted alcohol, serves 

 to distinguish carotin sharply from the xanthophylls, rhodoxanthin 

 and fucoxanthin, and affords the best means of effecting a separation 

 of the two classes of carotinoids. 



Solutions of carotin in alcohol and the fat solvents show a char- 

 acteristic absorption spectrum, exhibiting two, and under proper con- 

 ditions three absorption bands in the green and blue part of the 

 spectrum, the positions of the bands varying somewhat with the re- 

 fractive index of the solvent. The bands are identical in ether, alco- 

 hol and petroleum ether because of the close agreement in the indices 

 of refraction of these solvents, but are shifted somewhat towards the 

 red in chloroform, which has a higher refractive index, and still fur- 

 ther away from the blue in carbon disulfide. The marked shift of the 

 bands into the brighter part of the spectrum when in the last named 

 solvent makes it especially useful for observing the spectroscopic 

 properties of carotin, as well as the other carotinoids. 



Leaf extracts containing chlorophyll can not be used for a study 

 of the absorption spectra of the carotinoids because the absorption 

 bands of the chlorophylls cover the second and third bands of the 

 carotinoids. Even the first carotinoid band coincides very closely 

 with Band VIII of chlorophyll b. 



The width and intensity of the absorption bands of carotin depend 



