Chapter IX 



General Properties and Methods of Identification of 



Carotinoids 



The preceding chapter shows clearly the difficulty of securing 

 appreciable quantities of the carotinoids in crystalline form. It is 

 not difficult, however, to obtain solutions of the carotinoids which 

 show a number of characteristic properties that can serve for the 

 identification of the pigments. For the sake of convenience, there- 

 fore, the properties of the carotinoid solutions and the properties of 

 the crystals of the pigments will be presented separately. It may be 

 stated that the facts to be presented have been drawn largely from 

 the observations of Kohl, Tswett, Willstatter and his coworkers, to- 

 gether with the writer's own experience with these pigments. These 

 researches have already been referred to specifically a number of times 

 in the preceding pages. 



Properties of Carotinoid Solutions 



Carotin. Carotin forms well colored solutions in ether, chloroform, 

 petroleum ether, benzene, carbon tetrachloride and carbon disulfide, 

 as well as in ethereal and fatty oils and oleic acid. The carbon disul- 

 fide solutions are characterized by their red orange to blood red color. 

 The solutions in the other solvents mentioned are yellow to golden 

 yellow, depending on the concentration. Amorphous carotin or caro- 

 tin in the presence of lipoids, will dissolve in 95 per cent alcohol or 

 even absolute alcohol, giving yellow to golden colored solutions, espe- 

 cially if hot alcohol is used for dissolving the pigment. Very faintly 

 colored solutions are secured with dilute alcohol, as a rule. Carotin 

 crystals are insoluble in absolute alcohol, but oxidation of carotin 

 as well as melting the crystals greatly increases the solubility in this 

 solvent. At the same time the solubility in carbon disulfide decreases. 

 According to van den Bergh, Muller and Broekmeyer (1920) col- 

 loidal, aqueous solutions of carotin can be obtained by a slow evapo- 

 ration of a concentrated alcoholic solution to which several volumes 



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