240 CAROTINOIDS AND RELATED PIGMENTS 



Fucoxanthin crystals correspond with the other carotinoids in dis- 

 solving in concentrated H 2 S0 4 and HN0 3 with a blue or purple color, 

 and in addition readily form a blue oxonium salt with HC1, as has 

 already been described. The pigment also forms an iodide, but ap- 

 parently one containing 4 atoms of iodine, instead of di-iodide which 

 the other carotinoids form. This product is obtained in the form of 

 dark violet, short, pointed prisms with a copper luster, which have a 

 gray to blue-green color by transmitted light when viewed under the 

 microscope. One obtains those crystals by adding the iodine to an 

 ether solution of the pigment. The crystals are easily soluble in 

 chloroform and acetone with a deep blue color. They melt at 134- 

 135 C. A bromide of the pigment does not appear to have been 

 made. 



Methods of Identification in Biological Products 



It is at times very desirable to be able to identify carotinoid pig- 

 ments in the plant or animal tissues in which they occur. So far as 

 plant tissues are concerned it is possible to make a gross identification 

 of carotinoids with certainty and even to differentiate carotin and 

 xanthophylls and lycopin with a reasonable degree of accuracy. 

 These results are made possible because of the excellent researches of 

 Molisch (1896), Tammes (1900) and particularly van Wisselingh 

 (1915). A similar identification of carotinoids in animal tissues has 

 not yet been devised; at least it will be pointed out presently how in- 

 secure the foundation is upon which the demonstration of animal 

 lipochromes (undoubtedly carotinoids) has been built. Attention 

 will be directed first to the possibilities in connection with plant 

 tissues. 



Plant tissues. The demonstration and identification of carotinoids 

 in the plant tissues in which they are formed rests upon a microchemi- 

 cal crystallization of the pigments in the tissues and a study of the 

 effect of certain solvents, and reagents producing color reactions, upon 

 these crystals. As has already been pointed out in a previous chap- 

 ter, carotinoids occur almost entirely in the plastids in plant tissues 

 and very rarely as crystals in the cells. As van Wisselingh has stated, 

 the carotinoids occur mostly bound to fluid, fat-like, saponifiable 

 substances or actually dissolved in them. These substances are in 

 the plastids or they form oily drops in the cells. It becomes neces- 

 sary, therefore, first to set the pigments free from their union or solu- 

 tion in the plastids. It has been shown by van Wisselingh that of the 



