112 CHEMISTRY OF PLANT LIFE 



are known as the " carotinoids." This group includes the two 

 brilliant yellow pigments, carotin and xanthophyll, and the reddish 

 brown fucoxanthin and the brilliant red lycopersicin, which are 

 similar in their chemical composition. The first two are found 

 universally distributed in plants, associated with the chlorophylls, 

 and may be regarded as vegetative pigments, although the char- 

 acteristic ornamental yellow and orange colors of many flowers 

 and fruits, as well as that of the roots of carrots, etc.. are due to 

 these pigments 



Carotin. This pigment occurs in various forms in plants, both 

 amorphous and crystalline. It crystallizes out of solution in 

 flat plates, which are orange-red by transmitted light, and green- 

 ish-blue by reflected light, and have a melting point of 174. 

 Carotin is insoluble in water, only very slightly soluble in acetone 

 or cold alcohol, readily soluble in petroleum ether, ether, chloro- 

 form, and carbon disulfide. Its solutions are strongly fluorescent. 



Its molecular formula is C^Hso. It is, therefore, a hydro- 

 carbon of a very high degree of unsaturation. On exposure to 

 dry air, it absorbs 34.3 per cent of its own weight of oxygen, 

 which corresponds to 11J atoms of oxygen, computed on the basis 

 o the molecular formula C4oH56, and would indicate a formula of 

 (C4oHs6)2023 for the oxygenated compound; this being three oxy- 

 gen atoms less than would be required to bring the compound to 

 the theoretical stage of saturation represented by the unimolecular 

 formula C n H2 ra +2. In moist air, two more oxygen atoms are 

 absorbed, probably forming two OH groups in the molecule. 

 Moreover, carotin absorbs iodine. When the calculated amount of 

 iodine is used, a definite compound having the formula C4oHs6l2 

 is produced; but in the presence of an excess of iodine 

 another compound having the apparent formula C4oH56l3 (or 

 2C4oH56l2+l2) is obtained. (Note that 2 atoms of iodine plus 

 12 atoms of oxygen, or 3 of iodine plus 11 J of oxygen, produce the 

 degree of saturation required by the formula C ra H 2w +2.) It is 

 evident from these experimental data, that a part of the unsat- 

 urated linkage in the carotin molecule is of a type which can easily 

 be saturated by direct addition of oxygen, while the remainder 

 may be saturated by iodine. 



The reaction of carotin toward bromine is peculiar. With 

 this element, it forms a compound having the formula 

 indicating the direct addition of two atoms of bro- 



