PIGMENTS 111 



ment of the magnesium to each one of the four nitrogen atoms in 

 the skeleton formula assumes the existence of subsidiary valences 

 of 2-4 for magnesium (and of 3-5 for iron), or of possible oscillating 

 valences similar to those supposed to be exhibited by carbon 

 in its closed-ring arrangements. 



PROPERTIES OF THE CHLOROPHYLLS 



The phytyl esters, or natural chlorophylls, are amorphous 

 solids; while the methylethyl esters (chlorophyllins) and the free 

 acids (phyllins) are crystalline compounds. All of these com- 

 pounds are easily soluble in ether and alcohol, but insoluble in 

 water. The chlorophylls and chlorophyllins are practically insol- 

 uble in petroleum ether and chloroform; but the monobasic acids 

 (pyrrophyllin and phyllophyllin) and the neutral aetiophyllin 

 dissolve easily in chloroform. 



Solutions of the chlorophylls are fluorescent, being green by 

 transmitted, and red by reflected, light. 



Chlorophyll a is a . blue-black solid, which gives dark green 

 solutions in all of its solvents. Chlorophyll b is a dark-green solid, 

 which yields brilliant green solutions. Solutions in ether of glau- 

 cophyllin and of cyanophyllin are blue; of rhodophyllin, deep 

 violet; of rubiphyllin, light violet; of erythrophyllin, red; and 

 of pyrrophyllin and phyllophyllin, bluish-red. Solutions of the 

 porphyrins are all red, the di-basic ones being usually a bluish- 

 red, and the simpler ones a brilliant red to deep brownish-red in 

 color. 



The several chlorophyll derivatives are further distinguished 

 by characteristic differences in their absorption spectra. These 

 differences have been pictured by Willstatter in his book dealing 

 with the results of his investigations concerning the chlorophylls, 

 and reproduced in one or two other texts which treat in detail 

 with the physical-chemical properties of these pigments, but need 

 not be presented in such detail here. 



THE CAROTINOIDS 



The characteristic brilliant green of healthy plant tissues is 

 due to the fact that there are always associated with the dark 

 bluish-green chlorophylls two (or more) yellow pigments. These 



