ASSIMILATION OF CARBON 7 



The method of Kraus 1 is based upon the relative solubilities of the pig- 

 ments in alcohol and benzine. If benzine is gradually added, with shaking, 

 to the green alcoholic extract diluted with water so as to be about an 85-per 

 cent, solution of alcohol, two sharply distinct layers are finally formed, an 

 upper, green layer (benzine) and a lower, golden-yellow one (alcohol and 

 water). By renewed shaking of the former solution, with further additions of 

 alcohol, the green pigment can be practically freed from the yellow coloring 

 matter. 



The green pigments 6 form an amorphous mass, readily soluble in alcohol, 

 ether and naphtha. The solution is intensely fluorescent, appearing cherry 

 red by reflected light and green by transmitted light. The chemistry of chloro- 

 phyll has been largely worked out by Willstatter and his co-workers. Two 

 closely related pigments are always associated to form chlorophyll, these having 

 been termed chlorophyll a and chlorophyll b. 



Alcoholic solution of chlorophyll a is blue-green by transmitted light and 

 blood-red by reflected light; it is said to fluoresce blood-red. Alcoholic solu- 

 tion of chlorophyll b is yellow-green by transmitted light and fluoresces brown- 

 red. This phenomenon of fluorescence (seen also in a solution of the red dye 

 eosin, which fluoresces green) appears to be due to an alteration in the wave- 

 length of radiant energy, brought about by a peculiar action on the part of the 

 molecules in the solution. By this action the chlorophyll solution gives off 

 energy of long wave-lengths (red light) when it is illuminated by energy of 

 much shorter wave-lengths (green and blue light). 



Of the total green pigment, as obtained from leaves, about 72 per cent, is 

 chlorophyll a and the rest chlorophyll b. The proportions vary somewhat, but 

 the variation is not over 10 per cent. Both form crystals. The two chloro- 

 phylls d have the following formulas, as so far known: 



Chlorophyll a, CasH^Os^Mg 

 Chlorophyll b, CssEUOe^Mg 



1 Kraus, Gregor, Zur Kenntnis der Chlorophyllfarbstoffe und ihrer Verwandten. Stuttgart, 1872. 



6 Some modifications have been made in this discussion of chlorophyll, so that it does not 

 agree entirely with Palladin's presentation. An attempt has been made to bring it more into 

 accord with Willstatter and Stoll's monograph. (Willstatter, Richard, and Stoll, Arthur, 

 Untersuchungen liber Chlorophyll, Methoden und Ergebnisse. Berlin, 1913.) For English 

 resumes of this work, see: West, Clarence J., A review of Willstatter's researches on chloro- 

 phyll. Biochem. bull. 3: 229-258. 1914. Willstatter, R., Chlorophyll. Jour. Amer. Chem. 

 Soc. 38: 323-345. 1915— Ed. 



c This explanation is not given by Palladin. For a discussion of the various theories regard- 

 ing the color and fluorescence of plant pigments, see : Horowitz, B., Plant pigments. Biochem. 

 bull. 4: 161-172. 1915. — Ed. 



d Stokes had long ago suspected that chlorophyll is a mixture of two green pigments. In 

 this connection see: Stokes, G. G., On the supposed identity of biliverdin with chlorophyll, 

 with remarks on the constitution of chlorophyll. Proc. Roy. Soc. London 13 : 144-145. 1864. 

 Sorby, H. C, On comparative vegetable chromatology. Ibid. 21: 442-483. 1873. 



On an interesting method for separating the yellow and green pigments by absorption in 

 paper on in a column of calcium carbonate, see: Tswett, M., Physikalisch-chemische Studien 

 iiber das Chlorophyll. Die Adsorptionen. Ber. Deutsch. Bot. Ges. 24: 316-323. 1906. 



