ABSORPTION OF CARBON 19 



for extraction, after which the chlorophyll is transferred to benzine 

 or petrol ether to be purified. 



According to the most recent investigations of Willstatter and 

 his coworkers, the purest chlorophyll, freed from the admixture of 

 yellow pigments, is still composed of two, though very similar sub- 

 stances, called chlorophyll a and b. The chemical composition of 

 chlorophyll may be expressed by the following formulae: 



Chlorophyll a, C 5b H. 72 Oo^Mg, 



Chlorophyll 6, CssHyoOe^Mg. 



Evidently the difference between the two kinds of chlorophylls 

 is that b has 2 atoms of hydrogen less and 1 atom of oxygen more 

 than a. The transformation of one into the other, however, may 

 be induced neither by oxidation nor by reduction, the difference 

 between them thus proving of a deeper kind. They differ some- 

 what also in their color, chlorophyll a being of bluish-green, and 

 chlorophyll b of a yellowish-green tinge. The amount of chlorophyll 

 a is always greater than that of chlorophyll b. In general, for every 

 3 molecules of chlorophyll a there is present 1 molecule of chloro- 

 phyll b. This ratio varies somewhat in different plants, but no 

 constant quantitative differences have been observed in various 

 plants. The total amount of chlorophyll in a plant is not great, 

 constituting, on an average, only about 1 per cent of the whole 

 dry weight of the organism. In order to secure such quantities of 

 chlorophyll as are required for exact chemical investigations great 

 masses of plant material have to be used. 



Chemically, chlorophyll may be considered a complex ester of 

 a tricarboxylic acid — chlorophyllin — in one carboxyl of which 

 hydrogen is replaced by the radical of methyl alcohol, in the other, 

 by the radical of an unsaturated alcohol with a rather long carbon 

 chain, called phytol, and of the formula C 2 oH 39 OH. The third 

 carboxyl group is connected with the nitrogen of the central nucleus 

 forming a connection of the lactam type, i.e., containing the 

 NH • CO group. The more detailed formula of chlorophyll a may 

 be represented as follows: 



/COOCH 3 

 C 3 2H 3 oON4Mg< 



X COO-C 2 oH 39 



The structure of the central nucleus of chlorophyll is of great 



