THE CHEMISTRY OF CHLOROPHYLL 437 



These results indicate that by the action of alkalis on 

 chlorophyll, followed by that of acids, a complex series of pro- 

 ducts is obtained. The introduction by Willstatter of a method 

 of fractional separation marks a great advance in the study of 

 the chemistry of chlorophyll. 



Chlorophyllin. — Investigations were next directed towards the 

 preparation of a pure chlorophyll, and to the study of the actual 

 change wrought by acids and alkalis on the original plant- 

 pigment ; as the result of which two facts of prime importance 

 were discovered. The first of these was the fact that magnesium 

 is an essential constituent of chlorophyll, and was readily elimi- 

 nated from the molecule by the action of even weak acids ; it 

 was not, however, readily removed by the action of alkalis. The 

 second important fact discovered was that chlorophyll, in part 

 at any rate, is the ester of an unsaturated alcohol called by 

 Willstatter phytol ; by treatment with alcoholic solutions of 

 caustic alkalis, the phytol ester readily undergoes saponification. 

 It was also found that the hypothesis of Hoppe-Seyler, that 

 chlorophyll is a lecithin derivative, is incorrect; phosphorus is 

 only an accidental contamination of chlorophyll preparations. 

 Preparations made from grass and stinging-nettles contained 

 either traces or no phosphorus at all. The chief difficulty in 

 this part of Willstatter's investigations was due to the admixture 

 of chlorophyll with other plant-pigments, notably xanthophyll 

 or carotin, which will be referred to in greater detail below. 



Attempts were first made to prepare a purified chlorophyll 

 solution, freed as completely as possible from other pigments. 

 This was accomplished in the following way : A double methyl- 

 alcoholic extract was mixed with an equal volume of light 

 petroleum (B.P. 35-50 ) and water added, so that the mixture 

 separated into two layers ; the petroleum layer was then washed 

 with diluted methyl alcohol, and afterwards with water, and the 

 solvent distilled off, after drying the solution with anhydrous 

 sulphate of sodium. 1 The crude 'chlorophyll thus obtained 

 was further purified by redissolving in methyl alcohol and 

 treatment of the solution with light petroleum in the way just 

 described. Another method of freeing chlorophyll from the 

 accompanying pigments was to mix a solution in acetone with 



1 The object of this operation was to separate the other pigments accompanying 

 chlorophyll. It was shown in subsequent researches (see below) that it is impossible 

 to separate carotin from chlorophyll in this way. 



