232 PIGMENTS 



confusion owing chiefly to the compounds obtained not being 

 pure substances and also to the terminology employed ; for 

 example, the compound called x by one author being anything 

 but the same material designated by the same name by another 

 investigator. 



It is, therefore, not proposed to deal with this earlier work 

 here — those who desire it are referred to an admirable summary 

 by Schryver* — but to start with the investigations of Will- 

 statter, who with his pupils have established the following two 

 facts of fundamental importance with regard to the constitution 

 of chlorophyll : — 



1. The existence of magnesium f as an essential consti- 

 tuent of chlorophyll, and organically combined in a complex 

 C3iH,,N,Mg. 



2. The fact that chlorophyll is an ester of the tricarboxylic 

 acid chlorophyllin, C3,H.,9N4Mg(COOH)3. 



They have further studied the action of acids and alkalis 

 upon chlorophyll, and have shown that it is possible to divide 

 the degradation products of chlorophyll into two groups: — 



1. Those that contain magnesium. 



2. Those that do not contain magnesium. 



The first class, known as Phyllins, comprises the two 

 isomeric dicarboxylic acids Glaucophyllin and Rhodophyllin, 

 C3iH3oN4Mg(COOH)2, and the two monocarboxylic acids Phyl- 

 lophyllin and Pyrrophyllin of the formula C3iH3iN4MgCOOH. 



The second class comprises the Porphyrins, which are 

 di- and mono-carboxylic acids exactly analogous to the 

 Phyllins, only having the magnesium replaced by two atoms 

 of hydrogen. Their names and formulae are Glaucoporphyrin 

 and Rhodoporphyrin, C3iH32N^(COOH)^, and Phylloporphyrin 

 and Pyrroporphyrin, C3iH33N,COOH. 



The mother substance of this group, namely the magnesium 

 free tricarboxylic acid, C3iH3jN^(COOH)3, is known as Pha^o- 

 phorbin. 



* Schryver: " The Chemistry of Chlorophyll," "Science Progress," 1909, 

 3. 425- 



+ This is of peculiar interest in view of the reactivity exhibited by this element 

 in the Grignard reaction, and also because it has been shown that carbon dioxide 

 may be reduced by this metal in cold aqueous solution to formaldehyde (Fenton : 

 "J. Chem. Soc, Lond.," 1907, 91, 687), a fact which has, of course, an im- 

 portant bearing on the question of assimilation. 



