446 SCIENCE PROGRESS 



3 methyl, 4 ethylpyrrol, and 3 methyl, 4 ethylpyrroline. The 

 relationship between the pyrrol and the imide may be represented 

 by the formula : 



CH3 . C C . C3H5 CH3 . C C . C2H5 



HC CH and OC CO 



NH NH 



Constituent of haemopyrrol Methylethyl maleinimide 



Groups of this nature are probably important constituents of 

 both the chlorophyll and haemin molecules. The constitutions 

 of such groups cannot be regarded, however, as definitely settled. 



Other Pigments which accompany Chlorophyll in Plants 



It has been already mentioned that one of the great difficulties 

 in the chlorophyll investigations related to the separation of the 

 green from the other pigments. Various methods were devised, 

 notably by Kraus and by Sorby, for the separation of these 

 substances. Kraus showed that by shaking an alcoholic extract 

 of green plants with benzene or benzine, and then separating 

 into two layers by means of water, the spirit solution became 

 yellow-coloured, whereas the hydrocarbon retained the green 

 pigment. Sorby employed a similar method, using carbon 

 disulphide instead of a hydrocarbon. In this way it was 

 supposed that chlorophyll could be separated from the yellow 

 pigment. 



The isolation of such a pigment in crystalline form which 

 had been repeatedly noticed by botanists in microscopic pre- 

 parations was the subject of numerous researches. The chief 

 of the earlier investigations are due to Arnaud, who thought 

 that the crystalline pigment which he isolated was probably 

 identical with the pigment of carrots. This supposition was 

 subsequently confirmed by Monteverde ; it was consequently 

 called carotin. 



Recently this substance has been the subject of a more detailed 

 investigation by Willstatter, who has assigned to it the formula 

 C 10 H 56 . He obtained it from green leaves by extraction with 

 petroleum ether, freeing the extract from the green pigments 

 by washing with alkali ; the carotin itself was purified by 

 fractional precipitation of its solution in carbon disulphide with 

 alcohol. 



