154 LECTURE IX. 



In the consideration of the chemical composition of chlo- 

 rophyll the first point is as to whether chlorophyll is a distinct 

 substance or a mixture of two or more colouring-matters. 

 Without going into the very extensive literature of the subject, 

 it may just be pointed out that both these views have found 

 supporters. Thus Fremy, Stokes, Sorby, and others, state that 

 it consists of a mixture of one or more blue with one or more 

 yellow colouring-matters, whereas Konrad, Pringsheim, and 

 others, regard it as a definite chemical substance. It is true 

 that an alcoholic extract of leaves contains colouring-matters 

 which are not green, but there is no evidence to prove that 

 these belong directly to the green colouring-matter. They 

 are present in the chlorophyll-corpuscles in addition to the 

 chlorophyll itself, and, as we shall see hereafter, are probably 

 either substances from which chlorophyll is formed or products 

 of its chemical alteration. 



Our knowledge of the probable chemical composition of 

 chlorophyll has been considerably extended of late years by 

 the researches of Gautier and of Hoppe-Seyler. Both these 

 observers have succeeded in obtaining crystals of a green sub- 

 stance by evaporating to dryness the alcoholic extract of 

 green leaves, but this substance is probably not pure chloro- 

 phyll, for, as the following table of analyses will shew, the 

 crystals contain a considerable percentage of ash. Hoppe- 

 Seyler has, in fact, termed the substance chlorophyllan in 

 order to emphasize this point. Analysis of the substance has 

 given the following results : 



Gautier. Hoppe-Seyler. 



C. 73*97 73-34 



H. 9-80 972 



N. 4-15 5'68 



O. 10-33 9-54 



Ash 175 P- i'38 



Mg. 0-34 



lOO'OO 



lOO'OO 



It is of interest to note that iron was not found to be 

 present, although, as we learned in a previous lecture, a supply 

 of iron is essential to the formation of chlorophyll in the plant. 



