92 THE CHEMISTRY OF CATTLE FEEDING 



Alizarin, it has been ascertained, is dihydroxyanthra- 

 quinone. The constitution is shown below. 



(Anthraquinone.) . (Alizarin.) 



Another dyestuff called purpurin is also obtained from 

 madder roots. It is the trihydroxyanthraquinone, C 14 H 8 O 5 . 



The bile contains several pigments known as bilirubin, 

 biliverdin, bilifuschin, etc. They appear to be related to the 

 red colouring matter of the blood haemoglobin (p. 80) or 

 haematin, and are probably formed from it, but they contain 

 no iron. The formula C3 2 H 36 N 4 O 6 is ascribed to bilirubin. 

 The substance is of a reddish-yellow colour, insoluble in 

 water, but soluble in alcohol and other organic solvents. 

 Alkaline solutions, when exposed to air, absorb oxygen, and 

 are converted into biliverdin, C 32 H 36 N 4 O 8 , which is of a 

 greenish colour. The constitution of these bodies is not 

 known. 



Chlorophyll is, as the name implies, the green colouring 

 matter of the leaves of plants. It is of special interest and 

 importance from several points of view, but it is an extremely 

 difficult substance to investigate. It is present only in minute 

 quantities even in leaves that are intensely green, and it is 

 always associated with fats, waxes, and other impurities which 

 are soluble in the same solvents and are not easily separated. 

 Also, it readily suffers change. 



Chlorophyll is found in all vegetable cells that are con- 

 cerned with the assimilation of carbon from carbon dioxide ; 

 not in others. The process apparently depends upon the 

 presence of chlorophyll, but it is not known how that sub- 

 stance acts. Sachs -has advanced the hypothesis that the 

 cells which do not assimilate carbon contain a colourless 

 substance which he called leucophyll, and that, on exposure 

 to light, this body is changed into the green chlorophyll. 



With regard to the chemical composition and properties of 

 chlorophyll but little information of a satisfactory character 

 is available. It is uncertain whether there is only one or 

 several different kinds. It appears, however, to be closely 



