238 



PIGMENTS 



It is a neutral substance, reacting neither as an alcohol nor 

 as an add. 



It absorbs 36-55 per cent of its weight of oxygen, and 

 forms an additive compound with iodine of the formula 

 C^oHjpOgls, which crystallizes in dark violet tufts. 



The more important physical constants and solubilities of 

 Carotin and Xanthophyll are given in the appended table, 

 compiled by Willstatter: — 



FURTHER LITERATURE. 

 General. 



Hansen : " Die Farbstoffe des Chlorophylls," Darmstadt, i88g. 



Krauss : " Zur Kenntniss der Chlorophyllfarbstoffe," Stuttgart, 1872. 



Stahl : " Zur Biologie des Chlorophylls," Jena, 1909. 



Tschirsch : " Unters. ii. Chlorophyll," Berlin, 1884. 



Annual Reports of the Chemical Society of London, igio, 1911. 

 On the constitution of the Blood Pigment and its relation to Chlorophyll. 



Nencki and Zaleski : " Ber. deut. chem. Gesells.," 1901, 34, 997. 



Piloty: id., 1910, 43, 489; " Annalen," 1910, 377, 314. 

 On the constitJition of Hamopyrrole, etc. 



Knorr and Hess: "Ber. deut. chem. Gesells.," 1911, 44, 2758. 



Kiister : "Annalen," 1906, 345, i. 



FLAVONES AND XANTHONES. 



Under the headings of Flavones and Xanthones (two words 

 derived from the Latin and Greek words respectively for 

 yellow) are included a number of substances occurring in the 

 vegetative organs and in the petals of many plants. 



These yellow pigments are often of considerable economic 

 value as dye-stuffs. They occur naturally either in combina- 



