330 



PIGMENTS 



LYCOPIN, C40H56. 



Under this name is described a red hydrocarbon isomeric 

 with carotin which was isolated by Willstatter and Escher * 

 from the tomato. Lycopin forms carmine coloured prisms or 

 needles which melt at i68''-i69° ; its solution in alcohol is 

 deep yellow in colour. Like carotin it absorbs oxygen with 

 avidity. 



XANTHOPHYLL, QoH^gO^. 



This substance is closely related to carotin, having the 

 molecular formula C40H56O2. Ewart f claims to have shown 

 that xanthophyll may be converted into carotin by the action 

 of zinc dust or magnesium powder and water. 



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

 as an acid. 



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

 forms an additive compound with iodine of the formula 

 C40H56O2I2, 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 : — 



Xanthophyll. 

 Pleochroic dark red- 

 dish-brown plates. 



Appearance 



Colour by transmitted 

 light 



Melting-point 



Solubility in light petro- 

 leum 



Solubility in alcohol 



Solubility in acetone 

 Solubility in carbon di- 



sulphide . 

 Concentrated sulphuric 



acid. 



Carotin. 

 Copper coloured leaf- 

 lets. 



Red. 

 i67-5°-i68°. 



Appreciably soluble. 

 Practically insoluble in 



cold ; very sparingly 



soluble in hot. 

 Very sparingly soluble. 



Very readily soluble. 

 Dissolves ; deep blue 

 colour. 



Yellow to orange. 



172°. 



Insoluble. 



Sparingly soluble in 



cold ; fairly readily 



soluble in hot. 

 Readily soluble. 



Sparingly soluble. 

 Dissolves ; deep blue 

 colour. 



RHODOXANTHIN, C^^U^^O^. 



This substance, which is a red isomer of xanthophyll, was 

 discovered by Monteverde in Potamogeton natans ; it has since 



* Willstatter and Escher : " Zeit. physiol. Chem.," 1910, 64, 47. 

 t Ewart : " Proc. Roy. Soc," B., 1915, 89, i. 



