26 CAROTINOIDS AND RELATED PIGMENTS 



alcohol when added to the concentrated carbon disulfide solution will 

 throw down the carotin in crystalline form. The beautiful, glistening, 

 copper colored crystals were described by Zeise, who also mentioned 

 their insolubility in alcohol and their difficult solubility in ether and 

 acetone. The crystals melted at 168 (+)C. Zeise made the first 

 analysis of carotin and ascribed to it the formula C 5 H 8 . He was thus 

 the first to show the hydrocarbon nature of the pigment, but due to 

 the authority of the next investigator (Husemann (1861)), this fact 

 was not proved until Arnaud (1886) made his careful analyses of the 

 carrot pigment. 



Husemann (1861) pressed the juice from finely grated carrots and 

 then added weak sulphuric acid to the diluted juice, following Zeise's 

 method, throwing down a coagulum which was partially dried and 

 then extracted with hot 80 per cent methyl-alcohol. The residue was 

 then dried completely and extracted with carbon disulfide. Carotin 

 crystals were thrown out of the concentrated carbon disulfide solution 

 by addition of absolute alcohol. Husemann purified the crystals 

 merely by repeated washing on a filter with hot 80 per cent alcohol 

 and finally with absolute alcohol. Husemann described the ruby-red 

 color and velvety appearance of the carotin crystals, and their violet- 

 like odor, which he found was especially noticeable on warming. He 

 noticed the bleaching of the crystals in the air with the complete re- 

 versal of solubility, the bleached crystals being very difficultly soluble 

 in carbon disulfide and benzine, but easily soluble in alcohol and ether. 

 Husemann found that carotin was not precipitated by metallic salts 

 but he observed the green color produced by adding ferric chloride to 

 an alcoholic solution of the pigment. Palmer and Thrun (1916) have 

 recently studied the reaction of ferric chloride on the carotinoids and 

 have found it a most useful test for confirming the presence of these 

 pigments in oils and fats and in various extracts of plant and animal 

 tissues. 



Husemann was the first to show the unsaturated nature of the 

 carotin molecule, although he regarded the chlorine and iodine deriva- 

 tives which he made as substitution products. Husemann's analyses 

 led him to propose the formula C 18 H., 4 for carotin and his figures 

 were accepted over those of Zeise. 



Arnaud (1886) was the next investigator of the carrot chromolipoid. 

 He isolated the pigment from 600 kilograms of carrots by pressing 

 the juice from the grated roots, adding lead acetate to the juice, drying 

 the precipitate in vacuum and extracting it with carbon disulfide. The 



