IX THE PHANEROGAMS 27 



dried press cake was extracted similarly and the carbon disulfidc dis- 

 tilled off of the combined extracts. The residue was washed with cold 

 petroleum ether and the pigment purified by crystallization from car- 

 bon disulfide with absolute alcohol and then allowing it to crystallize 

 spontaneously from cold petroleum ether. About 3 grams of crystals 

 per 100 kilograms of carrots were obtained in this way. 



Arnaud found the bleaching of carotin noticed by Husemann to be 

 an oxidation, analyses which he made of the bleached product show- 

 ing an addition of 21 per cent oxygen. The rapid bleaching of caro- 

 tin solutions was also noticed; and Arnaud pointed out the influence 

 of this fact on the securing of pure preparations for analysis. 

 Arnaud's analyses of freshly prepared crystals showed an average 

 composition of 88.67 per cent carbon and 10.69 per cent hydrogen, 

 definitely proving the correctness of Zeise's assertion regarding the 

 hydrocarbon nature of the pigment. This investigator was also the 

 first to prepare the crystalline iodine derivative of carotin by adding 

 iodine crystals a little at a time to a solution of carotin in anhydrous 

 petroleum ether, maintaining the while an excess of carotin in the 

 solution. It was the elementary composition of this product, con- 

 sidered together with the composition of the pure carotin, that led 

 Arnaud to ascribe to carotin the formula C 26 H 38 , and to the iodine 

 derivative the formula C 26 H 38 I 2 . 



Kohl (1902b) has given us one of the most detailed descriptions of 

 the chemical and physical properties of carotin. His analyses of the 

 crystalline pigment, however, gave unsatisfactory results, as did also 

 his molecular weight determinations, using the cryoscopic method. 

 He therefore accepted Arnaud's formula as representing the correct 

 composition of carotin. Certain of Kohl's detailed descriptions of 

 carotin will be summarized in Chapter IX, where the physical and 

 chemical properties of the carotinoids are considered. 



Willstatter and Mieg (1907) definitely settled the composition of 

 the carrot carotin at the time they proved its identity with the carotin 

 of the chloroplastid. Their data show a mean ratio of C:H of 1:1.406 

 for the carrot carotin, for which the simplest formula is C 5 H 7 . Molecu- 

 lar weight determinations in CHC1 3 and CS 2 , using the ebulloscopic 

 method, show an average of 536, which corresponds exactly with the 

 formula (C 5 H 7 ) 9 . or C 40 H GO , which thus appears to be the correct 

 formula for carotin. 



Escher (1909) and Willstatter and Escher (1910) have confirmed 

 these results completely. Escher furthermore attempted to ascertain 



