CAROTINOIDS IN THE PHANEROGAMS 45 



exhibited in the Kraus separation indicated to Tswctt (1906a> a fun- 

 dament ;il chemical difference between the two groups of carotinoids. 

 The proof of this theory as well as the nature of the difference was 

 soon brought to light by Willstattcr and Mieg (1907) when they iso- 

 lated (lie first crystalline xanthophyll and submitted it to analysis. 

 Working on the same elaborate scale, which has characterized all the 

 researches on carotinoids in Willst Jitter's laboratory, a crystalline 

 xanthophyll was isolated from 100 kilos of dried nettle (Urtica) leaves. 

 The average of five ultimate analyses of crystals prepared both by 

 recrystallization from methyl alcohol and from chloroform (by addi- 

 tion of petroleum ether) showed 84.22 per cent carbon and 9.92 per 

 cent hydrogen, which corresponds very closely with the theoretical 

 values of 84.44 per cent carbon and 9.93 per cent hydrogen for the 

 formula C 4 ,,H-,.,0.,. This was confirmed fairly well by a molecular 

 weight determination (found 512, theory 564), and better by an 

 analysis of the iodine content of the theoretically simplest iodine addi- 

 tion product, C 40 H 5(; 2 I 2 (found 31.68 per cent, theory 30.86 per cent). 



The chemical properties of the crystalline xanthophyll isolated by 

 Willstatter and Mieg will be considered in detail elsewhere. Several 

 points, however, may profitably be considered at this point. The 

 crystalline product showed the greatest solubility difference from caro- 

 tin in alcohol and low boiling petroleum ether, being practically in- 

 soluble in the latter, but readily soluble in the former, which is just 

 the reverse of carotin in these solvents. The Kraus method of separa- 

 tion of the pigments was further confirmed by Willstatter and Mieg 

 by applying the test in several ways to solutions of the purified pig- 

 ments. The difference between the position of the absorption bands 

 of carotin and the xanthophylls, first pointed out by Monteverde, was 

 confirmed, the first two bands as measured by Willstatter and Mieg 

 lying at 480-470i.in and 453-437^. 



Willstatter and Mieg expressed their belief in the existence of a 

 group of xanthophylls in the paper under consideration although they 

 were apparently not familiar with Tswett's demonstration of this fact 

 a year before their paper appeared. The question naturally arises as 

 to which xanthophyll was obtained in crystalline form by these in- 

 vestigators. 



Tswett (1910a) has expressed the opinion that the xanthophyll 

 crystallized by Willstatter and Mieg was a mixture of two or three 

 xanthophylls in which xanthophyll a predominated, a possibility which 

 was later acknowledged by Willstatter and Stoll (1913b). The evi- 



