CAROTIN, THE PRINCIPAL YELLOW PIGMENT OF MILK FAT 393 



standard was obtained by fixing the arbitrary scale attached to the 

 spectroscope at a constant figure which was furnished by a sodium 

 flame, the spectrometer slit being closed to furnish the narrowest 

 possible line. This standard did not of course give absolute meas- 

 urements of absorption bands but merely a means of comparing the 

 position of bands of various solutions, which was the desired end 

 in view. Before measuring the bands of an unknown pigment, the 

 strength of its solution was adjusted to give bands of as nearly the 

 same intensity and clearness as the bands whose arbitrary measure- 

 ments furnished the standard. The arbitrary standards for the ab- 

 sorption bands of carotin and xanthophylls, which were adopted, are 

 given in Table I. 



TABLE 1. SPIJCTROSCOPIC STANDARDS or CAROTIN AND XANTHOPHYIXS. 



The Solubility Properties. The relative solubility properties of 

 carotin and xanthophylls are based on the fact that organic compounds 

 are best soluble in solvents of similar composition. Accordingly car- 

 otin, which is a hydrocarbon, is much more soluble in hydrocarbons 

 like petroleum ether than in the alcohols. Similarly the xanthophylls 

 are much more soluble in the alcohols than in a hydrocarbon like 

 petroleum ether. These phenomena, as stated in the preceding paper 

 of this series, were discovered and elaborated by Tswett l and by 

 Willstatter and Mieg. 2 At this station they were found to be very 

 characteristic of carotin and xanthophylls and in addition very use- 

 ful for separating and differentiating the carotin and xanthophyll 

 constituents, not only of plants but also of the milk fat pigment. 

 Thus the xanthophyll constituents of a mixed pigment could be 

 readily separated by shaking the petroleum ether solution of the 



1. Ber. d. Deut. Botan. Gessel. 24, pp. 316, 384 (1906); 29, p. 630 (1911). 



2. Ann. d. Chemie. 355, p. 1 (1907). 



