174 



VITAMIN D GROUP 



suffice to show the absorption spectrum of ergosterol (Fig. 8) . The location 

 of the maxima at 262, 271, 282, and 293.5 m^t are based on recent deter- 

 minations with the Beckman spectrophotometer, and they are probably 

 a bit more accurate than earlier data obtained photographically. The 

 absorption minima at 263, 277, and 289.5 m/x are also shown in the figure. 



230 240 250 260 270 280 290 300 310 320 



Wavelength, millimicrons 



Fig. 8. Absorption spectrum of ergosterol in alcohol 1:50,000 w./v. Ergosterol 

 monohydrate recrystallized from alcohol-benzene 2:1. (Courtesy of the Sulphite 

 Pulp Manufacturers' Research League.) 



Other maxima, detectable in more concentrated solutions, will be discussed 

 in the section on the chemistry of activation. 



The wavelengths which affect ergosterol must be among those which it 

 absorbs. Ergosterol absorbs strongly from 300 mij. to 230 mju in the far 

 ultraviolet region, but it exhibits some absorption beyond these limits in 

 both directions. The shortest effective wavelength has not been ascertained, 

 but it is known that 230 m/x activates ergosterol readily.^"^ Wavelengths 

 as long as 313 m/x are known to activate ergosterol slightly ^''^ and this 



2«i A. L. Marshall and A. Knudson, /. Am. Chem. Soc. 52, 2304 (1930). 



202 R. W. Haman and H. Steenbock, Ind. Eng. Chem. Anal. Ed. 8, 291 (1936). 



