182 



VITAMIN D GROUP 



the production of crystalline calciferol is desired. It has been shown^^^- '^*' 2*2 

 that vitamin D, either in crystalline form or as the crude resin, is decidedly 

 more stable to oxidation than some of the non-vitamin substances which 

 are formed with it in irradiation. It is, however, somewhat less stable than 

 ergosterol itself .^^' 



By following the course of activation both spectrographically and bio- 

 logically, curves can be constructed which illustrate the absorption spectra 

 of the mixed irradiation products from time to time, and the corresponding 



Fig. 12. Potency changes during irradiation of ergosterol in alcohol by quartz 

 mercury lamp. Compare Fig. 11. (After Bills et aZ."^) 



rise and fall of vitamin D potency (Figs. 11 and 12). The illustrations 

 depict the changes observed when an alcoholic solution of ergosterol at 

 room temperature is exposed to the unfiltered radiations of a water-cooled 

 quartz mercury vapor lamp. As explained above, different conditions give 

 different curves. Early expectations that the study of the crude absorption 

 spectra would yield useful information on the products of irradiation have 

 not materialized. It has been necessary to isolate the products and examine 

 them individually. 



2« C. E. Bills, F. G. McDonald, L. N. BeMiller, G. E. Steel, and M. Nussmeier, 



J. Biol. Chem. 93, 775 (1931). 

 2" A. L. Bacharach, E. L. Smith, and S. G. Stevenson, Analyst 58, 128 (1933). 



