178 VITAMIN D GROUP 



the composition of the crude irradiation product varies with the wave- 

 length used .2^^ In particular, it has been demonstrated that long waves 

 favor the accumulation of lumisterol, and short waves of tachysterol, each 

 at the expense of the other. ^^^ 



The light sources used for irradiation are principally the quartz mercury 

 arc and the cored carbon arc, carbons for the latter containing compounds 

 of iron, magnesium, or other metals. A favorite experimental source in the 

 early years was the magnesium spark. ^^^ ^"^ 226-230 Light, filters have not come 

 into general use, but for special studies, the Corning^* or Jena^-^' ^-^^ -^"^ 

 glasses or Vitaglass^-^'' have been employed, or filter cells containing ben- 

 zene,^"- ^^^ xylene,^^^' 231-233 diphenyl,^^^ carbon disulfide,^^* chlorine,^^^' ^" 

 brominej^"^ chlorine-bromine,^*- ^°^' ^'^ tartrazine,^^^ salicylic acid,^^^ leadace- 

 tate,^^^ potassium nitrate,^^^ nickel sulfate,-^^ or alcoholic cobalt chloride.^^* 



The temperature coefficient of activation is small. Bills and Brickwedde^^^ 

 found that cholesterol containing 1.2 parts of provitamin D per 1000 was 

 readily activated at —183°, although the product was somewhat less potent 

 than the product of similar irradiation at room temperature. Webster and 

 Bourdillon224 irradiated ergosterol at temperatures between —195° and 

 +78° and observed that the effect of temperature was only moderate. 

 Knudson and Moore^^"^ noted that a "less potent product" was obtained 

 when ergosterol was exposed to cathode rays at liquid air temperature 

 than when the exposure was made at room temperature. These observations, 

 made before the structure of vitamin D was known, pointed to the fact 

 that activation is an intramolecular change, because bimolecular reactions 

 are generally inhibited at very low temperatures. More recently Dasler^i^ 

 has stated that temperature has "no effect upon the time-disappearance 

 curve of ergosterol nor upon the time-activation curve of ergosterol." The 

 fact that activation is best conducted in boiling solvents is not contra- 



225 E. H. Reerink and A. van Wijk, Biochem. J. 23, 1294 (1929); A. Windaus, Nachr. 

 Ges. Wiss. Gottingen, Math, physik. Kl. 36 (1930); F. A. Askew, R. B. Bourdillon, 

 H. M. Bruce, R. G. C. Jenkins, and T. A. Webster, Proc. Roy. Soc. (London) 

 B107, 91 (1930). 



22« P. Setz, Hoppe-Seyler's Z. physiol. Chem. 215, 183 (1933). 



2" E. H. Reerink and A. van Wijk, Biochem. J. 23, 1294 (1929). 



228 A. Windaus, Nachr. Ges. Wiss. Gottingen, Math, physik. Kl. 36 (1930). 



229 A. Smakula, Nachr. Ges. Wiss. Gottingen, Math, physik. Kl. 49 (1928). 



230 A. Windaus, Deut. med. Wochschr. 57, 678 (1931). 



231 I. G. Farbenindustrie, German Pat. 565,900 (1932). 



232 F. A. Askew, R. B. Bourdillon, H. M. Bruce, R. G. C. Jenkins, and T. A. Webster, 

 Proc. Roy. Soc. (London) B107, 91 (1930). 



2« E. H. Reerink and A. van Wijk, Biochem. J. 25, 1001 (1931). 



2" N. V. Philips' Gloeilampenfabrieken, British Pat. 385,626 (1932). 



235 G. Sperti, R. J. Norris, R. B. Withrow, and H. Schneider, U. S. Pat. 1,982,029 

 (1934). 



236 C. E. Bills and F. G. Brickwedde, Nature 121, 452 (1928). 



