Abstract

AT the temperature of liquid oxygen (− 183°), most bimolecular chemical reactions are largely inhibited. The rates of these reactions, in general, decrease rapidly with decreasing temperature. At very low temperatures the rates become too small to be measured, and for practical purposes it may be said that reaction ceases. This is especially true of oxidations, since, for example, neither sodium nor phosphorus immersed in liquid oxygen undergoes any apparent oxidation. However, the rates at which photo-molecular changes take place decrease more slowly with temperature. With this in mind, the irradiation of activatable cholesterol was carried out in liquid oxygen with the object of obtaining evidence as to the nature of the change involved. It was found that cholesterol of ordinary purity even at liquid oxygen temperature becomes antiricketic upon exposure to ultra-violet light.