PAPERS OX CHEMISTRY AND PHYSICS 137 



One other important attempt has been made to apply 

 the quantum hypothesis to photochemical processes. Per- 

 rin- has proposed a theory which has been discussed in 

 detail and modified to a certain extent by Tolman 3 . The 

 classical Arrheliius equation 



d In k E 



d T E T 2 



connects the constant in the equation for a nionomole- 

 cular reaction 



dx 



= k(A-x) 



dt 

 with a quantity E which has the dimensions of energy. 

 Perrin states that this term represents an energy of 

 ''activation'', and writes E— Xhv . Thus a molecule 

 might absorb an amount of energy hv and subsequently 

 either decompose or return to its original state. This 

 formula has been applied to the decomposition of nitro- 

 gen pentoxide with great care by Daniels and Johnston 4 

 and roughly to the decomposition of solid oxalic acid 5 . 

 In neither of these cases was the formula found to a 

 with the experimental far 



It is obvious, of course,- that an idea such as that pro- 

 posed by Perrin could at best hold true in an ideal 

 For the ordinary photographic action of light on the 

 silver halides all wave lengths of light seem to be active 

 from the red end of the spectrum to hard X-rays, a fact 

 which could not be explained by Perrin 's hypothesis.- 

 Berthelot 6 has suggested that the effect of radiation 

 would increase with increase in frequency according to 

 an exponential law, in much the same manner that the 

 rates of thermal reactions increase with the tempera- 

 ture. In the case of the decomposition of a crystalline 

 body by the action of radiation, it would seem that Per- 

 rin 's formula should fail for the following reasons 7 : a 

 molecule in a crystal lattice is held to the other niole- 



• Perrin, Annales de Physique, 11, 5 (1919). 



'Tolman, Journ. Amer. Chcm. Soc. :,2, 2506 (1920) : 45. 22S5 (1923). 

 ♦Daniels and Johnston, Journ. Amer. Chem. Soc, $3, 72 (1921). 



• X yes and Koupermah, ibid.. iJ. 1398 (1923). 



•Berthelot, Bull, de la Soc. chimique, Si, 241 (1924). This article sums 

 up manv of Berthelot's views. 



'Noyes, Comptes Rendus, i76, 1468 (1923). 



