o72 Prof. F. A. Lindemann on the 



reacting substances. The temperature coefficient of a re- 

 action is usually given by chemists as the factor n by which 

 the velocity is increased when the temperature is raised 10°. 

 Hence 



lh |^ = ?* 1/10 - 1 , so that %=T {n 1 ' 10 - 1) 



and an absorption-band would be found at a wave-length 

 oh c 2 



A = 



hT\nW-l) T 2 (^'io_i)' 



where c 2 = l*46 is the constant in Planck's radiation law 

 written in the form 



e^ -1 



In the case of the inversion of sucrose by 0'9 N. hydro- 

 chloric acid, Lewis finds « = 4'13 between 25° C. and 35° 0. 

 Therefore 



^=303(1-152-1) = 46 and \=l-05^*. 



The solution does absorb radiation between 1/jl and 10//., so 

 that Lewis concludes that his theory is supported by the 

 facts. 



The fundamental difficulty to which this note refers arises 

 from the fact that the radiation density may be profoundly 

 modified by exposing the reaction to some external source of 

 radiation. It* Prof. Lewis's theory were true, this should 

 completely change the velocity of reaction, but no such 

 phenomenon has been observed. As an example, one may 

 consider the change in radiation density produced by ex- 

 posing a reaction to sunlight. If a. is the apparent angular 

 semi-diameter of the sun and T its temperature, the energy 

 density in sunlight is given by 



hv 3 



:2-~ 2 



g'3 hv 



* Lewis finds a somewhat ditferent wave-length, \ = l'23/i, pre- 

 sumably because he uses Perrin's value 6*85 . 10 23 for N; which figure 

 one takes does not materially affect the argument. 



