RECENT ADVANCES IN SCIENCE 541 



intensity throughout the capillary ; when, however, a con- 

 denser and spark gap are placed in parallel with the terminals 

 of the induction-coil, the hydrogen lines appear faint inside the 

 capillary, and much stronger in the bright glows which appear 

 just beyond the ends of the capillary. On cutting out the 

 condenser these bright glows gradually extend into the capillary 

 in a manner suggestive of gaseous diffusion, until the Balmer 

 lines are once more of uniform brightness throughout the 

 capillary. Prof. Merton suggests that this change in the relative 

 intensity of the lines in the different parts of the tube is due to 

 an alteration of the relative proportions of helium and hydrogen 

 — the latter being driven out the capillary in some way when 

 the condensed discharge is applied — and that this may be the 

 explanation of many phenomena in vacuum tubes containing 

 two gases, which have formerly been attributed to changes in 

 the nature of the electrical discharge itself. 



PHYSICAL CHEMISTRY. By W. E. Garner, M.Sc, University College, 

 London. 



The Radiation Hypothesis. — This hypothesis, as developed by 

 Trautz, Lewis, Perrin, and others, has been criticised recently 

 by Lindemann {Phil. Mag., 1920, 40, 671) and Langmuir 

 {J.A.C.S., 1920, 42, 2290). This theory assumes that the 

 velocity of a chemical reaction is determined by the energy 

 density of radiation of a characteristic frequency, which is 

 emitted and absorbed by the chemical system. A possible 

 check on this theory is to establish some relation between the 

 value of V derived from the equation 



dlogk _ Nhu 

 dT "" RT» 



and the value obtained from the optical properties of the system. 

 Lewis has done this for the inversion of sucrose by hydrochloric 

 acid, and obtained satisfactory agreement for the two values of 

 the characteristic frequency (X = 1-05/^) 



Lindemann, however, raises the following objection to the 

 radiation hypothesis. The energy density of X = i-osi^ in 

 the light from the sun is 10" times that occurring in the dark, 

 in the case of Lewis's experiments. This radiation should 

 materially modify the velocity of the chemical reaction, whereas 

 the reaction proceeds at the same rate whether exposed to 

 sunlight or not. 



Langmuir points out that in the cases of the gases — PHg, 

 As 4, P4, COCI2, and NO — no absorption band is to be found 



