542 SCIENCE PROGRESS 



which agrees with the frequency calculated from the equation 



^ = hv. The values for the monochromatic radiation of these 

 N 



gases should be 390/^/* for PHg, 630/iyu. for As 4, 570/u,//, for P4, 

 467/*//- for COCI2, and 437/ti/i for NO ; and all of these wave- 

 lengths lie in the visible region. Since the gases in question 

 are colourless, they cannot absorb appreciable amounts of the 

 necessary radiation. There are also considerable discrepancies 

 between the amount of monochromatic energy radiated (black 

 body radiation) and the energy required for the activation of 

 the gaseous molecules. The amount of radiant energy available 

 is many times smaller than the heat absorbed in activation. 

 This discrepancy is very marked in the case of phosphine, where 

 the radiant energy is one million times too small. The rate 

 at which heat is dissipated from a tungsten filament in hydrogen 

 gas is also not in agreement with the hypothesis. 



Perrin pointed out that the velocity of a monomolecular 

 reaction is independent of the pressure and the number of 

 collisions between the molecules, and hence the energy of 

 collision could not be solely responsible for the chemical reaction. 

 Langmuir shows that the collision-energy is too small to supply 

 the heat of activation. It thus appears that neither the radiant 

 energy nor the energy from collisions is sufficient to activate 

 the molecules and to account for the velocity of chemical 

 reaction. He proposes a modification to the radiation hypothesis, 

 and suggests that chemical reaction is in many ways analogous 

 with the photoelectric effect, and that by a kind of trigger 

 action, energy at a low intensity would be able to control the 

 disposition of energy of a high intensity. (This action would 

 be presumably analogous to that of infra-red radiation on the 

 phosphorescent light emitted by a phosphoroid.) Baly {Phil. 

 Mag., 1920, [vi], 40, 15) suggests a very similar mechanism to 

 explain the discrepancy occurring between the velocity of 

 decomposition of phosphine and that calculated on the quantum 

 theory. The absorption of infra-red radiation by the phosphine 

 molecule may be regarded as initiating a change, which is 

 itself the origin of radiation of an absorbable type. The 

 decomposition of phosphine, being slightly exothermic, could 

 thus be brought about by a low density of infra-red radiation. 

 The reaction is compared with that investigated by Henri and 

 Wurmser, where 180 molecules of H2O2 were decomposed by 

 one quantum at the phase frequency. 



Lewis {Trans. Chem. Soc, 1916, 109, 806) indicates that it 

 is possible for catalysts to increase the natural radiation of a 

 system (black body radiation), but it is not clear whether the 

 density of such radiation would be sufficient to supply the whole 

 of the energy of activation. 



