304 REPORTS ON THE STATE OF SCIENCE, ETC. 



of which is due to the lact that the majority of their molecules exist in the 

 phase with visible colour. 



Analogous to the specific heat relation is the expression of the latent heat 

 of evaporation of a compound in terms of its molecular quantum. That this 

 is possible can readily be seen from the following examples (Baly, Phil. Mag., 

 40, 15 (1920^K 



In most cases the change in phase on vaporisation is restricted to those molecules 

 in the equilibrium the frequencies of which lie in the extreme ultra-violet, and. 

 therefore, no difference is found between the absorption spectra of the liquid 

 and vapour in the visible or near ultra-violet. Sometimes, however, on vaporisa- 

 tion there is also a phase change on the part of those molecules present, the 

 phase frequency of which lies in the visible or near ultra-violet. "Slention has 

 already been made of these substances, the best known examples being pyridine, 

 piperidine, and benzaldehvde. 



In addition to the ettect of temperature — that is to say, very long wave 

 radiations — in causing a phase change of molecules any method of supplying 

 energy to the molecules will be equally effective. There are two other methods 

 of supplying energy to substances — namely, by exposing them to short-wave 

 radiation nf frequency equal to their phase frequencies, and also by the action 

 of a solvent or catalyst. These two methods may be discussed separately, and 

 the effect of short-wave radiation may be dealt with first. It was stated in 

 the early part of this report that the molecular quantum is exactlv equal to the 

 amount of energy given out when the component atoms combined to form that 

 molecule. A freshly synthesised molecule, therefore, on absorbing one molecular 

 quantum will just be resolved into its atoms. After the molecular force field 

 has been established with the evolution of a number of molecular quanta, the 

 absorption of one molecular quantum will simply change the phase into the 

 next phase of higher energy content. It has already been shown that, if during 

 its force field condensation a molecule loses, say. 16 molecular quanta, the 

 resulting phase will be characterised by a quantum which is 17 times the 

 molecular quantum, and consequently when this molecule is exposed to radiation 

 of a frequency equal to its phase frequency, it will absorb a quantum which 

 is 17 times its molecular quantum. This molecule, however, was synthesised 

 with the loss of one molecular quantum, and has subsequently lost a further 

 amount of 16 molecular quanta, or 17 molecular quanta in all. The absorption 

 of one phase quantum, therefore, is always sufficient just to resolve a molecule 

 into its atoms. It does not follow that a molecule must be decomposed into it=; 

 atoms when it absorbs a phase quantum, for observation shows that in general 

 the molecule is thereby converted into a phase of higher energy contact, the 

 balance of energy being radiated to the surroundings. Let a freshly synthesised 

 molecule, for example, lose 19 molecular quanta in its force field formation and 

 then absorb its phase quantum, which is equal to 20 molecular quanta. In 

 general, the molecule is converted into another phase, and let this new phase 

 be that characterised by a phase quantum of 17 molecular quanta. Clearly, three 

 molecular quanta are required for this phase change, and. therefore, the balance 



