302 REPORTS ON THE STATE OF SCIENCE, ETC. 



resulting molecular phase will be endowed with the quantum (i+l) x2.772x 10-" 

 erg. In addition, therefore, to the atomic quanta, intra-molecular quanta, and 

 molecular quantum, a molecule will be characterised under normal conditions 

 by a phase quantum which is an integral multiple of its molecular quantum. 

 It will consequently exhibit ^ phase frequency which is an integral multiple 

 of the molecular frequency. It is a fact well established by observation that 

 the phase frequency is always situated in the visible or ultra-violet region of 

 the spectrum, and indeed the absorption bands on which the old structure- 

 absorption theory was based are those due to the molecular phases. If the 

 above molecule lost in the formation of its force field 14, 18, 22, 26, 30, or 34 

 molecular quanta, the phase produced would be characterised by an absorption 

 band with central wave-length of 474, 374, 309, 263, 229, or 203 jxfj. respectively. 

 These molecular phases may be considered in detail from the point of view 

 of absorption spectra in the visible and ultra-violet, the physical properties, 

 and the chemical reactions of molecules. 



The particular phase into which a freshly synthesised molecule will pass 

 when in the free state depends on two factors, the relation between the external 

 force fields of its atoms and the temperature. If the external atomic force 

 fields happen to be equally balanced — that is to say, if the positive and negative 

 affinities of these are equal and opposite — the condensation between them will 

 proceed very far, with the loss of a great number of molecular quanta. In 

 this case the phase frequency will be situated in the extreme ultra-violet which 

 lies beyond the working limit of a quartz spectrograph in air, and it has been 

 customary to record such a substance as being diactinic. This, however, is 

 utterly misleading, for it is now well known that every substance exhibits 

 selective absorption in some part of the spectrum with shorter wave-length 

 than 800 /jm. and a statement that any substance is diactinic is incorrect. If, 

 on the other hand, the external atomic force fields are not equally balanced, the 

 molecular force field condensation will not proceed so far, and the phase fre- 

 quency will then lie in the visible or near ultra-violet region and will be observed 

 with an ordinary spectrograph. 



When a large number of molecules are present it by no means follows that 

 they all exist in one phase, and observation shows that this is not the case, 

 but that two or more phases exist in equilibrium with one another, the equilibrium 

 for a given compound depending on the temperature. Even when a gas or 

 liquid shows an absorption band in the visilile or near ultra-violet, the pro- 

 portion of the molecules which exist in the phase with frequency in that region 

 is small, the great majority existing in a more condensed phase. Although 

 but little work has as yet been carried out on direct observations of absorption 

 bands in the extreme ultra-violet liy means of the vacuum spectrograph, the 

 existence of these bands can be proved and their frequencies calculated from 

 measurements of the refractivity. It has been shown (C. and M. Cuthbertson, 

 Fkil. Trans., 213, A, 1 (1913)) that the refractivities of the simple gases can be 

 expressed by a modified Sellmeyer formula : 



71 — 1 = 



I 



Vq- — V' 



where Vo is the central frequency of the absorption band in the extreme ultra- 

 violet, N is a constant, and )' is the frequency for which the refractive index 

 has the value v. This formula can readily be extended to apply to substances 

 the molecules of which exist in two or more phases in equilibrium. When two 

 phases are present, if Vx and Vi are the frequencies of the two phases, and 

 Vi and Vj are the volumes occupied by the two phases, then 



(n - 1) (Vi + V2) = -^, + -^—^ ■ 



This formula very accurately expresses the refractivities of a substance which 

 exhibits one absorption band in the near ultra-violet, and it is therefore 

 established that the substance also exhibits an absorption band in the extreme 

 ultra-violet. It is interesting to note that the number of molecules in the less 

 condensed phase is very small, being of the order of 0.2 per cent, of the whole. 



