Light 'Absorption and Fluorescence. 19 



condensation will be very great with the evolution ol' a largo 

 number of atomic quanta. Such an atom will under ordinary 

 circumstances possess little or no power of attracting other 

 atoms, and hence will have no measurable chemical reactivity. 

 I suggest that the atoms of the inactive gases — helium, 

 neon, etc. — are of this type. On the other hand, if there 

 exist more than one plane orbit of electrons, a condition of 

 asymmetry will be set up in the atomic force field, with the 

 result that the complete condensation to form a 7ion-reactive 

 atomic field is no longer possible. It does not seem im- 

 probable that in the various types of asymmetry likely to 

 exist the explanation is to be found of the various properties 

 of elementary molecules which are familiar to the chemist. 

 The extreme conditions resulting from this asymmetry would 

 be (1) the non-reactive diatomic molecule such as H 2 , N 2 , 

 etc., (2) the highly reactive monatomic molecule such a*< 

 Na, K, etc., (3) the highly reactive diatomic molecule such 

 as F 2 , (4) the non-reactive polyatomic molecule such as 

 that of carbon. Apart from this possibility, which need 

 not now be discussed, it is necessary to take into account 

 the fact that, at any rate in the case of elementary molecules 

 containing more than two atoms, the different molecular 

 phases may be capable of separate existence. Smits has put 

 forward the theory that the different allotropic modifications 

 of an element are equilibrium mixtures of different molecular 

 speeies of that element. Thus the various allotropic modi- 

 fications of sulphur are equilibrium mixtures of some or all 

 of four molecular species of sulphur known as S A , S^, S w , 

 and S^. There seems little doubt that what Smits calls 

 molecular species are in reality four different molecular 

 phases of sulphur, which differ in their energy content by a 

 definite number of quanta at the infra-red fundamental of 

 sulphur. It is of considerable interest to note that each of 

 the four varieties of the sulphur molecule exhibits a different 

 molecular frequency in the visible or ultra-violet region, and 

 that they therefore conform to the definition of molecular 

 phases. An investigation of these frequencies is now being 

 made in these laboratories. 



The molecular phase hypothesis throws a considerable 

 light on the mechanism of chemical reaction, and enables 

 accurate calculations to be made of the complete energy 

 changes which are involved in any reaction. In the first 

 place, the calculation may be made of the total energy which 

 is evolved during the combination of elementary atoms to 

 form molecules which arc in radiant equilibrium with their 

 surroundings. Whereas in the preceding paper it was 



C 2 



