III. The influence of molecular constitution and temperature on magnetic susceptibility. - Part III.On the molecular field in diamagnetic substances

Abstract

In the present communication an attempt is made to examine to what extent the crystalline state of diamagnetic substances (which form a very large proportion of the whole number of substances known to us) involves mutual actions between the constituent molecules and to obtain a measure of the forces which hold the molecules together in a definite space lattice characteristic of the substance. The work is thus a continuation of that published in ‘Roy. Soc. Phil. Trans.,' vol. 214, pp. 109-146, 1914, wherein it was shown how from determinations dealing with the change of diamagnetic property on crystallization information could be derived concerning the inner structure of crystalline media and the intensity of the interacting molecular forces. In the paper cited (p. 143) it was suggested that the local molecular field within diamagnetic crystalline media may be comparable with the ferro-magnetic molecular (525.) field. In the light of the experimental results on aromatic substances there described and of those given by DU BOIS, HONDA and OWEN, which are concerned with elementary substances, this suggestion has been found to lead to interesting results. It is clear that we can easily test whether such an intense local molecular field exists; for if so it must be of import in connection with the transition from the liquid to the crystalline state in general, and the changes of other physical properties which accompany this change of state must also depend directly or indirectly upon the molecular field. The object of the present communication is to test the experimental and theoretical work which has already been completed by applying the results obtained to a wider range of physical phenomena. Evidence of a change of specific diamagnetic susceptibility owing to crystallization has been obtained with about forty substances, but with some substances the change, if it exists, is exceedingly small. Ten additional substances have been investigated, and the results, in conjunction with the other physical properties, are used to extend the ideas concerning the molecular field to diamagnetic crystalline media in general.