96 MR. A. E. OXLEY ON THE INFLUENCE OF MOLECULAR 



on DEBYE'S theory. Every substance investigated by NERNST and LINDEMANN 

 discloses such a departure. 



The above evidence is sufficient to establish the existence of an intense local 

 molecular field of the order 10 7 gauss, if interpreted magnetically, in those diamagnetic 

 crystalline substances (about 40 of which have been investigated) which show a 

 measurable change of x on crystallization. We shall now pass on to some additional 

 experiments with the object of extending the above conclusions to diamagnetic 

 crystalline media in general. 



(6) ADDITIONAL EXPERIMENTS. 



COTTON and MOUTON have found that aromatic liquids show an abnormally large 

 double refraction compared with aliphatic liquids when subjected to the same external 

 magnetic field. According to the theory of molecular orientation, which (in the 

 opinion of these authors) is unique in accounting for all the observed phenomena of 

 induced double refraction, the extent of the double refraction is directly proportional 

 to the degree of dissymmetry of the molecule. Now assuming this to be so, we 

 should expect that an u asymmetrical molecule, whose electrons are more readily 

 displaced -in one direction than in another, would have a distortion produced in it, 

 when subjected to the local field of a neighbouring molecule, this distortion being 

 characterized by the molecule's own dissymmetry. Therefore those liquids which 

 show the larger induced double refraction when acted on by a magnetic field should 

 also be the ones which show a large value of BX on crystallization. All the aromatic 

 liquids examined in Part I. show an appreciable change of x on crystallization and, 

 according to COTTON and MOUTON, all these show an easily measurable magnetic 

 double refraction. With regard to aliphatic compounds, COTTON and MOUTON found 

 that liquid hexane, chloroforn, carbon-tetrachloride, acetone, hexamethylene, ethyl 

 and methyl alcohols, had no appreciable induced magnetic double refraction. I 

 therefore examined some of these for a change in the value of x on crystallization. 

 The results will now be briefly summarised. 



All the experiments were made with the apparatus designed for low temperature 

 work and most of the substances were investigated three times, the method being 

 exactly as described in Part I. 



Carbon tetrachloride, C.C1 4 . 



At the fusion point ( 30 C.) x passed through a minimum value, as in the case of 

 benzene, and, on further cooling the crystals, the susceptibility appeared to be the 

 same as that of the liquid. An effect of the same nature has been observed by 

 HONDA* with sulphur, x being a minimum at the fusion point (115 C.). 



* 'Ann. der Phys.,' vol. 32, p. 10 8, 1910. 



