((/ul Chemical Change. 549 



§ IK It is not difficult to explain how M. Le Bon arrived 

 at the conclusion that chemical change is accompanied by 

 radioactivity. All the actions with which he obtained large 

 effects are actions evolving a considerable amount of heat. 

 ]Sot only would he be liable to the heat effect which I have 

 been unable to avoid, but also the action, due to change of 

 surface electrification on the insulation, to which reference is 

 made in § o ; for the whole floor of his vessel was formed of 

 a block of sulphur. He mentions no experiments made with 

 the object of proving that the increase of leak was really due 

 to chemical action, and not to some secondary cause. 



§ 10. The nature of the connexion between the heating of 

 the vessel and the increase of the leak has not been explained. 

 It does not lie in any change of the insulation. The only 

 part of the insulation which could become electrified is that 

 exposed to the large difference of potential between the vessel 

 and the guard-rings : any induction effect due to a change 

 of the electrification of this portion is precluded by the design 

 of the apparatus. That the resistance of the insulation was 

 not affected by the heat was proved by direct experiment. 



There is considerable eA'idence of the existence of some 

 kind of polarization at the walls of the vessel, as if ions 

 moved up to the charged surface and clung there without 

 giving up their charge. For a leak considerably larger than 

 the normal is always found lor a short time after the direction 

 of the electric field is reversed, or put on afresh after being 

 left off for some hours. It may be that ions from this 

 polarized layer are driven off from the part of the surface 

 directly heated, and give rise to a larger current. It is 

 noticeable that pouring boiling water into the tray has no 

 effect upon the leak : the water may absorb the ions which 

 are detached by the action of the heat. 



On the other hand, it is noticeable that the effect of the 

 heat is larger and more persistent when the heated surface is 

 separated by ^ thin layer of foil or paper from the volume 

 of air whose ionization i< measured, than when no such layer 

 is present. 



§ 11. It seems then permissible to conclude: — 



(1) That there is no evidence that chemical change is 

 accompanied by radioactivity. 



(2) That the increase in the spontaneous leak, the obser- 

 vation of which has led some investigators to suggest such a 

 connexion, is due to the heating of the walls of the vessel : 

 the nature of the relation between the heating and the increased 

 leak requires further elucidation. 



( 'avendish Laboratory, Cambridge, 

 January L905. 



