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LI. Radioactivity and Chemical Change, By NORMAN li. 

 Campbell. B.A., Fellow of Trinity College, Cambridge*. 



§ 1. "IN the course of the experiments described in the 

 A. preceding paper (see p. 531) the effect of cleaning 

 the surface of a metal on the intensity of the rays emitted 

 from it was investigated. It was found that no mechanical 

 cleaning with sandpaper produced a change, but that an 

 increase in the ionization caused by a metal was brought about 

 by cleaning the surface with an acid that dissolved it. This 

 observation suggested that chemical action might be attended 

 by the emission of ionizing rays, and further experiments 

 seemed to confirm the suggestion. 



A shallow dish with a bottom of thin aluminium leaf was 

 placed above the window of the vessel described in § 9 of the 

 preceding paper ; when certain interacting reagents were 

 placed in the dish a notable increase in the leak through the 

 vessel ensued. 



§ 2. When these experiments had proceeded for a short 

 time, it was found that a similar effect due to chemical action 

 had been described by M. Gustave Le Bonf. But it was 

 soon remarked that the chemical actions which were attended 

 by the largest effect were those which gave out considerable 

 quantities of heat. Was it heat, and not chemical action, that 

 was the cause of the effects noticed ? 



The question seemed to be answered in the affirmative 

 when it was found that a metal plate heated to 80° placed 

 just outside the window caused an increase in the leak greater 

 than that given by the most violent chemical action ; while 

 melting ice or an action attended by absorption of heat 

 caused a remarkable decrease of the leak. 



§ 3. A similar increase in the leak through a vessel when 

 heated had been observed by Wood J, and traced to a change 

 of the surface electrification of the insulating material between 

 the high potential vessel and the earthed guard-ring. Anew 

 apparatus on a far larger scale was constructed in which the 

 device adopted by Wood for the cure of his trouble was 

 introduced. 



The new vessel (fig. 1) was a cylinder of galvanized iron 

 1 metre in diameter and 19 cms. high. A sheet of wire 

 netting, which served as electrode, was suspended by a wire 

 passing through the insulation which was arranged as shown 



* Communicated by tli" Author. 



t Gustave Le lion. Revue Scienli/lgue, Nov. L902. 



t A. Wood, infra, p. 550. 



