Mr Cunningham, On an Attempt to detect the lonisation, etc. 431 



On an Attempt to detect the lonisation of Solutions by the 

 action of Light and Rontgen Rays. By J. A. Cunningham, 

 St John's College, 1851 Exhibition Research Scholar. 



[Received 15 May 1902.] 



Solutions are in so many respects analogous to gases, that it 

 seemed quite worth while enquiring experimentally whether the 

 analogy would extend to the production of ions by ultra-violet 

 light and Rontgen Rays. There seemed room for hope that some 

 of the energy absorbed by a substance with an absorption spectrum 

 might be traced in this investigation. Some information might 

 also be obtained on the nature of photochemical action. 



Arrhenius (Wien. Ber. 96 (2), p. 831, 1887) has shown that the 

 conductivity of a film of silver chloride, or bromide, is doubled 

 or trebled by exposure to sunlight. He measured the change of 

 conductivity for illumination with light of different wave-lengths. 



It was thought desirable to look for the effect in Carey Lea's 

 solution of colloidal silver. Considerable difficulty was at first 

 experienced in preparing the solution. A strict adherence to the 

 methods described by Carey. Lea was not sufficient to obtain 

 a soluble precipitate so long as ordinary chemicals were used. 

 It was not until the very purest chemicals were procured that 

 satisfactory results were obtained. The water used was redistilled 

 and condensed in a block-tin tube. Other solutions at several 

 different dilutions tested for the effect were : — silver nitrate, am- 

 moniacal solutions of silver chloride, uranyl nitrate {U0 2 (N0 3 )2}, 

 and Hoffmann's violet. These were selected as being typical 

 members of several different classes of solutions which might be 

 expected to be affected by radiation. 



After many attempts to design a suitable electrolytic cell 

 which would expose a thin layer of the solution to the rays, 

 the one shown in the figure was finally adopted. The body 

 DE of the cell was made of paraffin cast under the exhausted 

 receiver of an air-pump in order to expel air bubbles. Two 

 vertical holes A and B contained the platinised wire electrodes, 

 and a carefully planed recess S was cut into the front of the 



