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