378 DR. MEYER WILDERMAN ON THE CHEMICAL STATICS AND DYNAMICS OF 
X. The Role of the Electrode. The System Ag Plates as Electrodes in Light and in 
the Dark , BrAg Solid at the Bottom of Cell and 0‘1 normal BrNa Solution in 
Light and. Dark. Polarisation (Plate 2V24, of July 16, 1903. Table IX.). 
The chemical composition of this system is the same as that ot the systems 
previously dealt with (Ag-BrAg plates in BrNa solution) which is reversibly constant 
in respect of the anion ; but the difference in reality proved to be very great. We 
find (see Plate N24 of July 16, 1903) that such a system behaves as the inconstant 
cell (Ag plates in BrNa solution), as is to be seen from the course of the induction 
and deduction periods, i.e., the presence of the solid BrAg at the bottom of the vessel, 
without an intimate connection with the Ag plates so as to make it to an electrode 
does not make it to a constant cell (as if the solid AgBr were an extraneous substance). 
This puts into special light the role of the electrode under the action of light. 
Under the action of light the solution pressure of the electrode becomes, under given 
electrostatic conditions, greater, and it is the nature of this that determines the kind 
and nature of the galvanic cell created and the kind of reactions which can go on in 
it under the action of light. In one case (Ag-BrAg electrodes) Br ions are passing 
from the electrode into the solution, in the other case the Ag plate could either send 
Ag ions into the solution if it contains an Ag salt, forming a constant cell, or in the 
absence of an Ag salt in solution form, as in our case, an inconstant cell showing 
polarisation. As to the effect of light upon the chemical potential of the solid BrAg 
at the bottom of the cell, the same increases under the action of light, the solubility 
of AgBr may increase in light, though not to a measurable extent, more BrAg 
molecules may be sent into the solution, but this will be an ordinary and not an 
electrolytic solution, when Br anions are passing into the solution. 
Table IX., giving the experimental data for the above system, and Plate N24 show 
that the maximum deflection, or the maximum E.M.F.’s produced by light, does not 
remain constant, but first drops again owing to the further increase of the E.M.F. of 
polarisation under light. This goes on till a constant value of the E.M.F. s is 
obtained, indicated by the lines (d) and giving the difference between the E.M.F. 
which light would have created, if there were no polarisation, and the E.M.F. of 
polarisation. As both E.M.F.’s are created simultaneously, the absolute values of both 
E.M.F.’s remain unknown. 
For the constant deflections obtained with the light of the arc passing the blue 
screen, we get from N3 and 4: 80 2 x 25‘5 = 163 xlO 3 ; 42^x72= 127x101 the 
value of the E.M.F. of polarisation thus seems to be in comparison with the principal 
E.M.F. small, since the law of intensity is still only partially obscured. Further we 
find that the arc (blue screen) gives much greater deflections than (total) acetylene 
(N4 : Nil or N12 = 72 millims. : 7'5 millims.), that the deflections got with the red 
and yellow-green screen are very small so as not to admit accurate measurement. It 
