982 REPORT—1885. 
the electrodes being formed of silver wire, and they all turned out to be more or 
less sensitive to light, and to exhibit other properties of annealed selenium. 
‘When, as in the case of these cells, a current of electricity passes between silver 
electrodes through a mass of sulphide of silver, silver will be deposited upon the 
cathode, and sulphur upon the anode. Now sulphur has an enormously high 
resistance, and the existence of a mere film of free sulphur upon one of the 
electrodes would be sufficient to stop the current altogether. The current is not, in 
fact, stopped, because the deposited sulphur combines with the silver of the anode, 
merely adding a new layer to the electrolyte. Thus the metal of the anode 
gradually combines with the sulphur of the electrolyte, and the conductivity of the 
arrangement will depend, to a great extent, upon the facility with which this com- 
bination is effected. It might therefore be expected that the resistance of a sulphur 
cell with silver electrodes would be diminished by any influence which assisted the 
combination of silver with sulphur. Experiment shows that such an influence is 
exerted by light. 
But it is not perhaps necessary to assume that the effective action of light is 
confined entirely to the electrode. It seems reasonable to suppose that any circum- 
stances which are favourable to the union of two substances when they have a 
tendency to unite would also be favourable to their separation when from any cause 
they have a tendency to separate. If, then, as is commonly supposed, electrolysis 
involves a series of decompositions and recompositions, both these processes would 
be assisted by the same agency which, under ordinary conditions, favours the union 
of the constituents of the electrolyte. The electrolysis of silver sulphide may there- 
fore be assisted by light, and its electrolytic resistance at the same time diminished. 
Although results similar to those above described have not yet been obtained 
when other metals than silver have been used in conjunction with sulphur, the 
author believes it probable that the action of light upon the resistance of selenium 
in conjunction with any metal whatever with which it forms a sensitive combina- 
Hon is of a nature analogous to that which occurs in the case of sulphur and 
silver. 
6. On the Generation of a Voltaic Current by a Sulphur Cell with a Solid 
Hlectrolyte.| By Surtrorp Bipwex1, M.A., DDB. 
While observing the secondary or polarisation currents, which are generated by 
sulphur cells (as by those made with selenium), after being disconnected from a 
battery, certain effects were noticed which seemed to indicate that when the 
electrodes consisted of two different metals, a sulphur cell might be capable of 
originating an independent or primary current. Experiments were therefore made 
with the object of investigating this point, and some of the results obtained are 
here given, though without any attempt to explain them, or to connect them to- 
gether by a complete theory. They appear, however, to possess sufficient interest 
to render them worthy of record from the fact that no voltaic arrangement with a 
solid electrolyte has hitherto been constructed which—at least at ordinary tem- 
peratures—was capable of producing the smallest effect upon the most delicate 
galvanometer. 
A plate of copper about one inch squaré was heated, and upon it was spread a 
mixture consisting of five parts of sulphur and one part of sulphide of copper. A 
plate of silver previously heated was then laid upon the melted mixture, and the 
two plates were squeezed together, thus forming a sandwich-like cell. When this 
cell, after cooling, was connected with a reflecting galvanometer, the spot of light 
was violently deflected off the scale. From very careful measurements it appeared 
that the E.M.F. of the cell was ‘0712 volt, and its internal resistance 6537 ohms. 
The direction of the current was from the silver through the electrolyte to the 
copper, and there could be no doubt that it was of a voltaic nature. After the 
cell had been in existence for about three months, its E.M.F. had not materially 
fallen off. 
1 Published iz extenso in the Electrician, September 18, 1885, and in the Chemica? 
News. See also Phil. Mag. October, 1885. ~ 
