A Spontaneous Electromotive-Force in Cells of Alkali Metals
I N working with photo-electric cells, it was found that when the cell was insulated in the dark the alkali metal would develop a negative charge. As all attempts to remove this effect were unsuccessful, it was decided to investigate the phenomena more carefully. The results of these experiments will be described in the following paper. The apparatus was set up as shown in Fig. I . The alkali metal was placed in the cell C and as high a vacuum as possible obtained by means of a Gaede pump so
... a Gaede pump so that a perfectly pure surface could be procured. The different metals investigated were caesium,potassium, and an alloy of sodium and potassium formed by melting together masses of the two ^UL^.^A^ or \ E proportional to their atomic pis j weights respectively. Throughout the investigation, the cell was kept carefully screened from the light by the box D. In measuring the potential, the electrode of the alkali metal which was connected to one pair of quadrants of the electrometer Q was insulated by raising the plunger of the key K. The other electrode and the other pair of quadrants were earthed. The maximum potential was determined from the deflection of the electrometer which had a sensitiveness of 160 mm. per volt. In order to measure the current which the cell would give, the interior of a small cylindrical condenser (capacity = 24.55 E.S.U.) was connected in as shown at H. The outer cylinder of the condenser was connected to a potentiometer by means of which any desired potential could be obtained. After raising the plunger of the key K, the potential on the exterior of the condenser was gradually increased so as to keep the electrometer always at the zero position. From the known potential and capacity, the charge drawn into the condenser in a given time was determined and from this the current was readily calculated.