332 Mr. E. Wilson. Aluminium as an Electrode 



another set of experiments undertaken to find the resistance of the 

 electrolyte. For this purpose the plates were separated to the extent 

 of 1 T 3 inch, and two platinum exploring electrodes used, the dis- 

 tance between them in the electrolyte being T f inch, along a straight 

 line perpendicular to the parallel surfaces of the plates. Each time 

 reversal took place from negative to aluminium, to positive to 

 aluminium, the potential between these electrodes changed sign, and 

 gradually returned to near zero. The results of the experiments on 

 resistance show that at this temperature the resistance of a layer of 

 electrolyte of area equal to the area of the plate submerged, and of 

 length equal to the distance between the electrode and the plate, 

 that is |- inch in the experiment of Table I, is 0'063 ohm. The cor- 

 rection is therefore small with current 3'6 amperes, and is negligible 

 when the positive pole is connected to the aluminium. 



The next set of experiments were carried out with aluminium 

 Y 1 ^ inch thick, of 99 '5 per cent, purity, the electrolytes being specially 

 pure, and only distilled water used. The cells used are of a smaller 

 size, and each consists of one aluminium plate, 1J inches wide, 

 having a carbon plate on each side of it, the distance between the 

 aluminium and carbon being g- 5 ^ inch, the carbon plates being 2f inches 

 wide and J inch thick. The aluminium plate was submerged 

 2f inches in the electrolyte, so that the total area for current is 

 8J square inches. 



Two such cells were prepared, one with a 10 per cent, by volume 

 solution of H 3 S04 in water, the other with a saturated solution of 

 potash alum, and left for forty-seven hours with a current of a ampere 

 passing through each in series, the positive of charging cells being 

 connected to aluminium. At the end of this time, and with this 

 current, the potentials across the cells were 2*4 volts for the H 2 S0 4 

 solution, and 9 volts for the alum solution. On breaking the 

 circuit, the potential of the H 2 S0 4 solution cell fell to about 0'38 volt 

 in one minute, and rose fairly gradually to 2*4 volts on making circuit. 

 The alum solution cell lost its potential immediately on breaking 

 circuit, that is, the electrometer needle appeared to return to zero, 

 as though there were no opposing electromotive force. When the 

 current was reversed, that is negative to aluminium, and still of the 

 value V ampere, the H 2 S0 4 solution cell gave 0'24, and the alum 

 solution 1'29 volts. 



The aluminium plate which was formed in the H 2 S0 4 solution, 

 together with its carbon plates, were next washed in distilled water, 

 and placed in a saturated solution of alum. Eleven storage cells 

 were connected without extra resistance in circuit to each of these 

 cells positive to aluminium, and the resulting current noted. The 

 plate which had been formed in H 2 SO 4 allowed about 0'2 ampere 

 to pass, and in 4 hours 10 minutes this current had risen to about 



