in Cells for Direct and Alternate Currents. 335 



In Table III we see that as the cell cools with a smaller current of 

 about 0'051 ampere, the potential between the aluminium and carbon 

 plates rises. In this case at 56, and 12 C., the electrolyte would 

 account for O0093 and O017 volt respectively. 



It was thought that if a plate of aluminium with its film were 

 submerged in mercury, the resistance between the metal and mercury 

 might give an idea as to whether resistance, pure and simple, played 

 an important part in the effects observed. The plate originally 

 formed in H 2 S0 4 solution was carefully removed, washed in distilled 

 water and dried, and half submerged in clean mercury. Storage 

 cells ranging in number from 1 to 15 were applied as in Table II, 

 but in each case the poles were also reversed so as to test the insula- 

 tion with the two directions of currents. The results show that this 

 film on aluminium is a fairly high insulator, but it was not stable. 

 At times .the resistance was zero, when a sharp noise occurred in the 

 cell like sparking between points in air, and the insulation was 

 immediately restored. With 16 volts applied, the apparent resistance 

 was about 10,000 ohms, whereas from Table II we see the apparent 

 resistance of the whole cell is 230 ohms at 14 volts, the positive pole 

 being connected to aluminium. I should say, judging from the 

 number of times the film broke down, that it was more stable when 

 the positive pole of the charging battery was connected to the 

 aluminium ; but in either direction the resistance, when established, 

 had the same order of magnitude. Up to six cells, no extra resistance 

 was included in the circuit as the film was stable, after this a resist- 

 ance was inserted so as to keep down the current when the film broke 

 down, as then the potential between Al and Hg was zero. Even at 

 30 volts the film was able to restore its insulating properties, but very 

 rarely. On removing the plate, a film was left on the mercury where 

 it had been in contact with the film on the aluminium plate. 



Another set of experiments was made with two cells having 

 as electrolytes a 5 per cent, solution of H 2 S0 4 in water, and a saturated 

 solution of potash alum in water. The area of the pure aluminium 

 plate exposed to the fluid was 17 square inches in each cell. A 

 current of 1 ampere was passed for four hours through the HzSO* 

 solution cell, and three hours through the other. At the end of these 

 times the temperatures were respectively 33 and 51 C. With the 

 1 ampere passing from Al to C, the potentials between the plates were 

 respectively 6'3 and 20 volts. The cell containing the plate formed 

 in potash alum solution was then heated, the current through it being 

 kept fairly constant by means of a considerable external resistance 

 and 110 volts. It was then cooled by placing it in a freezing mixture 

 of ether and carbonic acid snow. The temperature in this case was 

 reduced somewhat rapidly, and a portion of the electrolyte at the 

 bottom was frozen, probably a cryohydrate, leaving liquid above. 



