338 Mr. E. Wilson. Aluminium as an Electrode 



from a small negative value of about O2 volt to a positive value of 

 1*8 volts. After four minutes and forty minutes respectively the 

 potential with current O054 had the values 2*07 and 2'56 volts, the 

 temperatures being 13 and 15'5 C. This, I think, shows that a film 

 formed by exposure to the air after being submerged in a saturated 

 alum solution, has the same effect as another formed in this electrolyte 

 during the passage of current. This test was continued. After 

 twenty-four hours, during which the current was O0523 ampere, the 

 potential was 11 volts, with this current passing, and the temperature 

 16 C. 



The two cells were then placed in series and an average current of 

 0'048 ampere passed through them from the aluminium to carbon 

 plates for fifty hours. At the end of this time, with current 048 

 ampere, the potentials were 10 in the case of the plate partially 

 formed without current, and 10*3 in the case of the other; the 

 temperatures being 19 and 17J C. respectively. With current O121 

 ampere, the potentials were 26'2 and 27'4 respectively at tempera- 

 tures 21 and 19J C.] 



Sodium hydrate forming a weak solution in water was tried as an 

 electrolyte, the area of the Al plate being the same as before, 17 square 

 inches. The forming current of 0'8 ampere was passed from Al to C 

 for 2 hours 20 minutes, when the potential between the plates was 

 13*6 volts, the aluminium plate being covered with a thick black 

 deposit. 



PART II. 

 Alternate Currents. 



The experiments with alternate currents were undertaken in order 

 to investigate the instantaneous values of potential and current. 

 One object was to see if the effect we have dealt with in the first 

 part of this paper has time to properly develop with ordinary 

 frequencies, and if so under what conditions. Another object was to 

 see if aluminium is a valuable metal for use in condensers for alter- 

 nate currents. 



Aluminium- Carbon Cells. 



If the time taken to develop the effects dealt with in the first part 

 of this paper were very small compared to the time of a complete 

 period of an alternating potential applied to the cell, one would 

 expect to get a practically uni-directional current in the circuit of 

 the cell under favourable conditions as to temperature and applied 

 potential. This is not the case with the cells and frequencies dealt 

 with in this paper. In all these experiments the author has 

 endeavoured to make the cells the controlling part of the circuit, 



