in Cells for Direct and Alternate Currents. 345 



current, the ratio per period of the energy returned to the system by 

 the cell to the energy supplied to the cell, is given as a percentage. 

 If the electrolytic process were perfectly reversible, we shonld expect 

 the curves of cnrrent and potential to have a phase difference of one 

 quarter period, if they were sine curves. An examination of 

 Table V shows that maximum phase difference develops with the 

 smaller currents at lower temperature. In experiment (c) the 

 maximum amperes are 2'5, the maximum volts 53. The curve of 

 potential difference has a maximum rate of change of about 

 57'5 volts in g^Q- second, so that an ordinary condenser with 

 maximum current 2 '5 amperes would have a capacity of about 

 72 microfarads. We see, therefore, that aluminium is suited for the 

 plates of condensers. The average watts in Table V have been 

 deduced from the instantaneous product of potential and current at 

 twenty equal intervals during a period. 



The foregoing experiments employed saturated potash alum solu- 

 tion as electrolyte. The following experiments deal with soda, 

 ammonia, and potash alums, first when the solutions were saturated, 

 and second when non-saturated. In each of the non-saturated 

 solutions the proportions were thirteen parts of saturated solution at 

 about 12 C. by volume and seventy equal parts of distilled water. 

 Three cells were constructed, each containing two aluminium plates 

 of 99*5 per cent, purity, separated ^ inch apart, and each having 

 33 square inches of surface in the electrolyte opposed to the other. 

 The results of the experiments are given in Table VI. 



With regard to the saturated solutions one may say that at the 

 low frequency 7'5 Table VI the results are not so good as at the 

 high frequency 92'4 Table V. The non-saturated solutions also 

 show a better result with regard to efficiency at the higher 

 frequency. 



These plates were not specially formed with direct currents and 

 carbon cathodes before starting the above experiments. In a pre- 

 liminary experiment of about one hour's duration, before the first 

 series at frequency 33 in Table VI were made, and starting with 

 clean polished plates, the maximum volts for the soda, ammonia, and 

 potash were, a few minutes after starting, 4*4, 21'5, and 32. The 

 maximum current was 0'48 ampere and the phase differences in each 

 case about 70. The frequency was 23 and the temperature of each 

 cell about 14 C. 



An experiment was tried in which two aluminium discs 6 inches 

 diameter and separated -^ inch on an ebonite spindle were sub- 

 merged to within % inch of the centre in a saturated potash alum 

 solution and rotated at 108 revolutions per minute by a small electric 

 motor. In this manner more than half the discs were continuously 

 exposed to the atmosphere. Two brushes bearing on copper discs, 



2 c 2 



