Alternate Current Electrolysis. 415 



The abscissas of Curves Nos. 1 and 2 (fig. 8) have been plotted from 

 Curves A x and A 2 respectively in fig. 6, the ordinates being given for 

 corresponding epochs by the integral Curve C. 



Curve No. 1 (fig. 8) shows the cyclic variation of the potential 

 between the electrode and the platinum plate, in terms of coulombs. 

 Curve No. 2 shows the cyclic variation of the potential used in 

 decomposition, also in terms of coulombs. Oxygen begins to be 

 directed to the plate at the point A, as then the coulombs are a 

 maximum and the current changes sign. But the oxygen is evolved 

 on a hydrogen plate, and the E.M.F. aids the current; the work done 

 on the plate is negative. This continues to point B (Curve No. 2). 

 After this point (B) the character of the plate is that of a layer of 

 oxygen and the work done becomes positive ; this continues to the 

 point C. The area AEB is the work returned by the plate, whilst 

 oxygen is being evolved on a hydrogen surface. The area BCD is 

 the work done on the plate, whilst oxygen is being evolved on an 

 oxygen surface. In like manner the area CDF is the work returned 

 by the plate whilst hydrogen is being evolved on an oxygen surface, 

 and FAE the work done on the plate whilst hydrogen is being evolved 

 on a hydrogen surface. The above areas have been taken in square 

 centimetres, and are given in Table III. The area inclosed by Curve 

 No. 2 (25 '3 sq. cm.) represents the total energy dissipated by electro- 

 lytic hysteresis, whilst the area of Curve No. 1 (63*5 sq. cm.) gives 

 the total energy spent in the cell. The abscissae of Curve No. 3 are 

 the differences of potential differences of Curves Nos. 1 and 2, 

 the ordinates, as before, being coulombs. In fig. 8, 1 sq. cm. 

 = volt x 10~ 2 coulomb. 



In fig. 7 the frequency is 2'4 per second, and this is the case in 

 which practically the whole of the energy dissipated in the cell is 

 spent in decomposing the electrolyte at the plates. The correction to 

 be applied to Curve A! for resistance is so small as to be almost 

 negligible. The cyclic curve in fig. 9 has been plotted from 

 Curve A! and the integral Curve C, and its area (146'7 sq. cm.) 

 represents the energy dissipated per cycle by electrolytic hysteresis. 

 Areas have been taken in square centimetres from the curve, as in 

 the preceding case, and are given in Table III. In fig. 9, 1 sq. cm, 

 = T V volt x 10~ 2 coulomb. 



The potential curve in fig. 7 does not exhibit a level part at the 

 highest potential ; this is possibly due to the resistance of liberated 

 gas. 



A general conclusion of the experiments is that about one-tenth of 

 a coulomb suffices to fully polarise 150 sq. cm. of platinum. This 

 will liberate O'OOOOl of a gram of hydrogen ; hence 0'00000007 gram 

 of hydrogen serves to polarise 1 sq. cm. of platinum. O00000007 cm. 

 is probably a magnitude comparable with the distance between mole- 



