54 MK. S. W. J. SMITH ON THE NATURE OF ELECTROCAPILLAKY IMIKNo.MKNA 



The method of taking the electrometer curves and their degree of accuracy is 



discussed later. 



The dotted curve represents the indirect curve, while the continuous one represents 

 the ordinary capillary curve. In this particular experiment it apparently happened 

 that for some accidental reason (such as difference in purity of the mercury of the 

 large and small electrodes) the " natural" potential difference at the small electrode 

 was appreciably different from that at the large. In consequence of this, the surface 

 tension of the small electrode began to increase immediately the connection between 

 it and the large electrode was broken. As I have subsequently observed, this is an 

 effect which can be obviated when due care is taken, with pure mercury and a 

 solution of uniform concentration. The phenomenon does not affect the conclusions 

 in the present case, but in fact rather increases the interest attaching to the 

 observations. When the electrodes were joined by a short wire, the surface tension 

 was different from what it was when they were joined by the graphite resistance. 

 The reading in the latter case was not appreciably affected by reversing the resistance, 

 so it could be assumed that the graphite did not introduce any appreciable E.M.F. 

 into the circuit. 



At first the indirect readings for a given external E.M.F. give higher values for 

 the surface tension than the direct. The curves cut one another at an E.M.F. 

 corresponding to about 0'28 volt, so that for this E.M.F., the surface tension assumed 

 by the mercury is the same whether the E.M.F. is applied directly or through a very 

 high resistance. Hence, when the surface tension at the capillary has this particular 

 value, there can be no appreciable continuous current through the electrometer. It 

 was found that the surface tension in question was practically identical with that 

 assumed by the capillary, when the electrometer was disconnected from the rest of 

 the apparatus the electrodes being also unconnected. From this it is highly probable 

 that this surface tension corresponded to the natural potential difference at the 

 small electrode, and the significance of the disappearance of the depolarization current 

 becomes immediately clear. 



The horizontal distance between two points corresponding to the same surface 

 tension, one on each curve, is a measure of the depolarization at the small electrode 

 when the potential difference there has the value corresponding to the given surface 

 tension. The actual value of the current is equal to the above horizontal distance 

 (expressed in volts), divided by the value of the graphite resistance in ohms. 



The curve in fig. 2 shows how the depolarization current varies with the 

 externally applied E.M.F. The depolarization, apparently for a considerable range, 

 is nearly proportional to the extent by which the potential difference at the small 

 electrode has teen displaced from its natural value. The ordinate of any point on 

 this curve is the horizontal distance between a given point on the direct curve and 

 the corresponding point on the indirect curve ; the abscissa is the sain.- as that of 

 the given j)oint on the direct curve. Since each of the curves has a maximum 



