MR. S. W. J. SMITH ON THE NATURE OF ELECTROCAPILLARY PHENOMENA. 63 



portion. In the ascending portion the mercury is often apparently sluggish, and the 

 surface tension Incomes iliilimlt to measure. Further, the surface tension may take 

 up a certain value immediately after a given potential difference is established between 

 the terminals of the electrometer, and thru fall gradually as the time of contact 

 emit iiiut-s. In contrast with this, the surface tension in the descending portion of the 

 curve is almost always very definite. Moreover, while the form of the ascending 

 portion is widely different for solutions with chemically different anions, and even 

 noticeahly different for unequally concentrated solutions of the same salt, the form 

 of the descending portion, for a considerable part of its course, is the same (within the 

 limits of experimental error) for equally-concentrated solutions of quite different salts, 

 and only varies very slightly for unequally concentrated solutions of a given salt. 



(b.) Definite nature of the descending branches. 



While therefore both the ascending and descending branches have been observed, 

 the first conclusions are based upon observation of the descending portions of the 

 curves. These were definite and amenable to quantitative treatment. 



(c.) Method adopted in examining the electrocapHlary curves, and discussion of the, 

 degree of accuracy attainable in the experiments. 



The form of electrometer that I have used has a movable mercury reservoir in 

 direct communication with the mercury column supported by the surface-tension 

 effect at the capillary electrode. The mercury reservoir can be raised or lowered by 

 means of a flexible cord, wound upon a bobbin, having a tangent-screw fine adjust- 

 ment. By means of this arrangement the small electrode can be maintained at a 



('.instant position in tin- capillary tlll.r. Tin- ilialnet.-r of tin- capillary |1,,. vame "lie 



was used in determining the curves for a large number of solutions was about 

 0*003 centim., and the usual length of the column of solution between the meniscus 

 and the point of the capillary was 0*057 centim. The resistance of such a column 

 (supposed cylindrical) would, if the solution were normal KC1 at 18, be approximately 

 83,000 ohms. The position of the capillary meniscus was fixed by means of a scale 

 within the microscope. The apparent magnitude of a division of this scale is about 

 1*5 millim. Every tenth division of the scale is marked. When the position of the 

 microscope is so adjusted that the zero of the micrometer scale coincides with the end 

 of the capillary, the fortieth division (marked 4) of the scale is practically in the 

 centre of the field. The meniscus was always made to coincide as nearly as possible 

 with the central division of the scale. The height of the mercury column, supported 

 by the capillary electrode, when possessing its maximum surface tension in such a 

 solution as dilute sulphuric acid, was about 440 millima The variation of the surface 

 tension was observed by means of a scale divided into millimetres placed directly 

 behind the mercury column. The greatest error in the scale division was about 

 1 part in 500. The conclusions first drawn from the curves are practically 



