Mi;. S. \\. .1. SMITH ON THE NATURE OF ELECTKOCAPILLAIiY I'HKNoMl.NA. 65 



The mercury forming the large electrode was placed at the bottom of one limb ; the 

 capillary electrode dipped into the other limb. In order that the definition of the 

 capillary meniscus might be as good as possible, the capillary was placed close to the 

 siile of the limb that received it. After the curve for the solution had been 

 determined, the H tube, containing it, was removed and replaced by another 

 containing a different solution. It would have been very inconvenient to have 

 u i >rked always with the same H tube, as in many cases it was desirable to allow the 

 solution to stand some considerable time over mercury before examining it in the 

 electrometer. A number of H tubes were used, and naturally these were not precisely 

 similar. In every case the definition of the capillary meniscus, when at the fortieth 

 division of the scale, was made as good as possible ; but it did not always happen 

 that the definition of the capillary point was then correspondingly good. However, the 

 maximum error in the setting of the capillary point was not greater than about one 

 of the small scale divisions, while it could usually be set at the zero within 

 two-tenths of a small scale division. The capillary meniscus could be readily set at 

 the fortieth division with an error of less than one-tenth. An error of a scale division 

 in the setting of the meniscus produced a maximum error of about '4 millini. in the 

 reading of the summit of the mercury column. Under ordinary circumstances, there- 

 fore, the error introduced into the surface tension observations by the necessary 

 replacement of one H tube by another was not greater than '08 millini. 



In order to remove one solution from the interior of the capillary tube before the 

 introduction of the succeeding one, the following method of procedure was adopted. 

 The capillary tube was immersed in a beaker of distilled water, and by alternately 

 lowering and raising the mercury reservoir, the water could be drawn into the tube 

 and then again expelled along with & little mercury. This process was repeated 

 several times, the excursions of the meniscus in each case being very much longer 

 than any that occurred during the experiments, as the result of electrical effects. The 

 Ix'.ikrr \va.s then withdrawn, and as much of the water as possible was removed from 

 the capillary. A similar process was then adopted in order to fill the capillary with 

 the solution next to be examined. To test the sufficiency of this treatment, a second 

 set of observations upon a given liquid was made, several other solutions having been 

 used in the electrometer during the interval. The first and second sets were found to 

 agree within the limits of experimental error. In a case where one solution was 

 followed by a more concentrated one of the same salt, the intermediate operation with 

 distilled water was, of course, unnecessary. 



The potential difference between the terminals of the electrometer was varied by 

 means of an ordinary potentiometer arrangement. The potentiometer circuit consisted 

 usually of a secondary cell (E.M.F. about 2 '03 volts) and two resistance boxes in 

 series. The sum of the resistances introduced into the circuit by these boxes always 

 amounted to 10,000 ohms. Usually the resistance in each box was altered by 

 500 ohms at a time, so that the corresponding change in the potential difference 



Vol.. t \c III. A. K 



