Measurement of Electrolytic Conductivity. 28 



electrolyte used. The lengths of the tubes were about 30 

 centim. in the one case and 5 centim. in the other. The 

 tubas were calibrated by measuring their lengths and weighing 

 in a watch-glass the mercury required to fill them. In this 

 way a constant can be obtained for a particular pair of tubes 

 such that on multiplying by the observed resistance of the 

 electrolyte its specific resistance is at once obtained. 



In determining the weight of mercury required to fill the 

 tubes we found that the results were most concordant when 

 the finely ground ends of the tube were stopped by means of 

 a small piece of thin cover-glass backed with cork about ~ 

 inch thick, the diameter of the cover-glass and cork being 

 about the same as the external diameter of the tube, so that 

 the pressure of one finger might suffice to keep the cover- 

 glnss firmly against the end of the tube. In this way any 

 tilting of the cover-glass relatively to the end of the tube was 

 avoided. 



The following weighings of mercury and watch-glass for 

 one pair of tubes were made : 29*836, 29*837, and 29*835 

 grms. for the long tube, and 11*482, 11*481, and 11*481 for 

 the short one. The lengths of the tubes were 29*70 and 

 4*89 centims. From these data, assuming the density of 

 mercury to be 13*558 at the temperature of the experiment, 

 the constant for this particular pair of tubes w r as j^. 



If we were making fresh cells we should make them with 

 the cross-tube near the foot instead of in the middle of the 

 tubes. This would much facilitate mixing when a portion 

 of the electrolyte is removed and replaced by water so as to 

 alter the concentration. All that would then be necessary 

 would be to tilt the cell two or three times to ensure effective 

 mixing. The electrodes were pieces of platinum foil bent 

 into cylindrical form to fit the vertical tubes of the cells. A 

 platinum wire was welded on to each electrode and electrical 

 connexion established with the arms of the bridge by the 

 intervention of a mercury cup. By this means the electrodes 

 were easily removable from the cells. 



The cells and mercury cups were mounted on a wooden 

 stand placed in an oil bath, oil being used as it was found that 

 with a water bath the apparent resistance of the electrolyte 

 depended on the direction of the current. The explanation 

 of this was traced to leakage over the glass surface and 

 through the water, and was entirely obviated by the substitu- 

 tion of an insulating liquid for the fluid in the bath. 



The following tables give the results of some experiments 

 .made with a solution of potassium chloride, the strength being 



