Potential of Electrodes in Stationary Liquids. 29 



adopted consisted in the employment of electrodes of either 

 copper or mercury, the electrolyte under examination being 

 displaced in the vicinity of the electrode by a solution of 

 metal-salt which was run in slowly through the capillary 

 tap-funnel D (figs. 1 and 2). The displaced electrolyte was 

 generally remoyed through the tube W (fig. 1). The anode 

 solution, employed in conjunction with the copper electrode, 

 w r hen the electrolyte was an acid alcoholic solution, consisted 

 of cuprous chloride dissolved in a mixture of alcohol and 

 hvdrochloric acid. When the electrolyte was an alkaline 

 solution containing alcohol, and also in some experiments on 

 alcoholic acid solutions, a mercury electrode was employed 

 in contact with a solution of mercurous nitrate and a little 

 nitric acid. As the latter, howeyer, as a rule, produced a 

 precipitate in contact with the electrolyte under examination, 

 a solution of ammonium nitrate was interposed. The liquids 

 in this case were run under the electrolyte in the following 

 sequence : (1) ammonium nitrate solution : (2) mercurous 

 nitrate solution ; (3) mercury. 



The requirement that the apparatus should allow several 

 successive determinations to be performed without taking it 

 to pieces, was only met satisfactorily when the cathode was 

 at the top, as in fig. 1. For this purpose it was necessary to 

 renew the liquid at the cathode by stirring, without at the 

 same time causing anode solution to come into the cathode 

 compartment. As will be seen from fig. 1, the rubber tube 

 R with screw clips YY and the glass side-tube S were there- 

 fore introduced between the tubes B and 0. The method of 

 using thorn was the following : — When a determination was 

 finished, the side-tube S, which was generally left open during 

 the experiment, was closed, about 5 c.c. of air being left in it. 

 The standard electrode was then removed by undoing the 

 connexion at J, and a rubber stopper with a tap -funnel 

 introduced in its place. The screw clips YY were then closed. 

 A considerable amount of electrolyte was thus forced out of 

 the rubber tube R, and was allowed to escape through one 

 of the taps. The top part of the apparatus was then taken 

 from the retort-stand and moved up and down, the rubber 

 tube R being used as a hinge. Air-bubbles from the side- 

 tube S could thus be admitted to stir the liquid and after- 

 wards be returned to the tube S. When it was necessary to 

 leave the apparatus overnight, the anode solution was removed 

 through the tube u of the tap-funnel U; being replaced 

 by electrolyte run in through the funnel introduced at J. ft 

 was thus found possible to keep the cathode compartment 

 perfectly free from anode solution, even when experiments 



