Dilute Solutions of Hydrochloric Acid. 57 



completed when the work of the above authors became known 

 to him. The results already obtained had shown a large increase 

 in the apparent value of the migration constant ; the degree of 

 accuracy attained with the most dilute solutions was however not 

 very satisfactory. The experiments have not been continued, 

 since it appeared that no information as to the existence of any 

 variation of the true mobility of the hydrogen ion would be 

 obtained ; a short account of the method and of the preliminary 

 results is however given. 



Experimental. 



In conducting migration experiments with hydrochloric acid, 

 it was considered advisable to keep the electrolysing current 

 quite small, in order to prevent any evolution of chlorine at the 

 anode ; the values deduced from the anodic and cathodic changes of 

 concentration should then be equally trustworthy. For this reason 

 the vessel used to contain the solution was arranged in such a way 

 that a comparatively small volume of liquid near each electrode 

 might be separated from the rest ; the resulting change in con- 

 ductivity would thus be greater than if the liquid after the 

 passage of the current were merely divided into two equal 

 portions. 



The cell is shown in Fig. 1. The main portion consists of 

 a glass tube 1"3 cm. in diameter, bent into the form shown, the 

 total length of the column of liquid from A^ to A^ being about 

 80 cm. The current enters and leaves the solution by the 

 electrodes J.i, J.2, which are of stout platinum foil, platinized 

 and subsequently heated to redness. B^C^, BJJ^ are two pairs of 

 electrodes which are used for measuring the resistance of the 

 solution, connexion being made through the narrow tubes D, 

 which are slipped over the platinum wires which support the 

 electrodes, and fixed by sealing-wax. 



The upper end of each main tube is closed by the indiarubber 

 bellows F, which forms an air-tight joint, and at the same time 

 allows the electrode A to be raised and lowered for the purpose 

 of stirring the liquid. The separation of the anodic and cathodic 

 portions of the solution is carried out by increasing the pressure 

 of the air at K ; the effect of this is to depress the liquid below 

 the level of the bends at 8, S, and at the same time to cause it 

 to rise at each end of the tube to some distance above the 

 electrodes B, G. 



The solution is made up in the stoppered pipette M. A quantity 

 of distilled water is placed in it, and the required amount of a 

 standard solution of acid is then run in from a small filling vessel, 

 which is weighed before and after the operation. The pipette with 



