Dilute Solutions of Hydrochloric Acid. 



61 



equivalents per thousand grams of solution, and the current in 

 amperes. The migration constant for stronger solutions of hydro- 

 chloric acid, as measured by chemical methods, is given by Jahn* 

 as "167, remaining the same for dilutions varying from 31 to 151 

 litres per gram -equivalent. The strongest solution used in the 

 present experiments was 712 litres per gram-equivalent. 



From this table a few experiments have been omitted, in which 

 for some accidental reason the measurements on one side of the 

 apparatus were not trustworthy. The check given by the agree- 

 ment between the results obtained from the cathode and anode 

 was considered of great importance, for in such dilute solutions 

 absorption of impurities from the glass or from the air was very 

 likely to occur during the progress of an experiment. In fact 

 with the most dilute solutions there was generally a gradual 

 increase of the measured resistance with time, which became 



p 



Fig. 2. 



more marked when the liquid was stirred. This increase of re- 

 sistance would however tend to increase the value of p deduced 

 from the measurements at the cathode, and to diminish the value 

 deduced from the measurements at the anode. No experiment has 

 therefore been retained in which both results were not available. 



The values of the migration constant have been plotted against 

 the cube root of the concentration in the diagram (Fig. 2). Jahn's 

 value for the concentration n = ji^ is also given ; it is marked on 

 the diagram by a circle. 



Discussion of Results. 



The change in the migration constant is much greater than 

 that which has been observed by Whetham and Paine in the case 

 of sulphuric acid. It has already been remarked that the numbers 



* Jahn, Zeitschr. f. Phys. Chem. vol. lviii. p. 641 (1907). 



