Dilute Solutions of Hydrochloric Acid. 63 



itself, were however constructed of soft glass. It is however 

 quite impossible that the conductivity of the water could have 

 been greatly increased by solution of the glass ; in one case 

 a solution of which the strength was 1"63 x 10~^ gram-equivalents 

 per litre was allowed to stand in the pipette for a period of three 

 days, and the conductivity at the end of that time did not differ 

 by more than 2 per cent, from Kohlrausch's value. 



The observed results can probably be explained if we suppose 

 that the principal impurity in the water was ammonia dissolved 

 from the air. The ionization of ammonia is small, even in very dilute 

 solution ; when hydrochloric acid is added, ammonium chloride, 

 which is highly dissociated, is produced. The partial conductivity 

 of the ammonium chloride will then be considerably greater than 

 the conductivity of the original ammonia, and the quantity present 

 may be sufficient to produce the observed change in the apparent 

 migration constant for the solution. 



It is interesting to note, that Whetham and Paine concluded 

 from their experiments that the impurities in their water prob- 

 ably consisted of ammonium carbonate together with an excess 

 of carbonic acid. Goodwin and Haskell*, in an investigation of 

 the conductivity of dilute solutions of hydrochloric and nitric 

 acids, found that different samples of water, although their con- 

 ductivities might be equal, gave solutions of which the conduc- 

 tivities were markedly different ; the conductivity of the acid, 

 corrected for the effect of impurities, was however the same in 

 all cases. The large difference between the results of the present 

 experiments and those of Whetham and Paine is therefore prob- 

 ably due to the specific effects of different impurities, and affords 

 additional evidence in favour of the theory that both the change 

 in the migration constant and the drop in the equivalent con- 

 ductivity curve are due to an interaction between the acid and 

 the impurities present in the solvent. 



The author desires, in conclusion, to express his thanks to 

 Professor Sir J. J. Thomson for his kind interest and encourage- 

 ment during the progress of the work. 



* Goodwin and Haskell, Physical Review, Dec. 1904. 



