224 PROPERTIES OF ELECTRICALLY CONDUCTING SYSTEMS 



mean error is 1.15 per cent; for 0.02 normal solutions, 0.75 per cent; 

 and for 0.005 normal sodium chloride solutions, the mean deviation is 

 0.57 per cent. At the lower concentrations the agreement is measurably 

 better than at the higher concentrations, a result which is perhaps not 

 unexpected, since at concentrations as high as 0.1 normal viscosity effects 

 unquestionably come into play. The agreement between the measured 

 and calculated values based on Equation 52 is markedly better than that 

 of values based on Equation 51. In the case of the 0.1 normal solutions of 

 sodium chloride, the mean deviation is 0.85 per cent. In the mixtures 

 of sodium chloride of concentration 0.02 and 0.005, the mean deviations 

 are respectively 0.33 and 0.05 per cent, values which fall very nearly 

 within the limits of experimental error. In calculating the specific con- 

 ductances of the mixtures according to Equation 52, 424 was assumed 

 for the value of A for hydrochloric acid and 127 for that of sodium 

 chloride. These values may be somewhat in error, but it is to be noted 

 that the calculated specific conductances are affected to only a very 

 small extent by the value assumed for A . It must be concluded from 

 these results that the isohydric principle is not applicable to mixtures 

 of strong electrolytes. In the case of the mixtures of hydrochloric acid 

 and sodium chloride, at any rate, Equation 52 yields results which corre- 

 spond quite closely with the observed values at low concentrations. It 

 is uncertain, however, that a similar correspondence will be found in the 

 case of mixtures of other electrolytes. For the present, therefore, the 

 form of the function which should be assumed in the case of mixtures of 

 strong electrolytes remains doubtful. 



2. Hydrolytic Equilibria. Water itself is ionized to a slight extent 

 into hydrogen and hydroxyl ions. There therefore exists in water an 

 equilibrium which, if the law of mass-action holds, is expressed by the 

 equation: 



where K W is the ionization constant of water. The concentration of the 



hydrogen and hydroxyl ions in pure water has been determined by 

 Kohlrausch from the conductance of very pure water. At 18 this method 

 yielded the value 0.80 X 10~ 7 for the concentration of the hydrogen and 

 hydroxyl ions in pure water. The ionization constant has also been 

 determined from the electromotive force of gas cells, from the rate of 

 certain esterrification reactions and from the hydrolysis of certain salts 

 in water. In these latter methods, an electrolyte has, in general, been 

 present, which naturally introduces an uncertainty as to the effect of 



