Section 104. Ionization of Water. 



297 



To compare these results with those previously obtained the various 

 values for the hydrogen-ion or hydroxide-ion concentration in pure water 

 have been brought together in table 127. 



Table 127. The hydrogen-ion concentration (X io 1 ) in pure 

 water. Results of various investigators* 



Investigator. 



Method of determination. 



Wijs 



Nernst . . . 

 Lowenherz 



Arrhenius 'Hydrolysis of sodium 



acetate by ester-sa- 

 poniflcatiou 



Catalysis of ester by 

 pure water 



Electromotive force of 

 gas cell 



Electromotive force of 

 gas cell 



Conductance of pure 

 water 



Hydrolysis 



Kohlrauseh & 



Heydweiller.. 

 Kanolt 



o. 



0.36 

 0.30 



18. 



0.8 



0.80 

 0.68 



25 



1.1 



1.2 



1.19 



1.06 



0.01 



*For references to their articles see section 99. 



It will be seen that the new values are uniformly lower than those of 

 Kohlrauseh and Heydweiller, but only by from 16 to 20 per cent. This 

 approximate agreement is of interest not only in indicating the absence 

 of any considerable error in the values of Kohlrauseh and Heydweiller, 

 in spite of the somewhat uncertain correction that had to be applied 

 for the impurities in the water ; but also in proving that the ionization of 

 water is nearly, if not quite, the same when pure, as it is when an ionized 

 salt is present in it at a concentration of 0.02 to 0.05 normal. 



As the most probable values of the hydrogen-ion concentration in pure 

 water it would seem best to adopt for the present the lower ones derived 

 above ; for, although it is not impossible that these are in error by as much 

 as 10 per cent, yet it is reasonably certain that the error lies in such 

 a direction as to produce too high rather than too low results. This will 

 be evident when it is considered that the effect of impurities in the water 

 or the solutes would be to give rise not only to too high values for the 

 ionization-constants of the acid and base, but also, by combining with the 

 excess of either of them added in the hydrolysis experiments, to give too 

 great an increase in the conductance and therefore too great a value for 

 the hydrolysis. 



It will be seen from table 126 that the hydrogen-ion concentration 

 increases with great rapidity with the temperature, being three times as 

 great at 25 as at 0. It is of interest to calculate from this increase the 

 heat of ionization of water, and to compare its value with that obtained 



