Ionization constant of water by conductance

To calcnlate the ionization constant of water from measurements of conductance. 

Kohlrausch and Heydweiller (Ann. Phj. Lpz. 1894, 53, 209) succeeded in preparing a sample of water having a conductance lower than any recorded previously or subsequently. Their value at 18 C rdative to that of mercury was 

The concentration c of hydrogen and hydroxyl ions in the solution is given by 

Kohlrausch and Heydweiller did not use their experimental value for the specific conductance of water, but the smaller value 3.8 X IQf cm . This was obtained by appl3ung a correction for residual impurities, estimated by comparing the observed temperature coefficient of conductance with that calculated from the known temperature coefficient of mobility of the ions and the calorimetric value of the heat of ionization of water. This corrected value in conjunction with a more recent value of. djj+- -ylQg = 489 Q mole cm at 18 °C gives iCw=0.61 x 10 mole 1 , which is in astonishingly good agreement with modem values. 

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