344 



SCIENCE 



[N. S. Vol. XXVII. No. 687 



widely varying temperature conditions on the 

 specific volumes of water and water solutions, 

 on the equivalent conductivities of electro- 

 lytes, on the specific migration velocities of 

 the ions, on the degree of ionization of various 

 solutes, on the self-ionization of water and on 

 hydrolysis. 



The effect of rising temperature is to 

 enormously increase the equivalent con- 

 ductivity of aqueous solutions and the speed 

 with which the ions travel in such solutions, 

 the speed of the latter continuing to increase 

 even after the equivalent conductance has 

 reached a maximum value, thence to decline 

 with rising temperature. The significant ob- 

 servations have also been made that the spe- 

 cific velocities of all monovalent ions tend 

 toward equality with rising temperature, while 

 divalent ions approach a value double that of 

 monovalent ions. These tendencies, together 

 with the effect of rising temperature on con- 

 ductance, are illustrated by the behavior of 

 potassium chloride and hydrochloric acid. 

 The equivalent conductances of potassium 

 chloride and hydrochloric acid, extrapolated 

 for zero concentration, which at 18° are re- 

 spectively 130.1 and 379.0 reciprocal ohms, 

 have been found to be 1,120 and 1,424 re- 

 spectively at 306°. 



Various investigators have called attention 

 to the fact of a connection between the viscos- 

 ity of the solvent and ionic velocities. It is 

 shown in these investigations that the con- 

 ductance of salt solutions increases with rising 

 temperature at practically the same rate 

 as the fluidity of the solvent, at any rate up 

 to 156°, which is the limit to which viscosity 

 measurements have been made. 



Increase of temperature has been found to 

 be accofnpanied by a marked diminution of 

 the ionization of the solute and especially at 

 higher temperatures the rate of decrease be- 

 comes very great. For example, in a 0.01 

 normal solution of hydrochloric acid, the 

 percentage ionization at 18° is 97.1, while at 

 306° it is but 82 per cent. Of an 0.08 normal 

 solution of potassium sulfate, 73 per cent, of 

 the solute is present as ions at 18°, while at 

 306° only 23 per cent, is present in the ionic 

 condition. The effect of rise of temperature 



on the dissociation of weak acids and bases 

 is even more marked, as is shown by the 

 change of the affinity constant of acetic acid 

 from 0.0000183 at 18° to 0.000000139 at 306°, 

 and of ammonium hydroxide from 0.0000172 

 at 18° to 0.000000093 at 306°. 



In view of the diverse opinions which have 

 been expressed concerning the connection be- 

 tween the dielectric constant of a solvent and 

 its ionizing power, it is interesting to note 

 that these researches show that the ratio of 

 the concentration of the un-ionized portion of 

 the solute at two different temperatures (at 

 least up to 100°, the limit to which the 

 dielectric constant of water is known) agrees 

 very well with the ratio of the dielectric con- 

 stants for the same temperature interval. 



Since the equivalent conductance of an 

 electrolyte is a function of two variables, 

 specific speed of the ions and the degree of 

 ionization, and since the effect of changing 

 temperature on the ionization is most con- 

 spicuous at higher temperatures, it follows 

 that the equivalent conductance must pass 

 through a maximum value thence to diminish 

 continuously towards zero as the temperature 

 passes the critical point. This maximum has 

 been realized in the case of a considerable 

 number of solutes, especially in the more con- 

 centrated solutions. 



Quite contrary to the influence of rising 

 temperature in diminishing the dissociation of 

 electrolytes in solution is the effect on the 

 ionization of water itself. The ionization 

 constant of water rises with tremendous 

 rapidity up to 100°, thence more slowly, 

 reaching a maximum value over 5,000 times 

 the value at zero, after which it decreases 

 with further rise of temperature. This great 

 increase in the ionization of water with rising 

 temperature, together with its weaker ionizing 

 effect on electrolytes in solution, accounts for 

 the enormously greater tendency of salts to 

 hydrolyze at higher temperatures. 



As at ordinary temperatures, so also at 

 higher, the mass law does not apply to solu- 

 tions of salts, strong acids and bases. On 

 the other hand, the applicability of the law to 

 weak acids and bases has been shown to be 

 independent of the temperature. In this con- 



