Section 74. Summary. 189 



and 156 in table 70. The table also contains the concentration of the 

 hydrogen or hydroxide ion (Cm = Coh = \/Ky?) at all these temperatures. 

 It will be seen that the ionization-constant increases about 80-fold 

 between 18 and 100, but only 4*4-fold between 100 and 156. When it 

 is considered that at these higher temperatures not only the ionization- 

 constant of water is so much greater than at 18, but also that the ioniza- 

 tion of weak acids and bases is very much less than at 18, it will be evi- 

 dent that the tendency of salts to hydrolyze is enormously increased at 

 high temperatures. This is well illustrated by ammonium acetate itself, 

 which at 0.01 normal concentration is hydrolyzed to an extent of 0.4 

 per cent* at 18, 4.8 per cent at 100, and 18.3 per cent at 156. 



74. SUMMARY. 



In this article have been presented the results of conductivity measure- 

 ments at various concentrations with sodium hydroxide at 18, 100, 156, 

 and 218, with ammonium chloride and hydroxide at 18, 100, and 156, 

 and with ammonium acetate both alone and in the presence of an excess of 

 ammonium hydroxide and acetic acid, at these same temperatures. For the 

 final results see tables 59 and 67. From them the equivalent conductance 

 at zero concentration has been derived by extrapolation or by the law of 

 the independent migration of ions, and the ionization of all these sub- 

 stances has been calculated (see table 63). An indirect method of meas- 

 uring and computing the hydrolysis of a salt of a weak acid and base 

 from its conductivity alone and in the presence of free acid or base has 

 been described (in section 73), and the method has been applied to the 

 results with ammonium acetate. From the hydrolysis of this salt and the 

 ionization-constants of ammonium hydroxide and acetic acid, the ioniza- 

 tion of water at 100 and 156 has been calculated. 



The results justify the following conclusions: 



(1) The equivalent conductance of sodium hydroxide at zero con- 

 centration increases with rising temperature at a steadily decreasing rate 

 as in the case of hydrochloric acid, and the ratio of it to that of sodium 

 chloride approaches unity, showing that the hydroxide ion has a velocity 

 more nearly equal to that of the chlorine ion at the higher temperatures. 



(2) The degree of ionization of sodium hydroxide at all temperatures, 

 the law of its change with the concentration, and its decrease with the 

 temperature, all correspond closely to that of neutral salts of the same 

 ionic type. 



*The value at 18 is calculated from the ionization-constants of water, acetic acid, 

 and ammonium hydroxide. 



