Summary. 345 



With the help of this principle the ionization of the hydrosulphate-ion 

 at 18, 100, and 156 in the solutions both of the acid and acid salt 

 has been computed ; the final results will be found in tables 118 and 119 

 on pages 271 and 276. This ionization is thus found to be large at 18 ; 

 but it decreases very rapidly with the temperature. Thus in a 0.1 molal 

 potassium hydrogen sulphate solution equal quantities of sulphate-ion 

 and hydrosulphate-ion are present at 18 ; while at 100 there is only 15 

 per cent, and at 156 only 4 per cent, as much sulphate-ion as hydro- 

 sulphate-ion in the solution. 



Only rough values of the ionization-constant of the hydrosulphate-ion 

 into hydrogen-ion and sulphate-ion can be given, since they vary very 

 much with the concentration ; some idea of its magnitude is furnished 

 by the following' values which hold at about 0.01 molal (or 0.002 molal 

 at 156); 18500 X 10- s at 18, 1220 X 10" 6 at 100, and 115 X 10" 

 at 156, whereas the ionization-constant for acetic acid at 18 is 18 X 10~ 6 . 

 From the change of the ionization-constant with the temperature, the 

 heat absorbed (AC/) by the reaction HS0 4 ~ = H + -j- S0 4 = has been 

 found to be given by the expression: AC/ = 14,170 65 T, where T 

 represents the absolute temperature. From this it follows that the value 

 at 18 is 4750 calories, and at 100, 10,070 calories, while from 

 Thomsen's heat-of-neutralization measurements and our ionization data 

 at 18 the value 5020 calories is derived. 



In addition to the measurements with unhydrolyzed salts just dis- 

 cussed there have been presented in the preceding Parts of this publica- 

 tion measurements of the conductance of certain salts of weak acids or 

 bases both in water alone and in the presence of an excess of the acid or 

 base. Various methods of calculating the hydrolysis from the change in 

 conductance produced by the acid or base have been described (see 

 pages 143, 186, and 230) ; and values of the hydrolysis of the salts in ques- 

 tion have been obtained. From these, by combination with the ionization- 

 constants of the acid and base, the ionization of water has been calculated. 

 The salts so investigated are sodium acetate at 218 by A. A. Noyes and 

 H. C. Cooper; ammonium acetate at 100, 156, 218, and 306 by A. A. 

 Noyes and Yogoro Kato and by R. B. Sosman; and the ammonium 

 salt of diketotetrahydrothiazole, a very slightly ionized organic acid, at 

 0, 18, and 25 by C. W. Kanolt. The final conductance results will 

 be found on pages 186, 188, 233 and 295. 



Table 144 contains a summary of the computed values of the per- 

 centage hydrolysis of ammonium acetate in 0.01 normal solution, of the 

 ionization-constant of water (defined by the equation ivw == Ch-Coh), 

 and of the concentration (Ch or Coh) of the hydrogen-ion or hydroxide- 



