2Q8 



Conductivity of Aqueous Solutions. Part IX. 



for the heat of neutralization of strong acids and bases. The calculation 

 has been made for the two temperature-intervals by the equation 



1 ^_ Q_ T 2 T x 

 ge K x ~ R T X T 2 



where K and K 2 represent the ionization-constants of water at 7\ and T 2 , 

 R is the gas-constant (1.986 cal per degree), and Q is the heat of ioniza- 

 tion of one mol of water. The value of Q is thus found to be 14,500 

 calories at 9, and 14,200 calories at 21.5. The mean value of the heats 

 of neutralization of potassium and sodium hydroxides by hydrochloric 

 and nitric acids as recently determined by Wormann* is 14,240 calories 

 at 9 and 13,590 calories at 21.5. The agreement is a surprisingly close 

 one, and shows that the ionization values at the three temperatures, if 

 affected by errors, must be affected by them by the same percentage 

 amount. 



105. SUMMARY. 



In this article have been presented the results of measurements of the 

 conductivity at 0, 18, and 25 of ammonium hydroxide, diketotetrahy- 

 drothiazole, and of the salt of this base and acid, both alone and in the 

 presence of an excess of the base or acid. From these measurements have 

 been calculated the ionization-constants of the base and acid, the hydrol- 

 ysis and hydrolysis-constant of the salt, the ionization-constant of water 

 and the concentration of the hydrogen-ion or hydroxide-ion in it. The final 

 results may be summarized as follows : 



Table 128. Ionization-constants of ammonium hydroxide, of diketotetrahydro- 



thiasole, and of water. 



The values for the hydrogen-ion concentration given in the last column 

 are 16 to 20 per cent lower than those derived by Kohlrausch and Heyd- 

 weiller from the conductivity of the purest water. From their varia- 

 tion with the temperature the heat of ionization of water has been cal- 

 culated, and found to be in close agreement with the directly measured 

 heat of neutralization of strong acids and bases. 



*Drude's Ann. Phys., 18, 793 (1905). 



