Part IX. 



IONIZATION OF WATER AT 0, 18, AND 25 DERIVED FROM 



CONDUCTIVITY MEASUREMENTS OF THE HYDROLYSIS OF THE 



AMMONIUM SALT OF DIKETOTETRAHYDROTHIAZOLE. 



99. OUTLINE OF THE INVESTIGATION. 



The degree of ionization of water at ordinary temperatures has been 

 determined by a number of different methods namely (1) from the 

 hydrolysis of sodium acetate* as derived from the rate at which it 

 saponifies an ester,f and from that of aniline acetate^ as derived from 

 conductivity measurements ; (2) from the rate of saponification of 

 methyl acetate by water itself |[ ; (3) from the electromotive force of the 

 alkali-acid hydrogen cell TJ ; and (4) from the conductivity of the purest 

 water thus far obtained.** Although these entirely independent measure- 

 ments have all given for the ionization of water values of the same order 

 of magnitude and have thereby furnished one of the most striking evi- 

 dences of the Ionic Theory, yet for none of the values so obtained can 

 any considerable percentage accuracy be claimed. It has therefore seemed 

 advisable to make a special study of this constant at ordinary temperatures 

 by the same method that has been employed at higher temperatures by 

 Noyes and Kato (see Part VI) and by Sosman (Part VII), that is, by 

 measuring the increase in conductance produced by adding to a partially 

 hydrolyzed salt of a weak acid and a weak base an excess of the acid 

 or of the base, whereby the hydrolysis is reduced. 



In calculating from such data the ionization of water a knowledge 

 of the ionization-constants of the acid and the base and of the degree of 

 ionization of the salt is also necessary. 



The salt selected for this purpose must be sufficiently hydrolyzed to 

 give rise to a marked change in the unhydrolyzed portion of it when the 

 excess of acid or base is added. On the other hand, both the acid and 

 base of the salt must be strong enough to permit their ionization-constants 

 to be directly and accurately determined by conductivity measurements. 

 An examination of the available substances previously investigated seemed 

 to show that ammonium hydroxide was the most suitable base, and that 



*Arrhenius, Z. phys. Chem., 11, 822 (1893). 

 fShields, ibid., 12, 184 (1893). 



JArrhenius, ibid., 5, 19 (1890); Bredig, ibid., 11, 829 (1893). 

 Walker, ibid., 4, 334 (1889). 

 JlWijs, ibid., 11, 492 (1893). 



flOstwald, ibid., 11, 521 (1893); Nernst, ibid., 14, 155 (1894); Lowenherz, ibid., 

 20, 293 (1896). 



**Kohlrausch and Heydvveiller, ibid., 14, 330 (1894). 



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