Summary. 



343 



ized fraction of a salt at any concentration and the product of the valences 

 of its ions has now been proved by the measurements of Noyes and Mel- 

 cher to persist up to the highest temperatures, where the degree of ioniza- 

 tion has become much less. This is shown by the following summary, 

 which is a reproduction of table 29 on page 110. Under A are given the 

 mean values of the percentage of un-ionized salt, 100(1 y), for the 

 neutral salts of each type at the concentration 0.04 molal and for the uni- 

 univalent salts at 0.08 molal ; and under B are given the ratios of these 

 values to the product of the valences (v 1 v 2 ) of the ions. 



It will be seen that the principle continues to hold, especially when the 

 comparison is made at the same equivalent concentration, even when the 

 ionization has become very small ; thus it is only 26 per cent for the uni- 

 bivalent salts at 306 and only 7 per cent for the bibivalent salt (magne- 

 sium sulphate) at 218. 



The ionization tendencies of phosphoric acid, acetic acid, and ammonium 

 hydroxide, and the effect of temperature on them are best shown by 

 the summary of their ionization-constants which is given in table 143.* 

 The values for phosphoric acid were determined by Noyes and Eastman 

 (see page 269), those for acetic acid by Noyes and Cooper (page 142) 

 and by Sosman (page 228) ; and those for ammonium hydroxide were 

 determined by Noyes and Kato (page 178), by Sosman (page 228), 

 and by Kanolt (page 290). The concentration involved in the constant 

 is expressed in equivalents per liter, and the constants themselves have 

 been multiplied by 10 6 . 



It is evident from these results that the ionization-constant for ammo- 

 nium hydroxide increases considerably in passing from to 18, then 

 remains nearly constant up to 50, and finally decreases with increasing 

 rapidity as higher temperatures are reached, attaining at 306 a value 

 which is only about one-two-hundredth of that at 18 ; and that at all 

 temperatures the values for acetic acid are not very different from those 



*In the case of phosphoric acid the values vary considerably with the concentration 

 in correspondence with the fact that the exponent in the concentration-function was 

 found to be 1.8 1.9 instead of 2 as required by the mass-action law. The values 

 here given are those at the concentration 0.05 formula-weights (H 3 P0 4 ) per liter. 



