ELECTROLYTIC DISSOCIATION. 395 



dissociated part of a weak acid obeys very nearly the gaseous laws. 

 The same was afterwards demonstrated to be true for weak bases by 

 Bredig. The strongly dissociated electrolytes, chiefly salts, exhibit 

 even in dilute solutions (over 0.05 normal) anomalies, that are not 

 yet wholly explained. Professor Jahn, of Berlin, is at work upon this 

 most interesting question. 



The equilibrium between a greater number of electrolytes has been 

 investigated by myself, and found to be in good agreement with the 

 theoretical previsions. This section includes the questions on the 

 weakening of an acid by addition of its salts, and on the so-called 

 avidity of the different acids, that is, the proportion in which two acids 

 divide a base at partial neutralization. Calculation gives very nearly 

 the numbers observed experimentally by Thomsen and Ostwald. For 

 heterogeneous equilibria between electrolytes the theory is worked out 

 by van't Hoff and Nernst, who have in this way elucidated the com- 

 mon method to precipitate salts used in analytical chemistry. 



By help of the gaseous laws it is also possible to determine the heat 

 evolved at the dissociation of a weak acid or base, and in this way I 

 was able to calculate the heat of neutralization of acids and bases in a 

 general manner. In an analogous way, Fanjung calculated the changes 

 of volume at dissociation of a weak acid or base and at the neutraliza- 

 tion of these bodies. All these calculations gave values very nearly 

 agreeing with the observed ones. 



An important role is played by the water, which may be regarded 

 as a weak acid or base. By its electrolytical dissociation it causes the 

 hydrolysis of salts of weak acids and bases. By observation of the 

 hydrolysis, it was possible to calculate the electrolytic dissociation of 

 water, and this quantity was soon after determined by electrical meas- 

 urements by Kohlrausch and Heydweiller in perfect agreement with 

 the previous calculations. For physiological chemistry this question is 

 of the greatest importance, as is confirmed by the experimental results 

 of Sjogvist and others. Also for the explanation of volcanic phenom- 

 ena, the concurrence between water and silicic acid at different tem- 

 peratures has found an application. 



The catalytic phenomena in which acids and bases are the chief 

 agents, have been investigated by many observers, and it has been 

 found that the catalytic action depends on the quantity of free hydro- 

 gen or hydroxyl ions that are present in the solution. To this review, 

 that makes no pretension to be complete, may also be added the wide- 

 reaching researches of van't Hoff, Ostwald, and especially Nernst, on 

 the electromotive forces produced by the ions. By these investigations 

 we have now acquired an explanation of the old problem of the manner 

 in which electromotive forces in hydro-electric combinations are excited. 



I have now traced the manner in which the idea of electrolytic 



