LECTURE XV.] HISTORY OF CHEMISTRY. 315 



instead of the quantities /, q, p, and #', the relative numbers 

 of molecules; that is, the quotients obtained by dividing the 

 quantities present by the molecular weights. 



This " law of chemical mass action " has been tested in 

 various ways, and the observed facts have repeatedly been 

 found in agreement with it. In this connection, mention must 

 first be made here of the researches upon ester formation 

 carried out by Berthelot and Pean de Saint Gilles 94 as early as 

 1 86 1 and 1862, and thus several years prior to the investiga- 

 tions of Guldberg and Waage. The limit of ester formation 

 and the rate of the reaction were here studied, and the 

 numerical values found are sufficiently close to those calcu- 

 lated from theory. These experiments were continued and 

 extended by Menschutkin, 95 who examined the ester formation 

 in the direction referred to, in the cases of the most different 

 alcohols and acids, and thus furnished an important contribu- 

 tion to the varying behaviour of substances of different struc- 

 ture. Bearing also upon this subject are the interesting 

 experiments by Vernon Harcourt and Esson, 95 " the detailed 

 thermo-chemical researches of Thomsen, 96 and the studies 

 of Ostwald 97 on chemical volume, which not merely con- 

 firmed the theory but also extended it. These investigations 

 are chiefly connected with the affinity relations between acids 

 and bases. The conception of avidity is here introduced 

 an idea approximately corresponding to what used to be 

 somewhat less precisely designated as the strength of acids or 

 of bases. What is understood by this term is the proportion 

 in which two substances are shared by a third, the quantity 

 of which is insufficient for their complete saturation ; and it 

 appears that the avidity is proportional to the square root of 

 the affinity coefficient. 



94 Ann. Chim. [3] 65, 385 ; 66, 5 ; 68, 225. 95 Berichte. 10, 1728, 

 1898; II, 1507, 2117, 2148; 13, 162, 1812; 14, 2630. Annalen. 195, 

 334; 197, 193. Ann. Chim. [5] 20, 289; 23, 14; 30, 81. 95a Phil 

 Trans. 1866, 193; 1867, 117. 96 Pogg. Ann. 138, 65; and Thermochemische 

 Untersuchungen. I. 97 J. pr. Chem. [2] 16, 385; 18, 328; 19, 468; 



25, i ; Pogg. Ann. Erganzungsband 8, 154; Wiedem. Ann. 2, 429, 671. 



