240 THEOKIES AS TO ACTION OF 



which may be used in different special cases to reach the same end. 

 The end to be reached, in order that the reaction velocity may be 

 increased, is to diminish the resistance to reaction. The potential 

 factor, or vis a tergo, is dependent upon the energy freed in the reac- 

 tion, and this in turn upon the initial and final chemical energies of 

 the reacting substances; hence this factor may be regarded as 

 constant. But the velocity with which equilibrium will be reached, 

 and in fact whether it will be reached at all, depends, as pointed out 

 previously, upon what the value of the resistance is to the reaction. 

 Now all the above theories are explanations of various means 

 by which the resistance may be altered, and so the reaction velocity 

 varied, and which of these means is taken must vary with the 

 circumstances of each case. 1 



Thus, increase of molecular vibration, as in chemical reactions 

 induced by detonation, or by mere contact with a chemical catalyst, 

 may decrease the molecular stability, and so increase the velocity, 

 and by analogy this may also occur in less easily provoked reac- 

 tions; again, the formation of intermediate products may break up 

 the molecular stability, producing compounds in which the resist- 

 ance to reaction is lessened ; change in the properties of the solvent 

 may induce or hasten reaction by bringing new attractions to bear 

 upon the constituent groups of the molecule, so that the resistance 

 to these parting company may be increased or diminished, and the 

 reaction velocity correspondingly varied; this change may be 

 occasioned by the presence of a heterogeneous system with different 

 reaction velocities due to different solvents in its two phases; vary- 

 ing concentration may alter the relationships and attractions 

 between solvent and substratum and so alter resistance and reaction 

 velocity. 



There is hence nothing incompatible between the different 

 theories of catalytic action, and these must be regarded as theories 

 of the means by which the one common factor of chemical resist- 

 ance to reaction can be changed. 



1 It is not meant here that the means by which chemical resistance may 

 be studied are not of the highest value, and call for most careful study, but 

 only to point out that all these lead to the same end. 



