46 VELOCITY OF REACTION, AND 



reaction varies with the resistance of the path ; also by giving 

 various forms to the conducting path, the electrical energy may 

 be transformed into various forms ; and lastly, if a sufficiently 

 powerful dynamo be placed upon the conducting path and worked 

 in the right direction, instead of the path being a means for equating 

 potential it is converted into a means for heaping up difference 

 in potential. 



So also for any type of mechanical engine or motor, however 

 driven ; if the load is taken off, the engine races, as the load is 

 increased the velocity lessens, and with a sufficiently heavy load 

 the movement stops entirely. Always when the potential differ- 

 ences of the opposing forms of energy become greater than those 

 of the form of energy driving the motor, the latter becomes 

 ineffective and the engine must stop, or, if built so as to be capable 

 of reversal, must run in the opposite direction. 



Exactly similar reasoning applies to every known type of energy, 

 and since the law of conservation of energy holds and a definite 

 amount of chemical energy is equivalent to a definite amount 

 of any other form, it is clear that the reasoning must hold for 

 chemical energy also. 



Hence we see that while the difference in chemical energy gives 

 the driving force tending to cause chemical reaction, and a passage 

 towards a definite point of equilibrium, there is present something 

 in the nature of a resistance or load upon the engine, which deter- 

 mines by its amount whether a reaction shall occur at all, if it 

 occurs the speed at which it shall occur, and according as the 

 resistance is' modified by other factors, the path of the reaction 

 is determined and the very qualitative nature of the compounds 

 formed by the reaction. 



It is hence necessary for our purpose to inquire what is the 

 nature of the resistance to chemical reaction, what are the forms 

 of energy opposed to the reaction, and how is the action of these 

 opposing forms of energy altered under different circumstances, 

 so that the velocity of reaction becomes changed, the reaction 

 stopped or its actual direction reversed, or finally the path of 

 the reaction altered so that under different conditions, .different 

 products may be formed. 



The obvious forms of energy opposed to chemical reaction 

 are (1) molecular cohesion or chemical affin'ty, which must be 

 overcome, before the molecule breaks up or is rendered capable 



