214 BAENETT COHEN 



remains that if a disinfectant be applied in a medium having a 

 pH favorable to high bacterial tolerance, the result might be 

 appreciably affected. It appears that this tolerance constitutes 

 one element in the general condition termed "resistance." The 

 foregoing observations furnish corroboration of the present weU- 

 estabUshed principle of determining disinfectant values under 

 accurate control of the hydrogen ion concentration (Wright, 

 1917). 



The laws governing the disinfecting process 



We may now turn to a consideration of the process of disin- 

 fection and the bearing of our experiments upon the laws govern- 

 ing it. To treat the subject fairly and avoid the possibihty of 

 misunderstanding, we shaU begin from certain fundamental 

 concepts in physical chemistry. One of them is the assiunption 

 of the vaUdity of the mass law. This states that at any moment, 

 the velocity of a chemical reaction is dependent upon the rela- 

 tive masses of the reacting bodies as well as their nature. 



If only one substance is undergoing change in a reaction then 

 according to the mass law, the velocity of such change "noil de- 

 pend upon the nature of the substance and its amount at any 

 given moment, temperature and other conditions remaining 

 constant. This statement of the law of monomolecular reac- 

 tions is expressed concisely by the relation 



V=C-k (1) 



in which V represents the velocity of reaction, C, the amount of 

 substance and k, a characteristic factor depending upon the 

 nature of the substance undergoing change. 



dx 

 The velocity may be expressed by — -, in which x represents 



at 



the amount of substance changed in the time t; and if the oripnal 

 amount of the substance be designated by a, then a-x will repre- 

 sent the amount remaining after the time t. We may now ^\Tite 

 the above equation in the form 



