102 



DISINFECTANTS 



concentration exponent. They are the only unknowns 

 in the equation 



Ktc" = log 



initial number 

 survivors 



The values of K and n characterize the disinfectant far 

 better than the phenol coefficient, and if the temperature 

 coefficient were also known, the effect of the disinfectant 

 would be known for any combination of concentration, 

 exposure-time and temperature. 



TABLE 19 



Variation of the phenol coefficient of mercuric chloride with 

 different death times. (From Chick and Martin, 1908.) 



Phelps himself did not continue these studies and 

 did not attempt to show with experimental data the 

 practicability of his proposal. In fact, this proposal was 

 never given a thorough test. The idea was dismissed on the 

 ground that the deathrate constant K fluctuates enor- 

 mously. The data obtained by Chick are usually given 

 as proof of that inconsistency. The fluctuations are 

 quite large indeed, even when the test is made with the 

 same strain of bacteria, grown in the same medium, at 

 the same temperature, and to the same age. Despite 

 all attempts at uniformity, Chick obtained on different 

 days the following deathrate constants for Bad. paraty- 

 pJiosum exposed to 0.6% phenol at 20°C: 0.19, 0.45, 0.25, 

 0.82, 0.27. 



