DISINFECTANTS 75 



reaction". A temperature coefficient of disinfection sim- 

 ilar to that of chemical reactions excludes any theory 

 of disinfection based on rates of diffusion, e.g., that by 

 Henderson Smith, 1921^ because the temperature etfect 

 on diffusion is much smaller than that on most chemical 

 reactions. 



Most biologists are probably more familiar with the 

 conception of temperature coefficients than with that of 

 temperature increments, and therefore temperature co- 

 efficients will be used throughout this discussion, though 

 the increments would be preferable since they remain 

 constant while the temperature coefficients decrease 

 slightly with increasing temperature. 



Temperature coefficients of disinfection have been de- 

 termined by Madsen and Nyman (1907), by Chick (1908 

 and 1910), by Paul, Birstein and Reuss (1910), and by 

 many others. Table 16 lists some of the more recently 

 determined values of the temperature coefficient when 

 disinfection was accomplished by various means (by al- 

 cohols, Tilley, 1942; by chlorine, Charlton and Levine, 

 1937; and by high acidity, Cohen, 1922). 



A simple relation exists between temperature coeffi- 

 cients and death times. If the deathrate constant in- 

 creases Qi times for every degree increase in tempera- 

 ture, and if K is the constant at the temperature T, then 

 the constant at the temperature T -i- N is KQi^ and the 

 formula for death at this temperature is 



KtQ,^ = log initial number 

 survivors 

 In any set of experiments to measure death times, the 

 values for K, initial number and survivors are the same, 

 and we have the simple relation 



tQi^ = constant = A 

 and therefore, N log Qi = log A - log t. 

 This indicates that a straight line will be obtained if the 



1. See p. 35. 



