DISINFECTANTS 



77 



From such data the temperature coefficient can be de- 

 termined if the concentration exponent is known. The 

 equation is 



KtiCi" = Kt2C2"QN 



where ^n is the temperature coefficient for the interval 

 A^ in degrees centigrade. For equal disinfection times, 

 we have 



«-=(^j 



In the above example, assuming n = 6, we find from 20 

 to 40°, 



Q,o = (1.18/0.56)« or Q,o = (1.18/0.56)^ = 9.3. 



For the interval from 2 to 20°, 



Qi8 = (2/1.18)'' or Qxo = 1.695^^^« = 5.8. 



When n = l, the ratio of concentrations equally efficient 

 at different temperatures equals the temperature coeffi- 



Fig. 18. Effect of temperature on the death time of Bacterium para- 

 typliosuni treated with phenol. Abscissa: death time, on logarithmic 

 scale; ordinate: temperature. (From data of Chick, 1908.) 



