490 BACTERIOLOGICAL ANALYSES 



cisely similar experiment, in which five percentage 

 strengths of Phenol, (e. g., i.i, i.o, 0.9, 0.75, 0.7) are 

 arranged in the lower tier of the test-tube rack in 

 place of the five strengths of Germicide-x. 



Calculate the phenol coefficient by the following 

 method : 



(a) Divide the figure representing the percentage 

 strength of the weakest lethal dilution of the carbolic 

 acid control at the 2j-minute contact period by the 

 figure representing the percentage strength of the 

 weakest lethal dilution of the x-disinfectant at the 

 same period. The quotient = phenol coefficient at 2^ 

 minutes. 



(b) Similarly obtain the phenol coefficient at 30 

 minutes contact period. 



(c) Record the mean of the two coefficients obtained 

 in (a) and (b) as the mean phenol coefficient, or simply 

 as the Phenol Coefficient. 



The details of the Final Test of an actual determina- 

 tion are set out in the accompanying table. 



