162 STERILIZATION AND DISINFECTION 
taking into consideration the phenol coefficient and the cost of the disin- 
fectant per gallon. 
The cost of a disinfectant per 100 units of efficiency as compared 
with pure phenol is obtained by first dividing the cost per gallon of 
the disinfectant by the cost per gallon of pure phenol; the efficiency 
ratio of course is obtained by dividing the coefficient of the disinfectant 
by the coefficient of phenol, but as the coefficient is always 1 the effi- 
ciency ratio is represented by the phenol coefficient of the disinfectant. 
The cost ratio divided by the efficiency ratio (the coefficient of the dis- 
infectant) gives the cost of the disinfectant per unit of efficiency as com- 
pared with the cost per unit of efficiency of pure phenol=1. By mul- 
tiplying by 100 the relative cost per 100 units is obtained. Thus, 
Cost of disinfectant per gallon Coefficient of disinfectant 
Cost of phenol per gallon Coefficient of phenol(= 1) 
(efficiency ratio)=the cost of the disinfectant per unit of efficiency 
as compared with phenol=1. And by multiplying by 100 the cost 
per 100 units is obtained. 
For instance, the cost of disinfectant “‘ Car ’’ is $0.30 per gallon, and 
it has a coefficient of 2.12; the cost of phenol is $2.67 and has a coeffi- 
cient of 1. Then. 
(=cost ratio) + 
20 . 2.12 
677 TT OP? 
Therefore, the comparative cost per unit of efficiency of ‘ Car” and 
phenol, respectively, is as 0.052 is to 1; or, by multiplying by 100, 
the relative cost per 100 units—5.2 to 100—is obtained. 
The following table illustrates the value of the determination of the 
cost per 100 units of efficiency of a disinfectant as compared with the 
cost of 100 units of pure phenol: 
TasLeE XVII 
; Relative cost 
Efficiency | per 100 units 
Disinfectant. Price per Cost, Ratio. Ratio, which | of Efficiency 
Gallon. is the Phenol | as Compared 
Coefficient. | with Pure 
Phenol = 100 
On $0. 39 0.112 2.12 5.2 
0 0) a 1.00 374 4.44 8.4 
Phi... cee ee ee ee ee eee OL . 138 1.40 9.9 
Cre... ccc cc ee eee tee eee eene 44 . 164 1.13 14.5 
NY Al 153 44. 34.8 
1 10) 6 a 40 .150 25 60.0 
Pure phenol.................005. 2.67 1.00 1.00 100.0 
ee wn 
