142 



DISINFECTION 



Paul, Birstein and Reusz (19106) found that the value of the velocity constant k 

 for aqueous solutions of HCl was approximately proportional to the square root of 

 its concentration. 



TABLE 17 

 Disinfection of Paeatyphoid Bacilli by HgCla at 20° C. 



Calculation o£ Exponent n. — The exponent n may be regarded as a concentration 

 coefficient varying with each disinfectant. To calculate its value, we use the 

 formula 



1 KC" f = log ? 

 b 



ki is determined for concentration Ci, and k^ for concentration C^ in a given 



experiment. Then 



k C 



n = \og^^ log -' 

 k, Cj 



Taking the figures in Table 16, 



let 7-0 parts of phenol per 1000 = Cj and t = 105' 



let 5-0 parts of phenol per 1000 = Ci and t = 690' 



^2 = 7 • log - 

 t b 



B in this experiment was 30,000,000 ; b can be taken as 1. Then : 



;fc = J_ . log 30,000,000 

 '105 ^ ' ' 



k. 



= 0-0712 

 _ 1 

 ~690 

 = 0-0108 



log 30,000,000 



b"^2 . 1 ^a 

 g — — log — 

 ^ k, ^Ci 



, 0-0712 , 7 



= log -:- log - 



^ 0-0108 ^ 5 

 = log 6-5 -^ log 1-4 

 = 5-5 

 For HgCla, when the concentration of Hg-ions only was considered, the value of n 

 was found to be 3-8 ; for the Ag-ions of AgNOj, 0-86. If the molecular concentra- 

 tion of HgClj is considered, then n is equal to about 1. 



The value of n for any given disinfectant is very important, because it gives us 



1 K is the true velocity constant of the disinfectant, being independent of the concen- 

 tration, and thus differing from k, which is constant only at a given concentration. 



