TEMPERATURE COEFFICIENT 



143 



information that is not conveyed by the simple reaction velocity. For phenol let 

 us take w = 6, and for HgClg n = 1. Then a doubling of the concentration of 

 HgClj, i.e. C" or 2^ will halve the time taken for completion of the reaction ; 

 doubling the concentration of phenol, i.e. C* or 2^, will diminish it 64 times. 

 Conversely, halving the concentration of HgClj doubles the time of the reaction ; 

 halving the concentration of phenol increases it 64 times. 



A substance with a high value of n is actively germicidal above a given con- 

 centration ; it requires, however, but a low degree of dilution to abolish its germi- 

 cidal activity entirely. In contrast, a substance with a low value of n, while 

 being actively germicidal in solutions above a given concentration, exercises an 

 inhibiting effect on the growth of bacteria even when employed in high dilution. 



One further point may be dealt with here, namely the question of whether the 

 numbers of bacteria present in a suspension affect the reaction velocity. Working 

 with HgCla and anthrax spores, Madsen and Nyman (1907) found the numbers of 

 spores to be of no importance ; a suspension containing 124,800 was sterilized as 

 rapidly as one containing only 7,750. Eisenberg and Okolska (1913), however, 

 divided the disinfectants into 3 classes : in the first, comprising alcohol, phenol, 

 and formaldehyde, the numbers of bacteria had but little effect, i.e. a concentration 

 of disinfectant that would destroy a given number of bacteria would also destroy 

 100 times that number. In a second group, comprising acetone, HgClg and 

 KaMngOs, the numbers of bacteria proved to be of importance ; thus a con- 

 centration that destroyed a given number failed to destroy 10 times that number. 

 A third group comprising HCl, H2SO4, oxalic acid, KOH, and other bodies, occupied 

 an intermediate position between the first two classes. 



Temperature Coefficient. — As the temperature increases in arithmetical pro- 

 gression, the velocity of the reaction increases in geometrical progression, or mathe- 

 matically expressed 



T 



^ QiT'-T) 



in which k' and k are the velocity constants of the reaction at temperatures T' 

 and T respectively, and 6 is the temperature coefficient. 



In the disinfection of paratyphoid bacilli by 0-6 per cent, phenol at 20° and 

 at 30° C, Chick (1908) obtained the following figures (Table 18) : 



TABLE 18 

 Paratyphoid Bacilli. Phenol 6 pee 1,000. 



The mean value of k at 20° C. = 0-27. 

 The mean value of k' at 30° C. = 0-7. 



