DISINFECT AN Ti^ 93 



Two dissociation constants of HOCl are given in 

 chemical literature which ditfer greatly, namely 3.7X10-^ 

 and 6.7X10-^^ The latter is supposed to be the more ac- 

 curate ; it certainly comes from a later measurement, but 

 Holwerda based his calculations on the first, older con- 

 stant. His experimental data agree fairly well with his 

 assumption that the undissociated HOCl is the toxic part 

 of chlorine dissolved in water. But his experiments were 

 largely limited to alkaline and neutral solutions. The 

 increased efficiency of chlorine by a decrease in pH from 

 7 to 3 (Table 17) cannot be explained in this way. The 

 newer dissociation constant does not give as good a cor- 

 relation as the older one. 



Another unusual feature of chlorine disinfection is the 

 non-logarithmic type of survivor curve, as shown pre- 

 viously. Two very extensive investigations, one by Charl- 

 ton and Levine (1937) and the other by Mallmann and 

 Ardry (1940), bear out this observation. The explan- 

 ation must be sought in the usual mode of action of 

 chlorine as illustrated in the following case reported by 

 Anderson and Mallmann, in their recent study of the 

 penetrative powers of disinfectants (1943). They ob- 

 served under the microscope the effect of various disin- 

 fectants upon freshly hatched long-tailed strongylid lar- 

 vae (parasites of horses). Under the action of chlorine 

 ''the thin layer of cuticle which forms the tail of the or- 

 ganism dissolved first, followed by a splitting or shred- 

 ding of the posterior end of the organism, simultaneously 

 with the appearance of bubble-like rupture of the cuticle 

 along the whole length of the organism." The action of 

 phenol was quite different. At a concentration of 1 :100 it 

 "produced death of the larvae in 45 minutes without any 

 external changes of the organisms." In their summary, 

 they state: "Chlorine acts only by oxidation, i.e. first 

 destroying the cell surface." 



These observations and conclusions speak unequivo- 

 cally in favor of the explanation of chlorine action pre- 



