Studies in the dynamics of disinfection

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Abstract
1. Disinfection curves obtained from data on the action of phenol onBact. coliat 35° C. under conditions such that unfavourable circumstances, other than the presence of the germicide, were as far as possible eliminated, have been used for the calculation of the concentration exponent for phenol, i.e.nin the formulaCnxt=K.The death-rate was not constant throughout the germicidal process but showed initially a phase of slow but increasing death-rate which merged gradually into a phase which was treated (for reasons given) as one of constant rate. This was also the maximum rate for any given phenol concentration.2. The virtual sterilization times (v.s.t.'s), i.e. the times in min. required for the mortality to reach 99·999999 % as determined by slight extrapolation of the log survivors-time curves, the 99·9 % mortality times and the 99 % mortality times could all be used for the calculation of values ofnfor phenol as they all gave satisfactory linear relations between log concentration and log time.3. The 50 % mortality times did not show a satisfactory linear relation between log phenol concentration and log time over the full concentration range, and at this mortality level the concentration exponent appeared to increase for concentrations above 4·62 g. phenol per 1.4. The value ofnvaried according to the mortality level chosen. It was 5·8421 ± 0·1876, 6·6062 ± 0·2034 and 6·9638 ± 0·2164 when thev.s.t.'s,99·9 % mortality times or 99 % mortality times were used. The differences between the first and second and first and third values are significant, but that between the second and third values is not. The value calculated from thev.s.t.'sis regarded as being the most important.5. Evidence was obtained that, as expected on theoretical grounds,nincreases for very low concentrations of phenol. If the aberrant value obtained at the lowest phenol concentration be omitted from the calculations, the value ofncalculated from thev.s.t.'s becomes 5·6588 ± 0·1422, but the decrease is not significant.6. The maximum death-rate was related to the phenol concentration according to the expression km= 9·1743 × 10−6C5·0752, wherekmis the maximum (logarithmic) death-rate per min. andCthe concentration of phenol in g. per 1.