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Studies in the dynamics of disinfection: VII. The reaction between phenol and Bact. coli: the effect of temperature on the usually accepted concentration exponent and the calculation of a more satisfactory exponent based on theoretical considerations

Published online by Cambridge University Press:  15 May 2009

R. C. Jordan  and
S. E. Jacobs
R. C. Jordan
Affiliation:
From the Physiology Department, University College of South Wales and Monmouthshire, Cardiff
S. E. Jacobs
Affiliation:
Bacteriological Laboratory, Imperial College of Science and Technology, London
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1. Calculated values of the virtual sterilization time (v.s.t.) have been used in an analysis of the effect of temperature on the concentration exponent of the reaction between phenol and Bact. coli cultures under rigidly standardized conditions.

2. Within the experimental range of temperature and concentration employed, the exponent calculated from the formula Cn × t = K was satisfactorily constant from 20° to 35° C., but it apparently increased at 39° C.

3. This formula is unsatisfactory in that it cannot apply to concentrations near the threshold value without a change in the value of n. Accordingly, a new method of treating these data has been suggested which makes allowance for this threshold or minimum concentration. A corresponding ‘maximum’ concentration has been arbitrarily fixed at which the v.s.t. is 10 min. and the value of (v.s.t. – 10) thus varies from infinity to zero between these concentration limits.

4. Sigmoid curves asymptotic to ordinates at the minimum and maximum concentrations must be obtained when log (v.s.t. – 10) is plotted against concentration and the equation of the Pearl-Verhulst logistic curve, which is of the required type, has been used successfully to express the relationship between v.s.t. and concentration at constant temperature.

5. One of the constants of this formula partakes of the nature of a concentration exponent and this may be constant over the full effective concentration range and for all temperatures.

6. The logistic formula relating v.s.t. to concentration at constant temperature is closely related to that connecting v.s.t. with temperature at constant concentration. The two formulae become interconvertible if certain assumptions are made concerning the relationships between the minimum and maximum concentrations and temperature.

Type
Research Article
Information
Journal of Hygiene , Volume 44 , Issue 6 , September 1946 , pp. 421 - 429
Copyright
Copyright © Cambridge University Press 1946

References

REFERENCES

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