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Studies in the dynamics of disinfection: XIV. The variation of the concentration exponents for hydrogen and hydroxyl ions with mortality level, using standard cultures of Bact. Coli at 51°C

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, and the Bacteriological Laboratory, Imperial College of Science and Technology, London
S. E. Jacobs
Affiliation:
From the Physiology Department, University College of South Wales and Monmouthshire, Cardiff, and the Bacteriological Laboratory, Imperial College of Science and Technology, London
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1. Data obtained by the disinfection at 51° C. of standard cultures of Bact. coli at pH values ranging from 2·8 to 8·8 have been used for the calculation of the concentration exponents of hydrogen and hydroxyl ions. The times taken to reach various degrees of mortality from 50 to 99·99 % have been taken as measures of the activities of the ions.

2. The formula Cn×t = constant proved satisfactory for describing the data for all the mortality levels and at all the pH values tested except pH 2·8, 6·25, 6·4 and 7·0. In these instances the cultures exhibited heightened sensitivity, though the results at all, except pH 2·8, could be included when the 99·.99 % mortality times were used. The exponents increased sharply at pH values below 3·9.

3. The values of the concentration exponents varied similarly under both acid and alkaline conditions, according to the mortality level chosen. The largest value was obtained from the 90 % mortality times, there being a decrease when both higher and lower levels were employed. The changes were greater under acid conditions, when the values ranged from 0·60 to 0·25, compared with 0·60–0·47 for the alkaline reactions.

4. The mean of the pH values for maximal survival at the various mortality levels, derived from the regressions of log mortality time on pH, was ·51, but this was close to a point of greater susceptibility. Experimentally, maximal survival occurred at pH 6·65, which is very near to the neutral point of water at 51° C.

5. It is concluded that within the pH range 6·25–7.0 the hydrogen and hydroxyl ions were relatively inactive, the effects observed being due to other factors possibly including the action of undissociated water molecules.

The authors acknowledge with thanks the receipt of a grant from Messrs I.C.I. (Pharmaceuticals) Ltd. towards the expenses of this investigation.

Type
Research Article
Information
Journal of Hygiene , Volume 46 , Issue 3 , September 1948 , pp. 289 - 295
Copyright
Copyright © Cambridge University Press 1948

References

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