The Rideal–Walker coefficient, now only of historical interest, is a figure expressing the disinfecting power of any disinfectant. It is the ratio of the dilution of the

disinfectant A disinfectant is a chemical substance or compound used to inactivate or destroy microorganisms on inert surfaces. Disinfection does not necessarily kill all microorganisms, especially resistant bacterial spores; it is less effective than st ...

that kills a

microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...

to the dilution of phenol that kills the organism in the same time under identical conditions. The Rideal–Walker coefficient determines the

phenol coefficient The Phenol coefficient, is now largely of historical interest, although the principles upon which it is based are still used. It is a measure of the bactericidal activity of a chemical compound in relation to phenol. When listed numerically, the f ...

utilizing the method (test) described by English chemists Samuel Rideal (1863–1929) and J. T. Ainslie Walker (1868–1930). The arbitrary choice of contact time (sterilisation in 7.5 minutes),

diluent A diluent (also referred to as a filler, dilutant or thinner) is a Concentration, diluting agent. Certain fluids are too Viscosity, viscous to be pumped easily or too density, dense to flow from one particular point to the other. This can be prob ...

(distilled water) and test organism (

Salmonella typhi ''Salmonella enterica'' subsp. ''enterica'' is a subspecies of ''Salmonella enterica'', the rod-shaped, flagellated, aerobic, Gram-negative bacterium. Many of the pathogenic serovars of the ''S. enterica'' species are in this subspecies, includin ...

, then called Bacillus typhosa) did not reflect the conditions under which disinfectants were used. Because of this, impossibly high values were obtained for disinfectant activity and quoted by disinfectant manufacturers. The method was referred to by distinguished microbiologist Sir Ashley Miles as "...at best a grossly over-simplified answer to a very difficult problem, and at worst little short of bacteriological prostitution". It was replaced by a more realistic test devised by Dame

Harriette Chick Dame Harriette Chick DBE (6 January 1875 – 9 July 1977) was a British microbiologist, protein scientist and nutritionist. She is best remembered for demonstrating the roles of sunlight and cod liver oil in preventing rickets. Biography ...

and

Sir Charles James Martin Sir Charles James Martin (9 January 1866 – 15 February 1955) was a British scientist who did seminal work on a very wide range of topics including snake toxins, control of body temperature, plague and the way it was spread, dysentery, typhoid ...

, which in turn was replaced by other tests, not reliant on a comparison with phenol, in attempts to assess the effectiveness of particular disinfectants for different purposes.

References

Rideal-Walker coefficient.
Retrieved Nov. 6, 2006. {{DEFAULTSORT:Rideal-Walker coefficient Disinfectants

See also

References