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A test to determine the Germicidal value of a given substance.

In the year 1903 Rideal and Walker developed a test to determine the Germicidal value or measure the bactericidal activity of disinfecting agents and this process was later modified and accepted by the British Standards Institution.

The disinfectant value of Phenol (Carbolic Acid) is taken as 1 (unit) and thus disinfectant value of other products is relative or coefficient of phenol. Rideal Walker test measured the value of the agent for disinfecting pure cultures of Bacterium Typhosum. Later the Americans modified Rideal Walker test by changing the organisms and culture media depending on the type of disinfectant tested such as Staphylococcus Aureus. The test procedure mentioned here is what has been recommended in Schedule 'O' of Drugs Act and Bureau of Indian Standards IS 1061. Method of determination of Rideal Walker Coefficient (R.W.C.)