The Rideal-Walker coefficient is a figure expressing the disinfecting power of any substance and is obtained by dividing the figure indicating the degree of dilution of the disinfectant that kills a microorganism in a given time by that indicating the degree of dilution of phenol that kills the organism in the same space of time under similar conditions. Although very similar to the phenol coefficient, the Rideal-Walker coefficient determines the phenol coefficient utilizing the method (test) developed by English chemists Samuel Rideal, (1863–1929) and J.