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decreased by 2" times, i.e., 2l (where n= I), or in other words, by half. Again, n for phenol is approximately 6 (Jordan and Jacobs"); a twofold increase in concentration results in 26, i.e., 64 times decrease in the disinfection time. A threefold increase in concentration would result in a 36, i.e., 729 times decrease in disinfection time, and so on. The germicidal ability of aqueous dilutions of substances like phenol, having high concentration exponents will increase at a rapid rate with increasing concentration, and decrease equally rapidly with increasing dilution. Substances possessing low exponents, like mercuric chloride, will decrease in activity more slowly with increasing dilution. From the list prepared by ChicklZ, supplemented by Rahn13, and from the observations of Tilley", Withelll5, Brownlee and Tonkinl'j and Hoffmann and Rahn", it is evident that a wide range of concentration exponents exists amongst disinfectant substances. The effect of concentration of the bactericide on disinfection rate. Chick'* put forward the following empirical relationship connecting