PHENOL COEFFICIENT

number representing the disinfectant quality of an antiseptic or germicide in relation to that of phenol (carbolic acid), which is used as a standard. The phenol coefficient of a chemical is found by adding microorganisms to several samples of various concentrations of the chemical and to samples of phenol for a known period of time. The action of the chemicals is stopped before samples are removed from each solution and added to a suitable liquid growth medium. The sample in which no visible microbial growth occurs is considered the end-point sample for the chemical. An end-point concentration is recorded for phenol as well. A ratio is then determined by comparing the concentrations of the two end-point samples.