Studies on the Mode of Action of Compounds Containing Available Chlorine

Abstract

In a study of the bactericidal properties of various forms of active chlorine, certain preliminary results have been obtained which concern the mechanism by which N-chloro compounds react in aqueous solution. Information of this type is valuable because this form of active chlorine is frequently a useful means of application, and because in many cases where chlorine or hypochlorites are used there may be present nitrogen compounds capable of forming N-chloro derivatives. The extent to which this occurs, and the nature of the resulting compound, will largely determine the result obtained. In aqueous solution it is necessary to consider that the reactivity of the N-chloro compound may be due in whole or in part to the hypochlorous acid and hypochlorite ion that are present in accordance with the hydrolysis and ionization equilibria. Although the degree of hydrolysis may be very slight in many cases, its effect can be significant if the activity of hypochlorous acid is sufficiently great compared to the unhydrolyzed N-chloro molecule. The experimental results indicate, in a few representative cases, under what conditions and to what extent the bactericidal properties of N-chloro compounds can be attributed to the small concentrations of hypochlorous acid that may be present under equilibrium conditions. It is assumed that the speed of hydrolysis is greater than the rate at which hypochlorous acid is consumed in killing the organisms and therefore need not be considered. The experimental conditions have been limited to dilute aqueous solutions, the pH values of which range from 4 to 9. With these restrictions, active chlorine in the form of dissolved molecular chlorine need not be considered, since its concentration would be insignificant (Jakowkin, 1899). EXPERIMENTAL PROCEDURE Organisms. The spores of Bacillus metiens (Rudolph and Levine, 1941) were grown on agar flats at 37 C for one week at which time most of the organisms were in the spore stage. They were suspended in saline solution, and the suspension was washed twice by centrifuging and stored in the refrigerator until used. The Escherichia coli cells were grown in nutrient broth, removed by centrifuging, washed twice, and used immediately. Reagents. Water, free from reducing properties, was prepared by adding 10 ppm chlorine to distilled water and permitting it to stand for about a week. It was then set in the sun for a few days to remove the active chlorine. Before use, it was checked to make sure that it had neither chlorine residual nor chlorine 299