With 1 Plate, 1 Text-figure and 6 Charts)The work described here was designed to determine the value of hypochlorites as disinfectants for dairy utensils and the extent to which they could safely be used to replace steam and boiling water under wartime conditions.The general results of our findings and their bearing on the methods of applying hypochlorites have already been published with tentative methods for the use of sodium hypochlorite on the farm(i, 2). Some of the evidence for the statements in these publications is now presented. The rest of the evidence will be presented in a later bulletin. It was not possible at the time to make the observations exhaustive, and the methods of practical application are not perhaps the simplest and most economical which could be devised.Since the observations of Andrewes & Orton (3) and of Halwerda (4) that the germicidal action of chlorine solutions is due to the H0C1 formed when chlorine or a hypochlorite is added to water and that the quantity formed is a function of pR, the most important are those by Rudolph (5), Weber (6) and Weber & Levine (7), who give a clear picture of the true relationship between piL, concentration, and reaction velocity of solutions containing available chlorine.We intended to work with bacteria on surfaces but expected, after reviewing theliterature, to find that the pK of the solutions containing chlorine* would be the chief factor affecting their efficiency as germicides under these conditions. Preliminary tests using well-washed milk cans rinsed with solutions at various pH values were made. The results differed little with changes in pH, whereas according to Weber & Levine, using bacterial spores in suspension, solutions at pH. 7 may be expected to act about 200 times as rapidly as similar solutions at pH. 10.It can be inferred from the work of Myers & Johnson (8) that for the destruction of bacteria on surfaces the pH. of solutions containing chlorine is of less importance than for bacteria in suspension. These workers sprayed infected milk bottles with trade brands of hypochlorites and found only very small differences in the efficiency of the solutions, though chloramine-T was much the slowest. These authors did not record the pR of their solutions, but, from the composition of the products used, there were undoubtedly marked differences in the pK of the diluted solutions.But C. K. Johns (9), working with bacteria in wet films on glass slides and also with artificially infected milk bottles, obtained good agreement with expected results, i.e. the lower the pH the more efficient the chlorine solutions. Tests on a commercial milk plant were much less definite; samples from a bottle-filler gave exceptionally high counts • The word chlorine is, in this paper, used to denote 'available chlorine' as determined by titration with sodium thiosulphate in the presence of acetic acid and iodine.
