HALOGENS AND THEIR MODE OF ACTION
The extensive use of various forms of chlorine and iodine as antiseptics has resulted in the accumulation of much information about efficiency of these halogens under various circumstances. There has been considerable study given to the factors affecting their germicidal activities and to the mechanisms of these effects.' Much less is known about bromine?. a* The qualitative similarities and quantitative differences in many of the properties of chlorine, bromine, and iodine afford an excellent opportunity for observing the effects of certain isolated factors on germicidal activity. Accordingly, this paper will be concerned, for the most part, with the extent to which a few basic chemical properties of the halogens, such as hydrolysis, ionization, and formation of complexes can be used to explain quantitative dfierences in antiseptic power. The mechanism of the reactions leading to the death of the organism will not be discussed here. The interested reader is referred to another paper in this series and to a published report6 for information on this subject. One would expect that the rate of bactericidal action would be characteristic of the particular halogen compound present. Under usual conditions of use, however, one may have present, in addition to elemental halogen, hypohalous acid formed by hydrolysis, hypohalite ion from ionization of the acid, complex ions involving elemental halogen with halide ion, and N-halogen compounds. Furthermore, factors such as concentration, pH, and temperature should have quantitatively different effects on the germicidal activities of the three halogens because the equilibrium constants of the reactions involved are different. Most of the work leading to quantitative conclusions has been carried out with bacterial spores, beginning with Levine and co-workers,6 Meyers,' Tilley and Chapin: and others. The advantages of using B. metiens spores, for example, have been pointed out by Charlton and Levine9 and need not be enumerated here. Accordingly, in FIGURE 1, we consider the comparative action on B. meliens spores over a suitable concentration range of chlorine,'O bromine, and iodine" at pH 7 and room temperatures. A solution of each halogen free of added halide was added to a buffered distilled water suspension of spores, extraneous organic matter being excluded as far as possible. The log of the time for 99 per cent kill is plotted against the log of the normality of the solution. Calculation shows that under these conditions chlorine exists chiefly as hypochlorous acid and bromine entirely as hypobromous acid, but iodine is present as molecular iodine. It is then not surprising that the usual order of halogen reactivities is not found and that iodine fails to show less germicidal power than bromine. It might be of some interest to note that on a weight concentration basis, iodine is considerably less active than chlorine, although still more active than bromine. Against
A Clinical investigation of the Effects of Aqueous Iodine Solutions
T1J7HE clinical effects of several types of dilute aqueous iodine solutions have been investigated. This was done to see whether the differences in chemical composition, antibacterial activity, and toxicity that have been reported by several investigators could be related in any way to clinical observations. Chemical Nature of Iodine Solutions.-An aqueous solution of elemental or diatomic iodine contains small quantities of other species of iodine. This can be seen from the equations: (1) I, + HO = HIO + H+ + I-. and (2) 12 + I=I,. The hydrolysis constant' for equation (1) is:
Ueber die Hydrolyse des Chlors
Die Frage, in welchem Zustande sich das Chlor in wässeriger Lösung befindet, beschäftigt die Chemiker schon mehr als ein halbes Jahrhundert. Einige Thatsachen weisen darauf hin, dass eine wässerige Chlorlösung sich wesentlich von den Lösungen anderer Gase in Wasser unterscheidet, und dass das Chlor unter Einfluss des Wassers eine gewisse Veränderung erleidet. Die saure Reaktion verdünnter wässeriger Chlorlösungen, die Ähnlichkeit des Geruchs solcher Lösungen mit demjenigen von unterchloriger Säure und ähnliche Beobachtungen lassen vermuten, dass das Chlor unter Einfluss des Wassers sich in Salzsäure und unterchlorige Säure umwandelt: