96 BACTERIOLOGY 



ions, which are atoms or groups of atoms having electro- 

 positive and electro-negative characteristics. According 

 to this theory, salts, when dissolved in water, undergo 

 electrolytic dissociation into metallic and acidic ions, the 

 former being the electro-positive -cation, the latter the 

 electro-negative anion; sodium chloride, for example, re- 

 solving itself, under these conditions, into its sodium, 

 or metal ion, and its chlorine, or acidic ion. The electro- 

 positive cations, according to Ostwald, comprise the metals 

 and metal-like radicals, such as ammonium (NH4) and hydro- 

 gen (H); while the electronegative anions include the halo- 

 gens, the acidic radicals (such as NO^ and SO4), and hydrosyl.^ 

 Using this theory as the basis of their investigations, Kronig 

 and Paul reached the following conclusions with regard to 

 the action of chemical disinfectants: 



The germicidal value of a metallic salt depends not only 

 upon its specific character, but also upon that of its anion. 



Solutions of metallic salts in which the metallic part is 

 represented by a complex ion and in which the concentra- 

 tion of the metal ion is very slight, have but feeble disin- 

 fecting activity. 



The halogen compounds of mercury act according to the 

 degree of their dissociation. 



The disinfecting power of the halogens — chlorine, bromine, 

 iodine — (as well as their compounds) is in inverse ratio to 

 their atomic weights. 



The disinfecting activity of watery solutions of mercuric 

 chloride is diminished by the addition to them of other 



' Consult Ostwald's Lehrbuch der Allg. Chemie; or Muir's transla- 

 tion of Ostwald's Solutions, p. 189, published by Longmans, Green & 

 Co., London and New York, 1891. Also The Rise of the Theory of Elec- 

 trolytic Dissociation, etc., by H. C. Jones, Ph.D., Johns Hopkins Hospital 

 Bulletin, No. 87, June, 1898, p. 136. 



