From 19th International Union of Pure and Applied Chemistry Congress, London. A systematic introduction is presented to the subject of the variation with pH of the polarographic half-wave potential, which is probably the most readily measured electrochemical energetic parameter of organic compounds. Emphasis is placed on (a) the types of relationships observed for both reversible and irreversible electrode processes, (b) the mathematical formulation of these relationships, (c) the structural, mechanistic, kinetic, and environmental factors influencing such relationships, and (d) the presumptive physical causes for such relationships, e.g., the effect of pH on the electrochemical kinetics. Although the discussion is primarily concerned with behavior in aqueous solution, the conclusions drawn are equally valid for nonaqueous media in which hydrogen ion or some other Lewis acid can play a significant role. The half-wave potential for an organic electrode process may be independent of pH, or may vary lineanly or sigmoidally; other types of relationships observed are likely to be combinations of such effects. These variations may be due (a) to direct participation of hydrogen ion in the transition state involving the electroactive site in the organic molecule and the electron source, e.g., polarization of the bond to be broken, (b) to control …

A survey is presented of three processes of water movement which will result in movement of chemicals: miscible displacement, diffusion, and leaching. Miscible displacement is discussed in some detail. Movement of pesticides in soils is considered. (D.L.C.)