The moving boundary method for the determination of transport numbers

Abstract

The lack of a simple and fairly complete theoretical treatment of the moving boundary method has been felt in this laboratory in the course of transport number measurements in dye solutions. The results of these measurements are shortly to be published by Dr. C. Robinson and one of us (J. L. M.). In the present paper we shall attempt to develop a theory of the method, of necessity including some previous work, and to explain experimental results in the literature and the aforementioned work on dye solutions. Doubts have been expressed as to the validity of the method, in spite of the convincing experimental work of MacInnes, Smith, Longsworth, and co-workers, to whom we shall frequently have occasion to refer. These attacks on the method, we believe, have arisen from a misunderstanding of the fundamental principles involved, and we shall endeavour to answer them in this paper. In order to avoid confusion, we shall first explain the terminology to be used, which we hope will be adhered to in future communications from ourselves and coworkers. In this paper we confine ourselves to electrolytes (including colloidal electrolytes). The application of the method to colloids will be the subject of a future communication from this laboratory.