Suchergebnisse

Two phenomenological diffusion theories based, respectively, on thermodynamics of irreversible processes and on a dynamical method are compared.
It is shown that both formulations correctly describe the diffusion process, and that the selection of the appropriate scheme for a particular problem is a matter of convenience. The formulation according to irreversible thermodynamics appears, however, -preferable for problems involving the differential diffusion equation.
The matrix of coefficients connecting the two formulations is calculated explicitly in a form applicable to all reference frames for the bulk velocity.

The behaviour of amphoteric electrolytes under the combined action of a gradient of pH and an electrostatic potential is investigated theoretically.
It is shown that ampholytes may be separated and concentrated if the positive electrode is placed on the acid side of the pH gradient. Results are presented which show that under these conditions, the distribution of the ampholyte at the stationary state will vary approximately as a Gaussian error function of distance with the maximum at the isoelectric point. The « bandwidth » of the maximum is found to depend inversely on the magnitudes of the gradients.
The relaxation time for the approach to the stationary state is calculated and found to be of the order of a few minutes.

The stationary state of electrodiffusion in a finite system is discussed. It is shown that the effect exists only in the presence of a second electrolyte which does not itself contribute to the electro-diffusion process.
The electric current through the system is calculated and is shown to contain essential terms due to the second electrolyte and to the divergence of the electric field. The variation in the effective diffusion coefficient due to the influence of these two factors is found to be very small.
In an alternating field, the electric current is shown to contain a rectified component and a first harmonic which could in principle be used for the experimental determination of the rate constants of ionic reactions.