Equipment and Experimental Methods for Interference Diffusion Studies

A single lens convergent light apparatus is described with which diffusion in liquids may be studied by an interference method. Details of the optical elements and their mounting and alignment are given as well as the design of a temperature control regulating near 0°C to within 0.01°C. A modified Polson sharpening technique has been used successfully in forming diffusion boundaries in a Tiselius cell. A modification of the Rayleigh interferometer has been employed as an aid in the measurement of the refractive index increment parameter, jm, which is required for the evaluation of the diffusion coefficient. During diffusion a reference slit image obtained by the employment of special cell and plate masks permits more accurate measurements of the undeviated slit image position than have been obtained from the interference diffusion fringe picture. Results indicate that the apparatus is capable of 0.1 percent precision.