The light-scatter technique has been used to study the nozzle-fluid concentration field in an isothermal, turbulent, axisymmetric air/air free jet with the nozzle air marked by an oil smoke. The data on the mean concentration field appear to be the most accurate yet obtained, due to the peculiar advantages of the technique. The turbulent concentration fluctuations have been characterized as to intensity, spectral distribution, and two-point correlation. The intermittency factor has been measured and the properties of the turbulent fluid computed. Comparison with the results of other investigators who used heat to mark the nozzle fluid indicates a close similarity between the concentration and temperature fields.

A study has been made of the varicose instability of an axisymmetrical jet with a velocity distribution radially uniform at the nozzle mouth except for a laminar boundary layer at the wall. The evolutionary phenomena of instability, such as the rolling up of the cylindrical vortex layer into ring vortices, the coalescence of ring vortex pairs, and the eventual disintegration into turbulent eddies, have been investigated as a function of the Reynolds number using smoke photography, stroboscopic observation, and the light-scatter technique.Emphasis has been placed on the wavelength with maximum growth rate. The jet is highly sensitive to sound and the effects of several types of acoustic excitation, including pure tones, have been determined.

A general mathematical approach to the rigorous treatment of experimental data on nonstationary‐state diffusion in solids of complex shape is developed. The general solution for a uniform initial concentration, c0, and a constant surface concentration, cs, at times greater than zero is shown to be of the form in the neighborhood of time zero, and in the neighborhood of time infinity, where c is the average concentration at time t; S and V are the surface area and volume of the solid, respectively; D is the diffusion coefficient; and f″ (0), α, and β are constants dependent on solid shape. The vacuum drying of wheat has been studied, and it is shown that, for the wheat kernel, f″ (0) = 0.588, α = 0.862; and β2 = 1.301. The diffusion coefficient is an Arrhenius‐type function of temperature given by D = D0 exp {‐E/RT} where D0 = 76.8 cm.2/sec. and E = 12.20 kcal./mole.

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