Volume 5, Issue 1, 01 January 1934
Index of content:
5(1934); http://dx.doi.org/10.1063/1.1745205View Description Hide Description
Optically mosaic crystals of zinc have been grown by the Czochralski‐Gomperz method. Three types have been distinguished. During growth mosaic crystals frequently change from one type to another. The conditions of growth under which they were obtained are described briefly. As yet their genesis and their evolutions during growth cannot be controlled or predetermined.
5(1934); http://dx.doi.org/10.1063/1.1745209View Description Hide Description
An exact solution is obtained for the problem of diffusion through a membrane separating two stirred solutions of different concentrations. For a diffusioncell in which the two liquid containers have the same volume and for which the ratio λ (``effective'' volume of membrane : volume of liquid) is small compared with unity, the solution gives explicit expressions for the concentrations at any time in terms of the initial distribution of concentration in the membrane. Two cases are treated: (1) zero initial concentration in the membrane and in one of the liquids; (2) an initial linear concentration gradient connecting the concentrations in the two containers. The usual assumption of a linear gradient across the membrane during the whole course of diffusion will not lead to an appreciable error in a determination of a diffusion constant unless λ exceeds 0.1 or the time of diffusion is much shorter than in the usual practice. Since λ is about 0.02 in the usual type of diffusioncell the use of the simple expression based on a linear gradient cannot be in error. If, however, the preliminary treatment of the membrane fails to yield an initial linear gradient in it, an appreciable error will be made even with λ less than 0.02.
5(1934); http://dx.doi.org/10.1063/1.1745204View Description Hide Description
Measurements are made of the fluctuations in currents passing through insulating materials subjected to high, constant electric fields. Applying the theory of the shot effect to these fluctuations we are able to calculate the average number of elementary charges (electrons or ions) which discharge onto the electrodes as a unit. In glass, this number increases exponentially with the field from about one at low fields to about 106 at fields just below breakdown. Considered with respect to various theories offered in explanation of electrical breakdown, our results indicate that the shot effect is caused by ``avalanches'' of electrons discharging through paths in the material over which breakdown occurs at higher fields, the avalanches increasing in size with the field until the material is ruptured. By making use of the Johnson effect (thermal agitation of electricity) a new and simple method has been worked out for calibrating the amplifier for shot effect measurements.
5(1934); http://dx.doi.org/10.1063/1.1745206View Description Hide Description
This paper is an analysis of the unsteady flow of a compressible fluid flowing radially to a well in a sand formation. The phenomenon of unsteady flow occurs as a result of fluid expansion. When the pressure in the formation is lowered, the fluids therein expand and the increase in volume imparts motion to the fluid which flows towards the region of lowest pressure in the formation. This process is continuous in the reservoir and extends further away from the well with increased production. By the ``equation of continuity,'' the solution for two specific cases of unsteady flow are derived. The first of these is that in which the fluid from a sand reservoir of limited size flows to a well in which the pressure at the level of the producing sand always remains constant. The variation of the pressure gradient, the rate of production, and the cumulative production with respect to time are given in Eqs. (11), (24), (29) and (30). The second case is that in which the flow of fluid to a well is such that the rate of production at the well is always constant. This case is derived by the assumption that the cylindrical body of sand, which is influenced by the well, is subject to a steady depletion of fluid, and in order that the rate remain constant at the well, fluid must flow into the reservoir from some extraneous source in increasing amounts. Eventually, however, the rate of flow of fluid into the reservoir becomes equal to the rate at which fluid is withdrawn from the well and steady flow is established in the sand. The equations for the pressure gradient and the decline of pressure at the well with respect to time are (39), (52) and (56).
5(1934); http://dx.doi.org/10.1063/1.1745207View Description Hide Description
In this investigation, the magneto‐optic apparatus was used, but it was modified to some extent from the original apparatus used by Allison. The modifications included a mercury vapor arc and a monochromator to furnish a steady source of monochromatic light, and a photoelectric cell and amplifier circuit to read the minima. The apparatus gave a distinct minimum, at 32.9 on the electrical path scale, for all substances tested which contained vitamin A but did not show this minimum for similar substances in which this vitamin was lacking. Pure carotene did not give this minimum. Pure carotene after irradiation with ultraviolet light, however, did give it.
Mutual Impedance of Grounded Wires Lying on the Surface of the Earth when the Conductivity Varies Exponentially with Depth5(1934); http://dx.doi.org/10.1063/1.1745208View Description Hide Description
This paper presents a formula for the mutual impedance of any insulated wires of negligible diameter lying on the surface of the earth and grounded at their end‐points, on the assumption that the conductivity of the earth varies exponentially with depth. Various special cases are briefly discussed.