Volume 7, Issue 1, 01 January 1936
Index of content:
7(1936); http://dx.doi.org/10.1063/1.1745339View Description Hide Description
A mathematical analysis is presented for the problem of determining stresses in a metal by x‐ray diffraction. The treatment is a general one, including as special cases the various methods for the determination of uniaxial stresses or the sum of two principal stresses in the plane of the metal surface. The analysis is extended to the problem of determining the two principal surface stresses individually. Methods are proposed by which these stresses may be determined with an accuracy calculated to be of the order of 1300 lbs./in.2 for iron and 320 lbs./in.2 for duralumin, under the best conditions. Camera design, exposure technique, and the applicability of the method to practical problems are discussed.
7(1936); http://dx.doi.org/10.1063/1.1745343View Description Hide Description
With air as the diffusing medium a method and apparatus have been developed for measuring the permeability of compacted, unconsolidated powders. A formula is given for calculating the average pore diameter from the permeability and the percent of voids in the compacted powder. By establishing a simple relationship between the degree of packing, as measured by the percent voids, and the average individual pore diameter it is possible to calculate the pore size in a comminuted solid for any degree of compaction. When liquids (e.g., bitumen, sulfur, etc.) are stabilized by the addition of solid particles, the degree of packing of the particles and the dimensions of the films and masses of liquid separating them exert a profound influence on the consistency of the mixture. Thus, a knowledge of the average pore diameter of a powder as present in a solid‐liquid system is of practical value. The influence of average particle size on average pore diameter was studied and data are presented for silica and slate powders.
7(1936); http://dx.doi.org/10.1063/1.1745338View Description Hide Description
The equilibrium diagram of the copper:copper oxide: oxygen system controls the conditions of formation of the cuprous oxide rectifier. The interface between the cuprous oxide and the copper from which it is formed can be studied with polarized light. Intimate contact exists for more than half the total area. The technique of preparing the rectifier has a marked influence on its characteristics. By using a method of measuring the resistancecharacteristic which did not cause an error due to current heating at the interface, unusual results were obtained from specimens made under various conditions. Measurement of the thermal conductance of the rectifier disclosed a new physical phenomenon, asymmetrical thermal conductance. This asymmetry is in the direction that would be expected from the electron theory of heat conduction.
The Electrical Conductivity of Glass Part III. Current‐Voltage Relationships with Highly Resistant Layers7(1936); http://dx.doi.org/10.1063/1.1745340View Description Hide Description
Some effects upon current‐voltage and temperature relationships as caused by the formation of ``impregnated'' layers in the vicinity of the electrodes are described. For ``unimpregnated'' samples, Ohm's law appeared to be valid. Upon ``impregnation'' various current‐voltage relationships from I=AVN to that of Poole were observed, the nature of the function apparently depending upon the characteristics of the layers produced. The Rasch and Hinrichson equation was found valid for fresh samples over the range of temperatures used, but the presence of these layers caused distinct changes in the characteristics of this relationship. The possible importance of such layers upon the electrical properties of glass and other insulating materials at the higher fields and temperatures and their possible effect in causing some of the apparent discrepancies in existing data is pointed out. The importance of much further detailed study of their properties is suggested.
7(1936); http://dx.doi.org/10.1063/1.1745341View Description Hide Description
The surface tensions of a number of different glasses have been determined by a new method. The method is termed ``The Bulb Method'' and is similar to the soap bubble experiment in which the excess of pressure within the bubble can be balanced against a small head of liquid in a manometer. The weight of the glass bulb is taken into consideration. The method is applicable to a temperature range of approximately 200°C above the annealing point of the glass. The variation of surface tension with change in temperature over the upper range of temperature investigated is found to be of the order of 0.04 dyne per cm per degree C. The magnitude of the surface tension for this range varies from 230 to 360 dynes per cm depending upon the kind of glass. A survey of previous results on surface tension discloses values of widely different magnitudes. One group of experimenters has obtained values of the order of 150 dynes per cm and another group, values of approximately 400 dynes per cm. The results obtained by the bulb method fall approximately midway between the values obtained by previous experimenters.
7(1936); http://dx.doi.org/10.1063/1.1745342View Description Hide Description
The deflection of a strip of plywood is calculated for the case in which the load is concentrated along a line through the center of the strip and perpendicular to its edges. This type of loading is commonly used in tests to determine the effective modulus of elasticity in bending. Use is made of the differential equation for a flat plate of plywood. Explicit expressions in terms of the elastic constants of the component plies are given for the coefficients that occur in this equation. For the smaller span‐depth ratios the flat plate theory does not lead to exact results. A method is given for calculating the appropriate correction to the results obtained on the basis of this theory.