Volume 5, Issue 12, 01 December 1934
Index of content:
5(1934); http://dx.doi.org/10.1063/1.1745221View Description Hide Description
An effort is made to distinguish more clearly between two types of phenomena which may occur in some glasses: (1) a ``reversible absorption'' current due to the formation of a high counter electromotive force, and (2) an ``irreversible absorption'' current due to the formation of a highly resistant layer in the glass. Characteristic curves showing one type of the latter which may occur under certain conditions are given. Although many observers seem to have observed both phenomena previously, considerable confusion still seems to exist in distinguishing between them. Combinations of both phenomena may be one possible cause of some of the large discrepancies in current‐time behaviors reported. A study of the relatively small, slowly decreasing residual electromotive force observed upon discharging the sample shows a linear increase of this electromotive force with increase in temperature for temperatures as high as 150°C.
The Electrical Conductivity of Glass Part II. Current Increase Phenomena with Highly Resistant Layers5(1934); http://dx.doi.org/10.1063/1.1745222View Description Hide Description
With the production of certain types of highly resistant layers in some glasses, increases of current with time are observed, similar to those reported qualitatively by several earlier investigators. The nature of these current increases have been studied quantitatively and found to follow, for the cases here studied, the relationship, log (Im —It ) =log a 1—b 1 t, where Im is the maximum value of the current,It is the current at any time t after application of the field, and a 1 and b 1 are constants. The time T for the current to reach its maximum value seems related to the applied voltage by the equation T=K 1/V—K 2. The values of the constants K 1 and K 2 seem to decrease with increase in temperature. The time for the current to reach its maximum value decreases rapidly with increase in glass temperature. The possible importance of the phenomena observed in an explanation of the processes involved in the conductivity of glass is suggested, and the need for further investigation is emphasized. No theoretical explanation is given because of the apparent necessity for further investigations.
5(1934); http://dx.doi.org/10.1063/1.1745223View Description Hide Description
In continuation of a previous investigation, the mechanism of division of small liquid droplets, which are the seats of physico‐chemical reactions, is being studied now not from thermodynamical, but from the kinetic point of view. Thermodynamical considerations give us conditions under which the whole drop is less stable, than its two halves. It does not say however anything about the degree of stability. The present investigation makes this next step, and shows under what conditions a drop becomes so unstable, that an infinitesimal deformation will lead to a division. The critical sizes calculated here are close to those calculated by thermodynamical method. The importance of ``release phenomena'' and ``valve action'' in the cases considered is pointed out.
5(1934); http://dx.doi.org/10.1063/1.1745224View Description Hide Description
The effect of electrode surfacing on arc stability is studied for arcs between copper and silverelectrodes in air at atmospheric pressure. For the copper arc it is shown that the random fluctuations in arc voltage and light intensity may be reduced to a very small value by giving the anodesurface a high polish. Observations of the spectrum and volt‐ampere characteristic are described. For the silver arc partial stability of arc voltage and light is obtained by electrodepolishing.
5(1934); http://dx.doi.org/10.1063/1.1745225View Description Hide Description
The problems of sealing are adhesion and strain. The simplest, but perhaps not the only means of adhesion is a firm layer of metal oxide. Strains can be avoided if, and only if the thermal expansions of metal and glass are the same. This postulate is thoroughly tested. Equations are derived for the stresses in cylindrical seals, in terms of the difference in expansion of metal and glass, and the stresses thus calculated are compared with those observed photoelastically in carefully annealed test seals. Such tests are carried out on all the important sealing materials. These tests include accurate contraction coefficient measurements of glass and metals, (Fig. 8); graphical exhibition of axial stresses by photographs through crossed Nicols and a quartz wedge, (Figs. 9 and 10); and numerical evaluation of all the stresses, both theoretical and experimental, (Table VII). Two new sealing alloys are described: fernichrome (Fe 37 percent, Ni 30 percent, Co 25 percent, Cr 8 percent) which matches standard leadglass; and fernico (Fe 54 percent, Ni 28 percent, Co 18 percent) which matches Corning glasses G‐71 and G‐705 A O. The unique feature of these alloys is that their expansion characteristics are curved in such a manner that they match those of the glasses mentioned with considerable fidelity. The seals made with these combinations are found to be practically free from strain.
5(1934); http://dx.doi.org/10.1063/1.1745226View Description Hide Description
Equations are derived for the thermal stresses in long sealed cylinders due to different coefficients of expansion, on the basis that the material of the cylinder is elastic. The optical retardation due to this stress distribution is computed for a ray traveling normal to the axis, and is found to depend upon the axial stress only. The modification in the stress distribution is then investigated for the case when plastic or viscous flow takes place during annealing.
5(1934); http://dx.doi.org/10.1063/1.1745227View Description Hide Description
The previous x‐ray work on fatigue in metals is reviewed. Such work has been confined to copper,silver and steel. The present note reports on the results of an investigation of service fatigue fractures in high voltage transmission cables made of commercially pure aluminum. The crystals composing the shallow surface layer of the fractures were found to have recovered sufficiently from the microscopic distorsion due to cold drawing that individual monochromatic diffraction spots could be identified. Two possible contributing causes are suggested to explain this crystalline recovery.