Volume 13, Issue 2, 01 February 1942
Index of content:
13(1942); http://dx.doi.org/10.1063/1.1714843View Description Hide Description
13(1942); http://dx.doi.org/10.1063/1.1714844View Description Hide Description
COLLOIDAL particles present in solutions and suspensions increase the effective viscosity of the solvent. Einstein has presented the theory of this effect valid for spherical particles, and given an equation, deviation between which and experiments being due to either solvation or electric charge of the particles. Elongated particles require a further modification of the formula. The theory is being successfully applied to the study of synthetic fiber molecules, and valuable information as to the shape of the latter can be derived by viscometric measurements on colloidalsolutions of such polymers.
13(1942); http://dx.doi.org/10.1063/1.1714834View Description Hide Description
Measurements of the magnetic moment of sediments of ferromagnetic particles deposited in a magnetic field show that the particles are magnetically anisotropic. The dependence of this anisotropy on the magnetic field is investigated for sediments prepared under different conditions, and its probable origin discussed.
13(1942); http://dx.doi.org/10.1063/1.1714835View Description Hide Description
Two methods of indexing powder diffraction patterns of isomorphous substances are presented: the first method depends on matching the log d values of two or more isomorphs (d being the interplanar spacing of a given reflection); the second method relates the spacing shifts Δd/d of two isomorphs to the symmetry of the particular crystal system. These methods are made practical by the publication of tabulated powder diffraction data.
13(1942); http://dx.doi.org/10.1063/1.1714836View Description Hide Description
From photographs, and from the marking on the electrodes, Slepian and Haverstick found that short duration arcs of 25 amperes in gases at a pressure of a few centimeters had apparent current densities at the cathode of less than 100 amperes per cm2. This is in sharp contradiction to the density of several thousand amperes per cm2 which seems to be required by generally accepted theories of the cold cathode arc. Similar results have been found up to currents of 5000 amperes, burning for 1/120 sec. with electrodes of various metals in air at less than 10‐cm pressure. Apparent cathodecurrent densities calculated from the observed marking on the electrodes were less than 1000 amperes per cm2. The markings on the electrodes were apparently produced by oxidation only, the energy density developed at the electrodes being insufficient to bring the electrodesurface to the melting point in the 1/120 second duration of the arc. The circuit interrupting capacity of these short low current densityarcs are found to be not less than that of short arcs at atmospheric pressure.
13(1942); http://dx.doi.org/10.1063/1.1714837View Description Hide Description
13(1942); http://dx.doi.org/10.1063/1.1714838View Description Hide Description
An operational method of determining the free and forced vibrations of non‐linear dynamical systems is presented. The method is an operational adaptation of the one developed by Lindsted and Liapounoff. The advantage of the operational procedure is that by using a table of operational equivalents, one may write the various successive approximations almost at a glance. The procedure is illustrated by applications to non‐linear problems in mechanics and electricity.
13(1942); http://dx.doi.org/10.1063/1.1714839View Description Hide Description
The problem of correcting calorimetric data for thermal leakage has been discussed by King and Grover in a recent paper in this Journal. From their analysis of the problem these authors have concluded that large errors are involved in the usual methods of correcting the data of bomb‐calorimetric measurements, and of experiments by the method of mixtures. In the present note it is shown, in agreement with W. P. White's treatment of calorimetric lag, that in the case of bomb‐calorimetric measurements the errors in question are practically completely eliminated by calibrating the calorimeter experimentally. Since experimental calibration of the calorimeter is the usual practice in modern bomb‐calorimetric measurements, the results of such measurements are not affected by the errors discussed by King and Grover. In the case of measurements by the method of mixtures these errors can be avoided by so conducting the experiment that the final temperature of the calorimeter will be very near the convergence temperature.