Concentric Cylindrical Electrodes Research Articles

A Versatile Oil-Testing Cell of Novel Design

An inexpensive oil-testing cell for use in routine determinations of the electrical properties of insulating oils, liquid dielectrics, plasticizers, etc., is described. The cell consists of two concentric cylindrical electrodes designed to fit snugly inside a standard-sized test tube. The electrodes are insulated from each other by a standard type ceramic stand-off insulator fitted with banana plugs. The cell is assembled by plugging in the inner electrode. Satisfactory electrical measurements with cells of this type have been made over wide temperature and frequency ranges.

Societies and Academies

Dublin Royal Irish Academy, March 16. J. J. DOWLING and T. G. BULLEN: Precision measurements with a radial deflection oscillograph. An extra pair of concentric cylindrical electrodes are fitted between the XY deflector plates and the screen of a gas focused cathode ray oscillograph. Employing a double frequency circular time-base locked to the signal frequency a so-called Radioid curve (resembling a Limacon) is obtained, and the position of the node around the time base circle serves to measure phase or frequency differences in high-frequency circuits. Another application is as a ‘time-comparator’, and comparisons of the periods of a pair of two-seconds pendulums to within five parts in a million are easily obtained while the pendulums are executing twenty swings. An improved design of tube is described and further work promised.

Ionization in Reacting Gases

Ionization associated with the oxidation of ethyl alcohol in contact with electrodes.—Previous work had shown that various gaseous reactions are accompanied by ionization. The oxidation of ethyl alcohol was chosen because of its simplicity. Nitrogen carrying 3 cc of alcohol per minute and also dry oxygen at the rate of 200 cc per minute were sent into a reaction chamber between two concentric cylindrical electrodes. The currents were measured with an electrometer provided with a radioactive shunt. Although potential differences up to 1800 volts (2400 volts per cm) were used, the current was always proportional to the voltage, being evidently far from saturation. The variation with temperature, 150° to 330°C, was exponential, increasing in the case of gold electrodes 20 fold from 200° to 320°C. With Al electrodes the current was only 1/25th as great, and chemical analysis of the products of reaction indicated that the oxidation was also greatly reduced. The results show that the reaction occurs at the electrode surfaces, the rate depending on the material and on the temperature, and that both positive and negative ions are produced. The absence of saturation is probably due to the ions being formed so close to the surface. Copper electrodes gave anomalous results, a negative Cu electrode behaving like Au while a positive Cu electrode behaved like Al. A soft glass electrode behaved like gold, except that the logarithmic increase with temperature was twice as fast for the negative as for the positive electrode.

Relative Production of Negative and Positive Ions by Electron Collisions

In the tube used, either positive or negative ions produced by an axial beam of electrons accelerated from a filament by a voltage $V$, were collected on a concentric cylindrical electrode $D$ by maintaining it at a potential slightly lower or higher than that of the beam, the primary electrons being prevented from reaching $D$ by means of a solenoidal magnetic field of 100 gauss parallel to the axis. While saturation was not always reached, the relative values of the positive and negative ion currents are significant. Contrary to the ordinary theory, the polar compounds mercuric chloride and hydrogen chloride gave results quite similar to those for the elements mercury and iodine. With electron currents of the order of ${10}^{\ensuremath{-}6}$ amp. and pressures of about.001 mm, the negative ion current is in all cases small compared with the positive ion current above the ionization potential. With larger currents the negative current increases sharply at the ionization potential and the ratio to positive current is greater. For vapors other than mercury there are some negative ions produced at all voltages, the negative ion currents each having a maximum at zero and increasing again at certain critical potentials, the voltages being 4 for Hg${\mathrm{Cl}}_{2}$, 6.5 for HCl and 2.4, 4.6, 8.4 for ${\mathrm{I}}_{2}$. As far as is known, these potentials are equal to potentials of inelastic collision. These experiments give no support to the theory that electron collisions dissociate polar molecules into positive and negative ions. In agreement with the results of the magnetic analysis of positive ions, they indicate that the primary effect of an electron impact is the production of a positive molecule ion. The negative ion curves obtained can be explained by the hypothesis that only slow moving electrons attach themselves to molecules to form ions, but the absence of low voltage negative ions in the case of Hg is not understood.

Ionization in Reacting Gases

Ionization associated with the oxidation of ethyl alcohol in contact with electrodes.---Previous work had shown that various gaseous reactions are accompanied by ionization. The oxidation of ethyl alcohol was chosen because of its simplicity. Nitrogen carrying 3 cc of alcohol per minute and also dry oxygen at the rate of 200 cc per minute were sent into a reaction chamber between two concentric cylindrical electrodes. The currents were measured with an electrometer provided with a radioactive shunt. Although potential differences up to 1800 volts (2400 volts per cm) were used, the current was always proportional to the voltage, being evidently far from saturation. The variation with temperature, 150\ifmmode^\circ\else\textdegree\fi{} to 330\ifmmode^\circ\else\textdegree\fi{}C, was exponential, increasing in the case of gold electrodes 20 fold from 200\ifmmode^\circ\else\textdegree\fi{} to 320\ifmmode^\circ\else\textdegree\fi{}C. With Al electrodes the current was only 1/25th as great, and chemical analysis of the products of reaction indicated that the oxidation was also greatly reduced. The results show that the reaction occurs at the electrode surfaces, the rate depending on the material and on the temperature, and that both positive and negative ions are produced. The absence of saturation is probably due to the ions being formed so close to the surface. Copper electrodes gave anomalous results, a negative Cu electrode behaving like Au while a positive Cu electrode behaved like Al. A soft glass electrode behaved like gold, except that the logarithmic increase with temperature was twice as fast for the negative as for the positive electrode.