Amplification of Electric Currents in the Bunsen Flame

Abstract

Modulation of Electric Currents in a Bunsen Flame; the Use of a Third Electrode.---When an electric current is sent through a Bunsen flame, entering and leaving the flame by platinum terminals, it has been found by the author that amplification effects similar to those in vacuum tubes may be secured by the use of a third electrode or grid placed near the lime-coated cathode in the flame. The potential of this grid is varied with respect to the cathode and direct current characteristic curves are given showing the current as a function of the grid potential. These curves are similar in appearance to those obtained with the audion, and may be utilized in the customary way for calculating the amplification constants. The factors influencing these amplification constants are discussed and it is found that under what are probably the most favorable conditions of the apparatus used, the voltage amplification is but little greater than unity. The power amplification is about 108 and the current amplification about 101. The theory of the action is outlined in a general way, the effectiveness of the grid being ascribed to its retarding influence on the electron emission of the cathode. A consequent change in the cathode fall of potential alters the current through the flame. The utility of the device is not comparable with that of the vacuum tube amplifiers, largely because of the difficulty of securing permanent flame conditions. The energy output of the simple device used was also necessarily small because of the high flame resistance. It could be used, however, for the detection of electric waves.