1024 



Voltaic Electricity. Section 8: Electric Conduction in Gases. 



No. 63 136 



63136. 1:4. 



63137. 1:4. 



63138. 1:4. 



Wehnelt Valve Tubes. 



s. .I. 



63.136. Small Valve Tube after Wehnelt, Figure (Drudes Ann. d. Phys. 1904, Vol. 14, 



p. 425; Ztschr. f. d. phys. u. chem. U. 18, 1905, p. 193) 1. 2. 



This tube is used more particularly for converting weak currents of high frequency into pulsating 

 direct current, and can be employed as a wave-detector (audion) for wireless telegraphy, as well as 

 for demonstrating saturation -current phenomena. It has a cylindrical metal anode, and wire-shaped 

 cathode coated with a metallic oxide. 



Metals coated with oxides behave very differently at high temperatures as regards the emission j 

 of electrons. If a discharge tube having an incandescent electrode coated with an oxide and one or 

 more metal electrodes is connected up to an A. C. circuit, the tube acts as a valve to the current, 

 allowing the current to flow in one direction only. By utilising a number of tubes both phases of the 

 A. C. can be used for conversion into pulsating D. C., or it is even possible to employ all phases of a 

 triphase current. The oxide-coated metal electrode of the valve tube is heated by means of a small 

 transformer or a few accumulators, a suitable regulating resistance being inserted until a yellow 

 glow is attained (1300 to 1400 C.). 



63.137. Large Valve Tube after Wehnelt, Figure, for transforming heavy currents, with 



base 1. 10. 



This tube has a second anode contained in a cylindrical annex, by using which a magnificent 

 stratified discharge is obtained. 



63.138. Cathode Ray Tube (Valve Tube), Figure, with base 1.10.0 



This is used for demonstrating the diffraction of the cathode rays into a circle in a homogeneous 

 magnetic field (determining the ratio of charge to mass and velocity of the cathode ray particles) and , 

 the practically parobolic curvature of the rays in the electrostatic field in this instance. 



The cathode has only a small oxide-spot from which a sharply defined cathode ray pencil issues 

 when the current passes through. The experiments in which the tube has not to act as a valve are mosi 

 conveniently carried out with a 110 120 volt D. C., in which case the incandescent oxide electrode 

 serves as a cathode. 



63.139. Liquid Resistance for putting in series with the Valve Tubes for preventing distur- 

 bance at the electrodes 



The liquid used is water, which can be rendered slightly alkaline for reducing the resistance. 



63.140. Vacuum Tube for Deflection Experiments after Braun-Wehnelt, with oxide cathode 

 (Physikal. Ztschr. 6, p. 732), Figure, with small horse-shoe magnet and stand . 



63.141. Vacuum Tube with Oxide Cathode and Phosphorescent Mineral, Figure, with base 



63,144. Thomson's Luminous Sphere for demonstrating the luminous zones in vacuum bulbs 



inside a discharge circuit (Ztschr. f. d. phys. u. chem. U. 5, 1892, p. 207) 



63,145. - - i d c m, larger, specially adapted for the experiment for demonstrating the elec- 

 tmdcless circular current in gases 



o. i.o 



2. 0. l> 

 1. 10. It 



0. 3. 



o. 14. o; 



rl. 5402. 3588, 3509. 



