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Sir William Crookes (17/6/1832 - 4/4/1919) was a chemist and physicist who studied at the Royal College of Chemistyy in London. He invented the Crookes Tube (known as a cold cathode tube) in 1875 after its development from Geissler tubes. The Crookes tube consists of a partly evacuated glass bulb, usually cone shaped,and mounted horizontally on a wood stand. Two electrodes, a cathode and an anode are in the bulb at either end. Under high voltage, usually from a Ruhmkorff coil, cathode rays are projected in straight lines from the cathode.These rays, or electrons, are generated by the ionization of the residual gases by the high DC voltage. A chain reaction occurs with these and as the rays approach the anode they multiply. This causes the stream of electrons to hit the anode and surrounding glass of the end of the bulb and to glow, usually a yellow green. It was found that by painting th inside back wall of the tube with a phosphor, like zinc sulfide, the glow would be more visible. In some tubes the screen, while it was square, had a Maltese cross painted on the front with phosphorised paint.
Crookes discovered that if he placed an external magnet below the tube, he could cause the electron stream to dip down. Conversely if the magnet was placed above the stream, they would bend upwards. Crookes tubes were unreliable and tempremental and over time the glass absorbed some of the internal gases causing falling pressure in the residual gases.
Crookes tubes were widely used in scientiic laboratories for the study of their physical properties. Manufacture of these continued for several years and it is understood that they were being made in Japan just before World War Two.
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