Document G5YXDdrJ1Y5Ywv1DQ4gjx5mqN

tag about it. Fig. 10. In a normal atom, negative electrical charges of electrons equal positive charges on the protons in the nucleus, so the atom is electri cally neutral. When an electron emitted from the cathode at high velocity collides with a gas atom the impact knocks one or more electrons out of the atom. Fig. U. In a gas-filled electron tube that is in operation, a tremendous number of gas atoms are being bombarded by the elec trons shot out into space by the hot cathode. As a result the number of free electrons is greatly increased in the space between cathode end anode. Atoms that lose one or more elec trons become positively charged, be cause the negative charge of their elec trons is less than the positive charge of their nucleus. These positively charged atoms are called ions and the process uf forming them is ionitation. The positive charge on the Ions neu tralizes most of the negative spacecharge effects existing in a high-vacuum tube, and permits more electrons to reach the anode. This effect, combined with a Urge Increase in free electrons, previously mentioned, results in a Urge increase in current Sow through the tube compared to a high-vacuum tube under similar conditions. In Fig. 9, the symbol for a gas-fflled tube is the same as for the high-vacuum tube In Fig. 7 except'that it contains a Urge dot This dot represents inert gas, or a drop of mercury that partly vaporises when the tube operates. AU electron tubea ore essentially rec tifiers; that is, they let current flow through them in one'direction'only. This characteristic permits using them to change alternating to direct current, which will he explained in Uter articles. A simple diode, 2-element electron tube, has no means of controlling cur rent flow through it except by external means, as explained. To moke it pos sible for electron tubes to control cur rent flow through them a third element, or grid, Is odded, Fig. 12. Such a tube Is called a triode end its grid is placed between cathode and anode as shown. In Fig. 12.the grid connects to a termi nal in the lube base. In other designs, this connection is placed in the side of the tube. Grids differ in both form and material (Fig. 25 to 29, Power, June, pp 98, 100) depending on tube design, alzo and,application. Fig. 13 shows the symbol for o gridcontrolled ' high-vacuum tube with a directly heated cathode, and Fig. 14 for ffgrid-controlled gas-fflled tube with an indirectly heated cathode. Fig. 15 (Continued on page 142) Hot and Cold Cathodes l 16 Current change mode by adjusting potenlioi on grid of vacuum tubs 17 The symbol of o high-vacuum tube with both control ond screen grid A4 .One design of cold-cothode electron^ ft I tube thot is controlled by o grid/ 111 (Ol) I*!"- tjj***b jells of the supposedly indestructible Achilles nod how finally he was slain when on arrow found its mark in his only vulnerable spot--his heel. Too often in industry today. Production's vulnerable spot is the boiler plant ... a boiler plant made unprofitable by improper water conditioning. Correct water conditioning is a matter of careful ond scientific control. W. H. & L. D. BETZ is an organisation of engineers and chemista specializing in the solution of all industrial water problems. Years of experience have made Bets water conditioning service scientifically correct.. . complete .. . economical. Our staff of engineers will welcome the opportunity of discussing your boiler water problems . . . W. U. & L. D. BETZ, Gillingham and Worth Sts., Philadelphia 24, Pa. In Canada: Bets laboratories, Limited, Montreal 1. BETZ B'bus I drA tea CONOlVlOMINO * COOIINO WATS!CON6lllOHIMO.,*'iHOUj,TRAl,WASTS TIIAlJAtMT "JI POWER July 1918 II)