The Moving Picture World (July 1907)

276 THE MOVING PICTURE WORLD. men hold the pirate up to the scorn and contumely of his fellows, so that others may not be duped by his illegal practices. Electricity for the Operator By H. Meredith.Jones, M. E., C. E. '"V , Continued from Page 260 CHAPTER 3. > u Wires, Conductors and Cables. The construction of wires, conductors and cables will now be described, with a brief description of their manu- facture, so that the operator will have a knowledge which will facilitate him very much in the handling of wires in regular practice. The various instruments, switches, cut-outs, etc., that are used will be thoroughly described, including panel and switchboard construction; also the various mould- ings, casings and conduits used in regular practice will be shown and described. The metal in common use to-day in the manufacture of electric wires, conductors and cables is copper, on ac- count of its high conductivity, that is its power to carry an electric current without a great loss through the re- sistance of the metal. All metals have the power to resist the passage of an electric current through them, and the following table shows the comparative powers of resist- ance of various metals: Specific Resistance in C. G. S. : Units at o° C. Silver annealed 15 21 Silver hard drawn 1652 Copper annealed 1615 Copper hard drawn : 1642 Gold.hard drawn 2154 Zinc 5690 Platinum annealed 9*58 Iron annealed ,• , '.-. 9827 Nickel 12600 Tin 13360 Lead 19847 Mercury 96146. Alloys : German silver 21170 Platinoid • 34000 You will notice in this table that silver is the best con- ductor of electricity, but on account of its high cost is not practicable for every day use in the manufacture of elec- tric conductors. Therefore, copper being next in good conducting power and of comparatively moderate cost, also combining good jointing qualities, with flexibility, has become the universal metal for conductors. You will notice that lead has a high resisting power combined with a low melting point, therefore is very valuable for fuses of afl kinds, although in many cases the alloys of lead are used. Iron, on account of its high resisting power, is used-in the manufacture of rheostats or resistance coils; sometimes platinum is used, but only in laboratory work, and then only on account of its non-corrosive qualities, as it makes a more reliable metal for making a standard resistance coil for testing purposes. In the more com- mon forms of testing sets of resistance coils, the cheaper alloys of German silver and platinoid are used. We will turn for a few moments to the study of manufacture of the metallic copper into wires, com or cables. The metallic copper arrives from the smelters at mill in the shape of ingots, which are square lumps pure copper. Copper, by the way, must be over 98 pure to be of use for this purpose, which means that every hundred pounds of the ingot there must be at 1 ninety-eight pounds of copper, the rest other metals, impurities, although there are manufacturers using' per much purer than ninety-eight, even as pure as 99.1 of pure copper. Copper of this character is generally by means of the electrolytic process, that is the copper deposited in an electric bath just like plating is done, copper having first been treated and dissolved by a and made into a,solution after having most of the i purities dissolved out; the copper got in this way is ed in the mill the same way as the ingot, by first being nealed, then rolled and re-annealed, rolled again, ; so on annealing and rolling until it is reduced down i a round rod of the required size. Remember, in worl all copper it must be annealed regularly and const; to make it work smoothly and evenly without crai or breaking. It is then drawn by machinery or through dies (plates with round holes in them) u after having passed through one die after another, a trifle smaller than the last one, it arrives at its pri size. The very finest wires are drawn through diarro dies made of diamonds generally of the discolored black variety set in plates. Of course, through all t! drawing down the wire must be kept constantly anm to prevent its breaking. The wire is then ready for covering and braiding machines to manufacture it into finished conductor. The wire then passes into machines which cover with cotton, silk, rubber, gutta-percha, lead and od materials. Sometimes there are more than one wire a conductor; in flexible conductors as many as a hundr or more are twisted together, but they are extremely fis The commonest wire is that known as' the D. C (double cotton covered) wire, which has cotton lapp around it first in one direction and then in the other ( rection; this is largely used for dynamos and motors winding the fields and armatures* although single cotfa covered wire has been used but very seldom. This sac D. C. C. wire is used for telephones and other work the same class where small currents are used and of 1 pressure, but it is then dipped in paraffine wax and oft colored with various colors to denote different wires fro one another in laying and tracing your work. I may here state that all wires are covered by the ous materials used so as to prevent any loss of current far as it is possible by using materials to cover the r of a high non-conductivity, that is the power to resist passage'of electricity such as cotton, silk, rubber, Then again cables are armored by means of lead cot ing or having steel or iron galvanized wire woven area them to protect them from injury to their covering. The many other kinds of conductors are vanoa treated, covered and woven together to suit their vane needs; you can learn best their construction py «g small pieces of conductor apart and closely i" 5 !** their construction. It is very important that the ope tor should make himself thoroughly familiar «y entire construction of conductors from start to ^ be able to judge the kind to use, how to handle it, jom and install it, V (To be continued.) \