ELECTRIC RAILWAYS 497 ELECTRO-CHEMISTRV end of the trolley pole on the car effects the necessary contact, and transmits the current down the pole to the motor un- derneath the car. The current then strikes the track and thence returns to the power station. The conduit method is employed in crowded cities, where overhead wires would constitute a dan- ger to traffic. Trenches are dug along the streets, as was done with the old cable car system, and steel braces, or girders, shaped somewhat like horse- shoes, are set down into the trench every few feet. The sides and top are then covered in with concrete, a slot being left open along the top. Along the bot- tom of the trench, under the slot, runs the charged rail. A steel pole, with what is called the rubbing block at the end, runs along the slot and maintains contact with the charged rail. By this system the danger to traflfic is eliminated. New York City and Washington, D. C, are the two chief cities in which the con- duit system is employed. In many cities the old cable car underground trenches, or conduits, are now used in this way. The third-rail system is employed on all elevated railways and subways, where the exposed rail does not endanger the lives of the people. Wherever it is em- ployed the tracks must be carefully guarded against intrusion by the general public, as contact with the third rail is immediately fatal. The third rail runs along a track, beside one of the regular tracks. A shoe, or flat piece of steel, projected from the locomotive, and fur- nishing contact for the motor, runs smoothly along the track. This makes possible the transmission of a much stronger current than could be attain- able by a revolving wheel, such as the wheel at the end of the trolley pole. On May 31, 1919, it was reported that the vast extension of the electric rail- way systems of the United States repre- sented an investment of six billion dol- lars. Exclusive of main trunk lines, there were, in 1920, approximately 50,000 miles of trolley car track in operation in the United States. There are experts who believe that this development has now reached its apex, or has even passed it within the past few years, during the war, for it is a fact that during the recent increase in expense of operation, due to the higher cost of metals and coal, many hundreds of miles of electric railway track in the country have been abandoned, in many cases pei-manently. In a majority of the cities fares have had to be raised to meet the increased cost of operation. Here, and even in cities where fares have not been I'aised, the gasoline-driven car is now appearing as a keen competitor of the electric rail- way. The so-called "jitneys," now a familiar feature of every city street, are cutting deeply into the revenues of the electric railway companies, and that at a point where they are most vulnerable — where the short-haul traffic is thickest. Bus lines require no expensive capitali- zation; they may, moreover, adapt themselves quickly to sudden and chang- ing needs and they operate with more speed and despatch. Whether they shall, in the near future, check the extension of electric railway systems in the cities and surburban districts rests, probably, on the problem of a cheaper gasoline supply. In 1920 there were 8,300 miles of heavy trunk lines operating under elec- tric motive power. On these tracks were employed four hundred electric lo- comotives of twenty different types, the most powerful of which were capable of hauling trains of 1,200 tons along level tracks at the rate of sixty miles an hour. ELECTRIC TELEGRAPH. See TEL- EGRAPH. ELECTRO-CHEMISTRY, that branch of the science in which chemical reactions are brought about by the agency of an electric current. The fact that common salt can be split up into its elements, sodium and chlorine, by passing an elec- tric current through its solution, was discovered in the early years of elec- trical research, and during the last cen- tury the decomposition by electricity of all solutions of salts, acids and bases, and the laws under which that decom- position takes place, have been very thoroughly investigated. It has been discovered that when a solution is elec- trolyzed, it acts as a conductor, at the same time decomposing in such a man- ner that the metallic radicle is produced at the negative pole and the acid or hy- droxyl radicle at the positive pole. For instance, when an electric current is passed through a solution of common salt, sodium is produced at the kathode and chlorine at the anode. The amount of chemical decomposition brought about is directly proportional to the amount of current passing through the solution. When this method of manufacture is employed on a commei'cial scale, there- fore, it is customary to use a high am- perage (or current) and a low voltage (or electromotive force). To obtain these conditions the resistance of the cell must obviously be kept as low as possible, and it has been found that this diminishes with rise in temperature and with increase in strength of the solution. The cell is therefore filled with a hot, concentrated solution and for a similar reason the electrodes are placed as close
