PRACTICAL USES OF ELECTRICITY
Various effects of the current of electrons have been hinted at above. Considered in detail, the possible ways in which these currents may be utilized are multifarious. Yet, they may be all roughly classified into three divisions as follows:
First, cases in which the current of electricity is used to transmit energy from one place to another, and reproduce it in the form of molar motion. The dynamo, in its endless applications, illustrates one phase of such transportation of energy; and the call-bell, the telegraph, and the telephone represent another phase. In one case a relatively large quantity of electricity is necessary, in the other case a small quantity; but the principle involved—that of electric and magnetic induction—is the same in each.
The second method is that in which the current, generated by either a dynamo or a battery of voltaic cells, is made to encounter a relatively resistant medium in the course of its flow along the conducting circuit. Such resistance leads to the production of active vibrations among the particles of the resisting medium, producing the phenomena of heat and, if the activity is sufficient, the phenomena of light also. It will thus appear that in this class of cases, as in the other, there is an actual re-transformation of electrical energy into the energy of motion, only in this case the motion is that of molecules and not of larger bodies. The principle is utilized in the electrical heater, with which our electric street-cars are commonly provided, and which is making its way in the household for purposes of general heating and of cooking. It is utilized also in various factories, where the very high degree of heat attainable with the electrical furnace is employed to produce chemical dissociation and facilitate chemical combinations. By this means, for example, a compound of carbon and silicon, which is said to be the hardest known substance, except the diamond, is produced in commercial quantities. A familiar household illustration of the use of this principle is furnished by the electric light. The carbon filament in the electric bulb furnishes such resistance to the electric current that its particles are set violently aquiver. Under ordinary conditions the oxygen of the air would immediately unite with the carbon particles, volatilizing them, and thus instantly destroying the filament; but the vacuum bulb excludes the air, and thus gives relative permanency to the fragile thread.
The third class of cases in which the electric current is commercially utilized is that in which the transformations it effects are produced in solutions comparable to those of the voltaic cell, the principles involved being those pointed out in the earlier part of the present chapter. By this means a metal may be deposited in a pure state upon the surface of another metal made to act as a pole to the battery; as, for example, when forks, spoons, and other utensils of cheap metals are placed in a solution of a silver compound, and thus electroplated with silver. To produce the powerful effects necessary in the various commercial applications of this principle, the poles of the voltaic cell—which cell may become in practice a large tank—are connected with the current supplied by a dynamo. Various chemical plants at Niagara utilize portions of the currents from the great generators there in this way. Another familiar illustration of the principle is furnished by the copper electroplates from which most modern books are printed.
It appears, then, that all the multifarious uses of electricity in modern life are reducible to a few simple principles of action, just as electricity itself is reduced, according to the analysis of the modern physicist, to the activities of the elementary electron. There is nothing anomalous in this, however, for in the last analysis the mechanical principles involved in doing all the world's work are few and relatively simple, however ingenious and relatively complex may be the appliances through which these principles are made available.