Every-day Science: Volume 6. The Conquest of Nature

by Henry Smith Williams; Edward Huntington Williams

When, for example, a lump of salt is dissolved in water, the atoms of sodium and of chlorine which joined together make up the molecules of salt are held in much looser bondage than they were while the salt was in a dry or crystalline form. Could we magnify the infinitesimal particles sufficiently to make them visible we should probably see large numbers of the molecules being dissociated, the liberated atoms moving about freely for an instant and then reuniting with other atoms. Thus at any given instant our solution of salt would contain numerous free atoms of sodium and of chlorine, although we are justified in thinking of this substance as a whole as composed of sodium-chlorine molecules. It is only by thus visualizing the activity of the atoms in a solution that we are able to provide even a thinkable hypothesis as to the development of electricity in the voltaic cell.

What puts us on the track of the explanation we are seeking is the fact that the diverse atoms are known to have different electrical properties. In our voltaic cell, for example, sodium atoms would collect at one pole and chlorine atoms at the other. Humphry Davy discovered this fact in the early days of electro-chemistry, just about a century ago. He spoke of the sodium atom as electro-positive, and of the chlorine atom as electro-negative, and he attempted to explain all chemical affinity as merely due to the mutual attraction between positively and negatively electrified atoms. The modern theorist goes one step farther, and explains the negative properties of the chlorine atom by assuming the presence of one negative electron or electricity in excess of the neutralizing charge. The assumption is, that the sodium atom has lost this negative electron and thus has become positively electrified. The chlorine atom, harboring the fugitive electron, becomes negatively electrified. Hence the two atoms are attracted toward opposite poles of the cell.

This disunion of atoms, be it understood, must be supposed to take place in the case of any solution of common salt, whether it rests in an ordinary cup or forms a part of the ocean. Here we have, then, material for the generation of the electrical current, if some means could be found to induce the chlorine atom to give up the surplus electron which from time to time it carries. And this means is provided when two pieces of metal of different kinds, united with a metal conductor, are immersed in the liquid. Then it comes to pass that the electrons associated with the chlorine atoms that chance to lie in contact with one of these plates of metal, find in this metal an avenue of escape. They rush off eagerly along the metal and the connecting wire, and in so doing establish a current which acts—if we may venture a graphic analogy from an allied field of physics—as a sort of suction, attracting other chlorine atoms from the body of the liquid against the metal plate that they also may discharge their electrons. In other words, the electrical current passes through the liquid as well as through the outside wire, thus completing the circuit.

According to this theory, then, the electrical energy in evidence in the current from the voltaic cell, is drawn from a store of potential energy in the atoms of matter composing the liquid in the cell. In practice, as is well known, the liquid used is one that affects one of the metal poles more actively than the other, insuring vigorous chemical activity. But the principle of atomic and electrical dissociation just outlined is the one involved, according to theory, in every voltaic cell, whatever the particular combination of metals and liquids of which it is composed. It should be added, however, that while we are thus supplied with a thinkable explanation of the origin of this manifestation of electrical energy, no explanation is forthcoming, here any more than in the case of the dynamo, as to why the electrons rush off in a particular direction and thus establish an electrical current. Perhaps we should recall that the very existence of this current has at times been doubted. Quite recently, indeed, it has been held that the seeming current consists merely of a condition of strain or displacement of the ether. But we are here chiefly concerned with the electron theory, according to which, as we have all along noted, the seeming current is an actual current; the ether strain, if such exists, being due to the passage of the electrons.

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.