Electron History.

Progress, Volume IV, Issue 5, 1 March 1909, Page 152

Electron History.

(By Sir Oliver Lodge, in the Journal of the Society of Chemical Industry.)

The first inkling of the discovery of the atomic nature of electricity dates back to Faraday and his experiments in electrolysis. The indivisible atomic charge — the charge of a monadion — was then practically measured, at least as soon as the size of the atom was known; and an "atom of electricity" was spoken of, both by Maxwell and by Helmholtz. In amount, measurement indicates that it consists of 3.4 X 10- 10 electrostatic unit, some uncertainty affecting the second significant figure. On this basis, Dr. Johnstone Stoney gave to these unit charges their name "electron," and speculated ingeniously on some of their porperties. Then J. J Thomson found that in the rarefied air of a vacuum tube these charges were loose, flying as cathode rays; and identically the same, no matter what was the kind of residual matter in the tube. It was in this state that their mass was measured, and found to be a thousand times less than the previous material minimum — the hydrogen atom. Then Zeeman found that their orbital motion was the source of all bright line spectra — that is to say, that they emitted radiation, carving the ether into waves. The condition of electricity is due to the procession of electrons and positive charges ; and the good conducting power of metals, whether for heat or for electricity, is supposed to be due to a crowd of electrons freely permeating the interstices between the atoms, being handed on from one to another so readily that they are practically dissociated or free in vast numbers. And the long-known connection between heat conductivity and electric conductivity is found to be thus rationally and quantitatively accounted for. Furthermore, the regular gradation of electric properties exhibited by the elements in. Mendeleef 's classification can be stated electrically, in a way that certainly suggests an approximation to the truth. Bach octave has an electro-positive and an electronegative end, the most extreme members being at the ends, and an almost neutral body in the middle, of each series; and in the step from the extreme electro-positive of one octave to the extreme electro-nega-tive in the next, an intermediate halting place of a neutral and quite inert body is now known, by the discovery of the argon-krypton-xenon series. The atoms of the electro-negative set are those which can easily make room for, and have acquired, extra electrons — more than properly belong to their constitution; these are the non-metals, and are chemically active on that account. The atoms of the electro-positive variety are those which easily lose, and have lost, some of their electrons — thereby becoming good conductors by reason of the loose electrons which they have let go ; these are the metals. A strong electric attraction naturally exists between members of the electro-negative and the electro-positive group, because they are oppositely charged ; and the clinging together of these atoms, under electric attraction, constitutes chemical combination. Con-

ducting power usually disappears after combination, except the variety of it which may be brought about by the dissociation or breaking- xip of the compound molecules. The epithets positive and negative, which from the electrical point of view seem so interchanged and inconvenient, from the material point of view get right again. For the atom which is hungry for more electrons and has absorbed them is electro-negative; while the atom which has a surplus and has extruded some is electro-positive. A tetrad can be either the one or the other. In methane the carbon is presumably acting as a negatively charged body. In carbon tetraehloride the carbon is presumably acting as a positive. Chlorine seems to have much more residual affinity than hydrogen has, and accordingly the molecules tend to cling together, and the substance is a liquid instead of a gas. Once more I repeat that the term in Van der Waal's famous formula 4 or LapV lace's X, is the liquefying force, and is a measure of this outstanding affinity; it is determined by the latent heat of evaporation, or to some extent by the boiling point and the critical point.