LXXXVIII. Critical electron velocities for the production of luminosity in atmospheric neon
The London Edinburgh and Dublin Philosophical Magazine and Journal of Science
View related articles higher critical velocities being concerned with the ejection of a second electron from an alre;idy ionized atom, it seems desirable to mention briefly the preeautioas t, ken to ensure the purity of the gas used ill these experiments. The neon was purified by" Dr. Aston of Cambridge, using the elaborate fractionation apparatus which he devised for this purpose. The process of purification was accompanied by frequent determinations ot" the density of the gas, and was
... as, and was continued long beyond the stage when no alteration ot: density could be detected. In admitting th,~ gas to the ~,pparatus adequate precautions were taken to remove any i,npurities which might have found their way into the neon from the glass walls of tile vessel in whicL it wits stored, or from the walls o~' the tubes through which it passed, and, during most of' the experiments, the purr gas was slo~'ly streaming through the ionizationchamber. With these precautions tile only possil)le impurity in the gas used was helimn, and in view of the lengthy and careful treatment of Dr. Aston it is unlikely that more than a minute trace of helium was present. A spectroscopic examination of the gas showed no lines but those of the neon spectrum. Tile presence of helimn in sufficient quantity might have accounted for the detection of a critical ionization velocity at 20 volts--apprexinlately the resonance velocity for electrons in helium,--but the experiments about to be described show that this electron velocity is essential for the production of the l)rilmipal series tin~s i" tlle neon speet,'um. In view of tile results of the positive ray exi~eriments of Sir J. J. Tho_,nson'X" ,nd of the more recent experiments of Dr. Aston ]', which have shown that atmospheric neon contains two constituents of atomic weights 20'00 and 2200 and possibly a sm~,ll proportion of a third constituent ot' atomic weight 21, the detection of three critical electron velocities for ionization of the gas is of particular interest. In order to explain his results, Dr. Aston assumed that tile constituents of atmospheric neon are isotopes, an assumption which is justified by the fact that according to Moseley's theory of atomic numbers there can be no u"known element of atomic weight between 20 and 23. The existence of three isotopes would not, however, be expected to lead to three different ionization velocities, since tile atoms of isotopes have tile same nuclear charge and the same numbe," of su,'rounding electrons, which would presumably t)e dis-* J.