The positive Ions from hot metals

Abstract

It is well known that when a metal wire or strip is heated for the first time there is a large emission of positive ions from it at a comparatively low temperature. This emission takes place even if the wire is carefully cleaned and the heating is carried out in a good vacuum. It decays to a small value under continuous heating in a vacuum, and can be revived to a varying extent by a number of different modes of treatment, such as heating in air, or in a bunsen flame, or by subjection to high pressure. Very different conclusions as to the nature of these ions have been reached by different experimenters. One view, which has, perhaps, had more advocates than any other, is that the ions consist of positively charged atoms or molecules of various gases evolved by the hot substances. For several years I have suspected that these ions would turn out to be atoms or molecules of the commoner alkali metals which are present in the heated metals as impurities. The experiments to be described were undertaken in the hope of deciding the question in a definite manner. The direct and obvious way of attacking the problem is to determine the specific charge ( e / m ) of the carriers. Since the value of the corresponding quantity for the standard chemical element in electrolysis is known, this is equivalent to measuring the electric atomic (or equivalent) weight ( m /H). I have already made experiments with a large number of metallic substances in this way, partly in collaboration with Mr. Hulbirt. The results showed that the electric atomic weight of the ions was of the order of 30 for the 14 different substances tested, but the measurements were not sufficiently exact to determine with certainty whether the ions were atoms of sodium and potassium or molecules of some of the commoner gases, such as carbon monoxide. The electric equivalent weight of CO + is 28, and is thus intermediate between Na + (23·05) and K + (39·1). There are a number of other alternative constituents which suggest themselves.