I. The ionisation produced by hot platinum in different gases

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Abstract
The principal objects of this investigation have been to examine the part played by the surrounding gas in the production of ions by hot metals and to discover, if possible, the mechanism by which the positive ions originate. In what follows, previous work on ionisation by hot metals will not be described, except in so far as it bears directly on the questions investigated, since the historical part of the subject has been fully treated in previous papers by the writer, and others. The present communication deals chiefly with the emission of positive ions from hot platinum, as earlier work has yielded much more information concerning the negative ionisation. In 1901 the writer showed that a great number of facts in connection with the negative ionisation from hot metals could be explained by supposing that the electrons, of which the ions consist, were produced in the metal itself, from which they escaped by virtue of their kinetic energy. This theory makes the negative ionisation a function only of the metal surface and its temperature, and therefore independent of the nature and pressure of the surrounding gas, except in so far as this may have the effect of modifying the nature of the metallic surface. H. A. Wilson has confirmed this part of the theory by showing that the negative leak, except when ionisation by collision occurs, has the same value in air, nitrogen, and water vapour over a wide range of pressures. Wilson also showed, however, that hydrogen greatly modifies the negative leak. The experiments in the present paper seem to show that the effect of hydrogen is due to some change it produces in the platinum surface; its abnormal behaviour is probably bound up with its electropositive character.

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