The vapour pressure of lead.—I

The accurate determination of the vapour pressure of an element enables many of the other properties to be found, such as the chemical constant, the latent heat of vaporisation, and the change of specific heat with temperature. Unfortunately, the degree of accuracy required for this purpose is very considerable, and only in the case of mercury is the vapour pressure known with sufficient accuracy to determine the chemical constant within 2 per cent. The vapour pressures of zinc and cadmium have previously been determined by the writer, using a method depending on Knudsen's work on the effusion of gases at low pressure. The present paper described an extension of this method to the determination of the vapour pressure of molten lead, and an attempt to improve the accuracy.