The Freezing Point of Silver

THE subject of high temperature thermometry has recently attracted considerable attention, and on account of the ease with which silver can be obtained in a pure state, coupled with its great thermal conductivity, the freezing point of this metal has been suggested as a standard temperature. We therefore wish to call attention to an error into which we believe M. le Chatelier has fallen with regard to this constant. In the Zeitschrift für Physikalische Chemie, Band viii. p. 186, he says that the melting point of silver can be lowered by as much as 30° through the absorption of hydrogen; again, in the Comptes rendus for August 12, 1895, he states that the melting point of this metal is lowered by a reducing atmosphere. He therefore recommends that when the melting point of silver is used as a fixed point in calibrating pyrometers, the experiment should be performed in an oxidising atmosphere. This conclusion is contradicted by Prof. Calendar's experiments and by our own, for in the Phil. Mag., vol. xxxiii. p. 220, Callendar shows that the freezing point of silver is lowered and rendered irregular by an oxidising atmosphere; and our own results confirm this conclusion. But serious doubt having been raised on this point by so high an authority as M. le Chatelier, we have thought it right to make further experiments.