Phenomena occuring in the melting of metals

The problem of the melting and solidification of pure substances has, in the last few years, been given a considerable amount of attention, owing to the importance of the study of the physical properties of single crystals. Experimentally, great advances have been made in the development of methods of growth of single crystals and in our knowledge of their physical properties, and this work has yielded a considerable amount of information about the nature of the solid ↔ liquid transition. For metals, at least, there is ample evidence to show that this transition is not always a simple one occurring at a sharply defined temperature. In the solid state, the metal can show a gradual change of some of its properties as the temperature is raised towards its melting point where, without discontinuity, it acquires the characteristics of the molten metal. For example, Roberts, and Goetz and Hergenrother have shown that the bulk linear coefficient of expansion of bismuth begins to decrease anomalously 20°-30°C. below the melting point. Carpenter and Harle have found that in this same region the specific heat of bismuth increases anomalously. These results suggest that as bismuth is heated some fundamental characteristic of the solid state is disappearing, and latent heat of melting is absorbed long before the actual melting point is reached. Further, after the conventional melting point had been reached, Carpenter and Harle found that with further increase of temperature the specific heat decreased in contradiction to the normal behaviour of molten metals, suggesting that the process of melting did not finish at the melting point.