Intermetallic Compounds Classic Reprint

Excerpt from Intermetallic Compounds

The fact that metals are capable of forming chemical combinations among themselves has only gradually received recognition. Alloys were generally regarded as mixtures, and their variability of composition was cited during the controversy between Proust and Berthollet as to the definiteness of proportions in chemical combination. The earliest suggestions that compounds might be present in certain alloys were based on thermal observations. In the course of a series of careful determinations of the freezing-points of some fusible alloys, Rudberg observed that the thermometer generally showed two arrests during cooling, the first depending on the composition of the alloy, whilst the position of the second was constant throughout any one series. Such a constant lower freezing-point was observed in the series lead-tin, lead-bismuth, bismuth-tin, bismuth-zinc, and zinc-tin, and was attributed to the formation of a compound or "chemical alloy Formulæ were assigned to several of these supposed compounds, which are now known to be eutectic mixtures. This view long survived, and received much support from the work of Levol, who observed that liquation occurred in all alloys of silver and copper, with the exception of that containing 71.89 per cent of silver, which he therefore assumed to be a definite compound, with the formula Ag3Cu2 (using the modern atomic weights). At a much later date, Guthrie, in the course of a study of salt solutions, observed the occurrence of a constant minimum freezing-point in many series, and this he regarded as due to the chemical combination of salt and water to form a "cryohydrate," stable only at low temperatures. This erroneous view unfortunately prevailed, although the true nature of the minimum, as the point of intersection of the ice curve and the salt solubility curve, had been shown earlier by Rudorff.