6o 



NATURE 



[September 9, 1920 



Scientific Studies of Non-ferrous Alloys.* 

 By C. T. Hevcock, M.A., F.R.S. 



T^HE production of metals and their alloys undoubt- 

 •*• ediy constitutes the oldest of those chemical arts 

 which ultimately expanded into the modern science of 

 chemistry, with all its overwhelming mass of experi- 

 mental detail and its intricate interweaving of 

 theoretical interpretation of the observed facts, lubal- 

 cain lived during the lifetime of our common ancestor, 

 and was '"an instructor of every artificer in brass and 

 iron"; and although it may be doubted whether the 

 philologists have yet satisfactorily determined whether 

 Tubal-cain was really acquainted with the manufac- 

 ture of such a complex metallic alloy as brass, it is 

 certain that chemical science had its beginnings in 

 the reduction of metals from their ores and in the 

 preparation of useful alloys from those metals. In 

 fact, metallic alloys, or mixtures of metals, have been 

 used by mankind for the manufacture of implements 

 of war and of agriculture, of coinage, statuary, 

 cooking vessels, and the like from the very earliest 

 times. 



In the course of past ages an immense amount of 

 practical information has been accumulated concern- 

 ing methods of reducing metals, or mixtures of metals, 

 frgm their ores, and by subsequent treatment, usually 

 by heating and cooling, of adapting the resulting 

 metallic product to the purpose for which it was 

 required. Until quite recent times, however, the 

 whole of this knowledge was entirely empirical in 

 character, because it had no foundation in general 

 theoretical principles ; it was collected in haphazard 

 fashion in accordance with that method of trial and 

 error which led our forerunners surely, but with exces- 

 sive expenditure of time ■ and effort, to valuable 

 results. 



To-day I purpose dealing chiefly with the non- 

 ferrous alloys, not because any essential difference in 

 type exists between the ferrous and non-ferrous alloys, 

 but merely because the whole field presented bv the 

 chemistry of the metals and their alloys is too vast 

 to be covered in any reasonable length of time. 



The earliest recorded scientific investigations on 

 alloys were made in 1722 by Reaumur, who employed 

 the microscope to examine the fractured surfaces of 

 white and grey cast-iron and steel. In 1808 Widman- 

 statten cut sections from meteorites, which he polished 

 and etched. The founder, however, of modern metallo- 

 graphy is undoubtedly H. C. Sorby, of Sheffield. 

 Sorby's early petrographic work on the examination of 

 thin sections of rock under the microscope led him to a 

 study of meteorites and of iron and steel, and in a 

 paper read before the British Association in 1864 he 

 describes briefly (I quote his own words) how sections 

 " of iron and steel may be prepared for the microscope 

 so as to exhibit their structure to a perfection that 

 leaves little to be desired. They show various mixtures 

 of iron, and two or three well-defined compounds of 

 iron and carbon, graphite, and slag ; these constituents, 

 being present in different proportions and arranged 

 in various manners, give- rise to a large number of 

 varieties of iron and steel, differing by well-marked 

 and very striking peculiarities of structure." The 

 methods described by Sorby for polishing and etching 

 allovs and his method of vertical illumination (after- 

 wards improved by Beck) are employed to-day by 

 all who work at this branch of metallographv. 



From i8.!;4-68 Mattheisen published in the Reports 

 of the British Association and in the Proceedings and 



* Fro"i the openinc address of the President of Section B (Chemistry) 

 delivered at the Cardiff meetitig of the British Association on Atlgust 24. 



NO. 2654, VOL. 106] 



Transactions of the Royal Society a large number of 

 papers on the electrical conductivity, tenacity, and 

 specific gravity of pure metals and alloys, he con- 

 cluded mat alloys are either mixtures of definite 

 chemical compounds with an excess of one or other 

 metal, or solutions of the definite alloy in the excess 

 of one of the metals employed, forming in their solid 

 condition what he called a solidified solution. This 

 idea of a solidified solution has developed into a most 

 fruitful theory upon which much of our modern 

 notions of alloys depends. Although, at the time, 

 the experiments on the electrical conductivity did not 

 lead to very definite conclusions, the method has since 

 been used with great success in testing for the 

 presence of minute quantities of impurities in the 

 copper used for conductors. In the Philosophical 

 Magazine for 1875 F. Guthrie, in a remarkable 

 paper quite unconnected with alloys, gave an 

 account of his experiments on salt solutions and 

 attached water. He was led to undertake this 

 work by a consideration of a paper by Dr. J. Rea, 

 the Arctic explorer, on the comparative saltness of 

 freshly formed and of older ice-floes. Guthrie showed 

 that the freezing point of solutions was continuously 

 diminished as the percentage of common salt in- 

 creased, and that this lowering increased up to 236 per 

 cent, of salt, when the solution solidified as a whole 

 at about 22° C. He further showed, and this is of 

 great importance, that the substance which first 

 separated from solutions more dilute than 23-6 per 

 cent, was pure ice. To the substance which froze 

 as a whole, giving crystals of the same composition as 

 the mother-liquor, he gave the name "cryohydrate." 



In the Philosophical Magazine for 1876 Guthrie gave 

 an account of his experiments, using solvents other 

 than water, and states that the substances which 

 separate at the lowest temperature are neither atomic 

 nor molecular; this lowest melting-point mixture of 

 two bodies he names the eutectic mixture. In the 

 same paper he details the methods of obtaining various 

 eutectic alloys of bismuth, lead, tin, and cadmium. 



We have in these papers of Guthrie's the first 

 important clue to what occurs on cooling a fused 

 mixture of metals. The researches of Sorby and 

 Guthrie, undertaken as they were for the sake of 

 investigating natuial phenomena, are a remarkable 

 example of how purely scientific experiment can lead 

 to most important practical results. It is not too 

 much to claim for these investigators the honour of 

 being the originators of all our modern ideas of metal- 

 lurgy. Although much valuable information had been 

 accumulated, no rapid advance could be made until 

 some general theory of solution had been developed. 

 In 1878 Raoult first began his work on the depression 

 of the freezing point of solvents due to the addition of 

 dissolved substances, and he continued at frequent 

 intervals to publish the results of his experiments up 

 to the time of his death in 1901. 



In a paper in the Zeit. Physikai. Chem. for 

 1888 on " Osmotic Pressure in the Analogy between 

 Solutions and Gases," van't Hoff showed that the 

 experiments of Pfeffer on osmotic pressure could te 

 explained on the theory that dissolved substances were, 

 at anv rate for dilute solutions, in a condition similar 

 to that of a gas ; that they obeyed the laws of Boyle, 

 Charles, and Avogadro; and that on this assumption 

 the depression of the freezing point of a solvent could 

 be calculated by means of a simple formula. He also 

 showed that the exceptions which occurred to Raoult's 



