Recent Advances in Metallography

DURING the last quarter-century it has gradually become apparent that the science of metallog-raphy must deal not alone with the constitu-tion and structure of metals and alloys, but with the correlation of chemical composition, constitution, thermal treatment, mechanical treatment, structure, and temperature, with their physical and mechani-cal properties. The development of technique in microscopy, etch-ing, thermal analysis, and general physical measure-ments has been no small factor in the progress of metal-lographic science. This development has been largely incident to the study of alloy systems and impurities in metals and alloys. About 270 binary, 40 ternary and 3 quarternary alloy systems have been investigated to date. Only preliminary investigations have been made on most of these systems, and much work remains to be done in this direction. In Vol. I of The Metallographist, January, 1898, we find the following definition of metallography as offered by F. Osmond: Metallography, generally, speaking, signifies the structure of metals and of their alloys. The science is not confined to the use of a single instrument, the microscope for instance, whose manipulation requires a certain training, giving rise, therefore, to a specialty and to specialists. In reality we begin by using our eyes in the examination of metals and when they show us all that they can see, we provide them with lenses of increasing magnifying power, until we are stopped, at about 2000 diam¬eters, before the mysteries of the ultra-microscopic. But the naked eye and the optical instruments are only an incomplete means of investigation; They take, so to speak, a first inventory; the indications furnished by the visible characters, form, color or luster must be controlled by chemical analysis, micro-chem¬istry and crystallography, by the determination of physical and mechanical constants, in a word, by all the available means for the differentiation and identification of bodies. In the same issue of The Metallographist, A. Sauveur epitomizes the results in the field of metallography up to that time (1898). The last decade has witnessed an activity in metallurgical researches which has probably no parallel in the history of the science, owing to the strictly scientific spirit with which they have been conducted. Scientists in all metallurgical countries have taken hold of the industrial metals, and are applying to them the scientific methods of investigation of this highly scientific age. Witness the work of Sorby, Abel, Muller, Osmond, Howe, Martens, Arnold, Wedding, Roberts-Austen, H. Le-Chatelier, Charpy, Ledebur, Behrens, De Benneville, and others. The metals and their alloys are being dissected, and the high-power objective, that wonderful instrument of modern researches, is revealing to us their intimate structure, throwing a flood of light upon their constitution, chemical and physical, the prac-tical as well as the theoretical value of which could hardly be overestimated. Their physics, hitherto much neglected, is being minutely investigated. Their thermal behavior is being ascer-tained with a precision rendered possible only by the extremely delicate pyrometer of H. LeChatelier. Their magnetic, prop-erties, their electric conductivity, their diffusion, their physical and mechanical properties in general, are being investigated with a degree of accuracy never before attained. The chemist is energetically at work, in his endeavor to establish the true chemical relation between the metals and their impurities, and successful excursions are being taken into the, domain of their proximate compositions. As Mr. Osmond has aptly said, modern science is treating the industrial metal like a living organ-ism, and we are led to study its anatomy, i.e., its physical and chemical constitution; its biology, i.e., the influence exerted upon its constitution by the various treatments, thermal and mech-anical, to which the metal is lawfully subjected; and its path-ology, -i.e., the action of impurities and, defective treatments upon its normal constituents."