INTRODUCTION TO THE STUDY

OF

METALLURGY.

CHAPTER I.

THE RELATION OF METALLURGY TO CHEMISTRY. THE distinguished metallurgist who may be said to have created the English literature of the subject concluded the introductory lecture he delivered at the Royal School of Mines, by pointing out to the students who were then beginning their course, that "in proportion to the success with which the metallurgic art is practised in this country, will the interests of the whole population, directly or indirectly, in no inconsiderable degree, be promoted." During the period of more than forty years since Dr. Percy began to teach, the conditions under which metallurgy is practised have changed considerably; for the field of knowledge has so widely extended, the scale on which operations are conducted is now so great, and the mechanical appliances they involve are so varied and complicated, that while the interest of the subject is deepened, its difficulty is gravely increased. Metallurgy involves not only a knowledge of "the art of extracting metals from their ores," but also of the means of "adapting them for use," which is effected by complicated mechanical operations, and, strange as it may seem, by varying the degree of purity, often to a very slight extent. It will thus be evident that the student must possess adequate knowledge of Inorganic Chemistry, Mechanics, and Physics. Besides this, he must acquire aptitude for dealing with economic details.

* Records of the School of Mines, vol. i. pt. i. (1852), p. 127

A

2

AN INTRODUCTION TO METALLURGY.

Historical Sketch.-In turning to the history of metallurgy, it is easy to be led away by the charm of the antiquarian store of riches into devoting too much time to literary research. It should be remembered, however, that much of what is both interesting and full of suggestion, even at the present day, is to be found buried in the treatises by the old writers whose work we inherit and continue.

Primitive metallurgical processes are referred to in some of the oldest known historical records; naturally, therefore, the scientific development of metallurgy must have been long preceded by its empirical practice as an art, an art for which a place has even been claimed among the religious systems of antiquity.* The earlier literature of the subject consists mainly of descriptions of processes; but it is well known that chemistry was to a great extent built up on a metallurgical basis, and Black's singularly advanced definition of chemistry as the "effects produced by heat and mixture" might well be applied to metallurgy. The library of Leyden contains a papyrus which has been described by M. Reuvens, and which is considered by Kopp§ to be the oldest known chemical manuscript, its date being possibly as early as A.D. 200. It treats generally of metallurgical matters, and the purification of gold and silver is frequently mentioned. Of all chemical phenomena, probably none have more contributed to advance chemistry as a science than those bearing upon the relations between oxygen and lead; and the interest attaching to the mutual behaviour of these two elements is so great that the student will do well to consider the influence of one very ancient metallurgical process on the scientific views of the present day.

When lead is melted with free access of air, a readily fusible substance forms on its surface. This substance may be allowed to flow away, or, if the metal is contained in a suitable porous receptacle, the fusible oxide sinks into this containing vessel; in either case the oxidation of the lead affords a means of separating it from precious or inoxidisable metals, if any were originally present in the lead. The above fact has been known from remote antiquity, and the early Jewish writers allude to it as old and well-known. They clearly show, for instance, that lead can be removed from silver by being "consumed of the fire," while the silver is not affected. That the Greeks knew and practised this

* Rossignol, Les Métaux de l'Antiquité (1863).

+ Lectures. By Joseph Black, M.D., vol. i. pp. 11, 12 (Edin. 1803). Reuvens, Lettres à M. Letronne (Leyden, 1830), quoted by Prof. Ferguson in an address to the Glasgow Phil. Soc. (1876), p. 19.

§ Beiträge zur Geschichte der Chemie, 1869.

method of cupellation is abundantly proved, if only by certain specimens of gold and silver which were discovered by Dr. Schliemann on the site of ancient Troy. The Arabians investigated the subject, as is shown by the writings of Geber,* the greatest of the early chemists (he died in 777), who gives a remarkable account of cupellation; he also describes the conversion of lead into a fine powder by calcination with much clearness, and he noticed the fact that after calcination the mass has "acquired a new weight in the operation." His subsequent observations on the reduction of altered metals from their "calxes" show that he knew the weight to be increased; in any case it is interesting to remember that his work was, in a sense, quantitative. He, moreover, was cognisant of the fact that two different substances may be produced by heating lead in air, and he assumed that "in the fire of calcination a fugitive and inflammable substance is abolished." The alchemists refer continually to the subject, and "deliver themselves," as Roger Bacon said, in his Speculum Alchimie, "in the enigmas and riddles with which they clouded and left shadowed to us the most noble science." Eck of Sulzbach showed (1489) that metals augment in weight by calcination, and that what we now call red oxide of mercury gives off" a spirit" when heated; had he named and isolated the spirit, he would have discovered oxygen. The great metallurgist of the sixteenth century, Agricola,† points out that lead increases in weight when it is exposed to the action of moist air. In the middle of the sixteenth century, the equally accomplished metallurgist, Biringuccio, contemporary of Paracelsus and Agricola, seems to have been specially attracted by the phenomenon in question, and he remarks:"If we had not lead we should work in vain for the precious metals, for without its aid we could not extract gold or silver from the stones containing them. . . . . The alchemists also," he says, "make use of it in their operations, calcining it by itself or with other substances; but," he goes on to observe, the calcination, conducted in a reverberatory furnace is accompanied by a marvellous effect, the result of which should not be passed by in silence, for lead thus treated increases ten per cent. in weight, and considering that most things are consumed in the fire, it is remarkable that the weight of lead is increased and not diminished." Although he subsequently gives evidence of much accurate know

234.

66

The works of Geber, translated by R. Russell (1685), pp. 74, 78, 220,

De ortu et causis subterraneorum, p. 519.

Pirotechnia (Vinezia, 1540), translated into French by T. Vincent (Rouen, 1627), p. 41.