Popular Science Monthly/Volume 32/December 1887/The Metals of Ancient Chaldea
|THE METALS OF ANCIENT CHALDEA.|
By M. P. E. BERTHELOT.
IN the pursuit of my studies of the origins of alchemy and the metals of antiquity, I have had occasion to examine substances recovered from the Palace of Sargon at Khorsabad, and from the excavations made by M. de Sarzec at Tello, as they are preserved in the Museum of the Louvre. I intend to describe the results of my analyses, and then to examine a number of new or little-known documents relative to the origin of the tin used by the ancients in the manufacture of bronze.
In the course of his excavations, in 1854, M. Place discovered, under one of the angular stones of the Palace of Sargon, at Khorsabad, a stone chest containing votive tablets, covered with very clear cuneiform inscriptions commemorating the foundation of the building, b. c. 706. According to M. Place, there were five of these tablets; but the form of the inscriptions indicates that there were seven of them, designated by names. Only four of them are in the Louvre Museum, the other three are lost. The four which are known bear long and detailed inscriptions, of which M. Oppert has published translations of three in M. Place's work on "Nineveh and Assyria." The sense is nearly the same in all the three, and relates to the construction of the palace. According to this translation, the tablets were of gold> silver, copper, and two other substances, the names of which have been identified with lead and tin—the last rather doubtfully, according to M. Oppert; and, lastly, of two additional substances, bearing the determinatives of stones employed as materials of construction, which are considered to be marble and alabaster. Unfortunately, the several tablets do not contain separately the name of the material of which they are made. I have examined the four tablets in the Louvre. They are rectangular, and a few millimetres in thickness. The golden plate is the thinnest, and may be easily recognized, although it has lost its brightness. It weighs about 167 grammes. It was shaped by hammering. The metal is not alloyed in any notable proportion. The silver plate is quite or nearly as pure. It is slightly blackened on the surface by the formation of a sulphuret, as usually happens to silver which has been exposed for a long time to atmospheric agencies. It weighs about 435 grammes.
I give these weights as matters of fact, without prepossession on the question of whether they corresponded with the relative values of the metals at the time of the foundation of the palace.
The plate supposed to be of copper is deeply altered and partly exfoliated by oxidation. It weighs, in its present condition, 952 grammes, which shows that its dimensions were considerably greater than those of the other two plates. Its color is a dark red, which is determined for the most part by the presence of the protoxide of copper. It is not pure copper, but bronze; a specimen, filed off from the edge, contained, by analysis, tin, 10·04; copper, 85·25; oxygen, etc., 4·71.
Neither lead nor zinc, nor any other metal, is found in noticeable quantity. The proportion of tin corresponds with that in golden-yellow bronze, but the presence of protoxide of copper has changed the color. This composition is also found in a large number of ancient bronzes; of which I will mention only an Egyptian mirror of the seventeenth or eighteenth century b. c., which I once analyzed for M. Marriette. It contained 9 parts of tin and 91 of copper.
The fourth tablet is the most interesting of all, on account of its composition. It weighs about 185 grammes. It is composed of a bright white substance, hard and opaque, carefully cut and polished. It had till now been thought to be of a metallic oxide, and had first been designated as the antimony tablet; others said tin, because it was thought to have been made of a metal which time had gradually oxidized. But neither antimony nor tin possesses the property of undergoing a change of this kind, especially when inclosed in a stone chest. At most, lead and zinc are susceptible of being converted into oxide or carbonate in a moist medium; but under such conditions they are disintegrated and fall into dust, while the tablet is quite compact and covered with a very fine and extremely clear inscription. Its real nature was therefore a riddle. We then first carefully sounded it, and ascertained that there was no central metallic leaf in its thickness. Chemical analysis indicated that it was a pure, crystallized carbonate of magnesia—a substance that is more refractory to dilute acids and atmospheric agencies than carbonate of lime. The polishing of the tablet appeared to have been completed with the aid of an almost insensible trace of fatty matter, which manifested itself on calcination. We observe here that our magnesia and its salts were not known in antiquity and the middle ages, and that pure and crystallized carbonate of magnesia is a very rare mineral, and was not known by Haüy at the beginning of the present century. But in intimate association with carbonate of lime it constitutes dolomite, a very abundant rock. Carbonate of magnesia is found principally in veins intercalated in talcose schists, serpentine, and other magnesian silicates, where it results from the slow decomposition of the rocks by natural agencies. The material of the tablet in question also includes a few traces of silica, which indicate the same origin. The choice of so exceptional a mineral for the fabrication of a sacred tablet can not have been made by chance. It doubtless responded to some particular religious idea. At any rate, it proves that the Assyrians were acquainted with the carbonate of magnesia as a proper substance. To what word did this tablet correspond in the inscription, in which it appears to figure under the name of one of the supposed metals? Notwithstanding the absence of a special denomination on this tablet, M. Oppert believes that it was designated by the word a-bar, which had been supposed to mean tin. I thought it might be useful, in the effort to obtain new light in this matter, to analyze the substance of which the great bulls in the Louvre Museum are made, and see if it contained dolomite. The analysis determined, however, that this matter was a crystallized carbonate of lime representing the physical constitution of marble, or rather of that variety of limestone which was formerly confounded, under the name of alabaster, with anhydrous sulphate of lime.
While I was studying the tablets of Khorsabad, M. Heuzey called my attention to some metallic fragments of a vase and a votive figurine which came from M. de Sarzec's excavations at Tello. The fragment represents a portion of a cylindrical circular band which formed the mouth of a cast vase, and had been prepared by melting and casting. A part of the throat that separated this band from the body of the vase proper can still be seen. It is very simple in form, and without any inscription or even light delineation. The surface is covered with a very thin, yellowish-black patina. The mass is formed of a brilliant black metal, the fracture of which exhibits voluminous, glittering crystals, of very hard but fragile material. On analysis it appeared to be nearly pure metallic antimony, containing no notable proportion either of copper, lead, bismuth, or zinc, but only some traces of iron. The patina was an oxysulphuret, which had been formed by the action of the traces of sulphureted hydrogen which exist in the atmosphere. The existence of such a fragment—of a cast vase of pure antimony—is singular, for this metal is not employed pure for any such use in modern industry, although it is often used in alloys; and I know of no similar example in the vessels either of the present or of past times. I had been told, however, that the Japanese used antimony in their manufactures, and I had been presented with a little winged dolphin which was supposed to be made of antimony. But the analysis of this dolphin showed that it was composed of zinc and other associated metals, and was far from being formed of pure antimony. If pure antimony has really been employed by the Japanese—which I doubt—there would have been a curious relation with ancient Chaldean customs.
An extremely curious circumstance, moreover, is the finding of this authentic manufactured fragment of antimony at Tello, a place which had been uninhabited since the time of the Parthians, and which contains the remains of the oldest Chaldean civilization. Antimony, in fact, is supposed not to have been known to the ancients, and not to have been discovered till toward the fifteenth century. Yet we find that the ancients were very well acquainted with our sulphuret of antimony, a natural mineral which they called stibium or stimme, and which they employed for many uses, particularly in medicine. A passage in Dioscorides, repeated by Pliny, leads me to believe that metallic antimony had been obtained in his time. We read, in short, in Dioscorides ("Materia Medica," book iv, chapter xcix): "This mineral is burned by placing it on coals and blowing them to incandescence; if the calcining is prolonged, it changes into lead (μολνθδοῡῑαι)." Pliny says, likewise ("Hist. Nat.," book xxxiii, chapter xxxiv): "The calcining must be done with precaution, in order not to change it into lead (ne plumbum fiat)." These observations agree with phenomena well known to chemists. In fact, the calcining of sulphuret of antimony, particularly in the presence of charcoal, may easily bring it to the condition of fusible and metallic antimony, a substance which Pliny and his contemporaries confounded along with all other dark and easily fusible metals, with lead. The existence of the Tello vase proves that in Mesopotamia, likewise, and in probably a much more ancient age, they had tried to make cast vases with this supposed variety of lead, which was less liable to change than ordinary lead.
The metallic votive figurine of Tello suggests no less curious observations. It represents a divine personage, kneeling and holding a kind of metallic point or cone. It has engraved upon it the name of Gudeah, a king who belongs to the most ancient age of which relics have yet been found in Mesopotamia—M. Oppert attributing to him an antiquity of four thousand years b. c. We are thus carried back to extremely remote times of metallurgical history. The figurine is covered with a thick, green patina, below which is a red layer, formed by the oxidation of the metal in the greater part of its thickness. Then comes a red metallic nucleus, having the appearance and tenacity of copper. It is the last remainder of the primitive metal, which has been progressively destroyed by natural actions. I have analyzed these different parts. The superficial green patina is a mixture of oxide of copper and a hydrated oxychloride of copper, the latter compound being known by mineralogists as atakamite. It is formed by the action on the metal of brackish waters, with which the figurine had been in contact, through the course of ages. The middle layer is a nearly pure protoxide of copper, free from notable quantities of tin, antimony, lead, or any similar metal. It results from a slow alteration of metallic copper. The nucleus was pure metallic copper.
The absence of any other metal than copper in this figurine deserves to be noticed. Objects of this kind are usually made with bronze, an alloy of tin and copper which is harder and more easily worked. The absence of tin from the Tello copper has a peculiar historical significance. Tin is much less diffused over the surface of the earth than copper, and its transportation has always been the object of a special commerce, in ancient days as well as in ours. In Asia, in particular, there had not till very lately been any deposits of tin found in any abundance except those of the Sunda Islands and the southern provinces of China. The transportation of this tin to Western Asia was formerly carried on by sea, to the Persian Gulf and the Red Sea, by long and arduous voyages; and it was carried thence to the coasts of the Mediterranean, where it came in competition with the tin of the British Isles which had been brought across Gaul, and with the less abundant deposits of Central Gaul, and, perhaps, also of Saxony and Bohemia. Voyages so long and arduous, and systems of navigation so difficult could not have been established till after many centuries of civilization. The Phœnicians, who had come from the borders of the Persian Gulf to those of the Mediterranean, seem to have been the first promoters of this navigation.
But I have recently become cognizant with two documents, which tend to fix a less distant origin for the tin of the bronzes of Assyria and Egypt. According to a note published by M. G. Bapst, a Russian traveler, M. Ogorodnikoff, was informed by the inhabitants of Meshed that there were at one hundred and twenty kilometres from that city, and at various places in Khorassan, mines of tin now worked. These statements should, however, be received with caution, on account of the uncertain quality of the oral declarations of Tartars. But it is a remarkable fact that they agree to some extent with a passage in Strabo that has been pointed out to me by M. P. Tannery. Strabo (book xv, chapter xi, 10) mentions tin-mines in Drangiana, a region which corresponds with our Khorassan, below Herat, and toward the western boundaries of modern Afghanistan.
While tin is rare throughout the world, it is very different with copper, the ores of which are found at a great number of points. The mines of Sinai, not to mention more distant ones, were celebrated in ancient Egypt. The extraction of metallic copper from its ores is also easy. Reasoning from these facts, many archaeologists have supposed that an age of pure copper, or an age in which arms and tools were made of this metal, preceded the bronze age. In order to judge the value of this hypothesis and determine the date at which this ancient navigation began, it would be necessary to possess the analyses of the most ancient objects to which a certain date can be fixed, among the remains of antiquity that have come down to us. According to analyses of this character, bronze existed in Egypt nearly two thousand years before the Christian era. The analysis of the figurine of Tello seems to indicate, on the other hand, that tin was not yet known at the time when that object was made, or that it had not yet been brought to the Persian Gulf. This is, however, only an induction, since some religious circumstance or another may have determined the exclusive employment of copper in the making of the figurine; and it would be necessary to examine many more objects and more various to reach certainty in that matter. It has, nevertheless, seemed to me that it would be interesting to indicate the problems of a general character that are raised by the analyses of the metals of Tello.—Translated for the Popular Science Monthly from the Revue Scientifique.