Popular Science Monthly/Volume 53/August 1898/The Genealogy of Chemistry
|THE GENEALOGY OF CHEMISTRY.|
By M. E. BERTHELOT.
MODERN science is the child of ancient science—that is, of Grecian science; for it was the Greeks who constituted science under the form which we recognize now. Before the Greeks no really rational science existed, free from mystical and priestly attachments. While astronomy was cultivated in Egypt and Chaldea, it was at first with the object of determining the times of the religious festivals and of keeping agriculture correlated with natural phenomena; and next for the discovery of the mysterious connection which astrology predicated between the positions of the stars and public and private events, under the belief that the life of men and the development of phenomena were determined by the fatality of the sidereal influences which presided at their birth or origin. Geometry and mechanics made considerable advance at Babylon, Thebes, and Memphis, being applied to the measurement of the lands and the construction of buildings, as is attested by the study of the indestructible monuments of ancient Egypt; and the equilibrium of the Chaldean structures of brick, now in ruins, required knowledge of the highest quality, yet more developed, perhaps, than that of the Egyptians. But both peoples always accompanied their work with prayers and magical invocations. The excellence of the processes of ancient times in the treatment of metals, pottery ware, colored glasses, and dyed cloths, with which experimental science is now very busy, is demonstrated by the relics of ancient civilization which we have collected in our museums. The old alchemical manuscripts tell us that these practices were explained in the Book of the Sanctuary of the Temple. The origin of medicine was traced to the temples, and this was not an empty metaphor; for the temples were the repositories of all knowledge in the East, and even to-day all Mussulman instruction gathers round the mosques. But the members of the old priesthood never imagined that it would be possible to separate the double part they were playing of priest and scientific student. They combined scientific practices with prayers and religious rites, the performance of which was deemed indispensable to the success of the processes. The idea of a miracle granted by the favor of the gods, and, if necessary, imposed upon their will by the formulas of magic, was held inseparable from the secret action of natural forces. The Greeks dissolved this connection of ideas, and founded, in the sixth century b. c., rational science, stripped of mystery and magic, as it is now current among us. The Alexandrian period witnessed the triumph of the new method; when astronomy was fully disengaged from astrology, geometry separated from the ancient rites of the field measurers, medicine and surgery rid of pilgrimages and superstitious practices, and chemistry rendered independent of the incantations by which it was thought the success of its manipulations could be assured.
This took place, in principle at least, with the most enlightened minds. But the mysterious and charlatanish part of these sciences, and their association with mysterious prayers and invocations, did not disappear all at once. They persisted in antiquity, and even acquired new favor as the ancient culture fell into decay; they were held in honor during all the middle ages, and still rule in the East.
European science has gradually, since the sixteenth century, regained the firm tradition of the Hellenic philosophers. It has rid itself of the old train of dogmas and chimerical operations, and has pursued steadfastly the construction of the edifice founded by the Greeks. While the accumulated work of generations has raised it to a height not dreamed of by the ancients, and while it has extended its dominant applications to all branches of the social organization, we still have no right to say that our methods and our modern spirit would be rejected by Archimedes or by Aristarchus of Samos. On reading our works they would recognize their legitimate heirs.
There was, however, an interval of sixteen centuries between Grecian science and that of the moderns, during which no transmission of facts, ideas, and methods took place directly, but it was effected through intermediaries of less stable minds, who were imbued with the ancient prejudices. Hence arose a mixture of pure reason and mysticism, which dominated science toward the end of the Roman Empire and during all the middle ages. By virtue of this association of two contradictory elements, now become irreconcilable, Greco-Alexandrine science took on a strange figure at the beginning of the Christian era, when the pure rationalism of Democritus, Aristotle, and their earliest disciples had declined. Hence that curious amalgam in which the positive notions of genuine chemistry were confounded with the contradictions of gnosticism and the survivals of the religious traditions of ancient Egypt. This mixture lasted longer in chemistry than in any other science, and it was not till the end of the last century that chemistry was completely freed from these singular ideas and constituted under a purely scientific form. The long history of its successive advances and its systematic tentatives, in both the practical and the philosophical departments, is most remarkable.
In the period that followed the Alexandrine epoch and preceded the definite recognition and naturalization of alchemy in western Europe, in the thirteenth century, the name of the Arabians is predominant; and the most widely known authors usually ascribe to them the progress which the Greeks made in most of the sciences. They have sometimes even gone so far as to attribute to the Arabs the discovery of chemistry—a view which has to be abandoned on obtaining an exact knowledge of the original authors.
I have devoted nearly ten years to the study of this subject, and have published for the first time the texts of the Grecian chemists, as well as those of their Syrian and Arabian followers, drawing them from their hiding places in the libraries of London, Paris, and Leyden—works which no one would read, because they were supposed to be chimerical and unintelligible. Yet there is a real and profound science in these old texts, mingled, it is true, with erroneous notions concerning the transmutation of metals, and with illusionary and often charlatanish pretensions.
Except gold, which has been mined native from the earliest times, pure metals are rarely found in Nature. A native alloy of gold and silver is found in similar conditions as gold, which was called white gold or electrum by the ancients, and was considered a separate metal till the sixth century a. d. It was used as a material for money by the Lydians, and by the Grecian cities of Asia Minor, till near the time of Alexander. This alloy, however, has no constant properties, for the relative proportions of its two components are variable. By reason of this diversity it had an important place in the thought and attempts of the alchemists seeking for the transmutation of metals; for we can extract gold or silver from it at will, according to the treatment we give it. Hence the opinion that electrum was susceptible of being changed into one or the other of these two noble metals.
These notions and experiments were confirmed by the metallurgical methods employed in the fabrication of other metals. Iron, copper, lead, tin, and silver do not exist as such in Nature except in unusual minerals. They are ordinarily found in oxide or sulphide compounds, and are, when separate, products formed by human art. In fact, it is by submitting these compounds to more or less complicated reactions, in which fire, combustible agents, drying, or roasting in contact with the air are applied, that the different metals are prepared. These preparations were formerly made according to a traditional empiricism, the origin of which is lost in the night of the ages. It has hardly been more than a century since chemists first succeeded in accounting for the reactions and in improving upon them by the aid of more precise notions founded on the theories of modern science; and our own age has witnessed a still more radical transformation in metallurgy resultant upon the discoveries in electro-chemistry. But everything rested, in antiquity, upon empiricism, unguided, except by vague analogies.
The metals which the ancients thus obtained and made use of were not always pure metals. The ancients had a number of varieties of copper and of lead. First, a distinction was made between black lead and white lead; the first being our modern lead, while the second has become our tin. These names were, however, applied to other metals and alloys, including antimony, which was obtained by roasting and reducing its sulphuret, under conditions which are described by Dioscorides; and some alloys of silver originally designated by the name of cassiteros, which was afterward applied to our tin. The stannum of Pliny also has this double meaning.
The white alloys, of brilliant and little changeable surface, were given a special name—asem, or Egyptian silver—a name which was continually reappearing with the Greek alchemists, and was confounded with the name of silver without definite title—asemon—a designation which was given to very diverse substances, from pure tin to electrum. So it was with the metal called chalkes in Greek, aes in Latin—a name which included innumerable species; whence modern translators use indifferently the words brass, copper, and bronze to represent it. modern pure copper is too soft to be used for forging arms or solid tools, and the Greek and Latin names usually refer to alloys. The ancients had copper of different colors, and specified the species by adjectives derived either from these colors, or from the place of origin of the substance. Thus, they had red copper and Cyprian copper, aes Cyprium—an epithet which, in the time of the Roman Empire, became the name of the metal, cuprum—besides yellow copper, white copper, etc. Yellow copper in its turn included several varieties, for its composition varied greatly. First, there were the bronzes, alloys of copper and tin, used for many centuries in the manufacture of arms, till they were dethroned by the advances in the manufacture and tempering of iron. In the Roman Empire one of these alloys, which was used for mirrors, was designated, after the name of Brindisium, where the manufacture was carried on, aes Brundusinum, whence our word bronze is derived; in other alloys of various shades, yellow or whitish, copper was combined with lead or zinc—a metal which the ancients did not know in a state of purity, but of which they were acquainted with the minerals, natural cadmies or calamies as they were called, whence our word calamine. The fusion of these minerals with those of copper produced alloys similar to our brass.
While some of these compounds of copper, by virtue of the importance of their applications, thus acquired special names, there were others among the yellow alloys which, employed in antiquity and the middle ages, have fallen into disuse; compounds of copper with arsenic and antimony, for instance, which were useful for promoting the combination of substances like iron with copper or tin, which would not readily unite with them directly. Modern chemistry has very little to do with such alloys. But an alloy of copper and antimony has been revived and patented within the past twenty years which has the appearance and many of the properties of gold. It was known to the Greek alchemists, and is mentioned in the Syriac translations of their works. There existed, therefore, in antiquity and the middle ages, a multitude of artificial metals, passing under the general names of lead, iron, tin, electrum, and gold and silver. Furthermore, as pure silver was confounded in goldsmiths' practice with various alloys designated under the name of asem, so the name of gold was not applied to pure gold alone, but was extended to alloys of that substance with copper and other metals; alloys which differed greatly in richness, but were used for making base goods for which the goldsmiths tried to make their customers pay the price of pure gold. These fraudulent practices and tricks have continued down to our own time in countries where the law has not fixed the standard of merchantable gold and silver with severe penalties for violating it.
With these facts before us we can easily comprehend the ideas and theories of the alchemists, and imagine on what their practices and hopes were based. One of the first ideas their experience gave them was, doubtless, that the properties of the metals varied. The theoretical definition of our simple bodies, which we now know continue unchanged in nature and weight through the course of their metamorphoses, was developed slowly, and was not recognized as a certainty till within a century. The positive minds of the Roman lawgivers no doubt perceived the necessity of employing pure gold and silver, or alloys of a fixed standard, for coinage; but this was a practical prescription, and not a scientific principle. Although the artisans who worked these metals knew how to obtain substances of legal purity, they had no sign to inform them whether these substances really represented a single metal of unchangeable quality, or whether they were dealing with a conventional stage in the undefined series of transformations of matter. These legal divisions applied to gold and silver. There is nothing to prove that any one of the innumerable species of copper, lead, and tin represented more than another the fundamental state to which all of them bore relation. In short, gold, silver, copper, and lead were really, in the eyes of the alchemists, mixtures or compounds, the properties of which could be modified at will by adding or subtracting certain of the components.
The idea of this fundamental unity of matter was derived from a more remote principle. It was subject to the existence of the four elements—earth, water, air, and fire—from the association of which, according to Plato and Aristotle, all the substances in Nature were constituted. We know now that these ancient elements were not real substances, but symbols of the fundamental states of matter, such as solidity, liquidity, the gaseous and all static conditions; the fourth element, fire, represented a dynamic state of bodies. These symbols had, on the other hand, a really substantial value for the alchemists, a character defined by the approximate identification of their supposed elements with certain products, in which the properties corresponding with one of the elements seemed to reside in a more eminent degree. Modern science has become more precise. At the same time the substantial elements of the ancients have come to be regarded by it as symbols of qualities and phenomena. Still, the Grecian philosophers conceived, behind the elements which were supposed to add their peculiar properties to bodies, an essential unity, residing in a higher degree in indeterminate primary matter; modified by multiple forms and accidents, it concurred in forming all things. The elements, they said, are opposite by their quality and not by their substance. This more general notion did not cease to prevail in the Cartesian conceptions and in those of our own times too.
Such metaphysical views were, however, too vague to furnish the goldsmiths and alchemists a clear explanation of the facts which their daily practice offered them. In this a special state of mind is manifested. Chemistry, indeed, has always had a singular aptitude for creating a sort of materialistic metaphysics, in which the names of beings and of first principles are employed with a restrictive and in a certain way a tangible significance. The Grecian chemists said that the metals were like man: they had a body and a soul. The soul was, however, to most of the ancient philosophers, nothing else than a more subtle matter. The alchemists were thus led to imagine a primary matter, appertaining to the metals alone, which constituted their common essence. It seemed to be indicated by that general condition of fusion which all metals take under the action of fire, in which they are ready to go into alloys and receive coloration and the impression of new properties. The ancient Egyptians regarded lead as this primary matter, and gave it the name of Osiris. About the time of the Peloponnesian war a new substance came under notice—mercury, or liquid silver—which corresponded still more nearly with the idea of the primary metallic matter, 'o author has informed us concerning the origin of the discovery of this singular metal. We only know that the Carthaginians were at that time working the mines of Betica, and that the minerals of mercury, situated in the same region, were well known and operated in the time of the Roman Empire. At any rate, the appearance and properties of this liquid and vaporizable silver, which was almost as refractory to chemical reagents as its ancient solid homonym, struck the imagination forcibly. It only seemed necessary to fix it—that is, to take away its liquidity and volatility—to obtain the other metals, particularly real silver. Mercury thus became the primary metal of the alchemists. A letter is extant from Synesius, a writer of the end of the fourth century, to Dioscorus, embodying a kind of catechism concerning the qualities and relations of this substance, from which we gather that, being the primary matter of metals, the first essential proceeding was to fix it or make it solid and stable as to fire, like other metals; then to color it, by the aid of some white or yellow tinctorial substance, such as sulphur or the sulphurets of arsenic, by which it would finally be changed into gold or silver. The name mercury had a variety of significations. It represented native mercury, extracted directly from the mines; artificial quicksilver, prepared from cinnabar, which was called copper mercury, lead mercury, or tin mercury, according as it was prepared in the cold by crushing cinnabar in a mortar with copper, lead, tin, etc., when the mercury produced appeared to participate in the qualities of the metal which had been used in its preparation. To us it is always the same mercury, rendered impure, indeed, by some trace of the precipitating metal; but in the eyes of the alchemists there were different metals. Furthermore, the term mercury was applied to two substances which we know were radically different: modern mercury, or mercury extracted from cinnabar, and metallic arsenic, which they called mercury extracted from orpiment. Both are, in fact, volatile and susceptible of sublimation, and both form red sublimates; both turn copper white, and both form red sulphurets. From these particulars we can see how broad was the meaning of the common word mercury, and how the mercury of the philosophers represented a kind of quintessence, common to these various kinds of mercury, or the primary matter of the metals, susceptible of being changed by coloring into gold or silver. The work to be done, then, was to extract this mercury from ordinary metals, and then color it to gold or silver; or to operate on its substance as it was contained in the copper, lead, tin, and iron, so as to eliminate the contrary qualities and perfect the conformable qualities by means of suitable reagents, which would at the same time color it. These coloring reagents were designated, generally, the philosopher's stone.
Governed by these ideas, the Greco-Egyptian alchemists obtained a great variety of metallic alloys, some white and nearly as unchangeable as silver, to which they assimilated them; others yellow, and having a stability like that of gold, of which they gave them the name. Real gold and silver were besides often included in the composition of these alloys, when they were regarded as the seed, and were supposed to multiply, as if they had been living beings, under the action of certain ferments. The alchemists frequently found that their recipes for transmutation were not sufficient to produce gold and silver; that after combining a certain number of properties, others were still wanting; at this point they fell back upon the mystic part of their science. The confusion between real silver and gold and the white and yellow alloys was carefully nursed by the alchemists, who even went so far as to call gold and silver metals which were only superficially colored by the action of mercury and the sulphurets of arsenic, and metals that were only covered with a golden varnish. This confusion of language exists even in the industries of our own times, as when manufacturers speak of the gold of a color or a cloth.—Translated for the Popular Science Monthly from the Revue des Deux Mondes.