History of Chemistry (Thorpe 1909, NY & London)/Volume I/Chapter II
CHAPTER II
The Chemical Philosophy of the Ancients
SPECULATIONS, as to the origin and nature of matter, and as to the conditions and forces which affect it, are to be found, more or less imperfectly developed, in the oldest systems of philosophy of which we have any record. These speculations are not based, in any real sense, upon the systematic observation of natural phenomena. Still, as they appealed to human reason, they must be held to be founded upon experience, or at least not to be consciously inconsistent with it: All the oldest cosmogonies regarded water as the fundamental principle of things from Okeanos sprang the gods—them selves deified personifications of the “elements” or principles of which the world was made.
In the course of time this doctrine of the origin and essential nature of matter came to be more particularly associated with the name of Thales of Miletus, who lived six centuries before our era, and who, according to Tertullian, is to be regarded as the first of the race of the natural philosophers—that is, the first of those who made it their business to inquire after natural causes and phenomena. Thales is known to have passed some years of his life in Egypt, and to have been instructed in science by the priests of Thebes and Memphis; and it is therefore possible that he may have been influenced by the Egyptian teaching in the formulation of his cosmological theories.
It is significant of the tenacity with which the mind clings to dogma and reveres authority that the teaching of Thales should have survived through the space of twenty-four centuries. It can be shown to have affected the course of chemical inquiry down to the close of the eighteenth century. It influenced the experimental labours of philosophers so diverse in character as Van Helmont, Boyle, Boerhaave, Priestley, and Lavoisier—all of whom made attempts to prove or disprove its adequacy. Van Helmont, indeed, was one of the most strenuous supporters of the doctrine of Thales, and sought to establish it by observations which, in the absence of all knowledge of the true nature of air and water, seemed at the time irrefutable. Perhaps the one most frequently cited is his observation on the growth of a plant which apparently had no other form of sustenance than water. He describes how he planted a willow weighing 5 lbs. in 200 lbs. of earth previously dried in an oven.
The plant was regularly watered, when at the end of five years it was found to weigh 169 lbs. 3 oz., whereas the earth, after redrying, had lost only 2 oz. in weight. Hence, 164 lbs. of woody matter, leaves, roots, etc., had been, produced seemingly from water alone. More than a century had to elapse before any clue to the true interpretation of Van Helmont's experiment was gained. It was first furnished by the observations of Ingenhousz and Priestley.
Although the idea of a primal “element” or common principle is to be found in every old-world philosophical system, the ancient philosophers were by no means in agreement as to its character. Anaximenes, who lived circa 500 B.C., taught that it was earth. The supposition that a single primordial principle could be made to account for all forms of matter and all the phenomena and manifestations of the material world had its difficulties. Attempts to group qualities as principles, and to construct from these principles the universe, were indeed made even prior to the age of Thales. It was a comparatively simple evolutionary step to regard these principles or “elements” as mutually convertible. Anaximene’s theory of the formation of rain was an implicit admission of such convertibility. This philosopher taught that rain came by the condensation of clouds, which in their turn were formed by the condensation of air. Everything comes from air and everything returns to air. That water might be converted by fire into air was surmised from the earliest times. Such a supposition naturally sprung from the circumstance that water was everywhere recognised to disappear or to pass into the air under the influence of fire or solar heat. The supposition had grown into a fixed belief in the Middle Ages.
Even Priestley, as late as the end of the eighteenth century, imagined for a time that he had obtained proof of such a mutual conversion. The possibility of the transmutation of water into earth was a belief current through twenty centuries, and was only definitely and finally disproved by Lavoisier in 1770. The conception of fire as the primal principle has its germ in the fire- or sun-worship of the Chaldeans, Scythians, Persians, Parsees, and Hindus, and it is not difficult to trace, therefore, how heat came to be regarded either as antecedent to, or as associated with, the other primal principles. Empedokles, apparently, was the first whose name has come down to us to reintroduce the definite conception of four primal elements—fire, air, water, and earth. These he regarded as distinct, and incapable of being transmuted, but as forming all varieties of matter by intermixture in various proportions. These principles he deified, Zeus being the personification of the element of fire, Here of air, Nestis of water, and Aidoneous of earth. The doctrine of the four elements was also adopted by Plato and amplified by Aristotle, with whose name indeed it is commonly associated. Aristotle, the greatest scientific thinker among the Greeks, exercised an authority almost supreme in Europe during nearly twenty centuries. His influence is to be traced throughout the literature of chemistry long after the time of Boyle. It may be detected even now. Probably few who write chemical memoirs to-day, and who follow the time-honoured practice of prefacing their own contributions to knowledge by a statement of what is already known on the subject, are aware that in so doing they are obeying the injunctions of Aristotle. His theory of the nature of matter is contained in his treatise on Generation and Destruction. It mainly differed from that of Empedokles in regarding the four “elements” as mutually convertible. Each “element” or principle was regarded as being possessed of two qualities, one of which was shared by another element or principle.
Thus: Fire is hot and dry; air is hot and wet; water is cold and wet; earth is cold and dry.
In each primal “element” one quality prevails. Fire is more hot than dry; air is more wet than hot; water is more cold than wet; earth is more dry than cold. The relative proportion and mutual working of these qualities determined the specific character of the “element.” Thus, if the dryness of fire is overcome by the moisture of water, air is produced; if the heat of air is overcome by the coldness of earth, water is formed; if the moisture of water is overcome by the dryness of fire, earth results. Ancient chemical literature contains many illustrations or diagrams symbolising the convertibility or mutual relations of the four “elements”.
It has been frequently stated that the influence of the Peripatetic philosophy has been inimical to the development of science. But, in reality, the founder of that school, a descendant of Esculapius, and undoubtedly one of the greatest and most enlightened thinkers of antiquity, was an ideal man of science. This is abundantly evident from such of his works as can be proved to be genuine. Much of what is called Aristotelianism is entirely foreign to the spirit of the teaching of Aristotle. The Aristotelians of the Middle Ages were mainly dialecticians, and almost wholly concerned with the formulæ of syllogistic inference, and without real sympathy with, or knowledge of, his system. Much, too, that was attributed to him, and which was venerated accordingly, is undoubtedly spurious. The fame of the Master has consequently suffered at the hands of those who, calling themselves Peripatetics, were in no proper sense followers of his method or interpreters of his dogma. Aristotle affirmed that natural science can only be founded upon a knowledge of facts, and facts can only be ascertained through observation and experiment. He illustrates this particularly by a reference to astronomy, “which,” he says, “is based on the observation of astronomical phenomena, and it is the case with every branch of science or art.” It is erroneous and unjust, therefore, to suppose that Aristotle’s philosophy, as he taught it, is opposed to the true methods of science.
A knowledge of Aristotle’s works was transferred by Byzantine writers to Egypt; and, when that land was overrun by the Arabs in the seventh century, they adopted his system, spreading it abroad wherever their conquests extended. In the eighth century they carried it into Spain, where it flourished throughout their occupation of that country. From the ninth to the eleventh century the greater part of Europe was in a state of barbarism. The Moslem caliphate in Spain, under the beneficent rule of Jusuf and Jaküb, alone preserved science from extinction. Cordova, Seville, Grenada, and Toledo were the chief seats of learning in Western Europe; and it was mainly through “the perfect and most glorious physicist,” the Moslem Ibn-Roshd—better known as Averroes—(1126–1198), that Christian scholiasts like Roger Bacon acquired their knowledge of the philosophical system of Aristotle, and mainly through the Moslems Geber and Avicenna that they gained acquaintance with the science of the East.
The conception that matter is made up of particles or atoms, and that these particles are in a state of ceaseless motion, is to be met with in Hindu and Phœnician philosophy. It was taught by Anaxagoras, Leukippos, and Demokritos to the Greeks, and by Lucretius to the Romans. Leukippos and Demokritos explained the creation of the world as due solely to physical agencies without the intervention of a creative intelligence. According to their theories, the atoms are variable, not only in size, but in weight. The smallest atoms are also the lightest. Atoms are impenetrable; no two atoms can simultaneously occupy the same place. The collision of the atoms gives them an oscillatory movement, which is communicated to adjacent atoms, and these, in their turn, transmit it to the most distant ones. Anaxagoras taught that every atom is a world in miniature, and that the living body is a congeries of atoms derived from the aliments which sustain it. Plants are living things, endowed like animals with respiratory functions, and, like them, atomically constituted. This philosopher was so far in advance of his age that his countrymen accused him of sacrilege, and he only escaped death by flight. Further, the assumption that these atoms exert mutual attractions and repulsions is probably as old as the fundamental conception itself. At least, so far as can be traced, the conceptions of atoms and atomic motion are indissolubly connected. This is not the place to develop the subsequent history of the doctrine of the atom, nor need we now concern ourselves with the old metaphysical quibble of its divisibility or indivisibility. It may be, as Lucretius said, that the original atom is very far down. It may be that the physical atom is something which is not divided, not something that cannot be divided. This theory, dimly perceived in the mists of antiquity, has grown and strengthened with the ages, and in its modern application to the facts of chemistry has acquired a precision and harmony unimagined even by the poets and thinkers of old. We shall see later how the whole course of the science has been controlled, illumined, and vivified by it. It is not too much to say that the chemistry of to-day is one vast elaboration of this primeval doctrine.