Ideas similar to those of Aristotle concerning the elementary constitution of the universe were early prevalent in the East, whence they appear to have found their way into Europe. The elements, according to the Hindus, were earth, air, fire, water, and ether , and in the fourth book of “Chow,” forming part of the Chinese historical records known as the Shoo King, there is a document supposed to date from 2000 B.C., in which is given an account of the five elements, namely, earth, fire, water, metal, and wood. Of what precisely was meant by an “element” in the language of the ancient philosophers and early chemists it is difficult to get any definite idea; the term could hardly, in fact, be used otherwise than in a vague sense before the exact processes of chemical analysis had shown that the properties of matter vary according to the presence or absence within it of definite quantities of certain substances, distinct in properties from one another, and un-resolvable into other substances.

To the doctrine of a plurality of elements, as opposed to the systems of Thales and Heraclitus, may be ascribed the origin of the conception that by the analysis and synthesis of bodies the various kinds of matter with all their diversity of physical features might be produced, a conception that took practical shape in the processes of alchemy, which, as Liebig has remarked, “was never at any time different from chemistry.” During the alchemistical period a knowledge of the properties of bodies was acquired; afterwards chemistry showed the relations, connections, and limits of these properties. The first mention of chemistry (χημeia) is found in the dictionary of Suidas, who flourished in the 11th century; he defines it as “the preparaticn of silver and gold,” and relates that Diocletian, lest the Egyptians should become rich and capable of resisting the Roman power, caused their books on chemistry to be burnt. He further asserts that the art was known as early as the period of the Argonautic expedition, the golden fleece being a treatise written on skins (δ∈pμασι) concerning the making of gold. The belief in the art of making gold and silver, held by the Greeks from the 5th to the 15tlι century, was by them communicated to the Arabs, possibly not long after the conquest of Egypt in 640; and from the 11th to the 15th century alchemy was diligently studied by the philosophers of Italy, France, Germany, and England.

That the claims of alchemy, notwithstanding repeated demonstrations of their futility, so long received the serious attention of mankind, is attributable to various causes. Not only did impostors find free scope in the credulity of an age of ignorance for the exercise of their arts; but men of talent and culture, relying on tradition, were led honestly to support the doctrine of the transmutation of metals. The existence of the philosopher’s stone having once been accepted as an ascertained fact, it is not extraordinary that Isaacus Hollandus is able to indicate the method of its preparation from “adamic” or “virgin” earth, and its action when medicinally employed; that Roger Bacon, Raymond Lully, Basil Valentin, and John Price know the exact quantities of it to be used in transmutation; and that George Rippel, in the 15th century, has grounds for regarding its action as similar to that of a ferment. In the view of some alchemists, the ultimate principles of matter were Aristotle’s four elements, the proximate constituents were sulphur and mercury, the father and mother of the metals; gold was supposed to have attained to the perfection of its nature by passing in succession through the forms of lead, brass, and silver; gold and silver were held to contain very pure red sulphur and white quicksilver, whereas in the other metals these materials were coarser and of a different colour. Geber, judging from an analogy instituted between the healthy human being and gold, the most perfect of the metals, regarded silver, mercury, copper, iron, lead, and tin in the light of lepers that required to be healed.

To the evidence of their imaginations the alchemists were able to add that of actual observation; the fact that many ores resembling metals were changed and decomposed by heat could not but offer support to theories formed at a time when the nature of chemical combination was not understood; and the apparent transition of many bodies into one another, as, for example, that of clouds into water, was not less wonderful to them than the transmutation of the lighter metals into gold.

It was in the 16th century that a new race of alchemists, or spagyrists, as they were termed, arose, who, abandoning the search for the philosopher’s stone, began to direct their energies to the discovery of chemical remedies for the various diseases of the body. “The true use of chemistry,” says Paracelsus (1493—1541) “is not to make gold, but to prepare medicines.” Rejecting the teaching of Galen, he admitted three or four elements, the star, the root, the element, and the sperm or true seed, which were originally confounded together in the chaos or yliados ; these elements he asserted were composed of the three principles sideric salt and sulphur and mercury, the cause respectively of the qualities of fixity, combustibility, and fluidity and volatility. The theories of Paracelsus found many advocates, amongst whom may be mentioned Thurneysser (1531-1596), Bodenstein, Taxites, Dorn, Sennert, and Duchesne; and with some modifications they were maintained in the 17th century by Dr Willis (1621-1675), the celebrated English anatomist and iatro-chemist, and by Lefebvre and Lémery in France, according to whose system matter consisted of the active principles mercury or spirit, sulphur or oil, and salt, and the passive principles water or phlegm and earth.

Among the contemporaries but not the followers of Paracelsus, the German metallurgist Agricola (1494-1555) deserves mention; his great work, De Re Metallica, is the most valuable contribution to practical chemistry that appeared in the 16th century. Libavius also, who diedin 1616, did much to forward chemical science at this period. From his writings, however, in which he puts forward the views both of Paracelsus and of Aristotle concerning the constitution of bodies, it does not appear that his notions of chemical combination were more definite than those of his predecessors.

J. B. Van Helmout (1577-1644), who, like Paracelsus, repudiated the doctrines of the Galenists, held opinions that in many respects were no advance upon those of the former. He looked upon water as the true principle of all existing things, inclusive of the three principles salt, sulphur, and mercury, which therefore were not elements; to air, however, he granted the rank of a true element. The archoeus — something without form, and independent of the elements—he imagined to draw all bodies from water, to which its generating spirit was attracted by the odour of a ferment or aura vitalis. The vapour produced by the fermentation of water was, according to Van Helmont, a gas, and the same term was by him for the first time applied to carbon dioxide, which he termed gas sylvestre, and to other bodies resembling air.

To Francis de la Boë Sylvius (1614-1672), who studied with care the works of Van Helmont and of Descartes, is due the foundation of the iatro-chemical sect among physicians. In his view the health of the human frame depends upon the relation of its fluids, which were acid and alkaline (acidum aud lixivum), and these by union produced a neutral and milder substance; two kinds of diseases were distinguished, the result either of alkaline or of acid acridity. The new doctrine served to explain many chemical facts, and led to the establishment by Lémery and Macquer of a distinction between acid and alkaline or, as they were afterwards called, basic compounds. This recognition of this chemical difference in bodies and their consequent disposition to unite prepared the way for the conception of chemical attraction or affinity.

In the works of Glauber (1604-1668), alchemy, the preparation of chemical medicines, and the processes employed by him for that end are treated of. His Miraculum Mundi has for its subject the virtues of the sal mirabile, sulphate of sodium, or Glauber’s salt, of which he was the discoverer; and in other of his works he describes various chlorides of the metals, the sulphates of iron and copper, aud sulphuric, nitric, and hydrochloric acids, but with respect to their ultimate constitution he advances no theory; he variously states in his different works that mercury and salt are the principles of all metals, that salt is the origin of all things, aud again that water and earth have produced all the minerals and metals.

The first to attempt to overthrow the doctrines of the iatro-chemists was Robert Boyle (1627-1691), who in 1661 published the first edition of The Sceptical Chemist, or Ghymico-Physical Doubts and Paradoxes touching the Experiments whereby vulgar Spagyrists are wont to endeavour to evince their Salt, Sulphur, and Mercury to be the true Principles of Things, a treatise in which he shows the doubtful character of the doctrine of the threefold constitution of matter, and lays stress upon the influence of heat in the formation of new bodies, not necessarily preexistent as such in the substances from which they are produced. If, as he tells us, he is somewhat too indulgent of suspicion against the hypotheses or arguments of other chemists, he is only acting in compliance with the advice of Aristotle, and bending a crooked stick the contrary way, to reduce it at length to straightness. Into the mouth of

“Themistius” he puts the complaint that “Aristotle’s hypothesis had not been called in question till in the last century Paracelsus and some few other sooty empiricks, having their eyes darkened and their brains troubled with the smoke of their furnaces, began to rail at the Peripatetick doctrine, which they were too illiterate to understand, and to tell the credulous world that they could see the three ingredients in mixed bodies, which, to gain themselves the repute of inventera, they endeavoured to disguise by calling them—instead of earth, and fire, and vapour—salt, sulphur, and mercury, to which they gave the canting title of hypostatical principles.” Boyle inclines to a belief in “but one universal matter of things, as it is known that the Aristotelians themselves acknowledge, who called it ĭnateria prima; the portions of this matter seem to differ from one another in certain qualities or accidents, fewer or more.” He thinks that elementary corpuscles are of various sizes, and of more sorts than three or four or five; and that the combination of two of these corpuscles may give rise to a new body as really one as either of the corpuscles before they were mingled or confounded, this concretion being endowed with distinct qualities, and no more by fire or any known way of analysis divisible into the corpuscles that had first concurred to make it, than either of them could by the same means be subdivided into other particles. He furthermore deduces from his arguments the corollary, “That it may as yet be doubted whether or no there be any determinate number of elements; or, if you please, whether or no all compound bodies do consist of the same number of elementary ingredients or material principles.” In another work, The Imperfections of the Chemical Doctrine of Qualities, Boyle points out the arbitrary nature of Sylvius’s classification of all substances as acids and alkalies, and the needlessness and unsatisfactory character of his hypotheses. Iatro-chemistry was opposed also by Conring (1606—1681), Sydenham (1624-1689), Pitcairne (1652-1713), and his pupil Boerhaave (1668-1738), the author of the excellent Elementa Chemiae; and though vigorously supported by De Blegny, Borrichius, Viridet, Vieussens, and others, it gradually lost repute, and was finally overthrown by F. Hoffmann (1660-1742).

Of the labours of Kunckel (1630-1703) in the cause of chemistry it is impossible to give an account within the com- 'pass of the present sketch; but whilst the science was enriched by means of his numerous researches, amongst which may be mentioned those on phosphorus, it received no assistance from his theoretical views concerning the constitution of bodies; thus, for instance, he rejected the belief in the three principles of Paracelsus, yet maintained that all metals contained common quicksilver; and though their increase in weight by calcination was not, according to him, due to the absorption of ponderable fiery material, the explanation he offered of this phenomenon was even less satisfactory.

To Becher (1635-1682) and to Stahl (1660-1734) chemistry owes the introduction of the first consistent theory of the constitution of compounds and of chemical action. Becher held that the primary ingredients of matter were water and earth, and that from these were produced three earths—the fusible or stony, the fatty, and the fluid earths,—improperly called salt, sulphur, and mercury. Stahl, who developed the doctrines of Becher, enumeratedfour elements—water, acid, earth, and phlogiston. Becher had explained the calcination of metals on the supposition that they consisted of an earth and a something of which they became deprived on ignition; the burning of brimstone was, in like manner, thought to be its resolution into an acid and true sulphur, or that combustible part which was dispelled by heat. It was this supposed combustible body to which the name phlogiston (φλoγiστov, combustible) was applied by Stahl — the matena aut principium ignis non ipse ignis. The phlogiston of Stahl answers in some measure to the souls and spirits assigned to metals and salts by the alchemists, or to what Geber called the “humidity,” and Cardan the “celestial heat” of metals. When by means of charcoal a metallic calx was reduced, or a compound containing sulphur was obtained from fused sodium sulphate, phlogiston was supposed to be absorbed from the charcoal, which with 4 amp black and other reducing agents came in time to be regarded as nearly pure phlogiston. Bodies that would not burn were thought to have already parted with their phlogiston. From a consideration of the insolubility of most combustible substances arose the idea that phlogiston was a dry and earthy body, capable of receiving a motion of great velocity—the motus verticillaris — manifested when ignition or flame was produced. John Rey had in 1630 remarked that metals grow heavier when calcined by the absorption of “thickened air,” but had given no general theory of combustion, or explanation why many substances become lighter or are lost sight of when heated. Boyle, too, bad noticed the increase of weight caused by the calcination of metals, and had attributed it to the combination of the latter with heat particles; and Stabel and others were not slow to object that this fact negatived the supposition that calcination consisted in a subtraction of phlogiston; the Stahlians, however, met the difficulty by declaring that substance to be the principle of levity or negative weight.

F. Hoffmann, who contributed greatly to the progress of analytical chemistry in Germany, held with Stahl that sulphur consisted of acid and phlogiston, and that combustible bodies contained something which might be described as phlogiston, but thought it possible that the calces of metals were formed, not by the subtraction of phlogiston, but by the combination of the metals with an acid material. Boerhaave, without directly attacking the phlogistic theory, casts doubts upon the assumption of the existence of a combustible principle and of earthy substances in the metals. The view of Homberg (1652-1715) was that the principle of combustibility in inflammable minerals and in vegetable substances was sulphur; and E. F. Geoffroy (1672-1731) regarded phlogiston as a sulphurous or oily principle. Amongst the most active supporters of the doctrines of Stahl were Neumann (1683-1737); J. II. Pott (1692-1777), distinguished for his researches on the behaviour of mineral substances at high temperatures; Marggraf (1709-1782); and Macquer (1718-1784), the discoverer of arsenic acid. Other celebrated chemists who flourished during the phlogistic period were Réaumur (1683- 1757), Hellot (1685—1766), and Duhamel du Monceau (1700-1782), who first proved the nature of the base of common salt.

The phlogistic theory of Stahl, though incorrect, was of no small assistance towards a true understanding of chemical phenomena. It was based upon experimental data, the interpretation of which served for the correlation of facts of which but vague and enigmatic explanations had formerly been given. The supposed subtraction of phlogiston in the calcination of metals, though equivalent in reality to the addħion of oxygen, was yet a loss of potential energy, by virtue of the combination of the metal with the gas; and the gain of phlogiston was an increase of potential energy, attendant on the removal of oxygen.

It was only in the latter part of the 18th century that the influence of the presence of air upon the formation of many chemical compounds was generally perceived, and that through the use of the balance the nature of gases began to be comprehended and such airy nothingness became commonly regarded as an intimate and necessary constituent of various solid and fluid bodies. The phlogistic theory gave to its adherents so plausible and moreover so circumstantial an account of the modes of chemical action, that facts and observations which caused at a later time a complete revolution in the theory of chemistry, such, for instance, as regarded the existence and properties of oxygen, remained without explanation, and almost unheeded. Robert Hooke, so early as 1665, in his Micrograplιia, foreshadowed the discoveries of Priestley and his contemporaries, when he advanced the opinion that in common air there existed a substance like, if not the same as, that fixed in saltpetre, and which at an elevated temperature dissolved combustibles such as sulphurous bodies with a rapidity sufficient to occasion the motion of fire, and to create light; this solvent he considered to he far less for a given bulk of air than of saltpetre. The investigations of Mayow (1645-1679) are particularly interesting. In treatises published at Oxford in 1668 and 1674 oxygen is actually described by him under the name of fire-air, aerial spirit, and nitre-air ; all acids are said to contain it, and it is necessary for combustion and respiration, processes which are therefore analogous; it is the nitre-air of the atmosphere that causes fermentation and the souring of wines, that produces sulphuric acid from sulphur, and effects the calcination of metals.

Early in the 18th century Newton in his Opticks indicated the nature and the modes of formation of gases. “Dense bodies,” he tells us, “by fermentation rarefy into several sorts of air; and this air by fermentation, and sometimes without it, returns into dense bodies;” and further on he remarks that the particles shaken off from bodies by heat or fermentation, so soon as they are beyond the reach of the attraction of the body, recede from it, and also from one another with great strength, so as sometimes to take up above a million of times more space than they did before in the form of a dense body. This vast contraction and expansion seem to him unintelligible by feigning the particles of air to be springy and ramous, or rolled up like hoops, or by any other means than a repulsive power; the particles of fluids which do not cohere strongly are most easily rarefied into vapour; but those which are grosser, or cohere by a stronger attraction, are not separated without a stronger heat, or perhaps not without fermentation; being rarefied by fermentation they become true permanent air, those particles receding from one another with the greatest force, and being most difficultly brought...