air, whose properties could change in so inexplicable and mysterious a manner. Owing, therefore, to its elusive and, as it were, semi-spiritual properties, and to its unexpected changes of character, it was long before its true nature was discovered. It had not escaped observation that “air” obtained by distilling animal and vegetable matter, or by the action of acids on iron and zinc, differed from ordinary air by being inflammable; but such “airs” were regarded as atmospheric air, modified in some manner, as it is modified when perfumed. And “airs” escaping from fermenting liquids, or produced by the action of acids on carbonates, were neglected. For long no attempt was made to catch them; and the frothing and bubbling were regarded as a species of boiling, as is still seen in the use of our word “fermentation” (fervere, to boil).
Second, Erroneous ideas regarding the phenomena of combustion. While it was recognised that a burning candle was extinguished if placed in a confined space, its extinction was attributed not to the absence of air, but to the impossibility of the escape of flame. Indeed, flame was regarded as possessing the same semi-spiritual, semi-material nature as air. Together with earth and water, air and flame or fire formed the four elementary principles of the Ancients; and all substances—stones, metals, animals, and vegetables—were regarded as partaking of the properties of these elements, and often as being constituted of the latter in varying proportions, according as they were cold and dry (earth), cold and moist (water), hot and moist (air), or hot and dry (fire). It is not within the scope of this book to enter into details regarding such ancient views. Those who are interested in the matter will find them expounded in Kopps’ History of Chemistry, Rodwell’s Dawn of Chemistry, E. von Mayer’s History of Chemistry, and in other similar works. But we shall be obliged to consider the later developments of such ideas in the phlogistic theory, by means of which all chemical changes connected with combustion were interpreted from the latter part of the seventeenth to the end of the eighteenth century. With erroneous views regarding the nature of combustion, and ignorance as to the part played by the atmosphere in the phenomena of burning, the true nature of air was undiscoverable.
Third, The lack of attention to gain or loss of weight. It was in past times not recognised that nothing could be created and nothing destroyed. In popular language, a candle is destroyed when it is burned, nothing visible being produced from it. The products, we now know, are gaseous and invisible, and possessed of greater weight than the unburnt candle; but for want of careful experiment, it was formerly concluded that the candle, when burnt, was annihilated. The formation of a cloud in a cloudless sky; the growth of vegetables in earth, from which, apparently, they did not derive their substance; and the reputed growth of metalliferous lodes in mines—these were all adduced as proofs of the creative power of Nature. With such ideas, therefore, the necessity of controlling the gain or loss of material during experiment, by determining gain or loss of weight, did not appear imperative; and hence but few quantitative experiments were made, and little importance was attached to these few. It had, for example, long been noticed that certain metals gained weight when burned and converted into a “calx,” or, as we should now say, a metallic oxide, but such gain in weight was not regarded as of any consequence. When considered in relation to the supposed loss of “phlogiston” suffered by a metal on being converted into a calx, it was explained by the hypothesis that phlogiston possessed “levity”—the antithesis of gravity—and that the calx weighed more than the metal, owing to its having lost a principle which was repelled instead of being attracted by the earth.
Among the most remarkable early attempts to elucidate the true nature of air, we meet with one by the Hon. Robert Boyle, who published about the middle of the seventeenth century his Memoirs for a General History of the Air. Boyle was one of the most distinguished scientific men of his own, or indeed of any, age, and in his spirit of calm philosophical inquiry he was far in advance of his contemporaries. He was born in the early part of the year 1626, in Ireland, whither his father, Richard Boyle, had emigrated at the age of twenty-two. Boyle’s mother, daughter of Sir Geoffrey Fenton, principal Secretary of State for Ireland, died while he was still a child. Yet she must have lived in the recollection of her son Robert, for he wrote: “To be such parents’ son, and not their eldest, was a happiness that our Philarethes (himself) would mention with great expressions of gratitude; his birth so suiting his inclinations and designs, that had he been permitted an election, his choice would scarce have altered God’s discernment.”
In those days of early development, Boyle had finished his school-days at Eton by his twelfth year. He informs us that he devoured books omnivorously, and could hardly be induced to join in games. The next six years of his life he spent on the Continent with his elder brother; and on his father’s death, which happened when he was abroad, he returned to England, and settled at Stalbridge, in Dorsetshire, where he had inherited a manor. Here he passed most of his life in great retirement, with only an occasional visit to London; for though he lived through troublous times, he avoided politics. Indeed, he is known only to have appeared once on a public platform, and that was in defence of the Royal Society, then in its infancy, from attacks made upon it by some too scrupulously loyal Churchmen.
ROBERT BOYLE.
Boyle did not confine his attention exclusively to scientific pursuits: he interested himself deeply in theology, and published numerous tracts on religious subjects. He wrote with equal ease in English, French, and Latin, and his books appeared simultaneously in the first and last of these languages. His researches are remarkable for their wide range and for the boldness of his conceptions. But Boyle, ingenious though he was, was unable to fathom the mystery of atmospheric air. His views regarding it are succinctly stated by him in his Memoirs for a General History of the Air, and in the same work he sums up the views of the Ancients. His words are:
“The Schools teach the air to be a warm and moist element, and consequently a simple and homogeneous body. Many modern philosophers have, indeed, justly given up this elementary purity in the air, yet few seem to think it a body so greatly compounded as it really appears to be. The atmosphere, they allow, is not absolutely pure, but with them it differs from true and simple air only as turbid water from clear. Our atmosphere, in my opinion, consists not wholly of purer aether, or subtile matter which is diffused thro’ the universe, but in great number of numberless exhalations of the terraqueous globe; and the various materials that go to compose it, with perhaps some substantial emanations from the celestial bodies, make up together, not a bare indetermined feculancy, but a confused aggregate of different effluvia. One principal sort of these effluvia in the atmosphere I take to be saline, which float variously among the rest in that vast ocean; for they seem not to be equally mixed therein, but are to be found of different kinds, in different quantities and places, in different seasons. … Many men talk much of a volatile nitre in the air, as the only salt wherewith that fluid is impregnated. I must own the air, in many places, seems to abound in corpuscles of a nitrous nature; but I don’t find it proved by experiments to possess a volatile nitre. In all my experiments upon salt-peter, I found it difficult to raise that salt by a gentle heat; and spirits of nitre, which is drawn by means of a vehement one, has quite different properties from crude nitre, or the supposed volatile kind in the air, for ’tis exceeding corrosive.”[1]
Boyle then proceeds to collect and comment on the effluvia from volcanoes and from decaying vegetables and animals, and proposes tests for the presence of such ingredients. He even attributes the darkening of silver chloride to its being a reagent for certain salts present in air at one time and not at another, and draws attention to the sulphurous smell produced by “thunder.” Farther on (p. 61) he writes:
“The generality of men are so accustomed to judge of things by their senses, that because the air is invisible they ascribe but little to it, and think it but one remove from nothing. And this fluid is even by the Schoolmen considered only as a receptacle of visible bodies, without exerting any action on them unless by its manifest qualities, heat and
