Читать книгу The Fontana History of Chemistry - William Brock J. - Страница 21

Newton’s interest in chemistry was life-long and reputedly aroused when, as a schoolboy at Grantham Grammar School, he lodged with an apothecary. He wrote only one overtly chemical paper, but important and influential chemical statements are to be found in the Principia Mathematica (1687) and the Opticks (1704). As mentioned in Chapter 1, there also exist in manuscript thousands of pages of chemical and alchemical notes, much of them identifiable as transcriptions from contemporary printed or manuscript works. Newton seems to have been interested in both exoteric and esoteric alchemy, that is, his interest extended beyond the empirical and experimental information that might be gleaned from alchemical texts to the ‘mysteries’ and secrets that were imparted in metaphor and allegory.

Newton was principally influenced by Helmont and Boyle; he also found the nitro-aerial theory attractive as a sustaining principle reminiscent of Helmont’s blas.

I suspect, moreover, that it is chiefly from the comets that spirit comes, which is indeed the smallest but the most subtle and useful part of the air, and so much required to sustain the life of all things with us.

And in the Principia Newton more than hinted that all matter took its origin in water.

The vapours which arise from the sun, the fixed stars, and the tails of comets, may meet at last with, and fall into, the atmospheres of the planets by their gravity, and there be condensed and turned into water and humid spirits; and from thence, by a slow heat, pass gradually into the form of salts, and sulphurs, and tinctures, and mud, and clay, and sand, and stones, and coral, and other terrestrial substances.

Nature was a perpetual worker; all things, he wrote in the Opticks, grow out of, and return by putrefaction into, water.

Nevertheless, Newton subscribed wholeheartedly to Boyle’s corpuscular philosophy, to which he added the mechanisms of attraction and repulsion to explain not merely the gravitational phenomena of bulk planetary matter, but also the chemical likes (affinities) and dislikes (repulsions) that individual substances displayed towards one another. Such inherent powers of matter, which Newton attributed to a subtle ether that bathed the universe, replaced the astral influences of Paracelsus and the blas of Helmont as the causes of motion and change. Newton made this the subject of his only published chemical paper, ‘De natura acidorium’, written in 1692 but not published until 1710, as well as the ‘Queries’ 31 and 32 of the 1717 edition of the Opticks. In these writings Newton suggested that there were exceedingly strong attractive powers between the particles of bodies, which extended, however, only a short distance from them and varied in strength from one chemical species to another. This hypothesis of short-range force led him to speculate about what eighteenth-century chemists called ‘elective affinities’ and the reason why, for example, metals replaced one another in acid solutions. He gave the replacement order of six common metals in nitric acid.

The investigation of chemical affinity became one of the absorbing problems of chemistry. In 1718, Étienne Geoffroy (1672–1731) produced the first table of affinities, and more elaborate ones were produced by Torbern Bergman (1735–84) and others from the 1750s onwards. As the Newtonian world picture grew in prestige, chemists and natural philosophers also began to interpret these tables in terms of short-range attractions. In 1785 Buffon even identified the laws of affinity with gravitational attraction; but all attempts to satisfy what has been described as the ‘Newtonian dream’ to mathematize (i.e. quantify) affinity ended in failure. It was left to Claude Berthollet to point out in 1803 that other factors, such as mass (concentration), temperature and pressure, also decided whether or not a particular reaction was possible.

Newton’s ether, the active principle of chemical change, was exploited by large numbers of eighteenth-century chemists, including the important Dutch teacher, Hermann Boerhaave (1668–1738). The latter’s Elementa Chemiae (1732), which appeared in English in 1741, assimilated ether to fire. Fire, said Boerhaave, consisted of subtle, immutable bodies that were capable of insinuating themselves into the pores of bodies; it was ‘the great changer of all things in the universe, while itself remaining unchanged’. Like his German contemporary Georg Stahl, whose work he ignored, Boerhaave treated fire, together with the other three Aristotelian elements, as one of the four ‘physical instruments’ available to chemists. Because of the connections that were established between the Scottish universities and the University of Leiden, where Boerhaave taught, Boerhaave came to have considerable influence on the teaching of chemistry to medical students in Scotland by William Cullen (1710–90) and his pupil, Joseph Black (1728–99).

Cullen, for example, explained chemical attraction as due to the self-repulsive character of the particles of etherial fire and to the relative densities of ether within two attracting bodies compared with the density of ether in the external environment. The solid and liquid states similarly depended upon the relative quantities of ether and ordinary matter within a substance – a model that was to have important consequences for the conceptualization of gases. This identification of ether and fire, or heat, stimulated Cullen’s pupil, Joseph Black, to the study of calorimetry, the establishment of the concepts of specific heat capacity and latent heat, and the exploration of the qualitative difference between air and a ‘fixed air’ (carbon dioxide), whose presence in magnesia alba (basic magnesium carbonate) he had deduced in 1766.

Newton was also the inspiration behind the experimentally deft attempts made by Stephen Hales (1677–1761) to discover the mechanism of plant growth through an investigation of the movement of sap. It was while making these investigations in the 1720s that he discovered that plants and minerals contained, or held within their pores, large quantities of air. In his Vegetable Staticks published in 1727, Hales devoted over a third of the book to a demonstration of this finding, which he proved by heating solids and liquids in a gun barrel and collecting the ejected air over water in a vessel suspended from a beam. This discovery that air could be ‘fixed’ was the beginning of pneumatic chemistry, and a key factor in the eighteenth-century ‘chemical revolution’.