The Fontana History of Chemistry. William Brock J.

were neither the atoms of Epicurus and Gassendi, nor the particles of Descartes and the Cartesians. They were at once more useful and more sophisticated than either of them. Boyle’s mechanical philosophy was built on the principles of matter and motion. The properties of bulk matter were explained by the size, shape and motion of corpuscles, and the interaction of chemical minima naturalia (molecules), the evidence for which lay in chemical phenomena. Like Bacon and his fellow members of the Royal Society, however, Boyle always claimed to dislike and distrust ‘systems’.

      It has long seemed to me none of the least impediments of true natural philosophy, that men have been so forward to write systems of it, and have thought themselves obliged either to be altogether silent, or not write less than an entire body of physiology.

      Yet, while he disagreed with Cartesian physics, he seems to have felt that Descartes’ picture of the world as an integrated system, or whole, was a fruitful one. He agreed that there were no isolated pieces in Nature; that every piece of matter in the universe was continually acted upon by diverse forces or powers. The world was a machine, ‘a self-moving engine’, ‘a great piece of clockwork’ comparable to ‘a rare clock such as may be seen at Strasbourg’, then the engineering marvel of Europe. God was the clock-maker, the universe was the clock.

      All this sounds like a ‘system’, as indeed it was. What Boyle meant by opposing systems, as such, was that they were usually based upon an a priori, experimentally indefensible set of hypotheses. They had usually been assembled from hypotheses that were not verae causae (true causes), as Newton was to call the kind of hypothesis that ought to be acceptable in natural philosophy.

      We can see now why Boyle could accept a mechanical, corpuscular system of philosophy. The corpuscular philosophy was a vera causa, which could explain a tremendous range of diverse phenomena, and which could be experimentally defended. At the same time, it avoided and did away with ‘inexplicable forms, real qualities, the four peripatetick elements … and the three chymical principles’. Hotness, coldness, colour and the many secondary qualities and forms of Aristotelian physics were swept aside and explained solely in terms of the arrangements, agglomerations and behaviour of chemical particles as they interacted. Boyle’s assertion of the corpuscular philosophy was like Galileo’s claim that the book of Nature was written in mathematical terms. Boyle’s book was ‘a well-contrived romance’ of which every part was ‘written in the stenography of God’s omnipotent hand’, i.e. in corpuscular, rather than geometrical, characters. By revealing its design, like Gassendi and Charleton earlier, Boyle reconciled what had formerly been perceived as an atheistical system with religion and, indeed, with the tenets of the Anglican church that had become the re-established Church of England following the Civil War.

      Boyle demonstrated the usefulness of chemistry not merely to medicine and technology (where it had long been accepted) but also to the natural philosopher, who had long despised it as the dubious activity of alchemists and workers by fire. Boyle aimed to show natural philosophers that it was essential that they took note of chemical phenomena, for the mechanical philosophy could not be properly understood otherwise. It was true, he admitted, that the theories of ordinary spagyrical chemists were false and useless; nevertheless, their experimental findings deserved attention, for if they could be disentangled from false interpretations, much would be found that would illustrate and support the corpuscular theory of matter.

      In this way, Boyle strove to ‘begat a good understanding betwixt the chymists and the mechanical philosophers’. Chemists recognized him as a fellow chemist, even though he was a natural philosopher; while the natural philosophers recognized him as a respectable chemist because he was also a member of their company. By advocating a mechanical philosophy, Boyle would raise the social and intellectual status of ‘workers by fire’, reduce their proneness to secrecy and mysterious language, and make them into natural philosophers. As he wrote in another essay of 1661²:

      I hope it may conduce to the advancement of natural philosophy, if,… I be so happy, as, by any endeavours of mine, to possess both chymists and corpuscularians of the advantages, that may redound to each party by the confederacy I am mediating between them, and excite them both to enquire more into one another’s philosophy, by manifesting, that as many chymical experiments may be happily explicated by corpuscularian notions, so many of the corpuscularian notions may be commodiously either illustrated or confirmed by chymical experiments.

      Boyle may be said to have united the proto-disciplines of chemistry and physics. But the partnership proved premature, for Boyle succumbed to the danger of not replacing the elements and principles of the chemists with a mechanical philosophy that was useful to the working chemist. This criticism can be most clearly made when discussing Boyle’s definition of the element in the sixth part of The Sceptical Chymist.

      I now mean by elements, as those chymists that speak plainest do by their principles, certain primitive and simple, or perfectly unmingled bodies; which not being made of any other bodies, or of one another, are the ingredients of which all those called perfectly mixt bodies are immediately compounded, and into which they are ultimately resolved.

      Leaving aside the fact that Boyle made no claim to be defining an element for the first time (as so many modern chemistry textbooks claim), in his next sentence he went on to deny that the concept served any useful function:

      … now whether there be any one such body to be constantly met with in all, and each, of those that are said to be elemented bodies, is the thing I now question.

      A modern analogy will make Boyle’s scepticism clear. If matter is composed ultimately of protons, neutrons and electrons, or, more simply still, of quarks, this, according to Boyle, should be the level of analysis and explanation for the chemist, not the so-called ‘elements’ that are deduced from chemical reactivity. To Boyle, materials such as gold, iron and copper were not elements, but aggregates of a common matter differentiated by the number, size, shape and structural pattern of their agglomerations. Although he clearly accepted that such entities had an independent existence as minima, he was unable to foresee the benefit of defining them pragmatically as chemical elements. For Boyle an ‘element’ had been irreversibly defined by the ancients and by his contemporaries as an omnipresent substance.

      The seventeenth-century corpuscular, physical philosophy was all very well. It might explain chemical reactions, but it did not predict them, nor did it differentiate between simple and complex substances, the elementary and the compound. Nor, at this stage, did it align the supposed particles with weight and the chemical balance. Hence, although corpuscularianism was not overtly denied by later chemists, who were often content to accept it as an explanation of the physical character of matter, in chemical practice it was ignored. Chemists still needed the concept of an element and blithely returned to the four elements or to some other elementary concept. One thing had changed, however, as a result of Boyle’s criticisms. It was no longer possible to argue seriously that all of the possible elements, however many a chemist might postulate, were ubiquitously present in a particular material. Boyle’s scepticism suggested the possibility that some substances might contain less than the total number of elements; this made it possible for later chemists to be pragmatic about elements and to increase their number slowly and stealthily throughout the eighteenth century.

      This more pragmatic view is seen clearly in Nicholas Lemery’s Cours de chymie (1675; English trans. 1686)³:

      The word Principle in Chymistry must not be understood in too nice a sense: for the substances which are so-called, are Principles in respect to us, and as we can advance no further in the division of bodies; but we well know that they may be still further divided in abundance of other parts which may more justly claim, in propriety of speech, the name of Principles: wherefore such substances are to be understood as Chymical Principles, as are separated and divided, so far as we are capable of doing it by our imperfect powers.

      This comes pretty close to Lavoisier’s operational definition of an element (Chapter 3).

      It would be wrong to leave the impression that