The Fontana History of Chemistry. William Brock J.

see how plant perfumes and nectars arose from water alone. There was no evidence that an alcahest existed and, in any case, the mechanical philosophy saw no ultimate physical difference between a solvent and a solute. Thus although Helmont’s experiments were a useful stick with which to beat the Aristotelian and Paracelsian theories of elements, Boyle was no partisan of Helmont’s alternative interpretation.

      On the other hand, Helmont’s theory appealed to Boyle’s Biblical literalism, for the world, according to Genesis and Hebrew mythologies, had emerged ‘by the operation of the Spirit of God,… moving Himself as hatching females do … upon the face of the water’. This original water could never have been elementary, but must have consisted ‘of a great variety of seminal principles and rudiments, and of other corpuscles fit to be subdued and fashioned by them’. Possibly, then, common water had retained some of this original creative power.

      Boyle’s advice on the whole question of the evidence for the existence of elements was to keep an open mind and a sceptical front.

      The surest way is to learne by particular experiments what heterogeneous parts particular bodies do consist of, and by what wayes, either actual or potential fire, they may best and most conveniently be separated without fruitlessly contending to force bodies into more elements than Nature made them up of, or strip the severed principles so naked, as by making them exquisitely elementary, to make them laboriously uselesse.

      There was irony in that final remark, for through his adherence to the corpuscular philosophy Boyle proceeded to make the concept of the element ‘laboriously uselesse’. Before pursuing this point, however, what sceptical mischief did Boyle wreak on the acid – alkali theory?

      This theory was not discussed in either The Sceptical Chymist or its manuscript draft version. Instead, Boyle criticized Sylvius’ and Tachenius’ views in 1675 in Reflections upon the Hypothesis of Alcali and Acidium. Ten years previously, in his Experimental History of Colours (see chapter 5), Boyle had made an important contribution to acid – base chemistry with the development of indicators. He had found that a blue vegetable substance, syrup of violets, turned red with acids and green with alkalis. The test was applicable to all the known acids and could be used confidently to give a working definition of an acid: namely, that an acid was a substance that turned syrup of violets red. The test was also quantitative in a rough-and-ready way, since neutral points could be determined.

      When Boyle came to consider the Sylvius – Tachenius theory in 1675, he was able to object to the vagueness of the terms ‘acid’ and ‘alkali’ as commonly used in the theory. Effervescence, he pointed out, was not a good test of acidity, since it was also the test for alkalinity; it also created difficulties with the metals, which effervesced when added to acids. Were metals alkalis? If zinc was reacted with the alkali called soda (sodium carbonate), it was dissolved. Was zinc, therefore, an acid?

      Whereas in The Sceptical Chymist Boyle had only played the critic and not put forward any concrete proposal to replace the Aristotelian and Paracelsian theories, in the case of his criticism of the acid – alkali theory, he was able to offer an alternative, experimentally based classification of acidic, alkaline and neutral solutions, which could be used helpfully in chemical analysis. By building on this experimental work, succeeding chemists were able to develop the theory of salts, which proved one of the starting points for Lavoisier’s revision of chemical composition in the eighteenth century.

      There was also a second important criticism of the acid – alkali theory. In its vague metaphorical talk of ‘strife’ between acidic and alkaline solutions, the theory possessed a decidedly unmechanical, indeed, anti-mechanical, air about it. To a corpuscular philosopher like Boyle, the theory was occult, in the seventeenth-century sense that it appealed to explanations that could not be reduced to the mechanical geometrical principles of size, shape and motion with which God had originally endowed them. Even so, it is doubtful whether Boyle subscribed fully to the reduction of chemical properties to geometrical qualities, as early eighteenth-century philosophers were to do. The most Boyle was prepared to argue was that chemical properties depended on the way the particles that composed one body were disposed to react with those of others.

      He was, no doubt, acutely aware of the fact that, by abolishing Aristotelian formal causes, an explanation of the distinction between chemical species was lost. Gassendi’s solution, which Boyle followed, had been to introduce ‘seminal virtues’ or seeds, ‘which fit the corpuscles together … into little masses [which] shapes them uniformly’. Boyle’s experiments on variable crystalline shapes produced when the same acid was reacted with different metals enabled him to argue that each acid, alkali and metal had its own specific internal form or virtue, which could be modified in the presence of others. Here Boyle found the earlier idea of medieval minima and mixtion useful since, unlike physical atomism, it tried to explain combination by more than physical cohesion alone. As previously noted, another way forward, represented by Descartes, was to explain form geometrically by attributing chemical significance to the shapes of the ultimate physical particles. Descartes’ three elements came in three shapes, irregular, massive and solid, and long and thin. Although there was an obvious analogy with Paracelsian sulphur, salt and mercury, Norma Emerton has also noted the parallel with contemporary Dutch land drainage schemes in which a framework of sticks interleaved with branches was covered with stones to form a terra firma. For Descartes, therefore, composition (mixtion) and the new form was caused by simple entanglement.

BOYLE’S PHYSICAL THEORY OF MATTER

      Boyle used to be dismissed by historians of chemistry as only a critic, but this is certainly not the tenor of his work as a whole. He was an extremely prolix, rambling and, by today’s standards, unmethodical writer who published some 42 volumes. He adopted a Baconian method towards his scientific activities, and this was often reflected in the apparently random method of composition, which never allowed him time to write a comprehensive treatise on chemistry. We know that his manuscripts were delivered to the printer in bits and pieces, always behind schedule, and full of addenda and ‘lost experiments’ from previous research projects. It is small wonder, then, that Peter Shaw, Boyle’s eighteenth-century editor, found it necessary to apologize to readers for the lack of system in Boyle’s collected works:

      But as Mr Boyle never design’d to write a body of philosophy, only to bestow occasional essays on those subjects whereto his genius or inclination led him; ‘tis not to be expected that even the most exquisite arrangement should ever reduce them to a methodical and uniform system, though they afford abundant material for one.

      Despite Shaw’s defensive remark, there was in fact a system in Boyle’s ‘ramblings’. Elsewhere Shaw himself identified it when he referred to Boyle as ‘the introducer, or at least, the great restorer, of the mechanical philosophy amongst us’. This claim that Boyle had restored the mechanical philosophy had first appeared in one of Richard Bentley’s Boyle lectures, or sermons, several years earlier.

      The mechanical or corpuscular philosophy, though peradventure the oldest as well as the best in the World, had lain buried for many ages in contempt and oblivion, till it was happily restored and cultivated anew by some excellent wits of the present age. But it principally owes its re-establishment and lustre to Mr Boyle, that honourable person of ever blessed memory who hath not only shown its usefulness in physiology (i.e. physics) above the vulgar doctrines of real qualities and substantial forms, but likewise its great serviceableness to religion itself.

      By the mid seventeenth century there was no longer any conceptual difficulty involved in the acceptance of minute particles, whether atomic or (less controversially) corpuscular, which, though invisible and untouchable, could be imagined to unite together to form tangible solids. No doubt the contemporary development of the compound microscope by Robert Hooke and others helped considerably in stimulating the imagination to accept a world of the infinitely small, just as the telescope had banished certain conceptual difficulties concerning the possibility of change in the heavens. If only Democritus had a microscope, Bacon said, ‘he would perhaps have leaped for joy, thinking a way was now discovered for discerning