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The first beginnings of bodies, and of corporeal causes, are two, and no more. They are surely the element water, from which bodies are fashioned, and the ferment.
As we have already seen in the introduction, the justification for this belief was an interesting, quantitative growth experiment with a young willow tree. Additional supporting evidence came from the fact that fish were nourished ‘solely’ by water, that seashells were found on dry land, and that solid bodies could be transformed into ‘savoury waters’, that is, into solution. In the latter case, Helmont took a weighed amount of sand, and fused it with excess alkali to form water-glass, which liquefied on standing in air. Here was a palpable demonstration of the reconversion of earth back into water. More remarkably, this ‘water’ could be reconverted back to ‘earth’ by treatment with acid, when the silica sand recovered was found to have the same weight as the starting material.
There are a number of interesting features about these experiments and Helmont’s reasoning. Their most important feature is not that Helmont misinterpreted his observations because he ignored the role of air, but that they were quantitative. The experiments were also controlled. In the willow tree experiment, Helmont covered the vessel so as to prevent dust contamination, which might have affected the result. Similarly, he dried the earth beforehand and used only distilled water. He clearly had thought about the experiment and possible objections that might be raised against his conclusions because of the way the experiment had been designed. All this was the hallmark of the experimental method that was to lead to the transformation of chemistry. In addition, it is noticeable that he implicitly assumed that matter was conserved in any changes it underwent. When metals were dissolved in acids they were not destroyed, but were recoverable weight for weight. Helmont also postulated the existence of an alcahest, or universal solvent, which had the property of turning things back into water. Much time and effort was spent by contemporary chemists, including Robert Boyle, in trying to identify this mysterious solvent.
There is a further item of interest to be found in Helmont’s writings. Since air could not be turned into water, he accepted it as a separate element. However, his keen interest was awakened by the ‘air-like’ substances that were frequently evolved during chemical reactions. Helmont identified these fuliginous effluvia as ‘gases’, from a Greek word for ‘chaos’ that Paracelsus had ascribed to air in another connection. Where did these uncontrollable, dangerous materials fit in Helmont’s ontology?
Gases were simply water, not air, for any matter carried into the atmosphere was turned into gas by the cold and ‘death’ of its ferments. A gas was chaos because it bore no form. A gas might also condense to a vapour and fall as rain under the influence of blas, a term that did not stay in chemical language, and which Helmont coined to refer to a kind of ‘gravitational’, astral influence or power that caused motion and change throughout the universe.
In a typical gas experiment, Helmont heated 62 lb (28 kg) of charcoal in air and was left with 1 lb (2.2 kg) of ash, the rest having disappeared as ‘spiritus sylvester’ or wild spirit. When charcoal was heated in a sealed vessel, combustion would either not occur, or would occur with violence as the spirit escaped from the exploding vessel. This disruptive experience led to Helmont’s definition of gas:
This spirit, hitherto unknown, which can neither be retained in vessels nor reduced to a visible body … I call by the new name gas.
Although Helmont implied by this a distinction between gas and air, and even between different gases, these were features to which commentators paid scant attention. The reason for this is that, in the absence of any suitable apparatus to collect and study such aerial emissions, it was impossible to distinguish between them chemically. Helmont himself had to be content with classifying gases from their obvious physical properties: for example, the wild and unrestrainable gas (spiritus sylvester) obtained from charcoal; gases from fermentations; vegetable juices; from the action of vinegar on the shells of certain sea creatures; intestinal putrefactions; from mines, mineral waters and from certain caverns like the Grotto del Cane near Naples, which allowed men to breathe but extinguished the life of a dog.
In striking contrast to his French contemporary. René Descartes, who claimed that, apart from the existence of a human soul, life was a mechanistic process, Helmont refused to separate soul from matter itself. Matter became spiritualized and nature pantheistic. Such a spiritualization of matter proved especially attractive to various religious groups during the Puritan revolution in England. The writings of Paracelsus and Helmont circulated widely during the 1650s and 1660s, partly because they could be used as weapons in the power struggles between physicians and pharmacists, but also because religious ideology was in a state of flux. The Neoplatonic, unmechanical, vitalistic and almost anti-rational aspects of both Paracelsianism and Helmontianism appealed to many because they emphasized the significance of personal illumination against pure reason. This appealed to the Puritan conscience precisely because it could justify religious and political revolution for the sake of one’s ideals.
But along with the ideology went the ‘positive’ science of Helmont: gases, quantification and measurement, and iatrochemistry. Once the Commonwealth was achieved, the concept of personal illumination had to be played down (as Libavius had foreseen) in order to prevent anarchy. In the 1660s, therefore, Helmontianism came under attack. Whereas in the 1640s it had been argued by some that Oxford and Cambridge Universities ought to be reformed under Paracelsian and Helmontian lines, by the mid 1660s this was out of the question and the mechanical philosophy of Descartes, Boyle and Newton was to be triumphantly advocated by the new Royal Society. Nevertheless, echoes of Helmontianism remained in the works of Boyle and Newton.
THE ACID-ALKALI THEORY (#ulink_6536c121-6508-5d55-b3c7-15aa39f83a93)
This dualistic theory, based upon the old Empedoclean idea of a war of opposites, also stemmed directly from Helmont’s work. Helmont had explained digestion chemically as a fermentation process involving an acid under the control of a Paracelsian archeus or internal alchemist. At the same time, he was able to show that the human body secreted alkaline materials such as bile. One of his disciples, Franciscus Sylvius (1614–72), a Professor of Medicine at Leyden from 1658 until his death, and a leading exponent of iatrochemistry, extended Helmont’s digestion theory by arguing that it involved the fermentation of food, saliva, bile and pancreatic juices. For Sylvius, this was a ‘natural’ chemical process and involved no archeus, supernatural or astral mechanism of transformation. The pancreatic juices were a recent discovery of physiologists. By taste they were acidic, as was saliva; but bile was alkaline. Since it was well known that effervescence was produced when an acid and alkali reacted together, as when vinegar was poured onto chalk, Sylvius believed that digestion was a warfare, followed by neutralization, between acids and alkalis.
He did not hesitate to extend this conception of neutralization between two chemical opposites to other physiological processes. For example, by suggesting that blood contained an oily, volatile salt of bile (alkali), which reacted in the heart with blood containing acidic vital spirits, he explained how the vital animal heat was produced by effervescence. From this normal state of metabolism, pathological symptoms could be explained. All disease could be reduced to cases of super-acidity or super-alkalinity – a theory that was quickly exploited commercially by apothecaries and druggists and which is not unfamiliar from twentieth-century advertisements.
Sylvius’ theory was popularized by his Italian pupil, Otto Tachenius (1620–90), in the Hippocrates Chemicus (1666) – a title that advertised its iatrochemical approach explicitly. Amid its chemical explanations for human physiology lay a criticism that the greatest need in the 1660s was for a unifying theory of chemical classification and explanation to replace the tarnished hypotheses of the four elements and the three principles. Tachenius urged instead that physicians and chemists adopt a two-element theory that the properties and behaviour of substances lay in their acidity or alkalinity.
The fundamental problem with Tachenius’ suggestion was that there was no satisfactory definition of an acid or an alkali beyond a circular one that an acid effervesced with an alkali and vice versa.
A SCEPTICAL CHEMIST (#ulink_0a03ace7-f839-52bd-b85a-4ce1aaf12c8c)
Robert Boyle (1627–91), who was born in Ireland as the seventh son of the Earl of Cork, was educated at Eton and by means of a long continental tour from which he returned to England in 1644. In the 1650s he became associated with Samuel Hartlib and his circle of acquaintances, who sometimes referred to themselves as the ‘invisible college’. The Hartlibians were interested in exploiting chemistry both for its material usefulness in medicine and trade and for the better understanding of God and Nature. Since the group included the American alchemist George Starkey among its members, not surprisingly Boyle began to read extensively into the alchemical literature. Between 1655 and 1659 and from 1664 to 1668 Boyle lived in Oxford, where he became associated with the group of talented natural philosophers who were to form the Royal Society in 1661. Boyle was an extraordinarily devout man who, like Newton a generation later, wrote as much on theology as on natural philosophy. He paid for translations of the Bible into Malay, Turkish, Welsh and Irish, and left money in his will for the endowment of an annual series of sermons, to be preached in St Paul’s Cathedral, that would reconcile and demonstrate how science supported religion.
The generation before Boyle had seen a revival in the fortunes of the atomic theory of matter. Throughout the middle ages, as the text of Geber’s Summa perfectionis demonstrates, natural philosophers had been familiar with the Aristotelian doctrine of the minima naturalis, which they treated to all intents and purposes as ‘least chemical particles’. Lucretius’ poem, On the Nature of Things, had been rediscovered and printed in 1473. A century later, in 1575, Hero’s Pneumatica was published and disseminated an alternative non-Epicurean atomic theory in which the properties of bulk matter were explained by the presence of small vacua that were interspersed between the particles of a body. This theory, which allowed heat to be explained in terms of the agitation of particles, was exploited by, among others, Galileo, Bacon and Helmont in their search for an alternative to Aristotelianism. A century later, in 1660, the French philospher, Pierre Gassendi (1592–1655), advocated the Epicurean philosophy of atoms to replace Aristotelian physics. His work, Philosophiae Epicuri Syntagma, was a rambling summary of atomism, but its assertion of the vacuum provided an alternative to Descartes’ plenistic particle theory. Descartes’ three grades of matter, i.e. large terrestrial matter, more subtle or celestial matter that filled the interstices of the former, and still subtler particles that filled the final spaces, bore more than a passing resemblance to the elements of earth, air and fire, let alone Paracelsus’ principles of salt, mercury and sulphur. To those who have studied the matter, it is clear that Boyle was much indebted both to Gassendi and to his English disciple, Walter Charleton, whose Epicuro-Gassendo-Charletoniana (1654) had not only presented a coherent mechanical philosophy in terms of atoms or corpuscles, but placed it in an acceptable Christian context.
In 1661 Boyle published The Sceptical Chymist, a critique of peripatetic (Aristotelian), spagyric (Paracelsian and Helmontian) chemistry and the substantiation of physical and chemical properties into pre-existent substantive forms and qualities. Although designed as an argument in dialogue form between four interlocutors, Carneades (a sceptic), Themistius (an Aristotelian), Philoponus (a Paracelsian) and Eleutherius (neutral), Boyle’s rather verbose, digressive and rambling style makes it difficult for the modern reader to follow his argument. Much of the treatise becomes a monologue by Boyle’s spokesman, Carneades. Fortunately, there exists in manuscript an earlier, more straightforward, less literary, and hence more convincing, version of the essay, ‘Reflexions on the Experiments vulgarly alledged to evince the four Peripatetique Elements or the three Chymical Principles of Mixt Bodies’. Apart from one or two references to the later book, we shall follow the argument in this manuscript, which from internal evidence was written in 1658.
A typical defence of the four-element theory was to cite the familiar case of burning wood
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The experiment commonly alledged for the common opinion of the four elements, is, that if a green stick be burned in the naked fire, there will first fly away a smoake, which argued AIRE, then will boyle out at the ends a certain liquor, which is supposed WATER, the FIRE dissolves itself by its own light, and that incombustible part it leaves at last, is nothing but the element of EARTH.
Boyle, following Helmont quite closely, raised a number of objections to this interpretation. In the first place, although four ‘elementary’ products could be extracted from wood, from other substances it was possible to extract more or fewer.
Out of some bodies, four elements cannot be extracted, as Gold, out of which not so much as any one of them hath been hitherto. The like may be said of Silver, calcined Talke, and divers other fixed bodies, which to reduce into four heterogeneal substances, is a taske that has hitherto proved too hard for Vulcan. Other bodies there be, that can be reduced into more,… as the Bloud of men and other animals, which yield, when analyzed, flegme, spirit, oile, salt and earth.
Here Boyle seems to have stumbled upon a distinction between mineral and organic substances, but he did not develop this point. Instead, he objected to the assumption that the four products of wood were truly elements. A little further chemical manipulation suggested, indeed, that the products were complex.
As for the greene sticke, the fire dos not separate it into elements, but into mixed bodies, disguised into other shapes: the Flame seems to be but the sulphurous part of the body kindled; the water boyling out at the ends, is far from being elementary water, holding much of the salt and vertu of the concrete: and therefore the ebullient juice of several plants is by physitians found effectual against several distempers, in which simple water is altogether unavailable. The smoake is so far from being aire, that it is as yet a very mixt body, by distillation yielding an oile, which leaves an earthe behind it; that it abounds in salt, may appear by its aptness to fertilise land, and by its bitterness, and by its making the eyes water (which the smoake of common water will not doe) and beyond all dispute, by the pure salt that may be easily extracted from it, of which I lately made some, exceeding white, volatile and penetrant.
This criticism clearly shows how carefully Boyle had studied the products of the destructive distillation of wood – an experiment that used to be one of the introductory lessons in British secondary school chemistry syllabuses in the twentieth century.
Finally, Boyle turned his penetrating criticism to the method of fire analysis itself. Why was it, he asked, that if the conditions of fire analysis were slightly altered or a different method of analysis was used, the products of analysis were different? Thus, if a Guajacum log was burned in an open grate, ashes and soot resulted; but if it was distilled in a retort, ‘oile, spirit, vinegar, water and charcoale’ resulted. And whereas aqua fortis (concentrated nitric acid) separated silver and gold by dissolving the silver, fire would, on the contrary, fuse the two metals together. Moreover, the degree of fire (the temperature) could make the results of analysis vary enormously.
Thus lead with one degree of fire, will be turned into minium [lead oxide], and with another be vitrified, and in neither of these will suffer any separation of elements. And if it be lawful for an Aristotelian, to make ashes (which he mistakes for Earthe) passe for an element, why may not a Chymist upon the same principle, argue that glas is one of the elements of many bodies, because by only a further degree of fire, their ashes may be vitrified?
Boyle concluded, therefore, that fire analysis was totally unsuited to demonstrating that substances are all composed of the same number of elements. To do this was like affirming ‘that all words consist of the same letters’. Such a critique of the Aristotelian elements was by no means unique to Boyle. Indeed, there is considerable evidence that, apart from his own original experiments, he drew the main thrust of the critique from the writings of Gassendi, who had made similar points when reviving the atomic philosophy of Epicurus and Lucretius.
Once this is realized, the point of his objections to the three principles of Paracelsus becomes plain. Lying in the background to the ‘Reflexions’, and made explicit in The Sceptical Chymist, was a corpuscular philosophy. Boyle’s argument was that, even if there were three principles or elements inside a material, it did not necessarily follow that an analysis into these three parts was possible, or that they were the ultimate parts. Oddly enough, nineteenth-century organic chemists were to be faced by exactly the same problem: what guarantee was there that the products of a reaction told one anything about the original substance?
It is not altogether unquestionable that if three principles be separated from bodies, they were pre-existent in them; for, perhaps, when fire dos sever the parts of bodies, the igneous atoms doe variously associate themselves with the disjoined particles of the dissolved body, or else make severall combinations of the freed principles of the same body betwixt themselves, and by that union, or at least cohesion, there may result mixts of a new sort.
As Laurent discovered in the 1830s, such scepticism is valuable; but if taken too literally, it would prevent any use of reactions as evidence of composition.
Boyle therefore concluded of the Paracelsian principles that, until such time as someone analysed gold and similar substances into three consistent parts, ‘I will not deny it to be possible absolutely … yet must I suspend my belief, till either experience or competent testimony hath convinced me of it’.
There was one further card up Boyle’s sleeve; he was able to use the Helmontian theory of one element as an argument against the alternative three- and four-element theories. He appears at first to have had strong doubts concerning the truth of Helmont’s water hypothesis; but after experiments of his own he had to admit that it seemed plausible. In both the ‘Reflexions’ and The Sceptical Chymist, Helmont’s work appears in a favourable light. Nearly a third of the ‘Reflexions’ is devoted to a discussion of Helmont’s work. Some of Boyle’s own experiments seemed to support the water theory, though he remained agnostic on the question whether or not water was truly elementary. Indeed, in The Sceptical Chymist he argued that water itself was probably an agglomeration of particles.
Boyle’s experiments were very similar to those of Helmont:
I have not without some wonder in the analysis of bodies, marvelled how great a share of water goes to the making up of divers, whose disguise promises nothing neer so much. Some hard and solid woods yield more of water alone than all the other elements. The distillation of eels, though it yields some oile, and spirit, and volatile salt, besides the caput mortum, yet were all these so disproportionate to the water that came from them … that they seemed to have been nothing, but coagulated phlegme.
Boyle’s own astute version of the willow tree experiment, after verification with a squash or marrow seed left to grow in a pot for five months, involved growing mint in water alone, for, as he reasoned, if the plant drew its substance entirely from water, the presence of earth in which to grow the seed or shoot was irrelevant.
Helmont’s position, based upon a thorough experimental foundation, seemed on the face of things very attractive. But Boyle could find no evidence for the growth of metals or minerals from water; neither could he 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 (#ulink_d5882437-4991-56d3-bfff-880e4d436f05)
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 the atom’.
Boyle’s corpuscles 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 1661
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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)
(#litres_trial_promo):
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 Boyle was a modern physical chemist, or, rather, chemical physicist. As a corpuscularian, Boyle had no difficulty in accepting the plausibility of transmutation of metals; indeed, a particle theory made ‘the alchymists’ hopes of turning other materials into gold less wild’. We know that Boyle took stories of magical events and of successful transmutations extremely seriously. In 1689 Boyle helped to secure the repeal of Henry IV’s Act against the multiplication of silver and gold, on the grounds that it was inhibiting possibly useful metallurgical researches. Throughout his life he investigated alchemists’ claims, albeit privately and cautiously and even secretly since, as recent research has shown, he clearly identified transmutation with the intervention of supernatural forces.
THE VACUUM BOYLIANUM AND ITS AFTERMATH (#ulink_a8c2b4e2-13c6-5ddf-b290-e7536b391fb2)
Boyle’s other principal contribution to natural philosophy was his investigation of the air, made possible by the invention of the air pump. The vacuum pump was first developed in Germany by Otto von Guericke, who demonstrated at Magdeburg in the 1650s how air could be pumped laboriously out of a copper globe to leave a vacuum. He then found that the atmosphere exerted a tremendous compressing force upon the globe. This was demonstrated theatrically in the famous Magdeburg experiment, which involved sixteen horses in trying to tear two evacuated hemispheres apart. Details of Guericke’s pumping system, which were published in 1657, rapidly awakened interest throughout Europe; for if a vacuum really was formed, this was prima facie evidence for the fallibility of Aristotelian physics and evidence in favour of the corpuscular philosophy.
Assisted by a young and talented laboratory assistant, Robert Hooke, Boyle built his own air pump in 1658 and began to investigate the nature of combustion and respiration with its aid. Some forty-three of his experimental findings, most of which he had had carefully witnessed by reputable friends and colleagues, were published in 1660 in New Experiments Physico-Mechanical touching the Spring of the Air and its Effects. Boyle’s law, linking pressure (the spring) and volume of the air, was developed from an experimental investigation provoked by a controversy after the book’s publication. For many years subsequently the British referred to the vacuum affectionately as the ‘vacuum Boylianum’.
Experiments with birds, mice and candles slowly led Boyle to conclude that air acted as a transporting agent to remove impurities from the lungs to the external air. (Incidentally, Boyle’s observation that insects do not die in a vacuum was confirmed in the twentieth century by Willis Whitney at the General Electric Company.) Like Helmont, Boyle never conceived of the air as a chemical entity; rather, it was a peculiar elastic fluid in which floated various reactive particles responsible for the phenomena of respiration, the rusting of iron, deliquescence and the greening of copper. On the other hand, Boyle clearly perceived that something in the air was consumed or absorbed during respiration and combustion, but he remained suitably cautious about its identification. His followers, including Hooke, who, as Curator of Experiments for the Royal Society, soon carved out an independent career for himself, were more confident.
During the English Civil War, Oxford was a Royalist stronghold. King Charles’ physician, William Harvey, who had demonstrated the circulation of the blood in 1628, was Warden of Wadham College, where he stimulated the development of co-operative investigations of physiology. The arrival of Boyle in Oxford in the 1650s further encouraged an interest in chemical questions among this community of undergraduates and Royalist exiles from London, including Richard Lower, John Mayow, John Wallis, John Wilkins and Christopher Wren. In 1659 Boyle hired an Alsatian immigrant, Peter Stahl, to teach chemistry publicly in Oxford. Those who were particularly interested in solving some of Harvey’s unanswered puzzles, including what happened to blood in the lungs or what was the origin of the blood’s warmth, took Stahl’s courses in the hope of finding chemical solutions. Among Boyle’s assistants at this time were Hooke and Mayow.
In the Micrographia (1665), a pioneering treatise on microscopy and many other subjects, Hooke developed a theory of combustion that owed something to the two-element acid-alkali theory of Sylvius, and even more to a widely known contemporary meteorological theory that was based upon a gunpowder analogy. According to this ‘nitro-aerial’ theory, thunder and lightning were likened to the explosion and flashing of gunpowder, whose active ingredients were known to be sulphur and nitre. By analogy, therefore, a violent storm was explained as a reaction between sulphureous and nitrous particles in the air. Since it was also known that nitre lowered the temperature of water and fertilized crops, it could be argued that the nitrous particles of air were probably responsible for snow and hail and for the vitality of vegetables. Such ideas can be traced back to Paracelsus and to alchemical writers such as Michael Sendivogius.
Hooke laid out his version of this theory in the form of a dozen propositions. He assumed that air was a ‘universal dissolvent’ of sulphureous bodies because it contained a substance ‘that is like, if not the very same, with that which is fixt in saltpetre’. During the solution process a great deal of warmth and fire was produced; at the same time, the dissolved sulphureous matter was ‘turn’d into the air, and made to fly up and down with it’.
The nitro-aerial theory received its fullest development in the writings of the Cornish Cartesian physician, John Mayow (1641–79) in Five Medico-Physical Treatises published in 1674. How much of his work was mere summary of the ideas of Boyle, Hooke and the Oxford physician, Richard Lower, has been the subject of dispute. Even if his work was syncretic, it was of very considerable interest and influence. Mayow used the theory to explain a very wide range of phenomena, including respiration, the heat and flames of combustion, calcination, deliquescence, animal heat, the scarlet colour of arterial blood and, once more, meteorological events. He showed that, when a candle burned in an inverted cupping glass submerged in water, it consumed the nitrous part of the air, which thereupon lost its elasticity, causing the water to rise. The same thing happened when a mouse replaced the candle.
Hence it is manifest that air is deprived of its elastic force by the breathing of animals very much in the same way as by the burning of flame.
Calcination involved the mechanical addition of nitro-aerial particles to a metal, which, as he knew from some of Boyle’s findings, brought about an increase of weight – an explanation also propagated by Mayow’s obscure French contemporary, Jean Rey. This explanation seemed confirmed by the fact that antimony produced the same calx when it was heated in air as when it was dissolved in nitric acid and heated.
Early historians of chemistry liked to find a close resemblance between Mayow’s explanation and the later oxygen theory of calcination. But it is only the transference properties that are similar. Quite apart from different theoretical entities being used in the two theories, we must note that Mayow’s theory was a mechanical, not chemical, theory of combustion. A more serious historiographical point is that Mayow’s theory essentially marked a return to a dualistic world of principles and occult powers. Sulphur and nitre now replaced the tria prima of Paracelsus.
Nitro-aerial spirit and sulphur are engaged in perpetual hostilities with each other, and indeed from their mutual struggles they meet, and from their diverse states when they succomb by turns, all changes of things seem to arise.
Neither Boyle nor Hooke appears to have referred to Mayow’s work in their writings. In any case, Boyle was sceptical of the ‘plenty and quality of the nitre in the air’.
For I have not found that those that build so much upon this volatile nitre, have made out by any competent experiment, that there is such a volatile nitre abounding in the air. For having often dealt with saltpetre in the fire, I do not find it easy to be raised by a gentle heat; and when by a stronger fire we distil it in closed vessels, it is plain, that what the chemists call the spirit of nitre (nitric oxide), has quite differing properties from crude nitre, and from those that are ascribed to the volatile nitre of the air; these spirits being so far from being refreshing to the nature of animals that they are exceeding corrosive.
Despite the speculative character of the nitro-aerial theory, there is much to admire concerning Mayow’s experimental ingenuity. Although he did not develop the pneumatic trough, he devised a method for capturing the ‘wild spirits’ that Helmont had found so elusive by arranging for pieces of iron to be lowered into nitric acid inside the inverted cupping glass. As we can see, however, the results were inevitably baffling to Mayow, for although the water level in the cup eventually rose (as the nitro-aerial theory predicted), it was initially depressed. (Insoluble hydrogen would have been the first product of this displacement reaction; secondary reactions would have then produced soluble nitrogen dioxide.)
NEWTON’S CHEMISTRY (#ulink_09fa6d88-0e97-59d8-80fd-f8c81eb9e822)
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.
