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.
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.
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.