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CHAPTER 1

How Does Your Garden Grow?

Van Helmont’s Willow Tree and the Beauty of Quantification

Vilvoorde, near Brussels, early 17^th century—Jan Baptista van Helmont, a Flemish physician, demonstrates that everything tangible is ultimately made from water, by growing a willow tree in a pot of soil nourished by nothing but pure water. His identification of water as the ‘primal substance’ is consistent with the Biblical account of Creation and thus supports the Christian basis of van Helmont’s ‘chemical philosophy’. His ideas, published only after his death, represent the final flourish of a semi-mystical view of chemistry that was shortly to give way to the strictly mechanistic philosophy championed by René Descartes.

Perhaps the first thing school students of chemistry learn is that it is all about weighing things. So many grams of this added to so many grams of that: no wonder it so often seems like cookery.

There is nothing obvious about this need for quantification in the study of matter and its transformations. There is little evidence of it in the philosophies of ancient Greece, which sought to explain nature in terms of vague, qualitative propensities and tendencies, affinities and aversions. For Aristotle, things fell to earth because they possessed a natural ‘downward’ propensity. Empedocles claimed rather charmingly that the mixing and separation of his four elements to make all the bodies of the world were the result of the forces of ‘love’ and ‘strife’.

This is not to say, of course, that quantification was absent from the ancient world. Of course it wasn’t. How can you conduct trade unless you know what you are buying and selling? How can you plan a building without specifying the heights and proportions? Throughout the ancient cultures of the Middle and Near East, the cubit was the standard measure of length: the distance from the point of the elbow to the tip of the middle finger. The dimensions of Solomon’s Temple are listed in great detail in the Bible’s first Book of Kings: an illustration of how much quantification mattered in the court of ancient Israel. Double-pan balances are depicted in Egyptian wall paintings from around 2000 BC, and precious materials were weighed out in grains and shekels. (Because the number of grains to a shekel varied from one country to another, a merchant in the Mediterranean would have to carry several sets of standard stone weights.)

And artisans knew that if you wanted to make some useful substance by ‘art’ – which is to say, by chemistry, which was then indistinguishable from alchemy – then you had to get the proportions right. A Mesopotamian recipe for glass, recorded in cuneiform script, specifies that one must heat together ‘sixty parts of sand, a hundred and eighty parts of ashes from sea plants [and] five parts chalk’. In Alexandria such prescriptions were collated and recorded in alchemical manuscripts, where they began to take on a new character. No longer content with a purely practical, empirical science of matter, the Alexandrian alchemists sought the kind of unifying principles that Greek philosophy extolled. And so one finds tracts like Physica et Mystica (as it was known in later Latin translation) by the Egyptian sage Bolos of Mendes, who flourished around 200 BC, in which the recipes are accompanied by the cryptic comment ‘Nature triumphs over nature. Nature rejoices in nature. Nature dominates nature.’

Not all of Hellenistic practical science took on this mystical mantle: Archimedes and Hero conducted ingenious and quantitative experiments without conjoining them to some grand theory of nature. Yet for chemistry, the pragmatic and the numinous remained wedded for centuries. When the Arabic philosophers encountered Alexandrian texts during the Islamic expansion in the seventh century AD, they embraced all aspects of its alchemical philosophy. The writings attributed to the Muslim scholar Jabir ibn Hayyan, which were most probably compiled by various members of the mystical Isma’ili sect in the late ninth and early tenth centuries, expounded the idea that all metals were composed of two fundamental ‘principles’: sulphur and mercury. These were not intended as replacements for the classical Aristotelian elements – Aristotle’s philosophy was revered by the Arabs – but they added another layer to it. ‘Philosophical’ sulphur and mercury were not the elemental substances we now recognize; rather, they were elusive, ethereal essences, more like properties than materials, which were blended in all seven of the metals that were recognized at that time.

Despite their pseudo-theoretical veneer, the Jabirian writings are relatively clear and straightforward in so far as they provide instructions for preparing chemical substances. The great tenth-century Arabic physician Abu Bakr Muhammad ibn Zakariya al-Razi (Latinized as Rhazes) also offered recipes that were very precise in their quantities and procedures:

Take two parts of lime that has not been slaked, and one part of yellow sulphur, and digest this with four times [the weight] of pure water until it becomes red. Filter it, and repeat the process until it becomes red. Then collect all the water, and cook it until it is decreased to half, and use it.

This prescription produces the compound calcium polysulphide, which reacts with some metals to change their surface colour – a process that would have seemed to be related to the transmutation of one metal to another, the prime objective of later alchemists.

These quantitative recipes, relying on careful weighing and measuring, were copied and adopted uncritically by Western alchemists and artisans in the early Middle Ages. But alchemy was not respectable science: the scientific syllabus at the universities was largely confined to geometry, astronomy and the mathematics of musical harmony. And so while alchemy propagated quantification and motivated the invention of new apparatus, it was indeed largely a kind of cookery learnt from books, and the measurement it entailed did not become a regular part of scientific enquiry. As often as not, old errors of quantification were simply retained. A medieval recipe for making the bright red pigment vermilion from sulphur and mercury – a transformation of obvious alchemical interest – specifies far too much sulphur, because it is based on the Arab alchemists’ theoretical ideas about the ‘proper’ ratio of these substances rather than on their ideal proportions for an efficient chemical reaction.

Only a bold and extraordinary individual would have realized that one’s knowledge of the world could be increased by measuring it. The German cardinal Nicholas of Cusa (1401–1464) was such a man. He is one of the great forgotten heroes of early science, an iconoclast who was prepared to make up his own mind rather than taking all his wisdom from old books. In his book On Learned Ignorance (1440) (a title that reflected the penchant of scholars for presenting and then synthesizing opposing hypotheses) he argued, a hundred years before Copernicus, that the earth might not be at the centre of the universe. It is a sphere rotating on its axis, said Nicholas, and is larger than the moon but smaller than the sun. And it moves.

For his investigations into natural philosophy he used fine balances and timing instruments such as sand glasses. He suggested that one might observe the rate at which objects fall by dropping them from a tall tower, and cautioned that in such an experiment one should account for air resistance. This demonstrates not only that Nicholas thought to ask quantitative questions (everyone knew that objects fell to earth, but who worried about how fast they fell?) but also that he was able to idealize an experimental test: not just to take its outcome at face value, but to think about factors that might distort the result.

To Nicholas’s contemporaries, all manner of natural phenomena, such as the weather, were dictated by the influence of the stars. But he laughed at the astrologers, calling them ‘fools with their imaginings’, and suggested instead that the weather might be forecast not by charting the motions of the heavens but by testing the air. Just leave a piece of wool exposed to the atmosphere, he said – if wet weather looms, the increased humidity will make the wool damp. And what is more, you can put numbers to that: you can figure out how much more humid the air has become by weighing the wool to measure the moisture.

He also had a bright idea for investigating the mystery of how plants grow. The notion of growth from a seed was a central emblem of the mystical philosophy of Neoplatonism, from which most of the medieval ideas about magic and alchemy sprung. But Nicholas saw that this was a problem that could be addressed by quantitative experiment:

If a man should put an hundred weight of earth into a great earthen pot, and should take some Herbs, and Seeds, & weigh them, and then plant and sow them in that pot, and then should let them grow here so long, until hee had successively by little and little, gotten an hundred weight of them, hee would finde the earth but very little diminished, when he came to weigh it again, by which he might gather, that all the aforesaid herbs, had their weight from water.

It was a fine suggestion; but the experiment was not carried out for another two hundred years.

The troublesome recluse

Nicholas’s heliocentrism did not incite the kind of oppression that was famously suffered by Galileo, who had the misfortune to support the idea in less tolerant times. But Galileo’s ‘martyrdom’ was of a relatively mild sort. Giordano Bruno, another heliocentric rebel, was burnt at the stake in 1600 – not, however, for his scientific views but because of his religious heresies. House arrest, to which Galileo was condemned, might seem trivial in comparison; but there was always the threat that it might turn into something worse.

That was largely why the works of Jan Baptista van Helmont (1579–1644) went unpublished in his lifetime. Confined to Vilvoorde in the duchy of Brabant by order of the Inquisition, he did not want any more trouble with the Church. Van Helmont (Figure 1) was no rebel-rouser – in fact he chose to pursue a remarkably quiet, undemonstrative life, turning down offers for appointment as court physician from several princes. Yet this reticence belied an ambition to fashion a chemical philosophy of startling scope – the last, in fact, of its kind – and, when challenged, he did not mince his words.

Van Helmont studied at the University of Louvain, but he felt that academic qualifications were mere vanities and he turned down the degree he had earned. Despite this independence of mind, he was at first something of a medical traditionalist; it was only after he was cured of an itch by an ointment derived from the chemical medicine of the Swiss iconoclast Paracelsus that he converted to this new kind of ‘physick’. Whereas traditional medicine throughout the Renaissance was based on the ideas of the Greek doctor Hippocrates and the Roman Galen, which held that health was governed by four bodily fluids called humours, Paracelsus (1493–1541) maintained that specific diseases should be treated with specific remedies created from nature’s pharmacopoeia by the art of alchemy. Several decades after his death, Paracelsus’s ideas gained popularity throughout Europe, and by the early seventeenth century the medical community was divided into Galenists and Paracelsians.

Van Helmont studied the writings of Paracelsus and found much there that seemed to him to be sound advice. But he was by no means an uncritical disciple. Paracelsus tended to surround his chemical medicine with a fog of obscure terminology and overblown notions of how the world worked. Humankind, he said, was a microcosm reflected in the macrocosm of the universe, so that the disorders of the body could be compared to the disorders of nature – epilepsy, for example, known as the falling sickness, was akin to the tremors that shook the ground in an earthquake. This concept of a correspondence between the microcosm and the macrocosm was a central theme in Neoplatonic philosophy and was popular with the Jabirian alchemists. But to van Helmont it looked like sheer mysticism, and he would have none of it.

Figure 1 Flemish physician and alchemist Jan Baptista van Helmont

(Reproduced Courtesy of the Library and Information Centre, Royal Society of Chemistry)

Instead, he pursued the difficult task of separating what was worthy in the works of Paracelsus from what was nonsense: he wanted the chemical medicine without the chemical philosophy. But that did not mean he was free of mysticism himself, for like Paracelsus he felt it was essential that chemical science be based in Christian theology. In his own mind he was replacing speculation with rigorous theory; but from today’s perspective there is often not a great deal to differentiate the philosophy of Paracelsus from that of van Helmont.

For example, van Helmont supported the Paracelsian cure known as the weapon salve, an idea that seems now to be ridiculously magical. To cure a wound made by a weapon, you should prepare an ointment and then apply it not to the cut but to the blade that made it. However unlikely a remedy, van Helmont was convinced that it had a perfectly rational, mechanistic explanation. The natural magic of the Neoplatonists was not mere superstition; it was based on the belief that the world was filled with occult forces, of which magnetism was an incontestable example. The weapon salve mustered these forces to allow the vital spirits of the blood on the blade to reunite with that in the body.

When van Helmont published a defence of the weapon salve in 1621, it was criticized by a prominent Jesuit. Van Helmont responded by explaining the ‘mechanism’ of the cure, and he rather unwisely compared it to the way religious relics produce ‘healing at a distance’. The University of Louvain found this a scandalous thing to suggest, and van Helmont’s ideas were brought before the Spanish Inquisition (Spain ruled the Low Countries at that time). He was declared a heretic, and was lucky to escape with nothing more severe than a spell in prison before being freed through the intervention of influential friends. Thereafter, van Helmont was forbidden to publish anything further without the approval of the Church, or to leave his home without the permission of the Archbishop of Malines – a restriction that applied even in times of plague. During one outbreak, his family refused to leave the town without him, and two of his sons succumbed to the disease.

So his writings on chemistry and medicine were not published until after his death, when his son Franciscus Mercurius inherited his manuscripts. Van Helmont’s collected works appeared in Latin under the title Ortus Medicinae (Origins of Medicine) in 1648, which John Chandler translated into English in 1662 as Oriatrike; or, Physick Refined.

Ortus Medicinae contains a wealth of striking ideas, most notably the suggestion that digestion (which Paracelsus saw as an alchemical process conducted by an ‘inner alchemist’ called the Archeus) is a kind of fermentation involving an acid. The book is a curious mixture of new and old, prescient and regressive. Just as the mechanistic philosophy of Descartes and his followers was taking hold in Europe (and shortly before it was to be refined in Isaac Newton’s Principia Mathematica), van Helmont challenged the Cartesian division of body and soul by arguing for a kind of vital force that animated all matter. Van Helmont believed that he would find this ‘world spirit’, the spiritus mundi, by distilling blood.

At the same time, he called for an end to the sort of science that relied solely on logical thinking and mathematical abstraction – it should instead be based on observation, on experiment. As a demonstration of what could be gained that way, van Helmont explained how he had come to understand that everything was made from water.

Well, not quite everything. The other of the Aristotelian elements that he continued to countenance was air. But this air, he said, is inert and unchanging, and so all else is nothing but water. ‘All earth, clay, and every body that may be touched, is truly and materially the offspring of water onely, and is reduced again into water by nature and art.’

In support of this claim, van Helmont explained how ‘I have learned by this handicraft-operation, that all Vegetables do immediately and materially proceed out of the Element of water onely.’ Whether or not he knew of the experiment proposed by Nicholas de Cusa, he had actually gone ahead and done it.

It required the kind of patience that perhaps house arrest cultivates in a person. Van Helmont took 200 pounds of earth, which he dried in a furnace and then moistened with rain water. He placed it in a pot and planted within it a small willow sapling weighing five pounds. And then he waited for five years.

He watered it whenever necessary, but carefully excluded all other sources of matter. Van Helmont explains how, to keep out dust, he ‘covered the lip or mouth of the Vessel, with an Iron Plate covered with Tin’, which was ‘easily passable with many holes’ to let through water and air. In other words, like Nicholas de Cusa he was thinking about how to exclude influences that could corrupt his results.

At the end of that time he weighed the tree again, and also the soil, which was only about two ounces short of the original 200 pounds. The tree, however, had grown immensely. ‘One hundred and sixty-four pounds of Wood, Barks, and Roots arose out of water onely’, he said. And he added that he had not included in this estimate the weight of the leaves that had grown and then fallen over four autumns.

One might argue that the experiment hardly required such quantification. Anyone could see that the soil had not greatly diminished in volume, while the tree had very obviously gained a lot of mass. In any case, what was the significance of the figure of 164 pounds, if the leaves were neglected? But that wasn’t the point. Numbers are hard facts; they are irrefutable. If anyone doubted the interpretation, van Helmont could demand that they kindly explain where else one hundred and sixty four pounds of material had come from (and you can imagine how absurd it would have been to suggest that this matter came out of the air!).

The experiment was beautiful because of the clarity of its concept: it was hard to see what could possibly have been overlooked, or what could have led to any error. That beauty is enhanced by the reliance on quantification, which transforms an anecdote into a scientific result. All of which makes it perhaps rather shocking that van Helmont was of course completely wrong: wood is not made from water, but from atmospheric carbon dioxide absorbed through the leaves and converted into cellulose by photosynthesis. It is hard to fault either the experimental design or the logic of the interpretation; we can’t reasonably expect van Helmont to have come to any other conclusion. There is surely a humbling message in this for scientists today: if an important part of the puzzle is missing, what seems ‘obvious’ may in fact be fundamentally fallacious.

End of an era

This was not the sole extent of van Helmont’s evidence for making water the prime matter of the world. But the rest of his argument was largely circumstantial, and lacked such quantitative exactitude. What else nourishes fish, if not water? Don’t solids of all kinds turn into water when they come into contact with it – salts, for example, which produce ‘savoury waters’ when they dissolve? Of course, there are plenty of solids that do not dissolve, but van Helmont believed this was just because the right solvent hadn’t been found (and in certain respects he was right!). He spoke of a ‘universal solvent’ that would dissolve all things, which he called the alkahest, and he spent many fruitful hours searching for it. (It’s not clear what, if he had been successful, he proposed to keep it in.)

Equally important was the evidence from Holy Scripture. Was it not made clear in Genesis that God created the world out of water, by separating ‘water from water’ and placing in the gap first the expanse of the sky and then dry ground? At the dawn of the Age of Enlightenment, theology still carried some weight in matters of science.

Yet he also adduced an ingenious piece of alchemy to support his contention. He could even turn sand into water, by melting it with an alkali to make ‘water glass’ (sodium silicate), which will liquefy as it absorbs moisture from the air. Add an acid, and the sand is regenerated in precisely the same amount. The quantities were again important here: van Helmont was convinced that matter was indestructible, so that it was conserved in any transformation of this sort.

Van Helmont was not the first person to propose that the world could be built from water alone. The Greek philosopher Thales, founder of the influential Ionian school, said as much in the sixth century BC, and part of his reasoning was similar – for water can be converted into ‘air’ by evaporation, while freezing transforms it into ‘earth’, which is, to say, a solid. But Thales’ idea never caught on, even among the later Ionian philosophers – and neither did van Helmont’s.

There is no compelling scientific reason why this should have been the case; rather, one might say that the circumstances were not to van Helmont’s advantage. For one thing, all-embracing ‘chemical philosophies’ were about to be eclipsed by Cartesian mechanistic science in the mid-seventeenth century: van Helmont’s writings represent their final bloom. Although he helped to place Paracelsian science on a more rational basis, he didn’t go nearly far enough; men like the Germans Andreas Libavius and Johann Rudolph Glauber were yet more ruthless in stripping chemistry of its Neoplatonic, magical trappings. At the Jardin du Roi, the royal medical and pharmaceutical school in Paris, alchemy was evolving into the academic discipline of ‘chymistry’. And the year before van Helmont’s Oriatricke appeared in England, Robert Boyle published his epoch-making critique of earlier ideas on chemistry, The Sceptical Chymist, which warned that chemists should be rigorous about how they defined an element and should not extrapolate beyond what the evidence permitted.

Besides, there were many systems of elements to choose from in the seventeenth century – several of them amalgams of Aristotle’s quartet and Paracelsus’s alchemical triumvirate of sulphur, mercury and salt – and van Helmont’s two-element scheme really did not have much more to recommend it above any other. In addition, it did not help that chemical philosophies had come to be associated with politically radical factions, such as the Bohemian rebels who denied the authority of the Holy Roman Emperor in 1619 and thereby triggered the Thirty Years’ War. In England too, Cromwell’s Puritans looked askance at such radicalism.

But van Helmont left his mark in other ways. He was interested in the ‘spirits’ that could be produced in chemical processes such as combustion, which were clearly different from ordinary air. He collected one such vapour, the ‘spirit of wood’, that was released from burning charcoal, and found that it could extinguish a flame. He was sure that these vapours were derived not from air but from water, and he decided they needed a new name. He borrowed a term that Paracelsus had used, the ancient Greek word chaos, which he transliterated as it sounded on the Flemish tongue: ‘gas’. What were these gases? That question was to set the principal research agenda of the chemists of the next century.