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.