Van Helmont's weight balance and the willow experiment (Ortus medicinae)
A classical experiment with a willow that showed that the input and the output of a chemical transformation can be compared on the balance. The Flemish physician Jan Baptista Van Helmont planted a five-pound willow in 200 pounds of dried earth, watered it with nothing but water for five years, then weighed the tree (169 pounds) and the earth (the same mass less two ounces) and concluded that all the wood had come from water.
The conclusion was wrong (he did not reckon with air), but the method was new: in the same way Van Helmont showed that sand turned into glass and recovered with acid keeps its weight, and that metals dissolved in acid can be recovered in their former quantity.
The experiments were published posthumously in Ortus medicinae (Amsterdam, 1648). Newman sees here the first explicit statement of the principle of mass balance. Together with the word 'gas' that Van Helmont coined, this made him a foundation for Boyle and, through the Helmontian tradition, for the quantitative chemistry of the eighteenth century.
Why this date
exact for the publication: the Ortus medicinae was published posthumously in Amsterdam in 1648 by his son Franciscus Mercurius (Van Helmont died in 1644). The experiments themselves were made earlier, the willow experiment lasting five years; the sources give no exact date for the experiment, so the axis value is the year of first publication.
What it grew from
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Distillation and laboratory apparatus
influenced · Confidence: medium
Van Helmont's weight experiments grew out of the alchemical laboratory tradition of cycles of analysis and synthesis, in which mass balance had been implicitly assumed for centuries; without that tradition his method of comparing input and output on the balance would have arisen later or differently.
Dispute: Distillation is counted from Zosimos (c. 300), while Newman writes of the alchemical tradition in general, not of distillation; the willow experiment needs no distillation. The historians confirm the continuity of the tradition but do not name distillation itself.
Link sources
- Newman W. R. «What Have We Learned from the Recent Historiography of Alchemy?», Isis 102(2) (2011)
The work of the Flemish chymist Joan Baptista Van Helmont also capitalized on cycles of analysis and synthesis.
- Newman W. R. «What Have We Learned from the Recent Historiography of Alchemy?», Isis 102(2) (2011)
Although mass balance had been implicitly assumed by metallurgists and alchemists for many centuries, it had existed in a subterranean and uneasy relationship with the dominant Aristotelian physics of the Middle Ages.
- Newman W. R. «What Have We Learned from the Recent Historiography of Alchemy?», Isis 102(2) (2011)
Van Helmont made glass out of sand and salt of tartar, for example, employing an excess of the latter to produce the soluble silicate that we nowadays call 'water glass' (potassium or sodium silicate).
- Newman W. R., Principe L. M. «Alchemy Tried in the Fire: Starkey, Boyle, and the Fate of Helmontian Chymistry», University of Chicago Press (2002) Verified 20 Sep 2026
A common emphasis on quantification, material production, and analysis/synthesis, the authors argue, illustrates a continuity of goals and practices from late medieval alchemy down to and beyond the Chemical Revolution.
"Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.
- Newman W. R. «What Have We Learned from the Recent Historiography of Alchemy?», Isis 102(2) (2011)
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Mineral acids of the pseudo-Geber corpus
influenced · Confidence: medium
Strong acids were the working tool of Van Helmont's weight experiments: he recovered the sand from glass by analysis with acid, and demonstrated the indestructibility of matter on metals dissolved in acid and recovered in their former quantity.
Dispute: No historian derives Van Helmont's experiments directly from the pseudo-Geber acids; the quotes show only that acids were used in his weight experiments, and Newman describes the passage from the weak acids of the 13th century to the mineral acids on the example of Sennert, Van Helmont's contemporary. The willow experiment needs no acids, so the acids accompanied his work rather than being a necessary condition of it.
Link sources
- Newman W. R. «What Have We Learned from the Recent Historiography of Alchemy?», Isis 102(2) (2011)
He claimed, as a result, that the sand that went into the glass had the same weight as the sand that was released by analysis with acid.
- Pagel W. «Helmont, Johannes (Joan) Baptista van», Dictionary of Scientific Biography (via Encyclopedia.com) (1972) Verified 5 Oct 2026
On the indestructibility of matter, Helmont stated that metals dissolved in acid are not thereby destroyed or transmuted
- Newman W. R. «What Have We Learned from the Recent Historiography of Alchemy?», Isis 102(2) (2011)
Unlike Paul, however, Sennert was able to use the powerful mineral acids (nitric, sulfuric, hydrochloric, and aqua regia) to provide much more dramatic demonstrations of metallic destruction than had been possible with the weaker acids and bases available in the thirteenth century.
"Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.
- Newman W. R. «What Have We Learned from the Recent Historiography of Alchemy?», Isis 102(2) (2011)
What grew out of it
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Mass balance and the conservation principle
influenced · Confidence: medium
Van Helmont was the first to state explicitly the equality of input and output weights, and Lavoisier, his admirer, began his gravimetric method in 1768-1769 precisely by testing the Helmontian doctrine of the transmutation of water into earth, weighing the vessel before and after 101 days of heating.
Dispute: The Linda Hall Library notes that apart from Boyle nobody attached importance to the willow experiment before the 20th century, so the influence ran not through the experiment itself but through the Helmontian tradition (Starkey, Boyle) and through the polemic against the doctrine of the transmutation of water. No historian states directly that Lavoisier's mass-balance principle was taken from Van Helmont: Newman and Principe speak of a continuity of goals and practices, Guerlac of Lavoisier testing the Helmontian thesis. Hooykaas and Martins (2021) hold that Lavoisier started from a metaphysical principle, not from other people's experiments.
Link sources
- Newman W. R. «What Have We Learned from the Recent Historiography of Alchemy?», Isis 102(2) (2011)
It was only in the mid-seventeenth century that Van Helmont explicitly enunciated the identity of input and output weights and used this as a tool for undermining the traditional theory of the four elements.
- Guerlac H. «Lavoisier, Antoine-Laurent», Dictionary of Scientific Biography (via Encyclopedia.com) (1973) Verified 20 Sep 2026
The doctrine of transmutation had the authority of J. B. Van Helmont and of Robert Boyle, each of whom believed he had shown by experiment that the nutrition and growth of plants can only be attributed to water.
- Guerlac H. «Lavoisier, Antoine-Laurent», Dictionary of Scientific Biography (via Encyclopedia.com) (1973) Verified 20 Sep 2026
This well-known experiment demonstrates Lavoisier's experimental ingenuity and those gravimetric procedures that were to characterize his later work.
- Newman W. R., Principe L. M. «Alchemy Tried in the Fire: Starkey, Boyle, and the Fate of Helmontian Chymistry», University of Chicago Press (2002) Verified 20 Sep 2026
A common emphasis on quantification, material production, and analysis/synthesis, the authors argue, illustrates a continuity of goals and practices from late medieval alchemy down to and beyond the Chemical Revolution.
- Burns W. E., Newman, Principe «Alchemy Tried in the Fire», Albion 36(1) (2004)
an examination of eighteenth-century French chemistry and the roots of the quantitative chemistry of Antoine-Laurent Lavoisier (an admirer of Van Helmont)
"Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.
- Newman W. R. «What Have We Learned from the Recent Historiography of Alchemy?», Isis 102(2) (2011)
Node sources
- Van Helmont J. B. «Ortus medicinae, id est initia physicae inaudita», Amsterdam: Elzevir, 1648, «Complexionum atque mistionum elementalium figmentum», Howe 1965 (1648) Verified 5 Oct 2026
I took an earthen pot and in it placed 200 pounds of earth which had been dried out in an oven. This I moistened with rain water, and in it planted a shoot of willow which weighed five pounds.
- Van Helmont J. B. «Ortus medicinae», Howe 1965 (1648) Verified 5 Oct 2026
Finally, I dried out the earth in the pot once more, and found the same 200 pounds, less about 2 ounces. Thus, 164 pounds of wood, bark, and roots had arisen from water alone.
- Pagel W. «Helmont, Johannes (Joan) Baptista van», Dictionary of Scientific Biography (via Encyclopedia.com) (1972) Verified 5 Oct 2026
a willow tree weighing five pounds was planted in 200 pounds of earth
- Pagel W. «Helmont, Johannes (Joan) Baptista van», Dictionary of Scientific Biography (via Encyclopedia.com) (1972) Verified 5 Oct 2026
Helmont's scientific method and achievement resulted from his extensive use of the balance, quantification, and experiment
- Pagel W. «Helmont, Johannes (Joan) Baptista van», Dictionary of Scientific Biography (via Encyclopedia.com) (1972) Verified 5 Oct 2026
On the indestructibility of matter, Helmont stated that metals dissolved in acid are not thereby destroyed or transmuted
- Newman W. R. «What Have We Learned from the Recent Historiography of Alchemy?», Isis 102(2) (2011)
It was only in the mid-seventeenth century that Van Helmont explicitly enunciated the identity of input and output weights and used this as a tool for undermining the traditional theory of the four elements.
- Newman W. R. «What Have We Learned from the Recent Historiography of Alchemy?», Isis 102(2) (2011)
He claimed, as a result, that the sand that went into the glass had the same weight as the sand that was released by analysis with acid.
- Linda Hall Library, «Scientist of the Day: Joan Baptista van Helmont» (2019) Verified 5 Oct 2026
Four years after his death (in 1644), his son, Franciscus Mercurius van Helmont, issued this collection as Ortus medicinae (The Rise of Medicine, 1648).
- Linda Hall Library, «Scientist of the Day: Joan Baptista van Helmont» (2019) Verified 5 Oct 2026
Interestingly, except for Robert Boyle, no one seems to have attached any importance to the willow-tree experiment until the 20th century.
- «Jan Baptista van Helmont», Encyclopedia of World Biography (2001) Verified 5 Oct 2026
His son Franciscus Mercurius published his papers posthumously in 1648 under the title Ortus medicinae (Origins of Medicine).
"Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.