A Tree Grows in Brussels

At a time when measurement and experiment were just beginning to define science, Van Helmont performed his famous tree experiment. He believed that there were only two true fundamental elements, water and air, and that trees were composed of the element water. To test this hypothesis, he weighed 200 pounds of dried earth, moistened it with distilled water and added the stem of a willow tree weighing 5 pounds. After five years of judicious watering he determined that the tree weighed 169 pounds, the soil, when separated and dried, still weighed 200 pounds and, thus, the extra 164 pounds could only come from addition of the element water.  

These conclusions were, of course, totally erroneous. We now know that the mass of the tree is comprised of cellulose and water. Cellulose is derived from photosynthesis (only discovered some 140 years later) involving carbon dioxide and water. And again, how ironic that the person who coined the term gas (from chaos) and effectively discovered carbon dioxide did not understand its role in his tree experiment.  

The law of conservation of matter is typically associated with the father of modern chemistry, Antoine Laurent Lavoiser, who worked in the late eighteenth century. Van Helmont s tree experiment demonstrates that this law was a tenable hypothesis over 120 years earlier. And about 150 years after the death 

FIGURE 138. Frontispiece from Johanne Baptist Von Helmont s Onus Medicinae (Amsterdam, 1648) published by his alchemist son Franciscus Mercurius (right). 

Van Helmont, A Ternary of Paradoxes (translated by Walter Charleton), London, 1650, p. 7. 

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