Flemish physician, philosopher, mystic, and chemist who recognized the existence of discrete gases and identified carbon dioxide.

Van Helmont was born into a wealthy family of the landed gentry. He studied at Leuven (Leuven, Catholic University of) (Louvain), where he finished the course in philosophy and classics, and then flirted with theology, geography, and law before finally taking a doctorate in medicine in 1599. He later referred to his education as “reaping straw and senseless prattle,” gave away or threw away his books, and set out to try to find true knowledge. Van Helmont traveled to Switzerland and Italy (1600–02) and to France and England (1602–05), gaining practical medical skills that he put to use during an outbreak of plague in Antwerp in 1605. It was apparently during these sojourns that he came to know and appreciate some of the theories of the German-Swiss physician Paracelsus. He received several offers—from princes, an archbishop, and an emperor—to become a private physician, but he turned them down, refusing to “live on the misery of my fellow men.”

In 1609 van Helmont married into a noble family, thereby becoming the manorial lord of several estates. He retired to one of them—Mérode, in Vilvoorde—and for the next seven years dedicated himself to chemical research and “to the relief of the poor.” In fact, he spent his life in relative solitude and mostly in peace. He had several daughters and three sons (two of whom were lost to plague).

Van Helmont published very little until near the end of his life. This may be explained in part by the fact that his first known publication, “Of the Magnetic Curing of Wounds” (1621), led to trouble with the Spanish Inquisition (Spain). In addition to suggesting that saintly relics might display their curative effects through magnetic influence, he included very uncomplimentary comments regarding Jesuit scholastics. As a result, ecclesiastical court proceedings of one sort or another were pending against him for more than 20 years.

Van Helmont also published a treatise on the waters of Spa (1624) that criticized an earlier work and made him some enemies among physicians. Other tracts were issued in 1642 and 1644. At some time shortly before his death, van Helmont gave to his surviving son, Francis Mercurius, the responsibility for publishing all of his writings. The result was Ortus Medicinæ (1648; “Origin of Medicine”).

Van Helmont was a man of his age and accepted the ideas of spontaneous generation, transmutation of metals, and the existence of a medical panacea. However, he insisted that knowledge of the natural world could be obtained only by experimentation. Many of his treatises deal with the refutation of commonly held views and the experimental evidence for his own views. He rejected the ideas of the four elements (earth, air, water, and fire) of Aristotle and the three principles (salt, mercury, and sulfur) of Paracelsus (as received from Arabic alchemists). For him, the only true elements were air and water, and he demonstrated that these were not interchangeable, as some thought.

In what is perhaps his best-known experiment, van Helmont placed a 5-pound (about 2.2-kg) willow in an earthen pot containing 200 pounds (about 90 kg) of dried soil, and over a five-year period he added nothing to the pot but rainwater or distilled water. After five years, he found that the tree weighed 169 pounds (about 77 kg), while the soil had lost only 2 ounces (57 grams). He concluded that “164 pounds of wood, barks, and roots arose out of water only,” and he had not even included the weight of the leaves that fell off every autumn. Obviously, he knew nothing of photosynthesis, in which carbon from the air and minerals from the soil are used to generate new plant tissue, but his use of the balance is important; he believed that the mass of materials had to be accounted for in chemical processes.

In another experiment, he demonstrated that, contrary to the beliefs of many alchemists, a metal was not destroyed by dissolving it in acid. He weighed silver, dissolved it in acid, and then recovered all the original silver by reacting the solution with copper. He also showed, by using iron to recover the copper, that this displacement of one metal from its salt by using a second metal was not because of transmutation, as many had held.

Van Helmont was the first to recognize that many reactions produce substances that are, in his words, “far more subtle or fine…than a vapour, mist, or distilled oiliness, although…many times thicker than air.” To describe these substances, he invented the word gas (from “chaos”) and identified a number of gases, including carbon dioxide. (Ironically, carbon dioxide was the major substance overlooked in his willow tree experiment.) His work on gases was taken up by the British natural philosopher Robert Boyle (Boyle, Robert), among others, and the word gas, after being reintroduced by the 18th-century French chemist Antoine-Laurent Lavoisier (Lavoisier, Antoine-Laurent), became a standard chemical term.

Through many experiments in physiology, van Helmont demonstrated that acid was the digestive element in the stomach and was neutralized by alkali in the intestine and that blood combined with a “ferment from the air,” with venous blood removing a residue that escaped through the lungs. He studied extensively the formation and nature of kidney stones (kidney stone). His theory of “ferments” as the agents bringing about physiological processes is a crude precursor of the idea of enzymes (enzyme).

Perhaps the best verdict on van Helmont's work is that given by the British chemist James R. Partington: “【H】e represents the transition from alchemy to chemistry, and is a worthy predecessor of Boyle.”