Jan Baptist van Helmont (bapt. January 12, 1579 – December 30, 1644) was an early modern period Flemish chemist, physiologist, and physician. He worked during the years just after Paracelsus and iatrochemistry, and is sometimes considered to be "the founder of pneumatic chemistry". Van Helmont is remembered today largely for his ideas on spontaneous generation, his 5-year tree experiment, and his introduction of the word "gas" into the vocabulary of scientists.
Returning to his own country, van Helmont lived at Antwerp at the time of the great plague in 1605. In 1609 he finally obtained his doctoral degree in medicine. The same year he married Margaret van Ranst, who was of a wealthy noble family. Jan and Margaret lived in Vilvoorde, near Brussels, and had six or seven children. The inheritance of his wife enabled him to retire early from his medical practice and occupy himself with chemical experiments until his death on the 30th of December 1644.
Van Helmont is regarded as the founder of pneumatic chemistry, as he was the first to understand that there are gases distinct in kind from atmospheric air. The very word "gas" he claimed as his own invention, and he perceived that his "gas sylvestre" (carbon dioxide) given off by burning charcoal, was the same as that produced by fermenting must , which sometimes renders the air of caves unbreathable.
Van Helmont was a careful observer of nature, and an exact experimenter who realized that matter can neither be created nor destroyed. He performed an experiment to determine where plants get their mass. He grew a willow tree and measured the amount of soil, the weight of the tree and the water he added. After five years the plant had gained about 164 pounds. Since the amount of soil was basically the same as it had been when he started his experiment, he deduced that the tree's weight gain had come from water. Since it had received nothing but water and the soil weighed practically the same as at the beginning, he argued that the increased weight of wood, bark and roots had been formed from water alone.
At the same time, chemical principles guided him in the choice of medicines -- undue acidity of the digestive juices, for example, was to be corrected by alkalines and vice versa; he was thus a forerunner of the iatrochemical school, and did service to medicine by applying chemical methods to the preparation of drugs.
Over and above the archeus, he believed that there is the sensitive soul which is the husk or shell of the immortal mind. Before the Fall the archeus obeyed the immortal mind and was directly controlled by it, but at the Fall men also received the sensitive soul and with it lost immortality, for when it perishes the immortal mind can no longer remain in the body.
In addition to the archeus, which he described as "aura vitalis seminum, vitae directrix", van Helmont believed in other governing agencies resembling the archeus which were not always clearly distinguished from it. From these he invented the term blas, defined as the "vis motus tam alterivi quam localis." Of blas there were several kinds, e.g. blas humanum and blas meteoron; the heavens he said "constare gas materiâ et blas efficiente."
In 2003, the historian Lisa Jardine claimed a recently discovered portrait represented Robert Hooke. However, Jardine's hypothesis was disproved by William Jensen of the University of Cincinnati and by the German researcher Andreas Pechtl of Johannes Gutenberg University of Mainz. The portrait in fact depicts Jan Baptista van Helmont.
Steffen Ducheyne, Joan Baptiste van Helmont and the Question of Experimental Modernism, Physis: Rivista Internazionale di Storia della Scienza, vol.43, 2005, pp. 305-332.