1579-1644

Flemish physician, physiologist, and chemist who first recognized the existence of more than one air-like substance. He introduced the term "gas" to refer to the various substances he isolated, which include carbon dioxide and chlorine. Helmont conducted some of the earliest quantitative chemical experiments. In his most famous experiment he grew a willow tree in a measured quantity of soil, adding only water. After five years the tree had gained 164 pounds while the soil weight had decreased negligibly. Helmont also correctly noted the role of stomach acid in digestion.