Van Helmont, Jan Baptista
Jan Baptista Van Helmont (1577–1644), a Flemish physician, chemist, and physicist who made an important early contribution to our understanding of photosynthesis and chemistry. He performed a classic experiment where he measured the mass of a potted willow tree grown for 5 years in a tightly controlled environment. He discovered that the mass of the entire plant was far more than the weight of the displaced original 200 pounds of soil. This led him to reject the commonly held notion that plants were fed exclusively by the soil. He also discovered carbon dioxide and went on to distinguish gases as a class of substances (as contrasted with solids and liquids); he is credited with introducing the term gas in its present scientific sense.