The person who is credited with coming up with the word “gas” is Flemish physician Jan Baptista van Helmont (1577–1644). His experiments with gas and volume taught him that gases always take up all the space within a container (they do not leave a vacuum). Thus, he surmised that substances in a gaseous state exist in a chaotic form. The Flemish pronunciation for “chaos” sounds like “gas,” and thus the word was born.