This month marks the anniversary of the birth of pioneering Belgian physician and chemist Joannes Baptista van Helmont, who was born in 1579 (the exact date is unknown). His medical research led to the discovery that stomach acid is involved in digestion, and to the use of gravimetry--analysis by weight--to study urine. But he's perhaps best known for coining the word "gas." Interested in combustion, van Helmont conducted an experiment in which he burned 28 kilograms of charcoal and found only half a kilogram of ash remaining. He concluded that the rest of the matter had escaped into the air as "gas"--derived from the Greek word khaos. Van Helmont later went on to identify different kinds of gases, and his work in this area influenced 17th century British physicist and chemist Robert Boyle.
[Source: Williams, Trevor I., Ed., A Biographical Dictionary of Scientists, third ed., John Wiley & Sons, New York, 1982]