An illustration of Jan Baptista van Helmont (1580-1644), Flemish chemist and physician. (Note that this likeness was, for a time, misidentified as Robert Hooke. It has since been positively identified as van Helmont. No image of Robert Hooke survives, since all portraits of him were supposedly destroyed by Isaac Newton, who disliked him.) Van Helmont is considered 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.