Jan Baptist van Helmont
Jan Baptist van Helmont was a Flemish chemist, physiologist, and physician. He worked during the years just after Paracelsus and iatrochemistry, and is sometimes considered to be the founder of pneumatic chemistry. Van Helmont is remembered today largely for his ideas on spontaneous generation, his 5year tree experiment, and his introduction of the word gas into the vocabulary of scientists.
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Source: Wikipedia