SHEILA TERRY / SCIENCE PHOTO LIBRARY SHEILA TERRY / SCIENCE PHOTO LIBRARY
Joseph Louis Proust, French analytical chemist, 1754-1826. After studying chemistry and pharmacy in Paris, most of his working life was spent in Spain, becoming the Professor of Chemistry at the Royal Artillery College in Segovia, and then Director of the Royal Laboratories in Madrid. A skilled and prolific analyst he made two significant advances: in 1797 he developed the use of hydrogen sulphide as a reagent and in giving his results as percentages he discovered the Law of Constant Proportions, realising that the proportions of all the components of any compound remain the same regardless of the mass of the elements involved and the conditions of their formation. This became known as Proust's Law. In the 1780's he conducted aerostatic experiments with Pilatre de Rozier and Jacques Charles, and in 1784 was himself one of the first people to ascend in a balloon.
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