Claude Berthollet. Portrait of Comte Claude Louis Berthollet (1748-1822), French chemist. Originally a physician, he moved to chemistry and became an early supporter of Lavoisier's ideas. His research examined the nature of ammonia, the sulphides of hydrogen, hydrogen cyanide, and cyanogen chloride, and the reactions of chlorine. He deduced that some acids do not contain oxygen. He discovered potassium chlorate, but his use of it in gunpowder destroyed a powder mill in 1788. His work on bleaching fabrics with chlorine, and on dyes and steel-making, was more successful. Berthollet was a friend of Napoleon, but in 1814 he helped depose the Emperor 'for the good of France'.