The four pioneering toxicologists considered are Karl Wilhelm Scheele, Christian Friedrich Hahnemman, Johann Daniel Metzger, and Valentine Rose. Among various acids discovered by Swedish chemist Scheele was arsenous acid. German physician Hahnemman, the founder of homeopathy, discovered a test for arsenic oxide. In 1787 the German, Metzger, found that if a substance containing arsenic is heated over charcoal and a copper plate is held over the vapor, a white substance collects on the plate. In 1806, Valentine Rose of the Berlin Medical Faculty found a way to determine the presence of arsenic in organs. In 1836, James March reported a test for arsenic that permitted the accurate detection of one of the most widely used poisons of the 19th Century. Using his interest in forensic medicine and knowledge of analytic chemistry, Orfila produced Traite des poisons ... ou Toxicologie generale, which laid the foundations of modern toxicology.