James Marsh

British chemist. An expert on poisons, he worked at the Royal Arsenal, Woolwich, and assisted Michael Faraday at the Military Academy. He invented the standard test for arsenic, which has been given his name.

James Marsh (September 2, 1794- June 21, 1846) was a chemist who invented the Marsh test for detecting arsenic.

While he was most famous for inventing the test for arsenic that bears his name, Marsh was also a skilled and inventive scientist who held the post of Ordnance Chemist at the Royal Arsenal at Woolwich.

In 1832 Marsh was called as a chemist by the prosecution in a murder trial, wherein a certain John Bodle was accused of poisoning his grandfather with arsenic-laced coffee. While Marsh was able to detect arsenic as yellow arsenic trisulfide, when it came to show it to the jury it had deteriorated, allowing the suspect to be acquitted due to reasonable doubt. He combined a sample containing arsenic with sulfuric acid and arsenic-free zinc, resulting in arsine gas. The gas was ignited, and it decomposed to pure metallic arsenic which, when passed to a cold surface, would appear as a silvery-black deposit. So sensitive was the test that it could detect arsenic for as little as one-fiftieth of a milligram.