James Marsh (1794-1846) was a British chemist, primarily known for the invention of the Marsh test. An assistant to Michael Faraday at the Royal Military Academy in Woolwich, he developed his celebrated test for the detection of arsenic. His invention was prompted by a murder trial in 1832, in which an arsenic sample he had identified decomposed, failing to convince the jury. The Marsh test, perfected in 1836, converted arsenic into a stable metallic deposit, providing visible and irrefutable proof. This method revolutionized forensic toxicology, becoming a crucial tool in poisoning investigations. In addition to his work in toxicology, Marsh also invented a time fuze for artillery shells. For his discovery, he received the Isis Gold Medal from the Society of Arts in 1836.