James Marsh (chemist)

From Wikipedia, the free encyclopedia

James Marsh

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

[edit] Scientific work

While Marsh was most famous for inventing the test that bears his name, he was also a skilled and inventive scientist who held the post of Ordnance Chemist at the Royal Arsenal at Woolwich. He developed the screw time fuze for mortar shells and in 1830 the percussion tube. In 1832 the HMS Castor was the first ship to have her guns modified with these innovations. They were not approved for the Army until 1845, when Woolwich began their manufacture -- for coastal artillery only. They became obsolete in 1866. Marsh also worked as an assistant to Michael Faraday at the nearby Royal Military Academy from 1829 to 1846.

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. Marsh performed the standard test by mixing a suspected sample with hydrogen sulfide and hydrochloric acid. While he 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. Annoyed by this, Marsh developed a much better test. 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. He first described this test in The Edinburgh Philosophical Journal in 1836.^[1]

[edit] References

^ Marsh J. (1836). "Account of a method of separating small quantities of arsenic from substances with which it may be mixed". Edinburgh New Philosophical Journal 21: 229–236.