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James Marsh (2 September 1794 – 21 June 1846) was a British
chemist A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a scientist trained in the study of chemistry. Chemists study the composition of matter and its properties. Chemists carefully describe t ...
who invented the
Marsh test The Marsh test is a highly sensitive method in the detection of arsenic, especially useful in the field of forensic toxicology when arsenic was used as a poison. It was developed by the chemist James Marsh and first published in 1836. The meth ...
for detecting
arsenic Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, ...
. Born in Kent, he was working as a labourer in Woolwich in the late 1810s and early 1820s, before joining the Royal Artillery. He was married to Mary, and had four children, two of whom died in infancy. His surviving daughters were Lavinia Bithiah (1821-1896) and Lucretia Victoria (1829-1910).


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 The Royal Arsenal, Woolwich is an establishment on the south bank of the River Thames in Woolwich in south-east London, England, that was used for the manufacture of armaments and ammunition, proof test, proofing, and explosives research for ...
at
Woolwich Woolwich () is a district in southeast London, England, within the Royal Borough of Greenwich. The district's location on the River Thames led to its status as an important naval, military and industrial area; a role that was maintained thro ...
. He developed the screw time fuze for mortar shells and in 1830 the percussion tube. In 1832 ''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 Michael Faraday (; 22 September 1791 – 25 August 1867) was an English scientist who contributed to the study of electromagnetism and electrochemistry. His main discoveries include the principles underlying electromagnetic induction, ...
at the nearby Royal Military Academy from 1829 to 1846. Marsh invented the earliest form of vibrating electrical interrupter in 1824. It consisted of a straight wire electrically connected and flexibly suspended at the top while the lower end extending into a shallow mercury filled trough which served as a second electrical contact. The lower end of the wire was also positioned between the poles of a powerful permanent horseshoe-shaped magnet. When electric current flowed through the wire, the magnetic field of the wire created a force with the field of the permanent magnet such that the wire would rotate out of the mercury trough and interrupt the electrical circuit. Without the magnetic force, the wire would then fall back due to the force of gravity into the mercury thereby restoring the connection and restarting the cycle of vibration. In 1833 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 Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The unde ...
and
hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the digesti ...
. While he was able to detect arsenic as yellow arsenic trisulfide, when it came to showing 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 Sulfuric acid ( American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular fo ...
and arsenic-free
zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic t ...
, resulting in
arsine Arsine (IUPAC name: arsane) is an inorganic compound with the formula As H3. This flammable, pyrophoric, and highly toxic pnictogen hydride gas is one of the simplest compounds of arsenic. Despite its lethality, it finds some applications in t ...
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 as little as one-fiftieth of a milligram of arsenic. He first described this test in ''The Edinburgh Philosophical Journal'' in 1836.


References


Further reading

* The Inheritor's Powder: a cautionary tale of poison, betrayal and greed by Sandra Hempel (London, 2013). BBC Radio 4 Book of the Week * * * * {{DEFAULTSORT:Marsh, James 1794 births 1846 deaths British chemists British inventors