James Marsh
Encyclopedia
James Marsh was a British chemist
who invented the Marsh test
for detecting arsenic
.
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.
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 electrical 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 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.
Chemist
A chemist is a scientist trained in the study of chemistry. Chemists study the composition of matter and its properties such as density and acidity. Chemists carefully describe the properties they study in terms of quantities, with detail on the level of molecules and their component atoms...
who invented the Marsh test
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...
for detecting arsenic
Arsenic
Arsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.Arsenic is a metalloid...
.
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 ArsenalRoyal Arsenal
The Royal Arsenal, Woolwich, originally known as the Woolwich Warren, carried out armaments manufacture, ammunition proofing and explosives research for the British armed forces. It was sited on the south bank of the River Thames in Woolwich in south-east London, England.-Early history:The Warren...
at Woolwich
Woolwich
Woolwich is a district in south London, England, located in the London Borough of Greenwich. The area is identified in the London Plan as one of 35 major centres in Greater London.Woolwich formed part of Kent until 1889 when the County of London was created...
. 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
Michael Faraday
Michael Faraday, FRS was an English chemist and physicist who contributed to the fields of electromagnetism and electrochemistry....
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 electrical 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 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
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...
and hydrochloric acid
Hydrochloric acid
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....
. While he was able to detect arsenic as yellow arsenic trisulfide
Arsenic trisulfide
Arsenic trisulfide is the inorganic compound with the formula As2S3. This bright yellow solid is a well known mineral orpiment , has been used as a pigment, and has played a role in the analysis of arsenic compounds. This chalcogenide material is a group V/VI, intrinsic p-type semiconductor and...
, 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
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
and arsenic-free zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
, resulting in arsine
Arsine
Arsine is the chemical compound with the formula AsH3. This flammable, pyrophoric, and highly toxic gas is one of the simplest compounds of arsenic...
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.