Marsh test

Angered and frustrated by this, especially when John Bodle confessed later that he indeed killed his grandfather, Marsh decided to devise a better test to demonstrate the presence of arsenic.

Taking Scheele's work as a basis, he constructed a simple glass apparatus capable of not only detecting minute traces of arsenic but also measuring its quantity.

This would cause a cold ceramic bowl held in the jet of the flame to be stained with a silvery-black deposit of arsenic, physically similar to the result of Metzger's reaction.

Here are the two half-reactions: Overall, we have this reaction: In an acidic medium, As3− is protonated to form arsine gas (AsH3), so adding sulphuric acid (H2SO4) to each side of the equation we get: As the As3− combines with the H+ to form arsine: By eliminating the common ions: Although the Marsh test was efficacious, its first publicly documented use—in fact, the first time evidence from forensic toxicology was ever introduced—was in Tulle, France in 1840 with the celebrated Lafarge poisoning case.

The circumstantial evidence was great: it was shown that she bought arsenic trioxide from a local chemist, supposedly to kill rats that infested their home.

[citation needed] The existence of the Marsh test also served a deterrent effect: deliberate arsenic poisonings became rarer because the fear of discovery became more prevalent.

[citation needed] Marsh test is used in Bill Bergson Lives Dangerously to prove that a certain chocolate is poisoned with arsenic.

[9] Lord Peter Wimsey’s manservant Bunter uses Marsh’s test in Strong Poison to demonstrate that the culprit was secretly in possession of arsenic.

[10] In Alan Bradley's As Chimney Sweepers Come To Dust, 12-year old sleuth and chemistry genius Flavia de Luce uses the Marsh test to determine that arsenic was the murderer's weapon.

[12] In the episode "The King Came Calling" of the first season of Ripper Street, police surgeon Homer Jackson (Matthew Rothenberg) performs Marsh's test on the contents of a poisoning victim and determines that the fatal poison was antimony, not arsenic, since the chemical residue deposited by the flames does not dissolve in sodium hypochlorite.