Laboratory: Forensic Chemistry .........................................................................................
Laboratory:
Forensic Chemistry
Chemistry and forensics have been inextricably linked since 1836, when Scottish chemist
James Marsh announced the eponymous named Marsh Test, the first reliable forensic test
for arsenic and antimony. In the early nineteenth century, arsenic compounds were widely
used for many purposes, and were readily available at low cost. Would-be murderers then
considered arsenic an ideal poison, because arsenic compounds were lethal in small doses,
readily soluble, odorless, tasteless, and impossible to detect. Because the symptoms of
arsenic poisoning are very similar to the symptoms of gastroenteritis, an untold number of
murder victims were instead believed to have died of natural causes.But even if murder by arsenic was suspected, there was no easy way to prove it. Marsh
developed his test in frustration after watching just such a murderer go free. In 1832, Marsh
testified as an expert witness at the trial of John Bodle, who was accused of murdering his
grandfather by putting arsenic in his coffee. Marsh used the then-standard test for arsenic,
mixing a sample of the suspect material with hydrochloric acid and hydrogen sulfide to
precipitate the arsenic as insoluble arsenic trisulfide.Unfortunately, by the time Marsh testified the sample had degraded and the jury was not
convinced by Marsh’s scientific testimony. (This problem persisted for many years; until
the late nineteenth century, many juries and even judges gave little weight to the testimony
of forensics experts.) Bodle was acquitted, and Marsh watched a guilty man walk free.
Determined not to let that happen again, Marsh devoted much of his free time over the next
several years to developing a reliable test for arsenic. The test Marsh finally devised was
revolutionary then, and is still used today by forensics labs in jurisdictions that cannot afford
mass spectrometers and all of the other expensive equipment typically found in modern
forensics labs.