Marsh test, method for the detection of arsenic, so sensitive that it can be used to detect minute amounts of arsenic in foods (the residue of fruit spray) or in stomach contents. The sample is placed in a flask with arsenic-free zinc and sulfuric acid. Arsine gas (also hydrogen) forms and is led through a drying tube to a hard glass tube in which it is heated. The arsenic is deposited as a "mirror" just beyond the heated area and on any cold surface held in the burning gas emanating from the jet. Antimony gives a similar test, but the deposit is insoluble in sodium hypochlorite, whereas arsenic will dissolve. The test was named for its inventor, the English chemist James Marsh.
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