Marsh test


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Marsh test,

method for the detection of arsenicarsenic
, a semimetallic chemical element; symbol As; at. no. 33; at. wt. 74.92160; m.p. 817°C; (at 28 atmospheres pressure); sublimation point 613°C;; sp. gr. (stable form) 5.73; valence −3, 0, +3, or +5.
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, 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.

Marsh test

[′märsh ‚test]
(analytical chemistry)
A test for the presence of arsenic in a compound; the substance to be tested is mixed with granular zinc, and dilute hydrochloric acid is added to the mixture; gaseous arsine forms, which decomposes to a black deposit of arsenic, when the gas is passed through a heated glass tube. Also known as Marsh-Berzelius test.