Marsh test

As can be expected, antimony compounds resemble those of arsenic. In the Marsh test, antimony compounds again give a black deposit which, unlike that formed by arsenic compounds, is insoluble in sodium chloratefi) solution. 

Marshische Probe. Marsh test. Marsh s test. 

The hydrides of arsenic, antimony, and bismuth are unstable at elevated temperature. The Marsh test for arsenic depends on this instability when an arsenic mirror forms as arsine is passed through a heated tube ... 

Braman et al. [713] suggested the use of sodium borohydride (NaBH4) as a reducing agent to replace the metallic zinc used in the classical Marsh test, which is awkward to handle and often contains large blanks of the elements of interest. Sodium borohydride is now used almost exclusively in the various modifications of the hydride method. 

Marsh-Berzelius test See Marsh test. marsh ber za-le-3s, test ... 

Marsh test analy chem 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. marsh, test ... 

Most of the compounds of arsenic are toxic when in contact with the skin, when inhaled, or when ingested. As with arsenics cousin phosphorus above it in group 15 of the periodic table, care must be taken when using arsenic. The compound arsenic trioxide (As O ), an excellent weed-killer, is also carcinogenic. Copper acetoarsenite, known as Paris green, is used to spray cotton for boll weevils. A poisonous dose of arsenic as small as 60 miUigrams can be detected within the body by using the Marsh test. 

Arsenic compounds may be detected easily by the Marsh test. In this test, some metallic zinc is added to an acid solution of the material to be tested, and the mixture is heated. The arsenic is liberated as arsine, AsH3, which may be decomposed by heat to give an "arsenic mirror." The reaction is... 

The Gutzeit Test.3—This test is as accurate as the Marsh test and the apparatus necessary is comparatively simple. It consists in allowing the arsine to react with strips or discs of dry filter paper impregnated with silver nitrate or, in the more recent modifications of the method, mercuric chloride or bromide. 

Applied as a microchemical test, Bettendorff s test is ten times as sensitive as the Marsh test.8... 

Estimation Gravimetrically as Sulphide as Magnesium Pyroarsenate—Volu-metrically by Iodometric Methods with Potassium Bromate, etc.—The Marsh Test—The Gutzeit Test—Fleitmann s Test—Colorimetric Methods— Microohemioal Methods—Determination of Arsenic in Gases. 

Marsh test for arsenic [ARSENIC AND ARSENIC ALLOYS] (Vol 3)... 

The original Marsh test involved burning and deposition of the arsenic upon a cold surface. Nowadays the mirror test is usually applied. The silver nitrate reaction (sometimes known as Hofmann s test) is very useful as a confirmatory test. 

Arsine (AsH3) is extremely poisonous. Its ready thermal decomposition to arsenic, which is deposited on hot surfaces as a mirror, is utilized in tests for arsenic, for example, the well-known Marsh test, where arsenic compounds are first reduced by zinc in HC1 solution. 

Pentavalent hydrides of arsenic are not known in any form. The simplest hydride of arsenic , arsine (AsHs) is a very toxic gas (m.p. -116°C, b.p. —62°C) with a characteristic garlic-like odor, which in the presence of air oxidizes to AS4O6. It is thermally unstable depositing a mirror of As in hot smfaces, a property that is nsed in the qualitative determination of arsenic (Marsh test). 

The concept of traces in chemistry probably originates from descriptions of the purity of chemical reagents, which in the nineteenth century included a statement such as trace for minor components when a more accurate description was not needed or not possible. One early example of determination of traces was the Marsh test, developed as early as 1836 for the determination of very small amounts of arsenic, which was of primary importance in toxicology. 

Arsenic is readily detected the Marsh test was devised in 1836 and was used for over a hundred years. More sophisticated and very sensitive methods are now available, using X-ray analysis or a technique known as mass spectrometry which detects the arsenic atoms. Even before the Marsh test a careful scientific process of experiment would sometimes be successful, as demonstrated by the doctor in the case of Mary Blandy in 1752 (see case notes p. 223). Arsenic remains in tissues of the body for a long time, hence analysis of Napoleon s hair was possible long after his death (see case notes p. 222). The sensitive analysis of hair and nails from the body of American president Zachary Taylor, exhumed in 1991, also established that he was not poisoned in 1850. 

It also is formed by reduction of soluble arsenic compounds by zinc in acidic solution. This reaction is the basis of an important and sensitive test for arsenic, the Marsh test (Fig. 21-5). The arsenic is deposited as a steel-gray or black mirror from the burning gas onto a cold glazed porcelain dish held in the flame. Antimony produces a velvety brown or black deposit, which is not soluble in sodium hypochlorite solution, whereas the arsenic deposit is. The antimony deposit, but not that of... 

FIG. 21-5. The Marsh test for arsenic. The sample is introduced through the thistle tube. Both arsenic and antimony produce a mirror in this test the chemical properties of the deposit permit a distinction to be made between an arsenic mirror and an antimony mirror. 

Ores of arsenic orpiment, realgar, arsenolite, arsenopyrite. Compounds of arsenic arsine, arsenic trioxide, arsenious acid, cupric hydrogen arsenite, arsenic pentoxide, arsenic acid, sodium arsenate. The Marsh test for arsenic. U.ses of arsenic and its compounds lead shot, insecticides, weed killers, chemotherapy. 

Describe the Marsh test, and explain how it is possible to detect the presence of arsenic, antimony, or both elements in the sample tested. 

The Marsh test for arsenic involves the following steps (a) The generation of hydrogen gas when sulfuric acid is added to zinc, (b) The reaction of hydrogen with As(III) oxide to produce arsine, (c) Conversion of arsine to arsenic by heating. Write equations representing these steps and identify the type of the reaction in each step. 

Apparatus for the Marsh test. Sulfuric acid is added to zinc metal and a solution containing arsenicfllll oxide. The hydrogen produced reacts with AS2O3 to yield arsine (AsH I- On heating, arsine decomposes to elemental arsenic, which has a metallic appearance, and hydrogen gas. 

Box 14.4 Thermal decompositions of arsine and stibine the Marsh test... 

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