Hydrogen and arsenic

Calcium Arsenide, Ca3As2, is formed by the direct combination of calcium with arsenic vapour at dull red heat.11 When a mixture of hydrogen and arsenic vapour is passed over heated quicklime the product is mainly arsenite, only a little arsenide being formed.12 It is best prepared by the reduction of calcium arsenate by carbon in an electric furnace.13 Lebeau used a mixture of 100 parts of the arsenate with 31 parts of petroleum coke and employed a current of 950 to 1000 amperes at 45 volts, the heating being continued for 2 to 3 minutes. Guerin14 has shown that calcium arsenate is reduced by carbon slowly at 800° C. and rapidly at 850° C., the arsenite being first produced and... 

Uranium Arsenide, U3As4, may be obtained i by passing hydrogen over a fused mixture of sodium uranous chloride and sodium arsenide. It is a greyish powder which readily burns in the air. Sometimes it is obtained in a pyrophoric condition. An aluminium-containing product results when the aluminothermic process, using an oxide of uranium and arsenious oxide, is employed. The purest arsenide is obtained, in the crystalline form, when a mixture of hydrogen and arsenic vapour is passed over sodium uranium chloride. It is rapidly decomposed by nitric acid. 

Nitrogen, phosphorus and arsenic form more than one hydride. Nitrogen forms several but of these only ammonia, NHj, hydrazine, N2H4 and hydrogen azide N3H (and the ammonia derivative hydroxylamine) will be considered. Phosphorus and arsenic form the hydrides diphosphane P2H4 and diarsane AS2H4 respectively, but both of these hydrides are very unstable. 

The effect of a particular element on the odour of its compound seems also to lend support to the residual affinity theory, for it is only the elements which possess residual affinity in certain of their compounds, which function as osmophores. Oxygen, nitrogen, sulphur, phosphorous, halogens, arsenic, antimony, bismuth, etc., whose valencies vary under certain conditions are powerfully osmophoric whereas carbon, hydrogen, and many others which have a constant valency are practically non-osmophoric, and it is very instructive to note that the element is osmophoric when it is not employing its full number of valencies and therefore has free affinity. 

Oxidation of arsenic(III) by chromate in alkaline medium was studied by Kolt-hoff and Fineman. They found the reaction to be first order with respect to both chromate and arsenic(rir). At pH greater then 9.1 the rate coefficient is independent of the hydrogen-ion concentration. The average value of the rate coefficient at 30° in solutions of pH 9.1 and ionic strength 1.75 was found to be (1.61+0.08) x 10 l.mole sec . ... 

Diarsenic trisulphide produces particularly toxic sulphur dioxide, hydrogen sulphide and arsenic by thermal decomposition or acid treatment. 

Reactions similar to these provide convenient syntheses of hydrides of such elements as phosphorus, arsenic, tellurium, and selenium, because these elements do not react directly with hydrogen and the hydrides are unstable. 

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