[702] Chem. Centrbl., 1889, 569.
§ 709. Arsine—Arseniuretted Hydrogen, H3As.—Mol. weight, 78; vol. weight, 39; specific gravity, 2·702; weight of a litre, 3·4944 grammes; percentage composition, 95·69 As, 4·31 H; volumetric composition, 2 vol. H3As = half vol. As + 3 vol. H. A colourless inflammable gas, of a fœtid alliaceous odour, coercible into a limpid colourless liquid at a temperature of from -30° to -40°. The products of the combustion of arseniuretted hydrogen are water and arsenious acid; thus, 2H3As + 6O = 3H2O + As2O3. If supplied with air in insufficient quantity, if the flame itself be cooled by (for example) a cold porcelain plate, or if the gas pass through a tube any portion of which is heated to redness, the gas is decomposed and the metal separated. Such a decomposition may be compared to the deposit of carbon from ordinary flames, when made to play upon a cooled surface. It may also be decomposed by the electric spark,[703] e.g., if the gas is passed slowly through a narrow tube 0·7 to 0·8 mm. internal diameter, provided with wires 0·5 to 0·6 mm. apart, and a small induction coil used connected with two large Bunsen’s cells, then, under these conditions, arsenic as a metal is deposited in the neighbourhood of the sparks. For the decomposition to be complete, the gas should not be delivered at a greater speed than from 10 to 15 c.c. per minute. The gas burns with a blue-white flame, which is very characteristic, and was first observed by Wackenroder. It cannot, however, be properly seen by using the ordinary apparatus of Marsh, for the flame is always coloured from the glass; but if the gas is made to stream through a platinum jet, and then ignited, the characters mentioned are very noteworthy.
[703] N. Klobrikow, Zeit. Anal. Chem., xxix. 129-133.
Oxygen or air, and arsine, make an explosive mixture. Chlorine decomposes the gas with great energy, combining with the hydrogen, and setting free arsenic as a brown cloud; any excess of chlorine combines with the arsenic as a chloride. Sulphur, submitted to arseniuretted hydrogen, forms sulphuretted hydrogen, whilst first arsenic and then sulphide of arsenic separate. Phosphorus acts in a similar way. Arseniuretted and sulphuretted hydrogen may be evolved at ordinary temperatures without decomposition; at the boiling-point of mercury (350°) they are decomposed, sulphide of arsenic and hydrogen being formed; thus, 3H2S + 2AsH3 = As2S3 + 6H2, a reaction which is of some importance from a practical point of view. Many metals have also the property of decomposing the gas at high temperatures, and setting hydrogen free. Metallic oxides, again, in like manner combine with arsenic, and set water free, e.g., 3CuO + 2H3As = Cu3As2 + 3H2O.
Arsine acts on solutions of the noble metals like phosphuretted hydrogen, precipitating the metal and setting free arsenious acid; for example, nitrate of silver is decomposed thus—
12AgNO3 + 2H3As + 3H2O = As2O3 + 12HNO3 + 12Ag.