Arsenic pentasulphide

Arsenic trichloride Gallium arsenide Potassium arsenate Arsine Arsenic add Sodium arsenate Sodium arsenite CaicKjm arsenate Arsenic trioxide Arsenic pwtoxide Arsenic bisulphide Arsenic pentasulphide Arsenic hemiselenide... 

The reaction of arsenic acid solutions with hydrogen sulphide has been the subject of much investigation and it is found that arsenic pentasulphide or arsenic trisulphide may be precipitated as the main product, according to conditions.12 Thus, in an aqueous solution of the pentoxide at the ordinary temperature and in the presence of 8 to 14 per cent, of hydrochloric acid, the precipitate is the pentasulphide as the concentration of hydrochloric acid is increased, the trisulphide and sulphur are also precipitated in increasing proportion, and at 32 to 33... 

From solutions of pure arsenic acid the pentasulphide separates in a highly disperse form which adsorbs arsenic acid so strongly that the last traces of the latter react with great difficultv at the ordinarv temperature,6 although this is not the case at AO" C. In the presence of salts of multivalent cations which by hydrolysis yield colloidal hydroxides, the arsenic pentasulphide is flocculated, but the completion of the reaction is greatly delayed owing to adsorption of the arsenic acid, especially at low temperatures. 

Sodium thiosulphate also yields a precipitate of arsenic pentasulphide, slowly in the cold but more readily on heating and when hydrochloric acid is present 2 pentathionie acid is formed in the solution.3... 

Arsenic Pentasulphide, As2S5.—When arsenic is fused with an excess of sulphur the product contains arsenic, sulphur and arsenic pentasulphide the last-named may be extracted with liquid ammonia 8 or, by careful fractionation, the arsenic and sulphur may be removed, leaving the sulphide. If the elements are fused together in stoichiometric proportions, a greenish-yellow plastic mass is obtained which gradually hardens and becomes lemon-yellow if this product is powdered and digested with aqueous ammonia, a yellow solution results and insoluble sulphur remains. After filtering, the addition of an acid to the yellow solution precipitates the pentasulphide. 

Arsenic pentasulphide may also be prepared from aqueous arsenic acid or a solution of an arsenate by the action of hydrogen sulphide, but the nature of the product depends upon conditions. Berzelius reported 2 the formation of the pentasulphide when the gas acted on a moderately concentrated solution of arsenic acid, but Wackenroder stated 3 that the arsenic acid was first reduced by hydrogen sulphide to arsenious acid, even in the presence of hydrochloric acid, and that a mixture of arsenic trisulphide and sulphur was then precipitated. Rose,4 after passing hydrogen sulphide into a solution of arsenic acid, heated the solution and filtered off the precipitate, and then by the addition of silver nitrate showed that both arsenious and arsenic acids were present in the filtrate. It was therefore accepted that reduction takes place and the reaction was represented thus ... 

Bunsen 5 showed that the passage of a rapid stream of hydrogen sulphide through a hot solution of an alkali arsenate acidified with hydrochloric acid produced a precipitate of arsenic pentasulphide, and that this was a satisfactory method of determining arsenic quantitatively. These results were confirmed by McCay,6 and led to more systematic investigation of the subject,7 the result of which showed that the conditions favourable for the formation of arsenic pentasulphide, when hydrogen sulphide acts on aqueous arsenic acid or acid solutions of arsenates, are (a) a considerable excess of hydrochloric acid present, (b) a rapid passage of the gas, and (c) a comparatively low temperature—the liquid should be warm, as precipitation is extremely slow in the cold. Under these conditions arsenic pentasulphide alone is formed ... 

A convenient method of preparing arsenic pentasulphide is to boil arsenic pentoxide with piperazine, when a solution is obtained which, by the prolonged action of hydrogen sulphide, yields the compound As2S5.3C4H10N2.3H2S if this is treated with cold dilute hydrochloric or acetic acid, crystals of arsenic pentasulphide are formed.6... 

Arsenic pentasulphide acts as an acid thioanhydride and with metallic sulphides yields salts known as thioarsenates. These may be regarded as derivatives of the following hypothetical acids ... 

The alkali salts are generally formed when arsenic pentasulphide is dissolved in an aqueous solution of the hydrosulphide and the mixture evaporated or precipitated with alcohol, or when a solution of an arsenate is treated with hydrogen sulphide under suitable conditions. The thioarsenates of the heavy metals (except silver, see p. 279) may be formed by the action of an excess of an alkali thioarsenate on a salt of the heavy metal if the latter is in excess the sulphide is formed.4... 

The salts of the alkali and alkaline earth metals, as well as of gold, magnesium, beryllium and yttrium, are soluble in water, the solutions being colourless or pale yellow. They gradually decompose, however, when kept, with deposition of sulphur, arsenic and arsenic pentasulphide. The following thioarsenates have been described. 

Ammonium Thioarsenates. — Ammonium Orthothioarsenate, (NH4)3AsS4, separates as colourless prisms when alcohol is added to a hot solution containing arsenic pentasulphide and excess of ammonium hydrosulphide.5 The crystals gradually turn yellow in air and, when heated, melt and decompose, yielding ammonium sulphide, arsenious sulphide and sulphur. 

Beryllium Thioarsenate is formed in solution when arsenic pentasulphide and beryllium hydroxide are boiled with water for some time.3... 

Yttrium Thioarsenate.—Yttrium does not form an insoluble thioarsenate but, if yttrium hydroxide and arsenic pentasulphide are digested with wrater, thioarsenate is formed in solution. The compound is unstable, however, and gradually decomposes, with separation of sulphur and arsenic.5... 

Arsenious sulphide is completely precipitated from a hot acid solution of an arsenite, and arsenic pentasulphide from one of an arsenate, by the addition of sodium thiosulphate, whilst both arsenites and arsenates are precipitated quantitatively as arsenious sulphide by ammonium thioacetate.6... 

Arsenic Subsulphide—Tetrarsenic Trisulphide—Arsenic Disulphide—Arsenio Trisulphide Colloidal Arsenic Trisulphide—Arsenic Pentasulphide—Thio-arsenates—Oxythioarsenates—Sulphato-eompounds of Arsenic. 

If a large excess of concentrated hydrochloric acid is present and hydrogen sulphide is passed rapidly into the cold solution, yellow arsenic pentasulphide As2S5 is precipitated in the hot solution, the precipitate consists of a mixture of the tri- and penta-sulphides. 

Arsenic pentasulphide, like the trisulphide, is readily soluble in alkali hydroxides or ammonia (a), ammonium sulphide (b), ammonium polysulphide... 

Upon acidifying these solutions with hydrochloric acid, arsenic pentasulphide is reprecipitated ... 

Arsenic pentasulphide—As.S,—310—is said to have been formed by fusing a mixture of As.S, and S in proper proportions, ns a yellow, fusible solid, capable of sublimation in absence of air. There exiH well-dehiied sutphnvseuaies, p>TO- and meta sulpbui senates,... 

The crystal structure of tetra-arsenic pentasulphide, AS4S6, has been determined. The crystals are monoclinic, of space group P2i/w, withZ = 2 in a unit cell of dimensions a = 7.98, b = 8.10, c = 7.14 A / = 101.0 . The structure (10) is built up of discrete AS4S5 molecules of approximate symmetry with As— As = 2.55 A and mean As—S = 2.24 A. The structure of AS4S5 is quite different from those of P4S5 and P4Seg, which have an exo-cyclic sulphur and selenium atom, respectively, double-bonded to a quinque-valent phosphorus atom. 

Bunsen worked out a method for the separation of platinum metals (preparation of pure rhodium). He determined the composition, NIg,NH3, of nitrogen iodide, developed a volumetric method of iodimetry, using a solution of sulphurous acid, and worked on water analysis. Bunsen and L. Schischkoff investigated the chemical reactions in the explosion of gunpowder. Bunsen discovered arsenic pentasulphide, and measured the adsorption of carbon dioxide on glass. ... 

Despite the copious evolution of phenol and water during processing, Narmco s commercial adhesive system (Imidite 850) was based on prepolymer 28 mixed with aluminium powder, inorganic arsenic compounds such as arsenic thioarsen-ate or arsenic pentasulphide, and sterically hindered polyphenol antioxidant. Adhesive tapes were manufactured hy hot-melt deposition of this mixture on a 112-type glass cloth carrier used in conjunction with a heat-resistant primer (polybenzimidazole or polyimide). As with all other heat resistant polymers, surface preparation of flat and honeycomb metal surfaces is an important factor in... 

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