Arsenious sulphide

Experiments illustrating these various possible reactions have been carried out notably by Reinders (Z it. Roll. Ghem. xiii, 235, 1913) and by Hofmann (Zeit. Phys. Ghem. Lxxxiii. 385,. 1913). Finely divided calcium sulphate is preferentially wetted by water in the presence of liquids, such as chloroform and benzene which are frequently termed non-polar or slightly polar. Silver iodide suspensions in water will go into the dineric interface in contact with ether, chloroform and benzene, but are removed from the water by preferential wetting in the case of butyl and amyl alcohols, whilst the reverse holds true in the case of aqueous suspensions of arsenious sulphide. 

The precipitate on analysis gave the ratio Ba 90AsaS8. The constancy of the ratio however depends entirely on the size and charge of the arsenious sulphide particles, since the reaction proceeds to the isoelectric point, i.e. electrical neutrality, and is therefore independent of any definite stoichiometric ratio of reactants. 

Freundlich isotherm the bulk concentrations Ci, (7a, necessary to produce precipitation will evidently follow no regular order, but be dependent on the variables a and n of the isotherm expression. Thus on the addition of aluminium chloride to arsenious sulphide... 

Kruyt and van Duin (Kolloidchemie Beihefte, v. 269,1914) have examined the alteration in sensitiveness to electrolytes of a suspension of arsenious sulphide to which various non-electrolytes had been added. They found that the influence of various nonelectrolytes on the sensitiveness of the suspension ran parallel to the adsorption of the non-electrolytes from aqueous solution by powdered charcoal and that the most capillary active non-electrolyte exerted the greatest effect on the liminal concentration required for precipitation. Further it was observed that the addition of non-electrolytes lowered the liminal concentrations, i.e. increased the sensitiveness of the suspension to uni- and trivalent ions but increased the liminal concentrations, i.e. decreased the sensitiveness for divalent and tetravalent cations as will be noted from the following tables. 

If the non-electrolytes are in fact selectively adsorbed it necessarily follows that the ions are displaced from the colloid surface thus the non-electrol3 te cuts dovm the adsorption of the ions of the added electrolyte. It has already been noted that the anions and cations of an added salt are not equally adsorbed and it is likely that the extent to which the ionic adsorption is cut down by the preferential adsorption of the non-electrolyte is not equal for each ion. In the case of the negative arsenious sulphide sol if the non-electrolyte cuts down the adsorption of the cation of an... 

Small quantities of selenium in solution may be detected by the test described by Meunier,1 which is similar to Marsh s test for arsenic. If there is a relatively large amount of selenium present it is readily detected by its red colour, but if the amount of the element be small the deposit closely resembles that of arsenic, and in this case the following process may be adopted to detect the selenium. A current of hydrogen sulphide is passed into the hot solution containing a little sulphurous acid. The precipitate of finely divided sulphur carries down with it any selenium present and arsenic as arsenious sulphide, and it is clotted by stirring. In the presence of selenium the clots are brown they may be dried and the sulphur and selenium separated by careful sublimation in a closed tube. 

When sulphur is heated with arsine, hydrogen sulphide is formed and a sublimate first of arsenic and then of arsenic sulphide is produced.9 The reaction proceeds slowly at 100° C. and at lower temperatures in direct sunlight. Hydrogen sulphide does not react with arsine in the absence of air at the ordinary temperature even in direct sunlight, but on admission of air a deposit of arsenious sulphide is rapidly formed10 whether the reactants are in the gaseous condition or in aqueous... 

When dry arsenious oxide is fused with sodium thiosulphate a mixture of the di- and tri-sulphides results.13 In aqueous solution and in acidified solutions of arsenites the addition of aqueous sodium thiosulphate causes the precipitation of arsenious sulphide after a sharply defined induction period, the duration of which is in inverse proportion to the thiosulphate concentration and practically independent... 

The reaction commences at a temperature above 400° C., before the melting temperature is reached, and the fused product therefore always contains some arsenious oxide.1 When heated in hydrogen, the pentoxide is reduced first to arsenious oxide and then to free arsenic. Similar reduction occurs when it is heated with carbon or phosphorus with sulphur, arsenious sulphide is formed. Arsenic and metallic arsenides result when the pentoxide is heated with alkali metals,2 zinc, lead, iron or most other heavy metals mercury and silver react only at high temperature gold and platinum do not react. 

If arsenious sulphide is used instead of the oxide, arsenic acid and sulphuric acid are formed and may be separated by precipitation of the latter by addition of lime. In the absence of nitric acid, oxygen at 20 atmospheres, even at 200° C., produces only arsenious acid from arsenious oxide (cf. p. 146), and arsenious and sulphuric acids from arsenious sulphide. 

The oxidation may also be accomplished by means of chlorine,1 bromine 2 or iodine,3 hypochlorous acid,4 aqua regia,5 chromic acid6 or permanganic acid,6 and some metallic oxides 7 (see p. 180). Arsenic acid is also formed by decomposition of arsenic trichloride by the action of chlorine water 8 or chromic acid,9 or by the action of bromine water on arsenious sulphide.10... 

In cold aqueous solution, sodium orthoarsenate reacts with sodium hydrosulphite to form sodium arsenohydrosulphite,6 NagAs(S204)3, a creamy white granular powder. In the presence of sodium sulphite this compound decomposes, forming sodium arsenothiosulphate, an unstable intermediate product, and finally arsenious sulphide.7 If the reduction by sodium hydrosulphite takes place in the presence of hydrochloric acid, some arsenic subsulphide, As3S, is also precipitated,8 and this product is also obtained when the orthoarsenate in aqueous solution is treated with phosphorus trichloride and the mixture saturated with sulphur dioxide.9... 

Arsenic subsulphide is a dark brown powder. It is insoluble in carbon disulphide, in aqueous ammonia and in colourless ammonium sulphide. It dissolves, however, in yellow ammonium sulphide, which is at the same time decolorised, and the addition of an excess of hydrochloric acid to the solution precipitates arsenious sulphide. It is decomposed by caustic alkali. When heated, arsenic subsulphide is resolved into realgar and arsenic. 

It may also be obtained by fusion of a mixture of arsenic and arsenious sulphide 8 in the calculated proportions. A fiery red product is formed by melting arsenious oxide or arsenic pentoxide with sodium thiosulphate.9 The red sulphide has also been found mixed with other sulphides in the flue dusts obtained during the roasting of arsenical ores.10... 

Realgar may also he prepared in the laboratory by heating arsenious sulphide with an aqueous solution of sodium bicarbonate in a sealed tube at a temperature of 150° C. the sulphide dissolves and, on cooling, realgar crystallises from the solution.11 The same result is obtained by... 

Water does not sensibly attack realgar (at boiling temperature a little arsenious oxide and hydrogen sulphide are produced 2), but steam reacts at red heat to give a sublimate of arsenious oxide and arsenious sulphide.3... 

The arsenious sulphide may be formed as a crystalline precipitate under favourable conditions. When hydrogen sulphide is passed into a 0-2N solution of arsenious oxide in water, golden-yellow leaflets are formed in small quantity,7 and the amount increases with the concentration up to 0-3N. Beyond this concentration the amount of crystalline sulphide produced diminishes whilst, with very dilute solutions (0-05N), traces only are formed. The crystalline form is also obtained by heating in a sealed tube a mixture of arsenious oxide, ammonium thiocyanate and hydrochloric acid.8 If arsenic acid is used in place of the oxide, sulphur is also precipitated. A convenient... 

When heated, arsenious sulphide readily sublimes and fusion occurs, according to Borgstrom,8 at 320° C. Earlier determinations have put the melting point at 310°,9 300°10 and 325° C.11 Air must be excluded or oxidation occurs. Some degree of volatilisation may be observed at the ordinary temperature.12 According to Schuller,13 when... 

When arsenic trisulphide is exposed to dry hydrogen chloride or hydrogen bromide, it liquefies at the ordinary temperature and on heating complete volatilisation occurs.9 It is not readily attacked by halogen acids. When boiled with concentrated hydrochloric acid it is decomposed, but with great difficulty, and the hydrogen sulphide and arsenious chloride evolved reproduce arsenious sulphide in the receiver.10 A similar reaction occurs when heated with a chloride in the presence of concentrated sulphuric acid, but the decomposition is incomplete.11 The reaction is facilitated by the presence of cuprous chloride or ferric chloride. Only a slight reaction is observed with dilute acid,12 and the... 

Arsenious sulphide reacts with metallic sulphides as an acid thio-anhydride and forms a series of complex salts known as thioarsenites. These may be considered to be derived from the following hypothetical acids 9... 

The salts are usually prepared by the interaction of arsenious sulphide with the metallic sulphide, hydrosulphide or carbonate, taking care to exclude air to prevent the formation of thioarsenates. Thus, Nilson12 obtained the salts of the alkali and alkaline earth metals by dissolving arsenious sulphide in the aqueous solutions of the respective hydrosulphides and concentrating in vacuo. 

Wiinschendorff,1 using carefully purified arsenious sulphide and the alkali sulphide, prepared the following compounds ... 

The ortho-salt was reported by Berzelius (see above), and Nilson obtained ammonium metathiotriarsenite, NH4As3Ss.2H20, by evaporation of a saturated solution of arsenious sulphide in ammonium hydrosulphide. 

It was observed by Berzelius that arsenious sulphide, obtained by precipitation from aqueous arsenious oxide with hydrogen sulphide, after it had been washed with cold water, dissolved to a slight extent in hot water forming a yellow solution. Water containing hydrogen... 

There is a limiting concentration necessary for complete precipitation, and also a limiting concentration below which no coagulation occurs even after a long interval of time. Thus, with a hydrosol containing 9-57 millimoles of arsenious sulphide per litre, to portions of which potassium chloride was added in concentrations of 1-22, 2-44 and 3-90 millimoles per litre, respectively, no precipitation had occurred in the first two eases after 340 days, whereas in the third almost complete precipitation took place in that time.7... 

PRECIPITATION VALUES OF ELECTROLYTES FOR ARSENIOUS SULPHIDE HYDROSOL (7-54 MILLIMOLES PER LITRE). 

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