Solution Potassium Hydroxide Sulphide

The use of sulphur dioxide as precipitant was first proposed by Berzelius, but accurate results by this method are only obtainable under special conditions. Complete precipitation does not take place from a strongly acid solution, and in the presence of other metals small amounts of these are liable to be carried down. In the presence of heavy metals such as copper, bismuth and antimony, the following procedure has been recommended 2 The tellurium is oxidised to telluric acid by the addition of ammonium perdisulphate in the presence of potassium hydroxide, excess of perdisulphate being subsequently removed by boiling. The heavy metals present are next removed by means of hydrogen sulphide. The tellurium may then readily be estimated by reduction with hydrogen chloride and precipitation with sulphurous acid. 

Alumina, Calcium, and Heavy Metals. — 2.5 gm. of potassium hydroxide should completely dissolve in 10 cc. of water yielding a clear and colorless solution. Dilute the solution to 100 cc. and add 15 cc. of acetic acid (sp. gr. 1.041), followed by 10 cc. of ammonia water a slight turbidity may form within five minutes, but no flocculent precipitate of aluminum hydroxide should develop. The solution so tested, filtered if necessary, should not exhibit an immediate turbidity on adding ammonium oxalate solution and on the addition of ammonium sulphide solution should acquire at most a slight green color. 

Nitrogen. — Mix 100 cc. of the potassium sulphide solution in a distilling flask with 50 cc. of nitrogen-free sodium hydroxide solution (sp. gr. 1.3). Add 1 gm. of zinc dust, and distil off about 50 cc., collecting the distillate in a U-tube receiver containing about 20 cc. of water and 2 to 3 cc. of decinormal hydrochloric acid. Titrate the distillate with decinormal potassium hydroxide, using methyl orange as the indicator. The ammonia distilled over should not have neutralized more than 0.2 cc. of the decinormal acid. 

The potassium salt. K3As0 2S 2. H20, is unstable. It has been obtained in an impure form by treating the precipitate resulting from the action of hydrogen sulphide on aqueous potassium orthoarsenate with potassium hydroxide.6 On evaporation of the solution, the salt separates in yellow, hygroscopic crystals which cannot be recrystallised owing to decomposition to orthoarsenate and thioarsenate. 

The alcohol is purified by shaking with aqueous potassium hydroxide and extracting with diethyl ether that has been freed from peroxides with silver nitrate and sodium hydroxide. After being washed, the extract is treated with saturated sodium hydrogen sulphide solution, filtered, washed and dried over potassium carbonate. After removal of the ether, the alcohol is distilled under reduced pressure and the middle fraction dried over lime that has been burned in an atmosphere of nitrogen. 

Cold water has no effect, but boiling water slowly decomposes the sulphide into phosphoric acid and hydrogen sulphide.3 With potassium hydroxide solution the sulphide behaves like a mixture of sulphur and phosphorus, giving phosphine, hydrogen, etc., and potassium sulphide.8... 

Tin(II) sulphide is practically insoluble in solutions of caustic alkalis hence, if potassium hydroxide solution is employed for separating Group IIA and Group IIB, the tin must be oxidized to the quadrivalent state with hydrogen peroxide before precipitation with hydrogen sulphide. 

At ordinary temperatures an aqueous solution of sodium (or potassium) hydroxide dissolves sulphur, forming sulphide, polysulphides, thiosulphate, and sulphite. The reaction is very complex, but Calcagni11 thinks that the sulphide is probably formed first, thiosulphate next, and then polysulphides. Finally, sulphite is produced by decomposition of the thiosulphate. With concentrated solutions part of the sulphur probably dissolves without entering into combination. Ammonium hydroxide of density 0-888 behaves similarly.11... 

Potassium monosulphide, KaS.—The sulphide can be formed by direct union of the elements,13 by reduction of potassium sulphate with hydrogen or charcoal, and by the interaction of aqueous solutions of potassium hydroxide and potassium hydrogen sulphide. It is also produced by the action of sulphur on a solution of excess of potassium in liquid ammonia.14 On evaporation of its aqueous solution in vacuum at low temperature, the pentahydrate16 crystallizes. A dihydrate and a dodecahydrate are also known.18 The anhydrous salt can be obtained... 

Aurous cyanide forms yellow, microscopic laminae, very slightly soluble in Water. It is more stable than aurous iodide, but at red heat is decomposed into gold and cyanogen. Its insolubility renders it immune to the action of dilute acids and hydrogen sulphide, but solutions of ammonia, potassium hydroxide, ammonium sulphide, and sodium thiosulphate dissolve it, probably forming complex derivatives. In aurous cyanide the tendency to form complex compounds is much more marked than in the corresponding chloride, bromide, and iodide.3 Its interaction with potassium ferrocyanide has been studied by Beutel.4... 

When acted upon with dilute sulphuric acid, the potassium salt yields the free acid, hydrogen ferro-heptanitroso sulphide,KFe4(NO)7S3, as an insoluble, amorphous precipitate. It is very unstable. When boiled with dilute potassium hydroxide solution, the potassium hepta-nitroso derivative yields potassium ferro-dinitroso sulphide, KFe(NO)2S. 2H20 (see p. 181). 

H3[Fe(CN)5.C0]H20, is obtained3 by the action of hydrogen sulphide on the copper salt in solution. Upon evaporation in the dark over potassium hydroxide, the acid separates in colourless tabular crystals. It is acid to litmus, and is sufficiently powerful to decompose alkali carbonates. 

Bleed off surplus hydrogen sulphide either for re-use or into absorber bottles containing potassium hydroxide solution. 

With Potassium Hydroxide, (a) In Alcoholic Solution. By the action of a 20% solution of potassium hydroxide in alcohol, dichloroethyl sulphide is converted into divinyl sulphide ... 

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