Hydrogen sulphide, from decomposition

Natural waters may be contaminated with carbon disulphide and hydrogen sulphide from wastewaters from the chemical industry and more frequently by hydrogen sulphide formed during the anaerobic decomposition of organic matter. 

Electrochemical tree growth, the electrical equivalent of environmental stress cracking (Chapter 10), occurs at lower electric stresses. The chemical species vary. Lead salts from petroleum entered a cable buried near a petrol station, whereas hydrogen sulphide from the decomposition of seaweed entered an undersea cable. The whole gamut of polyethylene degradation reactions occur on a micro-scale inside such trees. To avoid such failures, the cable can be fitted with an impervious outer layer, such as a lead sheath. 

Shock-tube experiments on the decomposition of hydrogen sulphide have been performed but were unsuccessful because traces of oxygen and other oxidizers could not be removed from the reactant24. No data are available on the homogeneous decomposition of hydrogen polysulphides, nor have the kinetics of pyrolysis of selenium and tellurium hydrides been studied. 

Considerable attention has been given recently to the direct recovery of the hydrogen from hydrogen sulphide rather than conversion to water. Catalytic thermal cracking of H2S is possible (15,16) and improved catalysts permitting thermal decomposition at lower temperatures are being investigated. 

Hydrogen Disulphide, H2S2, in addition to being obtained from the distillation of crude hydrogen persulphide, is also formed when hydrogen trisulphide is distilled at 100° C. under a pressure of 20 mm. approximately one-third of the trisulphide is converted into disulphide, whilst the remainder passes into hydrogen sulphide and sulphur. The disulphide, therefore, is the most stable of the hydrogen polysulphides towards heat, and can actually be distilled under atmospheric pressure at 71° to 75° C. with only partial decomposition. 

This ammonium amylselenite decomposes slowly on standing in air, liberating red selenium. The action of light hastens the rate of the decomposition.3 Hydrogen sulphide produces a dark orange-coloured precipitate from the solution in tsoamyl alcohol.4... 

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. 

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