Hydrogen sulphide acid-released

Note. If certain sulphides are treated with hydrochloric acid, hydrogen sulphide is evolved and can be absorbed in an ammoniacal cadmium chloride solution upon acidification hydrogen sulphide is released. 

Polythene wash bottles are sometimes charged with wash liquids other than water. Attention must be drawn to the fact that the components of some wash solutions may pass into the polythene and may be released into the space in the bottle when it is set aside repeated fillings and rinsings may be required to remove the chemicals from the bottle. It is safer to label the wash bottle and to reserve it for the special wash liquid. Such wash solutions include a weakly acid solution saturated with hydrogen sulphide, dilute aqueous ammonia, saturated bromine water, and dilute nitric acid. 

The formation of iron sulphide, or any other metal sulphide, and subsequent hydrolysis to release hydrogen sulphide, represents a corrosion process. The various oxidation processes discussed ail involve the production of hydrogen sulphide, sulphur dioxide or sulphuric acid. In the absence of effective protection, any one of these is a potential corrodent, especially in association with any wear which takes place. 

Many methods for sulphide and H2S are based on the reducing properties of S(-II). Hydrogen sulphide reduces molybdate in acid medium to molybdenum blue, and the molybdophosphate to phosphomolybdenum blue [52]. Iron(III) reduced by H2S in the presence of 1,10-phenanthroline gives the orange Fe(phen)3 complex [2,53], Hydrogen sulphide may be determined after conversion into thiocyanate by the reaction with Fe(III) [54]. Sulphide has been determined also by a colour redox reaction with nitroprusside [55-57], In another sensitive reaction the sulphide ions decompose the Ag complex with Cadion 2B and Triton X-100 (e = 2.5-10 ) [58], In another indirect method sulphide releases the chloranilate ion from the Hg(Il) chloranilate [59]. Sulphide has also been determined by a method based on its reaction with bromate, followed by bromination of 2 ,7 -dichlorofluorescein by the bromine released [60]. 

A mixture of sulphides, sulphates and carbonates can be analysed [93, 94] after acid decomposition of the sample, releasing carbon dioxide, hydrogen sulphide and sulphur. The gas mixture evolved can be determined by GC. The acid decomposition method was used in the analysis of moon rock samples [95]. 

During the decomposition of proteins into simpler substances sulphur compounds are released which are reduced to hydrogen sulphide, and nitrogen compounds are reduced to ammonia. CoUoid proteins are transformed into solutions via degradation into peptones, amino acids and finally into ammonia and carbon dioxide. 

In spite of the success of the Leblanc process, it was evident from the outset that its operation involved serious drawbacks. Although the hydrogen chloride pollution problem was largely solved by the Gossage towers, there remained the problem of the residue left behind after the black ash had been extracted with water. The principal constituent of this alkali waste was calcium sulphide, but it also contained calcium hydroxide and unchanged coal. There was no alternative but to dump it near the alkali works, where it released hydrogen sulphide when acted upon by acidic rain water. Not only did this cause a serious pollution problem, but also all the sulphur of the original sulphuric acid was wasted. 

Formation of gases by reaction of waste with acids, e.g. hydrogen sulphide released by the reaction of acids witii sulphides, commonly found in gasworks waste, or hydrogen cyanide released by the reaction of acids on cyanides found in metal plating or refining residues... 

By using an acidic solution of hydrogen-peroxide at higher tanperature (this instrument is most frequently used), organic substance is broken down in an oxidized manner, with the process also leading to the release of all complex metal ions. At the same time, any sulphide minerals present are also broken down. 

In comparison with the acid digestion method, the hydrogenation method is more susceptible to matrix interferences. Two types of interferences are possible. Samples containing zinc, cadmium or mercury cannot be analyzed, as the high volatility of these elements results in the formation of a metallic mirror on the cooler parts of the tubing, which partially or completely absorbs the released sulphide. Sulphur may also be retained in the sample because it is present in the form of sulphur compounds which are not reduced or decomposed, e.g. manganese sulphide, or is held in crystal lattices which do not allow sufficiently rapid diffusion of sulphur at the temperature of 1150°C. 

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