Ferrous sulphide

Hydrogen sulphide. This poisonous gas is usually prepared from ferrous sulphide and dilute hydiochloric acid (1 3) in a Kipp s apparatus it should be washed with water to remove acid spray. 

The resulting hydrogen sulphide contains hydrogen because of the presence of free iron in commercial ferrous sulphide. 

If sulphur is present, a black precipitate of ferrous sulphide is obtained when the ferrous sulphate crystals dissolve. Boil the mixture for about 30 seconds, and acidify with dilute sulphuric acid the ferrous sulphide dissolves and a precipitate of Prussian blue forms if nitrogen is present. 

Hydrogen sulphide is usually prepared on a small seale by the aetion of hydroehlorie aeid on ferrous sulphide ... 

This is a simplified treatment but it serves to illustrate the electrochemical nature of rusting and the essential parts played by moisture and oxygen. The kinetics of the process are influenced by a number of factors, which will be discussed later. Although the presence of oxygen is usually essential, severe corrosion may occur under anaerobic conditions in the presence of sulphate-reducing bacteria Desulphovibrio desulphuricans) which are present in soils and water. The anodic reaction is the same, i.e. the formation of ferrous ions. The cathodic reaction is complex but it results in the reduction of inorganic sulphates to sulphides and the eventual formation of rust and ferrous sulphide (FeS). 

The presence of active sulphate-reducing bacteria usually results in graphitic corrosion and this has led to a useful method of diagnosing this cause of corrosion. The leaching out of iron from the graphitic residue which is responsible for the characteristic appearance of this type of corrosion leads to an enriched carbon, silicon and phosphorus content in the residue as compared with the original content of these elements in the cast iron. Sulphur is usually lost to some extent but when active sulphate-reducing bacteria are present, this loss is offset by the accumulation of ferrous sulphide in the residue with a consequent increase in the sulphur content of the residue out... 

Salmonella typhi, in the presence of glucose, reduces bismuth sulphite to bismuth sulphide, a black compound the organism can produce hydrogen sulphide from sulphur-containing amino acids in the medium and this will react with ferrous ions to give a black deposit of ferrous sulphide (Table 1.2). 

By digesting potassio cyanide with ferrous sulphide —... 

The major reactions are complicated by a number of minor or secondary reactions, and by impurities in the raw materials. As a result the black ash may contain 1 to 2 per cent, of sodium silicate to If per cent, of sodium aluminate 1 per cent, of sodium ferrous sulphide small proportions of sodium cyanide and thiocyanate derived from the nitrogen of the coal a relatively small amount of ultramarine etc. Proposals to use barium carbonate, etc., in place of limestone in the black-ash process are indicated in connection with the preparation of sodium carbonate from sodium sulphide. 

If we remember that arsenic meant usually the sulphide, orpiment, and sometimes realgar also, and that by magnesia very frequently was meant native sulphides of lead, zinc and other metals, and marcasite usually meant sulphides of the character of various colored pyrites, the above statement records the production of fusible ferrous sulphide when iron and these sulphides are heated together. The inclusion of lead in the list may also perhaps be explained by an ancient habit of occasionally using the same term for a metal and its principal ores in metallurgy as is sometimes seen in Pliny. Thus galena, the native sulphide of lead, heated with iron would also liquefy it as do the other sulphides. 

Hydrogen may be oxidised by sulphur dioxide under suitable conditions thus when a mixture of the gases is passed over finely divided nickel or over nickel sulphide at a dull red heat, water, hydrogen sulphide and sulphur are produced.3 If the gases are passed sufficiently slowly the whole of the sulphur dioxide is decomposed. Cobalt sulphide and, with less efficiency, ferrous sulphide, may also be used as catalysts in this hydrogenation.4 A similar reaction occurs at a slightly higher temperature in the absence of a catalyst, but in this ease the sulphur is obtained mainly in the free condition the presence of a little water vapour facilitates the reaction.5... 

Ferrous selenate can be prepared by the action of selenie acid on ferrous sulphide selenie acid does not dissolve iron (see p. 335) ... 

The metallic arsenides generally melt between 800° and 1200° C., many with decomposition,2 volatilisation of arsenic occurring below the melting point. The majority of mineral sulpharsenides melt between 400° and 600° C. Arsenopyrite decomposes to arsenic, sulphur and ferrous sulphide at 675° to 685° C., while lollingite (p. 10) loses 23-83 per cent, of arsenic at 735° C.3... 

Iron Thioarsenates.—Both ferrous and ferric salts, when treated with a solution of sodium orthothioarsenate, yield brown precipitates which are soluble in excess of the reagent. The ferric salt is stable in air and may be heated to fusion without decomposition at a higher temperature sulphur is expelled. The ferrous salt decomposes on drying in the air, ferric hydroxide and thioarsenate being formed.6 Ferrous sulphide dissolves in an aqueous solution of an alkah thioarsenate.7... 

Auction if the Hydrosulphite B X is insufficiently used (formation of ferrous sulphide). 

Sometimes the ore must be pretreated before it will adsorb the additive satisfactorily for example, zinc sulphide must be pretreated with dilute copper sulphate solution, which deposits copper on the ore surface by electrochemical action. Specificity of flotation may also be achieved by the addition of depressants for example, cyanide ions prevent ferrous sulphide and zinc sulphide from floating but allow... 

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