Ferrous sulphite

Hydrosulphurous acid is also formed by the action of many metals on sulphurous acid 7 the crust of ferrous sulphite and hydrosulphite formed on the surface of metallic iron is of great protective value in the iron cylinders used for storing liquid sulphur dioxide, which generally contains traces of water.8... 

Dithionic Acid, H2S2O0, is obtained only in aqueous solution. If sulphur dioxide is passed into an aqueous suspension of ferric hydroxide at 0° C., a red solution of ferric sulphite is first produced, which then changes to a pale green solution of ferrous sulphite and ferrous dithionate 4... 

Ferrous sulphite also results when solutions of ferrous salts and sodium sulphite interact,6 and wrhen ferrous hydroxide is dissolved in aqueous sulphurous acid. In these circumstances a red solution is usually obtained, probably because of interaction with dissolved oxygen. The colour quickly disappears, however, particularly on warming. On concentration the salt crystallises out. 

On passing a current of sulphur dioxide into an aqueous suspension of freshly precipitated ferrous sulphide, the latter passes into solution and ferrous sulphite is gradually deposited —7... 

Ferrous sulphite solution readily oxidises in air, yielding a red solution.6 From its colourless solutions alkalies precipitate ferrous hydroxide. 

The salt may also be obtained by triturating a concentrated solution of ferrous sulphate with barium thiosulphate,1 but it is less pure, as it contains some tetrathionate as well.2 It results when sulphur is digested with ferrous sulphate solution, and when iron is dissolved in aqueous sulphurous acid.3 This latter reaction is somewhat complicated, ferrous sulphite being first produced, thus —... 

The nascent hydrogen then attacks either the sulphurous acid (or ferrous sulphite), reducing it to thiosulphuric acid (or ferrous thiosulphate). Thus —... 

On concentration ferrous sulphite, being much less soluble, crystallises out first, leaving the thiosulphate in solution (see p. 145). 

Iron and Sulphur—Subsulphides of Iron—Ferrous Sulphide—Ferric Sulphide-Double Sulphides—Iron Pyrites—Marcasite—Magnetic Pyrites—Ferrous Sulphite—Ferri-sulphites—Ferrous Sulphate—Double Sulphates—Fern-sulphates—Alums—Anndo-sulphonates, Thiosulphate, Disulphate, and Thionates of Iron. 

The cultures are examined after 2 days and 4-5 days incubation. In the case of a negative result, the incubation time should be extended to 10 to 14 days in order to be quite certain. The sulphate-reducing bacteria appear as black colonies as a result of the formation of ferrous sulphite. 

Absolute diethyl ether. The chief impurities in commercial ether (sp. gr. 0- 720) are water, ethyl alcohol, and, in samples which have been exposed to the air and light for some time, ethyl peroxide. The presence of peroxides may be detected either by the liberation of iodine (brown colouration or blue colouration with starch solution) when a small sample is shaken with an equal volume of 2 per cent, potassium iodide solution and a few drops of dilute hydrochloric acid, or by carrying out the perchromio acid test of inorganic analysis with potassium dichromate solution acidified with dilute sulphuric acid. The peroxides may be removed by shaking with a concentrated solution of a ferrous salt, say, 6-10 g. of ferrous salt (s 10-20 ml. of the prepared concentrated solution) to 1 litre of ether. The concentrated solution of ferrous salt is prepared either from 60 g. of crystallised ferrous sulphate, 6 ml. of concentrated sulphuric acid and 110 ml. of water or from 100 g. of crystallised ferrous chloride, 42 ml. of concentrated hydiochloric acid and 85 ml. of water. Peroxides may also be removed by shaking with an aqueous solution of sodium sulphite (for the removal with stannous chloride, see Section VI,12). 

Di-teo-propyl ether. The commercial product usually contains appreciable quantities of peroxides these should be removed by treatment with an acidified solution of a ferrous salt or with a solution of sodium sulphite (see under Diethyl ether). The ether is then dried with anhydrous calcium chloride and distilled. Pure di-iao-propyl ether has b.p. 68-5°/760 mm. 

CAUTION. Ethers that have been stored for long periods, particularly in partly-filled bottles, frequently contain small quantities of highly explosive peroxides. The presence of peroxides may be detected either by the per-chromic acid test of qualitative inorganic analysis (addition of an acidified solution of potassium dichromate) or by the liberation of iodine from acidified potassium iodide solution (compare Section 11,47,7). The peroxides are nonvolatile and may accumulate in the flask during the distillation of the ether the residue is explosive and may detonate, when distilled, with sufficient violence to shatter the apparatus and cause serious personal injury. If peroxides are found, they must first be removed by treatment with acidified ferrous sulphate solution (Section 11,47,7) or with sodium sulphite solution or with stannous chloride solution (Section VI, 12). The common extraction solvents diethyl ether and di-tso-propyl ether are particularly prone to the formation of peroxides. 

Bismuth sulphite agar. This medium was developed in the 1920s for the identification of Salmonella typhi in water, faeces, urine, foods and pharmaceutical products. It consists of a buffered nutrient agar containing bismuth sulphite, ferrous sulphate and brilliant green. 

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). 

This hydroperoxide decomposes slowly, avoiding accumulation. However, if the conditions are ideal for peroxidation (heat, prolonged time exposure to air, solar light), the hydroperoxide converts into extremely dangerous peroxides. Phenolic antioxidants inhibit this peroxidation efficiently. If tetrahydrofuran is peroxidised, it is not possible to destroy peroxides with ferrous salts or sulphites since tetrahydrofuran dissolves in water. Alumina or active carbon (passing over an alumina column or activated carbon at 20-66 C with a contact period of two minutes) are used, or by stirring in the presence of cuprous chloride. 

Estimation of Selenium in Sulphide Minerals.s—In various sulphite-cellulose manufactories difficulties have occurred which have been traced to the presence of selenium in the pyrites used for burning. Part of the selenium remains in the burnt pyrites and part volatilises with the sulphur dioxide. 20 to 30 grams of pyrites are dissolved in hydrochloric acid (dens.=1-19) and potassium chlorate. Zinc is added to reduce the iron to the ferrous condition more hydrochloric acid is then added, the solution boiled and stannous chloride added to precipitate selenium. Since the selenium may contain arsenic, it is collected on an asbestos filter, dissolved in potassium cyanide and reprecipitated using hydrogen chloride and sulphur dioxide. The element may then be estimated by the iodometric method described below. In order to determine the relative proportion of volatile to non-volatile selenium, the pyrites may be roasted in a current of oxygen. After this treatment the contents of the tube are dissolved in warm potassium cyanide and the selenium reprecipitated and estimated in the ordinary way. 

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