Ferrous thiosulphate

On prolonging the passage of sulphur dioxide the salt dissolves and the acid sulphite, Fe(HS03)2 is produced in solution. The normal salt is re-deposited on boiling, but the solution now contains ferrous thiosulphate in consequence of the reaction between a portion of the dissolved acid salt and sulphur produced by hydrogen sulphide and sulphur dioxide inter-reacting. Thus —... 

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

Ferrous tetrathionate, FeS406, results in unstable solution on adding ferrous thiosulphate solution in small quantities at a time to ferric chloride —... 

Cyanogen, Chlorine, and Bromine.—Shake 0.5 gm. of powdered iodine with 20 cc. of water, and filter. To 10 cc. of the filtrate, add, drop by drop, decinormal sodium thiosulphate solution until decolorized, then add a granule of ferrous sulphate, 1 drop of ferric chloride solution and 2 cc. of sodium hydroxide solution. Warm to about 60° C., and add 10 cc. of hydrochloric acid. The liquid should not acquire a blue color. Filter, and to 10 cc. of the filtrate add 1 cc. of ammonia water, 5 drops of silver nitrate solution, and again filter. On adding to the filtrate 2 cc. of nitric acid no precipitate, and not more than an opalescent turbidity, should develop. ... 

The only other early determinations be mentioned are Dumas analyses of anhydrous ferrous and ferric chloride, in which the amount of silver required to combine with the chlorine was determined,1 and a few experiments by Winkler,2 in which a weighed amount of iron was dissolved in a solution of iodine in potassium iodide, the excess of iodine being determined by titration with sodium thiosulphate. The results were as follow (Cl =35 457, 1=126-92, Ag =107-880) —... 

Laboratory Preparation of Iron Disulphide.—In the laboratory iron disulphide may be prepared by several wet methods. Thus, it is formed when ferrous sulphide is boiled with flowers of sulphur and when sodium trisulphide is added slowly to a boiling solution of ferrous sulphate, provided excess of the trisulphide is avoided. Sulphur is simultaneously precipitated.4 It is obtained also by boiling the freshly precipitated monosulphide suspended in water with sulphur in the absence of alkalies 5 by the action of sodium thiosulphate solution upon ferrous sulphate6 in sealed tubes at temperatures even below 100° C. —... 

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 —... 

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

The double salt, Fe2S203.8Na2S203.8H20, is obtained 5 by precipitating a mixed solution of ferrous iodide and sodium thiosulphate with alcohol. It forms bright green crystals, readily soluble in water. 

Sodium ferro-heptanitroso sulphide, NaFe4(NO)7S3.2H20, may be obtained in a similar manner to the potassium salt by boiling a solution of sodium ferro-dinitroso thiosulphate, as also by the action of sodium nitrite and sulphide solutions upon ferrous sulphate. In this latter reaction the sodium sulphide may be replaced by sodium thiocarbonate, Na2CS3. 

Potassium ferro-dinitroso thiosulphate,1 KFe(N0)2S203.H20, results when nitric oxide is passed into a concentrated mixed solution of ferrous sulphate and potassium thiosulphate at room temperature. The solution becomes deep brown in colour, and reddish brown crystals of the potassium salt are obtained on concentration. The salt is but slightly soluble in cold water, and is insoluble in water-free alcohol and in ether. Concentrated sulphuric acid dissolves it without decomposition, yielding a greenish yellow solution. 

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. 

About 2 gm. benzyl iodide are weighed into a flask and then 50 ml. 20% alcoholic potash solution are added and the mixture refluxed for about an hour. At the completion of the saponification the contents of the flask are allowed to cool and then transferred to a 500-ml. flask and made up to volume with water. 100 ml. of the resulting solution are placed in a distillation flask and distilled in steam after adding 10 gm. ferric ammonium alum and acidifying with sulphuric acid. By this treatment, the ferric salt is converted to the ferrous condition, liberating iodine which is distilled over into 5% potassium iodide solution. At the end of the distillation, the free iodine in the potassium iodide solution is titrated with a decinormal solution of sodium thiosulphate. From this, the amount of iodine and so the quantity of benzyl iodide in the sample may be calculated. 

If ground glass is present, it remains as an insoluble residue which may be determined. The potassium chlorate is determined by difference. Heaven precipitates the mercury from the thiosulphate solution as sulphide, reduces the chlorate with ferrous sulphate and titrates the chloride formed. 

Dilute 50 ml of syrup to 400 ml, precipitate with sodium hydroxide and a little bromine water, to oxidise any iron in the ferrous state. Bring the mixture to the boil and allow the precipitate to settle. After filtration on paper in a Gooch crucible, dissolve the precipitate in hydrochloric acid, reprecipitate with sodium hydroxide and redissolve in hydrochloric acid. Add potassium iodide and titrate with 0 1 N thiosulphate. 1 ml = 0 005585 g Fe. 

Dissolve about 0 8 g in 100 ml of water and heat 10 ml of the solution at about 50° for twenty minutes in a stoppered bottle with 25 ml of acid solution of ferrous sulphate (freshly prepared by dissolving 7 g of ferrous sulphate in 90 ml of boiled and cooled water, to which is added sufficient concentrated sulphuric acid to produce 100 ml) and 5 g of potassium iodide. Cool, add 50 ml of water and titrate the liberated iodine with 0 1N thiosulphate. Repeat the operation without the potassium chlorate and deduct the titration figure in the test from that in the control. 1 ml 0 1N = 0 002043 g KClOg. 

Typical reducing agents used in a redox couple are thiosulphates, metabisulphites and hydrosulphides. Frequently the redox couple is combined with trace quantities of a ferrous salt providing an even more rapid generation of free radicals. 

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