Potassium Ferrocyanide Sulphate

Sulphates, Copper, and Alkalies. — Boil for a few minutes a solution of 5 gm. of ferrous chloride in 10 cc. of water and 5 cc. of nitric acid (sp. gr. 1.3), dilute to 120 cc., add 20 cc. of ammonia water, and filter evaporate 50 cc. of the filtrate and ignite the residue. The weight of the latter should not exceed 0.001 gm. Slightly acidulate 20 cc. of the filtrate with hydrochloric acid and add barium nitrate solution. No change should appear. 20 cc. of the filtrate acidified with acetic acid should show no change upon addition of potassium ferrocyanide solution. 

Sulphates. — Dissolve 1 gm. of potassium ferrocyanide in 20 cc. of water, and add 1 cc. of hydrochloric acid followed by barium chloride solution. No immediate turbidity should ensue. 

R. H. Robinson found sodium nitrite to be unsuitable as a fertilizer, particularly in acid soils, owing to losses of nitrogen by decomposition. According to C. Marie and R. Marquis, nitrous acid is liberated from aq. soln. of the alkali nitrites by carbon dioxide, so that a strip of potassium iodide-starch paper suspended over the liquid is coloured blue. 0. Baudisch found that the reduction of nitrite by potassium ferrocyanide and oxygen is sensitive to light. M. Oswald found that the presence of sodium sulphate lowers the solubility of sodium nitrite enormously— at 16°, a sat. soln. of the nitrite alone has 81-6 per cent. NaN02, but a sat. soln. of both salts together has 11-8 per cent, sodium sulphate, and 53-9 per cent, of sodium... 

Experiment Prepare a solution of a ferrous salt by dissolving 2 grams of ferrous ammonium sulphate in 20 cc. of water, adding a little dilute sulphuric acid and a piece of iron wire. Test both this solution and a solution of a ferric salt (nitrate or chloride) with potassium ferrocyanide, potassium ferricyanide, and potassium sulphocyanate. Tabulate the results. These constitute the standard tests for ferrous and ferric salts. Write equation. 

Namely, at least five molecules of copper sulphate to one of potassium ferrocyanide (E. Muller and co-workers, J. pralct. Chem., 1912, 86, 82). 

When a copper sulphate solution is added to excess potassium ferrocyanide, a mixture of di-potassium cupric and di-potassium tricupric ferrocyanides is produced, namely K2CuFe(CN)6 and K2Cu3[Fe(CM)6]2 respectively. 

If cuprous chloride is substituted for cupric sulphate, then different cuprous potassium ferrocyanides are obtained according to circumstances, namely K2Cu 2[Fe(CN)6] KCuCu 3[Fe(CN)6]2 and KCu a[Fe(CN)6]. The last of these is obtained, when cuprous chloride is in great excess, as a white precipitate. 

The crude coal gas is washed with ferrous sulphate solution, whereby the latter is converted into a suspension of ferrous sulphide in ammonium sulphate solution. This reacts with the ammonium cyanide, yielding ferrous ferrocyanide, Fe2[Fe(CN)6], or ammonium ferrous ferrocyanide, (NH4)2Fe[Fe(CN)6], according to circumstances. Potassium ferrocyanide may be obtained from these by treatment with lime, as m the spent oxide process. By repeatedly dissolving in water and precipitating with alcohol, the salt can be obtained in a very pure state.1... 

Concentrated sulphuric acid dissolves dry anhydrous potassium ferrocyanide, yielding potassium hydrogen sulphate and hydrogen ferrocyanide —... 

It may be conveniently prepared by heating potassium ferrocyanide with 50 per cent, nitric acid solution on a water-bath until a drop of the solution gives no colour with ferrous sulphate. The whole is cooled, the liquid poured from the precipitate, neutralised with sodium carbonate, and taken to dryness. Extraction with water, filtration from the insoluble iron compounds, and crystallisation from the clear aqueous solution yields the salt in ruby-coloured, rhombic prisms. The reactions involved may be represented as follows —... 

Copper, Nitric Acid, etc. (Alkali Salts, Calcium). — Dilute 20 iM. of ferric chloride solution (1 1) with 100 cc. of water, fuld 25 cc. of ammonia water, and filter. On evaporating 50 cc. of the colorless filtrate and igniting the residue, the weight of the latter should not exceed 0.001 gm. On mixing 2 cc. of the filtrate with 2 cc. of concentrated sulphuric acid, and overlaying tliis mixture with 1 cc. of ferrous sulphate solution, no brown zone should form at the contact-surfaces of the two licpiids. 20 cc. of the filtrate acidulated With acetic a

potassium ferrocyanide solution. 

Vanadium compounds (vanadic acid and vanadium chloride) have been proposed as substitutes for copper sulphide, but without much practical success. Potassium ferrocyanide and ferricyanide are also used to a certain extent. A mixture of these salts with aniline salt and potassium chlorate is printed, and the goods aged. The probable action is that the ferricyanide oxidises the aniline, and is continually regenerated from the ferrocyanide formed by the chloric acid present. Thus these salts play the part of oxygen carriers in a similar manner to the copper and vanadium compounds. In the opinion of technologists, the hlack produced by this process differs somewhat in its properties from that obtained with copper, but this may be ascribed to the presence of prussiaii blue in the former. In place of the aniline hydrochloride and potassium chlorate, a mixture of aniline sulphate and barium chlorate has recently been employed in black-printing. 

Manufacture.—Several different varieties of Prussian blue are on the marl The finest commercial Prussian blue goes under the name Paris blue, anc made by dissolving 50 kilos of potassium ferrocyanide in 250 kilos of water, < making simultaneously a solution of 43-45 kilos of ferrous sulphate (green vitr in 259 kilos of water, best in the presence of scrap iron to avoid formation of fe salts. The two solutions are now run simultaneously into a vessel contain 250 kilos of water, and the almost white precipitate which forms is allowed settle and is drained on a cloth filter. 

Still a third method is to oxidise ferrous sulphate with nitric acid and mu into the solu potassium ferrocyanide solution. Tire deep bine precipitate is collected and washed until from iron. 

NOTE.—The blue substance formed at times in this preparation is probably produced as the result of the following cause Commercial potassium cyanate may contain potassium ferrocyanide. If this is the case, when a solution of the salt is evaporated in the air with ammonium sulphate containing a trace of iron, Prussian blue is formed. 

Test for a Soluble Cyanide (Section 240).—To 1 cc. of a dilute solution of potassium cyanide add 5 drops of a solution of sodium hydroxide and 5 drops of a solution of ferrous sulphate heat to boiling, cool, and add dilute hydrochloric acid, drop by drop, until the solution shows an acid reaction. If no color develops add 3 drops of a solution of ferric chloride. Potassium ferrocyanide is formed from the potassium cyanide and ferrous sulphate the ferrocyanide and the ferric salt then form Prussian blue. (Eqs.)... 

For this the easiest method is to use potassium ferrocyanide and sponge or spray it with a dilute solution of iron sulphate or use copper sulphate and sponge or spray with ammonium hydrate. If we use acetate of cobalt—then this when heated gives a very similar result. 

Employ copper sulphate for the invisible writing or drawing and develop with potassium ferrocyanide, or heat or milk can also be employed. 

Materials Potassium ferrocyanide, solutions of ferrous sulphate and of sodium carbonate. 

Materials Solutions of cupric sulphate, and of potassium ferrocyanide. 

Materials Solutions of ferric chloride, of ferrous ammonium sulphate, of potassium ferrocyanide, of potassium ferricyanide, of ammonium thiocyanate. 

Directions Put 5 c.c. of ferric chloride solution into a small test tube, fill the tube with water, shake the solution and then pour a third of it into each of two other test tubes. Dilute and divide into thirds in the same way 5 c.c. of ferrous ammonium sulphate solution. Add a few drops of solutions of potassium ferrocyanide, of potassium ferricyanide, and of ammonium thiocyanate to the three solutions of ferric chloride respectively and likewise to the three solutions of ferrous ammonium sulphate. (1) Tabulate the results obtained in these six tests. (2) Do the results indicate the presence of any ferric salt in the ferrous salt Would you expect the production of any color in the absence of ferric salts (3) State one test for a ferrous salt and two tests for a ferric salt. 

Characters and Tests.—Blue crystalline salt, in oblique prisms, soluble in water, forming a pale blue solution which strongly reddens blue litmus. The aqueous solution gives with barium chloride a white precipitate (barium sulphate), insoluble in hydrochloric acid, showing the salt to be a sid-phate and with potassium ferrocyanide a maroon-red precipitate, indicating the presence of copper (cupric ferrocyanide). If an aqueous solution of the salt be mixed with twice its volume of chlorine water, to peroxidize any iron that may be present, and solution of ammonia be added, the precipitate (cupric hydrate) formed by the first addition of the ammonia will be dissolved by a further and sufficient addition of the alkali, and a violet blue solution (copper ammonio-sulphate) will be produced, leaving nothing un ssolved unless iron be present, in which case a reddish-brown precipitate will be left. 

John Mercer (Dean or Great Harwood, nr. Bolton, Lancs., 21 February 1791-Oakenshaw, Lancs., 30 November 1866), a calico-printer, discovered mercerising (1844), the use of potassium ferrocyanide and potash for the discharge of indigo (1848), the use of arsenates as a substitute for phosphates in dunging the manufacture of sodium stannite and stannate, stannous sulphate from tin and copper sulphate solution, Turkey-red oil, the solubility of cellulose in ammoniacal copper solution, and blue-print photography. He taught himself chemistry from a second-hand copy of the Chemical Pocket-Book of James Parkinson, of Hoxton Square, London (2 ed. 1801, 3 ed. 1803). ... 

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