Ferrocyanides, crystallizing

Add about 0 2 g. of ferrous sulphate crystals to the first portion of the filtrate contained in a boiling-tube. An immediate dark greenish-grey precipitate of ferrous hydroxide should occur if the mixture remains clear, add a few ml. of sodium hydroxide solution. Now boil the mixture gently for a few minutes to ensure formation of the ferrocyanide, cool under the tap, add one drop of ferric chloride solution, and then acidify... 

Transition metals readily form complexes, such as [Fe(CN)6], the ferrocyanide ion, Ni(CO)4, nickel tetracarbonyl, and [CuC ], the copper tetrachloride ion. MO theory applied to such species has tended to be developed independently. It is for this reason that the terms crystal field theory and ligand field theory have arisen which tend to disguise the fact that they are both aspects of MO theory. 

Water-soluble crystal modifiers such as yellow pmssiate of soda (YPS) (sodium ferrocyanide decahydrate) or ferric ammonium citrate may also be added to some types of salt as anticaking agents. Both are approved by the U.S. Food and Dmg Administration for use in food-grade salt. YPS and Pmssian Blue (ferric ferrocyanide), are most commonly added to rock salt used for wintertime highway deicing. Concentrations of YPS and Pmssian Blue in deicing salt vary, typically in the range of 20—100 ppm. 

Sodium chloride and sodium cyanide are isomorphous and form an unintermpted series of mixed crystals. The ferrocyanide ion has a marked effect on the habit of sodium cyanide crystallized from aqueous solution (50). Sodium cyanide and sodium carbonate form a molten eutectic at approximately 53 wt % sodium carbonate and 465°C. The specific conductivity of molten 98% sodium cyanide is 1.17 S /cm (51). 

Other inorganic crystals studied by Mark and his collaborators, sometimes leading to complete structure determinations, include strontium chloride, zinc hydroxide, tin tetraiodide, potassium chlorate, potassium permanganage, and ammonium ferrocyanide. Minerals investigated by them include CaSO (anhydrite), BaSO (barite), PbSO, Fe2TiO[j (pseudobrookite), and three forms of Al2Si05 (cyanite, andalusite, and sillimanite). 

Potassium ferrocyanide (200 g.) is completely dehydrated by careful heating in a porcelain basin or on an iron plate the crystals... 

NOTTS Use cod, but not very cold water in the condenser. Due to the high freezing point oi l 1CN the use of odd water may cause it to crystallize in the condenser. This process is an improvement over the old method using ferrocyanide in that it results in a product of greater purity. Commercial HCN is currently produced by reacting ammonia and methane gases in an arc furnace. While extremely cheap and effective, it is not very suitable fir small scale production. 

In dry state, NH4CN is made by heating a mixture of potassium cyanide or potassium ferrocyanide with ammonium chloride and condensing the vapors into ammonium cyanide crystals ... 

Although ferrocyanide anion is stable at ordinary temperatures, at high temperatures it oxidizes to ferricyanide. That is, when the aqueous solution of the complex is evaporated, red crystals of ferricyanide are obtained. Similar oxidation can also occur at ambient temperatures in the presence of oxidizing agents ... 

Potassium ferricyanide is prepared by oxidation of potassium ferrocyanide, K4Fe(CN)6. Thus, when chlorine is passed through an aqueous solution of potassium ferrocyanide, the ferricyanide separates as crystals. 

Chloro-pentammino-chromic Nitrate, [Cr(NH3)5Cl](NOs)2, is precipitated by the addition of excess of nitric acid at 0° C. to a solution of the chloride. It may be crystallised from water acidified with nitric acid, and obtained in red octahedral crystals which are more soluble in water than the chloride. The chloro-pentammino-salts react in aqueous solution with chloroplatinic acid, with precipitation of the very sparingly soluble chloroplatinate, [Cr(NH3)6Cl](PtCl6), which crystallises in yellow prisms. The oxalate, [Cr(NH3)5Cl]C204, and the ferrocyanide, [Cr(NH3)6Cl]2[Fe(CN)6].4H20, are precipitated by the... 

Put 20 g. of potassium ferrocyanide in a 250-cc. Erlenmeyer flask, adding 30 cc. of water. Place the flask on the water bath and heat till the ferrocyanide dissolves. Add 35 cc. of nitric acid (sp. gr., 1.24) and continue heating until a test portion shows no blue color but a dark green precipitate when treated with ferrous sulfate. Let stand for a day or two and filter off the tarry impurities. Now neutralize with sodium carbonate, taking care that no excess is added. Warm and, when cool, add from one to two times the volume of alcohol (ethyl). Set the flask in a dry place for a day or two, after which the impurities (chiefly crystals of potassium nitrate) may be filtered off, and the nitro-prusside crystallized out. Sometimes two or three treatments with alcohol are necessary. In order to expedite the operation of evaporating down to crystallization, the solution may be evaporated by heating in a suction flask under reduced pressure. Quick crystallization increases the yield. The yield should be above 75 per cent. 

Almost always, especially when the operation is arrested a little too soon, there ie not a sufficient quantity of cyanide of iron formed to saturate the cyanide of potassium, whioh is then present in exeess, and passes into the solution. To transform this excess of cyanide into ferrocyanide, before crystallizing the solution, a quantity of dissolved protosulphate of iron is poured in until a white or bluish and persistent prcoi-... 

On the basis of the foregoing generalization, it is reasonable to postulate that the simple transition metal cyanides with six or less d electrons will adopt the Prussian blue structure. However, metal cyanides with seven or more d electrons will crystallize in less symmetric structures. At the present there are insufficient data to thoroughly check this proposal, but the few known structures lend support to the idea. For example, ferrous cyanide (ferrous ferrocyanide) and ferric cyanide (ferric ferri-cyanide) crystallize with the Prussian blue structure while nickel and zinc cyanides do not. 

Sodium Ferrocyanide occurs as yellow crystals or as a crystalline powder. It is soluble in water, but it is practically insoluble in most organic solvents. 

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