Potassium ferrocyanide

“ Expose well-dried and powdered ferrocyanide of potassium to a moderate red heat, in a close vessel; when cold, powder the fused mass, place it in a funnel, moisten it with a little alcohol, and wash it with cold water; evaporate the solution thus formed to dryness, expose it to a dull red heat in a porcelain dish, cool, powder, and digest it in boiling rectified spirit; as the spirit cools, crystals of cyanide of potassium, nearly pure, will be deposited. The alcohol employed in both this and the preceding process may be recovered by distillation from calcined sulphate of iron. ”

“ Ferrocyanide of potassium gives a nearly white precipitate, becoming gradually blue in the air, and immediately so on the addition of a little weak nitric acid or chlorine water. Ferricyanide of potassium produces a rich deep-blue precipitate, insoluble in hydrochloric acid. In highly dilute solutions the effect is only a deep bluish-green coloration. Phosphate of sodium produces a white precipitate, which after a time becomes green. ”

“ The color of the red copper salt which now forms the picture may be modified or changed in many ways, viz., by soaking the picture, after the ferrocyanide of potassium has been washed out of the lights, in a solution of sulphate of iron (or the iron salt may, but not so advantageously, have been applied to the picture before the application of the ferrocyanide) . ”

“ Ferric, fer′ik, adj. pertaining to or obtained from iron: noting an acid compounded of iron and oxygen.—ns. Ferr′ate, a salt formed by the union of ferric acid with a base; Ferrocyanogen (fer-o-sī-an′ō-jen) , a compound radical supposed by chemists to exist in ferrocyanic acid and the ferrocyanides, the chief of which is potassium ferrocyanide, yielding Prussian blue; Ferr′otype, a photographic process in which the negative was developed by a saturated solution of protosulphate of iron. [L. ferrum, iron.]
Ferriferous, fer-rif′ėr-us, adj. bearing or yielding iron. ”

“ All of these complexes are decomposed rather readily by the addition of strong acids, whose hydrogen-ion breaks up the complex ions, by suppressing the anions491 of the much weaker organic acids and alcohols. Consequently, these organic compounds do not interfere with tests which may be carried out in strongly acid solution. For instance, the addition of potassium ferrocyanide to a solution of ammonium ferrioxalate (NH4) 3Fe (C2O4) 3, to which an excess of ammonium oxalate has been added, gives only a slight indication of the presence of ferric-ion (a greenish blue solution is obtained) ”

“ NCl, is formed in a similar manner from paraphenylene diamine. It is a strong oxidizing agent. Quinone-dioxime, HON: C6H4: NOH, crystallizes in colourless or yellow needles, which decompose when heated to about 240° C. Potassium ferrocyanide in alkaline solution oxidizes it to dinitrosobenzene, whilst cold concentrated nitric acid oxidizes it to para-dinitrobenzene. Quinhydrone, C6H4O2⋅C6H4 (OH) 2, is formed by the direct union of quinone and hydroquinone or by careful oxidation of hydroquinone with ferric chloride solution. On boiling with water it decomposes into quinone and hydroquinone. ”

“ The crude but clear solution of ferrocyanide of potassium (blood lye) is precipitated by a mixed solution of alum, 2 parts, and green sulphate of iron, 1 part; the dingy greenish precipitate that falls gradually becomes blue by absorption of atmospheric oxygen, which is promoted by exposure and agitation of the liquor; as soon as it has acquired its full colour, the sediment is repeatedly washed with water, and is then drained, and dried, at first in a stove, but afterwards on chalk stones. Product large, but inferior in quality. ”

“ They) are deliquescent solids which are exceedingly soluble in water. Potassium platinocyanide, K2Pt (CN) 4.3H2O, is obtained by dissolving platinum bichloride in potassium cyanide; by heating potassium ferrocyanide with spongy platinum; or by heating ammonium chlorplatinate with potassium cyanide. It crystallizes in needles which effloresce readily. The dry salt is exceedingly hygroscopic and is very soluble in water. When boiled with aqua regia it forms the chlorine addition product, K2Pt (CN) 4.Cl2.2H2O. It combines directly with iodine. ”

“ The elements of cyanogen, combined with sulphur, form a salt radical, sulphocyanogen, C2NS2, which is expressed by the symbol Csy. The sulphocyanide of potassium, KCsy, is prepared by fusing ferrocyanide of potassium, deprived of its water of crystallization, intimately mixed with half its weight of sulphur and 17 parts of carbonate of potassa. The molten mass, after having cooled, is exhausted with water, the solution evaporated to dryness, and extracted with alcohol, from which the crystals of the salt are separated by evaporation. ”

“ Bütschli also has recently described the microscopic appearance of precipitated membranes produced by ferrocyanide of potassium and acetate or chloride of iron.
"Like Linke and Gustav Rose, Famintzin has obtained spheroidal precipitates by the reciprocal action of concentrated solutions of chloride of calcium and carbonate of potassium. These grow rapidly and suddenly, with concentric layers showing a spherical or flattened nucleus. He also obtained forms resembling sphero-crystals and starch grains. ”

“ It is totally soluble in water; the solution is neutral to litmus and turmeric, unaffected by ferrocyanide of potassium, and not precipitated by acids nor alkalies, nor acted on by the magnet. Heated with potassa, 100 gr. throws down about 34 gr. of sesquioxide of iron. Entirely soluble in cold water; taste freely chalybeate. That of commerce has generally a feebly inky taste a slight alkaline reaction, is slightly deliquescent, dissolves in 4 parts of water, and is nearly insoluble in alcohol. ”

“ The mixture first assumes a milky appearance, but after a little while, the salt dissolves, forming a coffee-colored solution, and gases are disengaged in abundance. When the salt is completely dissolved, the solution is found to contain ferrocyanide (red prussiate) of potassium, mixed with nitroprusside and nitrate of the same base. It is then immediately decanted into a large flask, and heated over the water-bath. It continues to evolve gas, and after awhile, no longer yields a dark blue precipitate with ferrous salts, but a dark green or slate-colored precipitate. ”

“ It is anhydrous. Sp. gr. 1·450.
Pur. It should give a colourless solution with water; wholly sublime with heat; and neither chloride of barium, nor sulphuretted hydrogen, should affect its solution. A solution,134 to which a few drops of nitric acid have been added, should not yield a blue precipitate with ferrocyanide of potassium. It often contains sesquichloride of iron, and sometimes lead; both of which may be readily detected by the above tests. Its complete volatility may be easily determined by heating, in the flame of a candle, a small fragment held on the point of a knife. ”

“ Traube has pointed out that the very delicate membrane of ferrocyanide of potassium which is obtained with some difficulty by exposing it to the reaction of sulphate of copper, is permeable to water, but will not permit the passage of the majority of salts. Pfeffer, by producing these walls in the interstices of a porous porcelain, has succeeded in giving them sufficient rigidity to allow measurements to be made. It must be allowed that, unfortunately, no physicist or chemist has been as lucky as these two botanists ”

“ Platinum is practically unoxidizable; it combines directly with phosphorus, arsenic, antimony, silicon, boron, and fluorine, and with almost all other metals. It is practically unattached by all acids, dissolving only in aqua regia or in mixtures which generate chlorine. When fused with alkaline hydroxides in the presence of air it forms palatinates. It is readily attacked by fused nitrates, and by potassium cyanide and ferrocyanide. All the platinum compounds when heated strongly decompose, and leave a residue of the metal. Of platinum salts, in the true sense of the word, none exist ”

“ This brown stain can be removed by sulphurous acid, but in that case Prussian blue appears simultaneously, so that the forger has merely a choice between a brown and a blue stain.
When such paper is printed with a delicate design in some fugitive ink (common writing ink would be best) , the greatest attainable safety is obtained.
Ferrocyanide of manganese is easily formed by adding to the pulp pure crystallised chloride of manganese, and rather more than an equal weight of ferrocyanide of potassium, both in solution. ”

“ The box and its contents may then be withdrawn with the tongs, and thrown into a pail of cold water. The work may, when cold, be washed and brushed clean, made thoroughly dry, oiled, and put aside for use. Ferrocyanide of potassium is also extensively used for case-hardening, being either sprinkled over the work when hot, or mixed with some convenient substance, such as dried cow dung, and placed in the box ”

“ The most deadly of all poisons, prussic or hydrocyanic acid, is obtained from the ferrocyanide of potassium, or prussiate of potash, by adding diluted sulphuric acid and distilling the vapour into an ice-cold receiver. ”

“ An accurately weighed quantity of pure crystallised ferrous sulphate is dissolved in a definite amount of water, and the solution is treated with successive small portions of crude nitric acid, until all the ferrous oxide has been changed into the ferric state. The change can be detected by a very decisive test. If a liquid containing ferric oxide in solution is brought into contact with a solution of red prussiate of potash (potassium ferricyanide) , no precipitate is formed in the absence of ferrous oxide, but only a brown coloration ”

“ When the potash is saturated, the operation is completed. The Germans recommend a strong, alcoholic solution of potassa to be used in the second vessel, for in this case, the hydrocyanic or prussic acid combines with the potassa, forming a hydrocyanate of potassa, or, the water being abstracted, the cyanuret of potassium, which spontaneously precipitates, on the saturation of the fluid, the cyanuret, being insoluble in strong alcohol. The ferrocyanate of potash may be considered as containing three equivalents of hydrocyanic acid, two of potash and one of iron ”

“ The iron in ferrous and ferric compounds varies in its reactions. In addition to the above-mentioned facts, consideration ought to be given to the circumstance that the easy mutability of nitric acid undergoes modification in its alkali salts, and in general the properties of a salt often differ much from those of the acid. Every double salt ought to be regarded as a peculiar kind of saline compound: potassium cyanide is, as it were, a basic, and ferrous cyanide an acid, element. ”

“ Of course, I know that an odour of peach-blossom in the air, resulting in death, could only be associated with some vaporous effluvium of cyanogen, or of hydrocyanic ('prussic') acid, or of both; and when I at last managed to examine some of the dust under the microscope, I was not therefore surprised to find, among the general mass of purplish ash, a number of bright-yellow particles, which could only be minute crystals of potassic ferrocyanide. What potassic ferrocyanide was doing on board the Boreal I did not know, and I had neither the means, nor the force of mind, alas! ”

“ E. Frémy investigated this discovery, made by Stahl in 1702, and showed that the same solution resulted when chlorine is passed into strong potash solution containing ferric hydrate in suspension. Haber and Pick (Zeit. Elektrochem., 1900, 7, p. 215) have prepared potassium ferrate by electrolysing concentrated potash solution, using an iron anode. A temperature of 70°, and a reversal of the current (of low density) between two cast iron electrodes every few minutes, are the best working conditions. ”

“ Even if there did not seem to exist this affinity of cyanogen for metallic mercury, there is this also to be considered—that the sodium puts the mercury in an electro-positive state, thus increasing its affinity for gold; while the effects of cyanide of potassium appear to be entirely confined to its property of keeping the surface of mercury bright. ”

“ White spots are produced by particles of hypo or carbonate dust or splashes of a solution of these, settling on the toned film. The toned image consists of silver together with more or less silver ferrocyanide and the ferrocyanides of uranium, iron and copper as the case may be. Silver ferrocyanide is soluble in hypo while uranium and iron ferrocyanides are soluble in a solution of sodium carbonate, strong ammonia, etc., so that the white spots indicate those parts where the toned image has been dissolved away. ”

“ The commercial salt is very impure. Purchase that sold as potassic cyanide (gold) which contains about 95 per cent. of KCN. It is used for copper assaying and occasionally in separation. Make a 10 per cent. solution when wanted.
Potassium Bichromate, K2Cr2O7. It may be purchased nearly pure. It is used as an oxidising agent, for determining iron; and as a test solution. For this last purpose a 10 per cent. solution is prepared.
Potassium Chlorate (KClO3) can be purchased pure. It is used with hydrochloric acid as a substitute for aqua regia. ”

“ When concentrated the solution is nearly black, and on heating it yields a yellow solution of potassium ferrite, oxygen being evolved. Barium ferrate, BaFeO4·H2O, obtained as a dark red powder by adding barium chloride to a solution of potassium ferrate, is fairly stable. It dissolves in acetic acid to form a red solution, is not decomposed by cold sulphuric acid, but with hydrochloric or nitric acid it yields barium and ferric salts, with evolution of chlorine or oxygen (Baschieri, Gazetta, 1906, 36, ii. p. 282) . ”