=Potassium, Chromate of.= K_{2}CrO_{4}. _Syn._ CHROMATE OF POTASSA, NEUTRAL CHROMATE OF P., MONOCHROMATE OF P., YELLOW C. OF P., SALT OF CHROME; POTASSae CHROMAS, P. C. FLAVA, L. This salt is only prepared on the large scale. Its source is 'CHROME ORE,' a natural octahedral chromate of iron, found in various parts of Europe and America. For medicinal purposes the commercial chromate is purified by solution in hot water, filtration, and recrystallisation.
_Prep._ 1. The ore, previously assayed to determine its richness, and freed as much as possible from its gangue, is ground to powder in a mill, and mixed with a quantity of coarsely powdered nitre rather less than that of the oxide of chromium which it contains; this mixture is exposed, for several hours, to a powerful heat on the hearth of a reverberatory furnace, during which time it is frequently stirred up with iron rods; the calcined mass is next raked out and lixiviated with hot water, and the resulting yellow-coloured solution evaporated briskly over a naked fire, or by the heat of high-pressure steam; chromate of potassium falls, under the form of a granular yellow salt, which is removed from time to time with a ladle, and thrown into a wooden vessel, furnished with a bottom full of holes (draining box), where it is left to drain and dry. In this state it forms the chromate of potassium of commerce. By a second solution and recrystallisation, it may be obtained in large and regular crystals.
The next process has for its object the employment of a cheaper salt of potassa than the nitrate.
2. (Swindell & Co. Patent dated Nov., 1850.) A mixture of pulverised chrome ore and chloride of potassium is exposed to a full red heat, on the hearth of a reverberatory furnace, with occasional stirring for some time, when steam at a very elevated temperature is made to act on it until the conversion is complete, known by assaying a portion of the mass; the chromate is then dissolved out of the residuum, as before. Common salt or hydrate of calcium may be substituted for chloride of potassium, when the chromates of sodium or calcium are respectively produced.
3. On the small scale this salt may be prepared from the bichromate by neutralising it with hydrate of potassium.
_Prop._ Yellow; tastes cool, bitter, and disagreeable; soluble in 2 parts of water at 60 Fahr.; the crystals are efflorescent.
_Pur._ The salt of commerce is frequently contaminated with large quantities of sulphate or chlorate of potassium. To detect these, M.
Zueber adds tartaric acid, dissolved in 50 parts of water, to a like solution of the sample. As soon as the decomposition is complete, and the colour verges towards the green, the supernatant liquor should afford no precipitate with solutions of the nitrates of silver and barium, whence the absence of chlorides and sulphates may be respectively inferred. The proportions are, 8 parts of tartaric acid to 1 part of the chromate. If saltpetre is the adulterating ingredient, the sample deflagrates when thrown upon burning coals.
_Assay._ 1. A solution of 50 gr. of the salt is treated with a solution of nitrate of barium, the precipitate digested in nitric acid, and the insoluble portion (sulphate of barium) washed, dried, and weighed. 117 gr.
of this substance are equivalent to 89 gr. of sulphate of potassium.
2. The nitric solution, with the washings (see _above_), is treated with a solution of nitrate of silver, and the precipitate of chloride carefully collected, washed, dried, ignited, and weighed. 144 gr. of chloride of silver represent 76 gr. of chloride of potassium.
3. The nitric solution, with the washing (see _above_), after having any remaining barium thrown down by adding dilute sulphuric acid, in slight excess, is treated with ammonia, and the resulting precipitate of chromic oxide collected on a filter, washed, dried, carefully ignited in a silver, platinum, or porcelain crucible, and weighed. 40 gr. of this oxide represent 100 gr. of pure chromate of potassium. Any deficiency consists of impurities or adulterants.
_Uses._ Chromate of potassium is used in dyeing, bleaching, the manufacture of chromic acid, bichromate of potassium, &c. It is the common source of nearly all the other compounds of chromium. It is reputed alterative in doses of 1/12 to 1/2 gr.; and is emetic in doses of 1 to 4 gr. A solution in 8 parts of water is occasionally used to destroy fungus; 1 in 30 to 40 parts of water is also used as an antiseptic and desiccant.
_Concluding Remarks._--The first process is undoubtedly the best, when expense is not an object. To reduce this, a mixture of 'potash' or 'pearlash,' with about 1/2 of its weight of nitre, or 1-5th part of its weight of peroxide of manganese, may be substituted without much inconvenience. The assay of the chrome ore, alluded to above, may be made by reducing 100 gr. of it to powder, mixing it with twice its weight of powdered nitre, and a little hydrate of calcium, and subjecting the mixture to a strong red heat for 3 or 4 hours; the calcined mass may then be exhausted with boiling water, and the resulting solution, after precipitation with dilute sulphuric acid, in slight excess, and filtration, may be treated with rectified spirit, when its chromium may be thrown down by the addition of ammonia. (See _above_.) In the conversion of chrome ore into chromate of potassium care should, in all cases, be taken that the proportion of nitre or alkali should be slightly less than what is absolutely required to saturate the ore, as the production of a neutral salt is thereby ensured; for should not the whole of the chromate be decomposed by the first calcination, it may easily be roasted a second time with fresh alkali, should the remaining quantity he thought worth the trouble. The nature of the furnace to be employed in the conversion is not of any great importance, so long as carbonaceous matters from the fire are entirely excluded, and the required temperature is attainable.
=Potassium, Bichromate of.= K_{2}Cr_{2}O_{7}, or K_{2}CrO_{4},CrO_{3}.
_Syn._ BICHROMATE OF POTASSA, RED CHROMATE OF POTASH, ACID C. OF P.; POTASSae BICHROMAS, L. _Prep._ 1. To a concentrated solution of yellow chromate of potassium, sulphuric acid, or, better, acetic acid, is added in quantity equal to one half that required for the entire decomposition of the salt; the liquid is then concentrated by evaporation and slowly cooled, so that crystals may form.
2. (Jacquelain.) Chrome ore, finely ground and sifted, is mixed with chalk; the mixture is spread on a thin layer on the hearth of a reverberatory furnace, and heated to bright redness, with repeated stirring, for 9 or 10 hours. The yellowish-green product consists essentially of neutral chromate of calcium, mixed with ferric oxide. It is ground and stirred up with hot water, and sulphuric acid is added till a slight acid reaction becomes apparent, a sign that the neutral chromate has been converted into bichromate. Chalk is now stirred in to precipitate the ferric sulphate, and after a while the clear solution is run off into another vessel, where it is treated with carbonate of potassium, which precipitates the lime and leaves bichromate of potassium in solution. The solution is then evaporated to the crystallising point. This process, when carried out on a large scale, is very economical.
_Prop., &c._ It forms very beautiful square tables, or flat four-sided prismatic crystals; permanent in the air; soluble in 10 parts of water at 60, and in less than 3 parts at 212 Fahr.; it has a metallic, bitter taste, and is poisonous. It is chiefly used in dyeing and bleaching, and as a source of chromic acid. The tests, &c., are the same as for the yellow chromate.
=Potassium, Citrate of.= K_{3}C_{6}H_{5}O_{7}. _Syn._ POTASSae CITRAS, L.
_Prep._ From a solution of citric acid neutralised with carbonate of potassium, evaporated, and granulated, or crystallised; very deliquescent.
Or, extemporaneously, in the form of solution, by adding carbonate or bicarbonate of potassium to lemon juice, as in the common effervescing draught. (Ph. B.) The same.
=Potassium, Cyanate of.= KCyO, or KCNO. _Prep._ 1. By roasting, at a red heat, dry ferrocyanide of potassium, in fine powder, upon an iron plate, constantly stirring it until it becomes fused into one mass, which must be reduced to fine powder and digested in boiling alcohol, from which crystals of the cyanate will be deposited as the solution cools.
2. (Liebig.) A mixture of ferrocyanide of potassium, with half its weight of peroxide of manganese, may also be used to produce this salt, as the last; the compound should be kindled by a red-hot body, and allowed to smoulder away, after which it may be treated with alcohol, as before.
3. A mixture of ferrocyanide of potassium and litharge is heated as before, and dissolved out by alcohol, and crystallised.
_Prop._ Crystallisable colourless or white salt, readily soluble in alcohol and water, but readily decomposed when moist into bicarbonate of potassium and ammonia, or in solution into the carbonate of potassium and ammonium.
This salt is poisonous. The cyanates of silver, lead, and many other metals may be made by adding a solution of cyanate of potassium to another of a neutral salt of the base.
=Potassium, Cyanide of.= KCN, or KCy. _Syn._ CYANIDE OF POTASH, CYANURET OF POTASSIUM; POTASSII CYANIDUM, P. CYANURETUM, L.
_Prep._ 1. (MEDICINAL CYANIDE OF POTASSIUM.)--_a._ A solution of pure hydrate of potassium, 2 parts, in highly rectified spirit, 7 parts, is placed in a receiver furnished with a safety tube, and surrounded with bruised ice; the beak of a tubulated retort, containing ferrocyanide of potassium, in powder, 4 parts, is then adapted to it in such a manner that any gas or vapour evolved in the retort must traverse the solution in the receiver; the arrangement being complete, sulphuric acid, 3 parts, diluted with an equal weight of water, and allowed to cool, is cautiously poured into the retort, and the distillation conducted very slowly, a very gentle heat only being applied, as circumstances may direct; as soon as the force of ebullition in the retort has subsided, the distillation is complete, and the connection between the retort and receiver is broken; the contents of the receiver, now transformed into a mixture of a crystalline precipitate of cyanide of potassium, and an alcoholic solution of undecomposed hydrate of potassium, is carefully thrown on a filter, and the precipitate, after the mother-liquor has drained off, very cautiously washed with ice-cold and highly rectified spirit, and then drained, pressed, and dried on the same filter. The product is chemically pure, and equal to fully 10% of the ferrocyanide employed. This is a modification of what is commonly known as 'Wigger's process.'
_b._ 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.
2. (CRUDE or COMMERCIAL CYANIDE--Liebig.) Commercial ferrocyanide of potassium, 8 parts, rendered anhydrous by gently heating it on an iron plate, is intimately mixed with dry carbonate of potassium, 3 parts; this mixture is thrown into a red-hot earthen crucible, and kept in a state of fusion, with occasional stirring, until gas ceases to be evolved, and the fluid portion of the mass becomes colourless; the crucible is then left at rest for a few minutes, to allow its contents to settle, after which the clear portion is poured from the heavy black sediment at the bottom upon a clean marble slab, and the mass, whilst yet warm, broken up, and placed in well-closed bottles.
_Obs._ A cheap and excellent process. The product is said to contain about 1-8th part of cyanate of potassium, and, though not sufficiently pure for employment in medicine as potassium cyanide, is admirably adapted for the various technical applications of this substance, as in electro-plating, electro-gilding, photography, &c. It may also be advantageously substituted for the ferrocyanide in the preparation of hydrocyanic acid by the distillation of that substance along with dilute sulphuric acid.
_Prop., &c._ When pure, this salt is colourless and odourless; it forms cubic or octahedral crystals, which are anhydrous; it is freely soluble in water and in boiling alcohol, but most of it separates from the latter as the solution cools; it is fusible; and undergoes no change, even at a full red heat, in close vessels; it exhibits an alkaline reaction; when exposed to the atmosphere, it absorbs moisture, and acquires the smell of hydrocyanic acid. If it effervesces with acids, it contains carbonate of potassium, and if it be yellow it contains iron. It is employed in chemical analysis, and for the preparation of hydrocyanic acid; cyanide of sodium may be made in the same way. The dose is 1/12 to 1/4 gr., in solution; in the usual cases in which the administration of hydrocyanic acid is indicated.--_Antidotes._ The same as for hydrocyanic acid.
=Potassium, Ferricyanide of.= K_{3}FeCy_{6}, or K_{3},FeC_{6}N_{6}. _Syn._ FERRIDCYANIDE OF POTASSIUM, FERRICYANURET OF P., RED PRUSSIATE OF POTASH; POTASSII FERRICYANIDUM, P. PRUSSIAS RUBRUM, L. This important and beautiful salt was discovered by L. Gmelin. At first it was merely regarded as a chemical curiosity, but it is now extensively employed in dyeing, calico printing, assaying, &c.
_Prep._ 1. Chlorine gas, prepared in the ordinary manner, is slowly passed into a cold solution of ferrocyanide of potassium, 1 part, in water, 10 parts, with constant agitation, until the liquid appears of a deep reddish-green colour, or of a fine red colour by transmitted light, and ceases to give a blue precipitate, or even a blue tinge, to a solution of ferric chloride, an excess of chlorine being carefully avoided; the liquor is next evaporated by the heat of steam or boiling water, until a pellicle forms upon the surface, when it is filtered, and set aside to cool; the crystals are afterwards purified by re-solution and re-crystallisation.--Another method is simply to evaporate the original solution to dryness, by a steam heat, with agitation, then to re-dissolve the residuum in the least possible quantity of boiling water, and, after defecation or filtration, to allow the new solution to cool very slowly, that crystals may form.
2. (Extemporaneous.) Add nitric acid, very gradually, to a cold solution of ferrocyanide of potassium, with constant agitation, until a drop of the mixture ceases to impart a blue colour to a solution of ferric chloride, carefully avoiding excess of acid. It may be at once used in solution, or evaporated, &c., as before.
_Prop, &c._ Magnificent regular prismatic or, sometimes, tubular crystals, of a rich ruby-red tint; permanent in the air; combustible; decomposed by a high temperature; soluble in 4 parts of cold water; insoluble in alcohol. Colours ferric salts a pale brown, gives with ferrous salts a deep blue, and precipitates bismuth salts pale yellow; cadmium and mercuric salts, yellow; zinc salts, deep yellow; mercurous, cupric, molybdenic, silver, and uranic salts, reddish brown; cobalt salts, dark brown; manganous salts, brown; cupric salts, greenish; and nickelous salts, olive brown.
=Potassium, Ethylate.= (C_{2}H_{5}KO.) Loweg and Weidmann obtained this compound by heating together acetate of ethyl and potassium. Dr B. W.
Richardson, some few years ago, recommended the employment of the alkaline ethylates as caustics, and they are now frequently used as such in surgery. When first applied to the body the ethylates produce no action, but as they absorb water from the tissues they are decomposed, the potassium or sodium is oxidised, yielding caustic potash or soda in the fresh condition, while alcohol is reformed from the recombination of hydrogen derived from the water. Dr Richardson believes the ethylates of potassium and sodium will be found the most effective and manageable of all caustics, and that in cases of cancer, when it is important to destroy structure without resorting to the knife, and in the removal of naevus and other simple growths, they will be of essential service. The ethylates dissolve in alcohol of different strengths; the solution may either be applied with a glass brush or injected by the needle, and a slow or quick effect can be insured according to the wish of the operator. The ethylate of potassium is the more powerful agent.
=Potassium, Ferrocyanide of.= K_{4},FeCy_{6}, or K_{4},FeC_{6}N_{6}.
_Syn._ FERROCYANURET OF POTASSIUM, PRUSSIATE OF POTASH, YELLOW P. OF P.; POTASSae PRUSSIA FLAVA (B. P.), POTASSII FERROCYANIDUM (Ph. L., E., & D.), L. This valuable salt, the well-known 'prussiate of potash' of commerce, was discovered by the illustrious Scheele about the middle of the 18th century. It is now only manufactured on the large scale.
_Prep._ Good 'potash' or 'pearlash,' 2 parts, and dried blood, horns, hoofs, woollen rags, or other refuse animal matter, 5 or 6 parts, are reduced to coarse powder, and mixed with some coarse iron borings; the mixture is then injected into egg-shaped cast-iron pots in a state of moderate ignition; the mass is frequently stirred with an iron spatula, so as to prevent it running together, and the calcination is continued until fetid vapours cease to be evolved, and flame is no longer seen on stirring the mixture, care being taken to exclude the air from the vessels as much as possible; during the latter part of the process the pots are kept constantly covered, and the ignited mass stirred less frequently; the hot pasty mass is then removed with an iron ladle, and excluded from the air until cold; it is next exhausted by edulcoration with boiling water, and the resulting solution, after defecation or filtration, is concentrated by evaporation, so that crystals may form as the liquid cools; these are redissolved in hot water, and the solution allowed to cool very slowly, when large and beautiful yellow crystals of ferrocyanide of potassium are deposited.--_Product._ 1 ton of dried blood or woollen refuse, with 3 cwt.
of pearlash, yields from 2 to 2-1/2 cwt. of commercial ferrocyanide. The mother-liquor contains sulphate of potassium.
_Prop._ It forms large and very beautiful yellow crystals, which are permanent in the air, and very tough and difficult to powder; it is soluble in 4 parts of cold and 2 parts of boiling water; has a mild saline taste; at a gentle heat loses water; at a higher temperature, in closed vessels, it is for the most part converted into cyanide of potassium, and, when exposed to the air, into cyanate of potassium. Precipitates solutions of antimonous, bismuth, mercurous, and zinc salts, white; cadmium salts, of a pale yellow; cuprous salts, white, turning red; ferrous salts, white, turning blue; lead salts, white; manganous salts, white, turned red; mercuric salts, white, turning bluish; nickelous salts, white, turning green; silver salts, white; stannous salts, white; cobalt salts, green; cupric salts, chocolate red; ferric salts, dark blue; palladous salts, green; stannic salts, yellow; uranic salts, reddish brown; and zinc salts, white.
_Uses, &c._ Ferrocyanide of potassium is chiefly used in dyeing and calico printing, in the manufacture of Prussian blue, in electro-plating, and, in chemistry, as a test, and a source of hydrocyanic acid. As a medicine it is said to be sedative and astringent, and in large doses purgative, but appears to possess little action.--_Dose_, 10 gr. to 1/2 dr., dissolved in water; in hooping-cough, chronic bronchitis, night-sweats, leucorrha, &c.
D'Arcet swallowed a solution containing 1/2 oz. of this salt without experiencing any injurious effects.
=Potassium, Hydrate of.= KHO. _Syn._ POTASSA HYDRATE, HYDRATE OF POTASSA, POTASSA, CAUSTIC P., HYDRATED OXIDE OF POTASSIUM; POTASSA CAUSTICA (B.
P.), POTASSA (Ph. E.), P. CAUSTICA (Ph. D.), P. HYDRAS (Ph. L.), P. FUSA.
_Prep._ 1. (Ph. L.) Liquor of potassa, 1 gall.; evaporate the water in a clean iron vessel over the fire until the ebullition being finished, the residuum of potassium hydrate liquefies; pour this into proper moulds.
2. (Ph. E. & D.) As the last, but pouring the fused hydrate upon a bright and clean iron plate (silver or iron dish--Ph. D.); as soon as it solidifies, break it quickly (into fragments), and put it into stoppered glass (green-glass--Ph. D.) bottles.
3. (Pure.) The hydrate, obtained as above, is dissolved in alcohol or rectified spirit, and, after repose for a few days in a closely stopped green-glass or silver vessel, the solution is decanted, and cautiously evaporated in a deep silver basin, out of contact with the air.
4. (Pure.) M. Polacci states that he procures very pure hydrate of potash in a few minutes by the following process. He heats together in an iron vessel to a red heat a mixture consisting of 1 part of nitrate of potash well triturated with 2 or 3 parts of iron filings. The mass becomes red in a few minutes, and, after cooling, it is treated with water, left to settle, and then decanted. A more or less concentrated solution may thus be obtained, or it may be evaporated to produce the solid potash.
_Prop., &c._ When perfectly pure it is white, solid, very soluble in water and in alcohol; very deliquescent; intensely acrid and corrosive; and exhibiting the usual signs of alkalinity in the highest degree. That of the shops has usually a greyish or bluish colour.
=Potassium, I'odate of.= KIO_{3}. _Syn._ POTASSae IODAS. L. _Prep._ Neutralise a hot solution of hydrate of potassium with iodine, evaporate to dryness by a gentle heat, powder the residuum, and digest it in alcohol, to remove iodide of potassium, dissolve the insoluble portion in hot water, and crystallise.
_Obs._ Iodate of potassium is resolved at a red heat into oxygen gas and iodide of potassium. It has been recommended in bronchocele.--_Dose_, 1 to 5 gr.
=Potassium, Iodide of.= KI. _Syn._ POTASSII IODIDUM (B. P., Ph. L., E., and D.).
1. (Ph. L. 1836.) Take of iron filings, 2 oz.; distilled water, 2 quarts; iodine, 6 oz,; mix them, and heat the solution until it turns green, and then add of carbonate of potassium, 4 oz., dissolved in water, 1 quart; filter, wash the residuum on the filter with water, evaporate the mixed filtered liquors and crystallise.--_Product_, 1 oz. of iodine yields 1 oz.
45 gr. of iodide.