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. K3FeCy6, or K3,FeC6N6. 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. (C2H5KO.) Löweg 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 nævus 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. K4,FeCy6, or K4,FeC6N6. Syn. Ferrocyanuret of potassium, Prussiate of potash, Yellow p. of p.; Potassæ 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