Potassium, Nitrite of. KNO2. Syn. Nitrite of potassa; Potassæ nitris, L. Prep. 1. By heating nitre to redness, dissolving the fused mass in a little water, and adding twice the volume of the solution in alcohol; after a few hours the upper stratum of liquid is decanted, and the lower one, separated from the crystals, evaporated to dryness.
2. (Corenwinder.) Nitric acid, 10 parts, are poured on starch, 1 part, and the evolved gas passed through a solution of hydrate of potassium of the sp. gr. 1·380, to saturation; the liquid is then either neutralised with a little hydrate of potassium (if necessary), and kept in the liquid form, or at once evaporated. Fused pinkish mass, or clear colourless soluble crystals, used in chemistry as a reagent, and deoxidiser.
Potassium, Oxalate of. K2C2O4. Syn. Neutral oxalate of potassa; Potassæ oxalas, L. Prep. Neutralise a solution of oxalic acid, or the acid oxalates, with carbonate of potassium, evaporate, and crystallise. Transparent colourless rhombic prisms, soluble in 3 parts of water, and of the formula K2C2O4,Aq.
Potassium, Hydrogen Oxalate of. KHC2O4. Syn. Potassium binoxalate, Salt of sorrel, Essential salt of lemons; Potassæ binoxalas, L. Prep. By saturating a solution of oxalic acid, 1 part, with carbonate of potassium, adding to the mixture a similar solution of 1 part of oxalic acid, unneutralised, and evaporating for crystals. It may also be obtained from the expressed juice of wood or sheep’s sorrel, by clarifying it with eggs or milk, and evaporating, &c., as before. Colourless rhombic crystals of the formula KHC2O4,Aq., soluble in 40 parts of cold and 6 parts of boiling water, yielding a very sour solution.
Potassium, Trihydrogen Oxalate of. KH3(C2O4), or KHC2O4, H2C2O4. Syn. Potassium quadroxalate, Potassium acid oxalate. Prep. By neutralising 1 part of oxalic acid with carbonate of potassium, adding to the solution 3 parts more of oxalic acid, evaporating and crystallising. Resembles the last; has the formula KH3(C3O4)2,2Aq; but is less soluble, and more intensely sour, and forms modified octahedral crystals. The salt is occasionally sold under the names of ‘sal acetosellæ,’ ‘salt of sorrel,’ and ‘essential salt of lemons.’ Both are used to remove ink and iron stains from linen, to bleach the straw used for making bonnets, and, occasionally, in medicine, as a refrigerant.
Potassium, Oxide of. K2O. Prep. Burn pure potassium in a current of oxygen. White powder, rapidly absorbing water and forming the hydrate.
Potassium, Perchlorate of. KClO4. Syn. Potassæ perchloras, L. Prepared by projecting well-dried and finely powdered chlorate of potassium in small portions at a time, into warm nitric acid. The salt is separated from the ‘nitrate’ by crystallisation.
Potassium, Prus′siate of. See Potassium ferricyanide and FERROCYANIDE.
Potassium, Salicylite of. Formed by mixing salicylous acid (artificial oil of meadow-sweet) with a strong solution of hydrate of potassium; it separates, on agitation, as a yellow crystalline mass, which, after pressure in bibulous paper, is recrystallised from alcohol. Golden-yellow crystals, soluble in both water and alcohol; damp air gradually converts them into acetate of potassium and melanic acid.
Potassium, Silicate of. (Ure.) Syn. Potassæ silicas. Prep. Mix 1 part of powdered quartz or flint, or of fine siliceous sand with 2 parts of carbonate of potash, and fuse them in a Hessian crucible. Dissolve the mass in water, filter the solution and evaporate it to dryness—Dose, 10 gr. to 15 gr. in 6 or 8 oz. of water, twice a day. To dissolve gout concretions. An impure silicate of potash is used as a water-glass.