Potassii iodidum (v. vol. i., p. 59). Potassii bromidum (v. vol. i., p. 97).

LIQUOR POTASSAE - SOLUTION OF POTASH, KHO, = 56.

Preparation

By adding slaked lime to a boiling solution of about twice its weight of carbonate of potash; carbonate of lime subsides, and the clear solution of potash is transferred by means of a syphon to a bottle, which should be of green glass.

K2CO3 + CaH1O2 = 2KHO + CaCO3. (The solution would corrode wool or other organic filters, and would dissolve lead in white glass.)

Characters And Tests

A colorless liquid of acrid taste, and strongly alkaline reaction; sp. gr. 1.058; contains nearly 6 per cent. of caustic potash, or 27 gr. in the fl. oz.; it feels soapy when rubbed between the fingers, on account of its solvent action on the cuticle; it corrodes animal and vegetable substances, and forms soluble soaps with oily and fatty bodies. It is liable to contain carbonate of potash, lime, sulphates, chlorides and alumina. The best general test for potash salts in solution is perchloride of platinum, which precipitates a yellow double chloride.

P0TAS8A CAUSTICA - CAUSTIC POTASH - HYDRATE OF POTASH - P0TASSIC HYDRATE, KHO, = 56.

Preparation

By rapidly evaporating the liquor to dryness in a clean silver or iron vessel, then fusing and pouring into suitable moulds.

Characters And Tests

Occurs in hard fibrous pencils, which should be white, but are often bluish in color; of peculiar nauseous odor, and acrid taste. It has a strong affinity for water and carbonic acid, and readily deliquesces if exposed to the air: is soluble also in alcohol. Heat is evolved during its solution in water.

POTASSAE CARBONAS - CARBONATE OF POTASH, K2CO3, = 138.

Preparation

From the ashes of plants which consist of a soluble carbonate, and insoluble salts of lime, silica, etc. The carbonate is dissolved out by frequent washing with water, which is then evaporated, and the residue fused to a brown stony mass - the crude potashes of commerce (black potash). This is purified by calcination in a furnace, the dull white residue being termed "pearl-ash," and this again is further purified by solution in a small quantity of water, filtering, and evaporating to dryness. The carbonate may also be obtained by heating to redness the bicarbonate.

Characters And Tests

Occurs in small white opaque crystalline grains, having strong alkaline taste and reaction; it is distinguished from the bicarbonate and from sodium salts by its great affinity for water, for on exposure it soon deliquesces into a thick liquid.

POTASSAE BICARBONAS - BICARBONATE OF POTASH, KHCO3, = 100.

Preparation

By passing carbonic acid gas through a strong solution of carbonate of potash; the stream of gas should be disengaged slowly but continuously for a week: crystals of bicarbonate are gradually deposited.

K2CO3+ H1O + CO2, = 2KHCO3.

Characters And Tests

These crystals are large, transparent, colorless, rhombic prisms, which are not deliquescent and not caustic; they are soluble in four parts of cold, and less than their own weight of boiling water, insoluble in alcohol: nearly neutral to test paper.

POTASSAE ACETAS - ACETATE OF POTASH, KC2H3O2, = 98.

Preparation

By neutralizing acetic acid with carbonate of potash; the acetic takes the place of carbonic acid, which is liberated with effervescence.

K2CO3 + 2HC2H3O2 = 2KC2H3O2 + H1O+CO2. The liquid is evaporated, and the salt dried, melted, and crystallized.

Characters And Tests

Occurs in white, smooth, glistening, and generally long pieces, which are soft, fibrous in texture, and unctuous to the touch: neutral in reaction, very deliquescent, and soluble in alcohol, as well as in water.

POTASSAE CITRAS - CITRATE OF POTASH, K3C6H1O7, = 306.

Preparation

By neutralizing carbonate of potash with citric acid; a reaction similar to the last-mentioned occurs, but this acid being triba-sic, requires three equivalents of carbonate for saturation.

3K2CO3 + 2H3C6H6O7 = 2K3C6H1O7 + 3H1O + 3CO2.

Characters And Tests

Citrate of potash is a white, granular, crystalline powder, deliquescent, soluble in water, insoluble in alcohol. It is charred by hot sulphuric acid, and its solution gives a precipitate with chloride of calcium only when boiled - a test which distinguishes it from tartrate of potash.

POTASSAE TARTRAS - TARTRATE OF POTASH, K2C4H1O6,=226.

Preparation

By boiling the acid tartrate with carbonate of potash and water, when an equivalent of hydrogen in the acid salt is replaced by one of potassium, and carbonic acid given off.

2KHC4H1O6 + K2CO3 = 2K2C4H1O6 + H1O + CO2. The liquid is then concentrated to crystallization.

Characters

Occurs in small granular crystals, deliquescent, soluble, neutral in reaction, and somewhat bitter in taste.

POTASSAE TARTRAS ACIDA - ACID TARTRATE OF POTASH - CREAM OF TARTAR, KHC4H1O6, = 188.

Preparation

Grape-juice contains a large quantity of this salt, which is retained in solution by the saccharine matter. When this latter is converted into alcohol by fermentation, the acid tartrate is gradually deposited inside the wine casks, and is known as "crude tartar," or "argol," and this, when purified by recrystallization, constitutes "cream of tartar," a name originally given to the fine crystals which were "skimmed off" the evaporating liquid.

Characters And Tests

Occurs as a gritty white powder, or in fragments of cakes. It is distinguished from the neutral tartrate by its very sparing solubility in water, viz., 1 in 180 parts: in spirit it is insoluble, like other tartrates. It chars on exposure to heat, giving off inflammable gas and an odor of burnt sugar.