POTASSAE SULPHAS - SULPHATE OF POTASH, K2SO4, = 174.

Preparation

There is no process directed in the Pharmacopoeia, but the salt may be prepared from the residue left in the manufacture of nitric acid, this residue being an impure acid sulphate, which is converted into the neutral salt by treatment with lime, and afterward with carbonate of potash and sulphuric acid.

Characters And Tests

A very hard crystalline salt, sparingly soluble in cold water; decrepitates on heating: has a bitter, rather nauseous taste.

Potassa Sulphurata - Sulphurated Potash (Hepar Sulphuris)

Preparation

By fusing together carbonate of potassium and sublimed sulphur.

Characters And Tests

From its liver color, when fresh, it was formerly called "liver of sulphur," but it rapidly absorbs oxygen from the air and becomes green, and ultimately dull white, sulphate of potash being formed. It evolves sulphuretted hydrogen on the addition of any acid.

POTASSAE NITRAS - NITRATE OF POT ASH - NITRE - SALTPETRE, KNO3, = 101.

Preparation

Nitrates occur naturally in many waters, soils, and plants, but are mainly obtained either from certain soils in India by solution in water, or from artificial "nitre beds," i.e., heaps of manure and vegetable refuse, wood ashes and calcareous earth, which are exposed to the action of air and sun. The nitrogen of the organic matter is slowly oxidized into nitric acid, which combines with the bases present (potash, etc.), and the nitrates so formed are removed by washing.

Characters And Tests

Occurs in white crystalline fragments, or in striated, long, six-sided prisms, which are transparent. It is soluble in water, and has a cooling taste; at a red heat it deflagrates. When fused and cast into round moulds, it is known as "sal prunelle;" abroad, these are often colored purple (like a plum: prunelle - a sloe).

POTASSAE CHLORAS - CHLORATE OF POTASH, KC1O3, = 122.5.

Preparation

By passing chlorine gas over a mixture of potash carbonate and excess of slaked lime; chlorinated lime and chlorinated potash are first formed, and the latter is then converted into chlorate of potash on boiling; but the reaction may be simply expressed thus6Cl2 + K2CO3 + 6CaH1O2 = 2KC1O3 + CaCO3 + 5CaCl2 + 6H1O.

Characters And Tests

Chlorate of potash occurs in pearly-white, hard, crystalline plates, which are slightly soluble in water, and have a cooling taste. Rubbed with sulphur, or phosphorus, or tannic acid, or catechu, etc., the salt explodes; treated with sulphuric acid, it becomes red, and gives off vapors of chlorine peroxide.

POTASSAE PERMANGANAS - PERMANGANATE OF POTASH, KMnO4,= 158.

Preparation

The principal steps of the process are - (1) to prepare manganate of potassium (K2MnO4); (2) to convert this into permanganate (KMnO4) by boiling. Black oxide of manganese, caustic potash, and potassic chlorate are fused together, and a dark green mass of manganate of potash obtained.

3MnO2 + 6KHO + KC1O3 = 3K2MnO4 + KCl + 3H1O. This manganate, when boiled, filtered, and acidified with sulphuric acid, yields a purple solution of the permanganate.

3K2MnO4 + 2H1O = 2KMnO4 + 4KHO + MnO2. The green manganate, when turning into the purple permanganate, undergoes several changes of color, and hence has received the name, "mineral chameleon:" finally, the solution is evaporated, and the crystals purified.

Characters And Tests

Occurs in dark purple acicular crystals, one of which will impart its color to a large quantity of water. It yields up most of its oxygen (five-eighths) very readily; and if only a little spirit be boiled with its solution, it changes to yellowish brown, on account of its reduction to the state of peroxide. A similar brown stain is left on the hands when washed in it, on account of its oxidation from contact with the organic substance. In distilled water, the purple color may remain two years without change. (Manganese stains are removed by oxalic acid - "salts of lemon.")

POTASSAE BICHROMAS - BICHROMATE OF POTASH, K2Cr2O7, = 295.

Preparation

By roasting chrome iron-ore with a mixture of carbonate of potash and chalk; yellow chromate of potash is formed, and yields the red bichromate when treated with sulphuric acid.

Characters And Tests

Occurs in large, red, transparent, four-sided tables, soluble in ten times their weight of water. The solution readily gives up part of its oxygen, and when acidified with sulphuric acid, turns green from reduction of the chromic acid, and formation of green sulphate of chromium.

Absorption And Elimination

Liquor potassoe, taken on an empty stomach, is quickly absorbed; it then combines, probably, with carbonic acid in the blood, and is eliminated by the kidneys, mainly in combination with sulphuric acid (Parkes: Medico-Chirurgical Review, 1853). When taken with food, or in very small doses at any time, it forms with the gastric acid a chloride, and as such is absorbed; its elimination under these conditions is not recognized so readily.

The carbonates, when taken in small doses, are absorbed as chlorides; of large doses, the greater part passes out by the kidneys unchanged: a single large dose (2 dr.) is eliminated more quickly than the same amount given in divided doses (Thompson: Medico-Chirurgical Review, ii., 1864). The acetate and citrate are reduced in the system to carbonate, and eliminated as such; the tartrate is commonly unchanged. The chloride, chlorate, and nitrate are absorbed very rapidly, and have been detected in the urine, the saliva, etc., within five minutes after being taken.

Much interest attaches to the chemical changes which the chlorate undergoes in the system; it was believed to become a chloride, parting with its oxygen to the blood and tissues (Fourcroy) - the proportion even of oxygen furnished was calculated (Garnett). Gubler and some other modern observers also think it possible that a partial reduction of the salt may occur within the body, but it is difficult to reconcile this with the chemical fact of its being found unchanged in the urine passed after its administration (Wohler, 1824), as also in the saliva, milk, tears, bronchial mucus, etc. (Isambert). Rabuteau, taking himself small doses, also found the drug unchanged in the secretions, and of one large dose of 5 grammes, recovered 4.873 grammes from the urine within thirty-six hours (Gazette Med. de Paris, 1868). Hence it seems improbable that the chlorate should decompose and give up oxygen at the temperature of the body, and yet there is some clinical evidence of its improving oxygenation in whatever mode this may be effected (v. vol. i., p. 19, and vol. ii., p. 282).

When nitrate of potash has been taken in large doses (270 gr. in twenty-four hours), the greater part has been found unchanged in the urine - the rest probably passing as sulphate by the intestines (Taylor: Guy's Reports, 1863); that a certain amount of potash salt passes off in this manner has been shown by Kramer (Annales d' Hygiene, i., 1843).