(From clavus,a wedge; so called from the little wedges or billets into which the wood was cut to make them). Also called alumen ca-tinum, soda, sal alkali fixum, cineres Russici, kali, po-tassa, gastrinum, potash, and pearlash.
The ancients call the ashes of burnt wood lix, from whence the modern appellation lixiva: the moderns call them also cineres clavellati. The English name potash, is from the pots in which the lixivium was boiled.
Potashes are made in most countries that abound with the hard kind of wood; particularly the north of Europe and America from which last the -best is brought to us; produced from the ashes of vegetable substances, by dissolving their salt in water, decanting the clear solution, and evaporating it to dryness.
Oak, ash, and other trees that shed their leaves in autumn, are proper, and the smaller shrubs, commonly called underwood; but evergreens, as the pine, cypress, etc. yield very little salt. Fern, bean straw, and the greater number of annual plants, afford a large quantity of salt; dead trees seldom afford an alkali.
The timber may be cut down at any season of the year, but should be burnt as soon as possible. Pieces of eight or ten feet long should be laid in piles, filling the interstices with the chips and smaller wood; and the fire kindled at both ends. As soon as the pile is burnt down, rake such ashes as lie thin on the outside, a little towards the middle: add no fresh fuel, nor stir the ashes till you can bear your hand in them. When placed in a shade on a plank floor, they must be wetted until brought nearly to the consistence of mortar in the first mixture of lime and sand, or so as to stick together; then rammed in a heap, in which they must continue not less than twenty days, though they may remain many months. This is called wood ash.
Kilns are also made for the more advantageous burning of wood into ashes.
Wood ashes, put into vessels with latticed bottoms, covered with clean straw, are to be firmly pressed together; their surface covered, four or five inches deep, with soft water, and as it subsides more added. A receiver is then placed underneath to receive the solution, and water continually added until the ley is very weak. The weak ley is strengthened by again filtering through fresh ashes, and the whole conveyed into a pan to be evaporated to a dryness: the produce is called potash.
The ley of wood ashes, made strong enough to bear an egg, is boiled briskly, until a pellicle appears on the surface, then gently boiled until it thickens, and continued just bubbling until it is very hard. In that state it is taken out in pieces, which are cut out with a cold chisel, and spread on the floor of a furnace, so contrived that the salt may be just covered with the flame: if it is thus continued until it begins to look fair, and incline to look red, afterwards kept red hot, and turned occasionally, until it is of a pearl colour, it is called pearl-ash. When this pearlash is cold enough to handle,that which is imperfectly calcined, with such as falls into powder, must be replaced in a caldron, with fresh ley. From contact with some inflammable matter, or calcining with too much heat, it hath sometimes a blue colour, but it should be of a pearl colour.
Potash is said to be a creature of the fire. In some parts of Germany it is prepared from the same wood of which charcoal is made. A number of tubes, made of copper, or of iron, are so disposed in the pile of wood intended to be burnt into charcoal, that the water, acid, and oil, which are obtained in ordinary distillations, shall, when separated from the wood by fire, pass through these tubes into buckets placed to receive them. The oil is next to be separated from the acid liquor, which is then to be boiled in copper or iron vessels, and the residuum dried and calcined. By this calcination, the acid is decomposed and the alkali remains. These and many similar facts show that the alkali is a production of fire.
Pearlash is entirely soluble in water, and is, in all respects, the same as the fixed alkaline salt. See Al-cali.
Potash often, though carefully prepared, contains some portion of earth and a neutral salt, which is either a vi-triolated tartar or sea salt. The earth is separable by-dissolving the salt in water. The neutral salt dissolves with difficulty, and so may easily be separated by solution in cold water, which readily dissolves the alkaline salt, but leaves the neutral unaffected. The sea salt discovers itself by decrepitating, if laid on red hot iron; and is separated by dissolving one part of potash in two parts of water, for in this the sea salt will not dissolve.
Potash is met with of various colours; but when good, if it is exposed to the air, it first grows clammy, then runs to an oily liquid, which, when dried, leaves an impalpable powder of a whitish colour. It hath but little smell, and is of a pungent, urinous taste; does not crumble in solution, but dissolves gradually; it ferments with acid, and it unites, when pure, with oil.
As a medicine, the virtues of the alkaline salt of potash are the same as those of any other vegetable fixed alkaline salt.
See Alcali. Neumann's Chem. Works. Dict, of Chemistry, 4to.