Wood-ashes, when mixed with quicklime, and lixiviated, produce caustic ley, the strength of which depends on the quantity of alkali held in solution. It is this ley, when boiled with oils, fat, &c. that produces soft soap. Hard soap is a combination of oil or fat, and soda. The quantity of real alkali in potash may be known by the proportion of acid required to saturate a given weight of it. Potash, pearl-ash, salt of tartar, and salt of wormwood are all carbonates of potassa. This alkali is called the vegetable alkali, because it is obtained from vegetables. It is considered to be the hydrated deutoxide of potassium, and when decomposed will furnish potassium. _Table of the saline or soluble products of one thousand pounds of ashes of the following vegetables._ SALINE PRODUCTS. Stalks of Turkey wheat, 198 lbs. Stalks of sun-flower, 349 Vine branches 162.6 Elm 166 Box 78 Sallow 102 Oak 111 Aspen 61 Beach 219 Fern, cut in August, 116, or 125 according to Wildenheim. Wormwood 748 Fumitory 360 Heath 115 The observations of Mr. Kirwan on potash may be seen in _Aikin's Chemical Dictionary_. When a piece of hydrated potassa is placed between two disks of platinum, which are brought in contact with the poles of a galvanic battery, consisting of upwards of 200 pairs of plates, four inches square, the oxygen will separate at the positive surface, and small metallic globules of potassium will be formed at the negative surface. The potassa, in the mean time, will undergo fusion. Sir H. Davy discovered potassium, in 1807. It may be obtained by means of iron turnings, in the following manner: Heat the iron turnings to whiteness in a curved gun barrel, and suffer potassa, in a state of fusion, to fall upon them very gradually, air being excluded: potassium will form, and collect in the cool part of the tube. For the different facts respecting this metal, consult Sir H. Davy's communications on the subject, and the memoirs of Gay-Lussac and Thenard, Curadeau, &c. See also, Davy's _Chemical Philosophy_, and Thenard's _Traité de Chimie_. Potassa unites with, and neutralizes, acids, and forms salts; the principal of which are the sulphate, muriate, and nitrate of potassa. It unites also with sulphur, phosphorus, &c. Potassa, in the state of carbonate, is very soluble in water, for which it has so strong an affinity, that, when exposed to the atmosphere, it deliquesces and becomes fluid. Caustic potassa undergoes the same change, in a more remarkable degree. It is on account of its great avidity for water, that the carbonate is used in the preparation of alcohol from spirituous liquors; it retaining the water, while the alcohol may be distilled over.