POTASH. Alkali. Protoxide of potassium The substance popularly known under the name of potash is a combination of oxygen and of a metal called potassium. This metal was first separated from the alkali in 1807, by Sir Hum phrey Davy, and is interesting on account of its properties, and as having been the first of its class obtained by means of the galvanic pile. It is of a bluish color, is soft, and may be worked by the fingers as wax. Its luster is eminently metallic, and can not be retained in contact with the air. This metal must be kept under oil of naphtha, (which contains no oxygen,) because, if left in contact with the atmosphere, it will absorb oxygen, and again become potash, or oxide of potassium. It is lighter than water, its specific gravity being 0.865. At the temperature of freezing water 'it is brittle; temperature rises it first becomes soft, and then liquifies long before the thermometer reaches the boiling point; and, finally, is volatilized at a red heat, giving out vapors of a beautiful green color. When a piece of potassium is thrown upon water its affinity for oxygen is so great that the water is decomposed, the oxygen of the water uniting with the metal with such rapidity that the hydrogen is ignited, and continues to burn until the metal is completely oxydized. If the remaining water be then examined it will be found alkaline, and capable of turning reddened litmus blue. Potash, as known in commerce, is an impure compound of all the soluble salts extracted from wood ashes by lixiviation and evaporation to dryness. Pearl-ash contains fewer impurities, being prepared by a more perfect calcination in contact with the air, promoted by constant stirring, by which means the carbon aceous matter, as well as the sulphur, is dissi pated. Resolution and evaporation, toward the close of the process, produce a white granular appearance. Pure potash, (vegetable alkali, caustic potash, etc.,) is solid, white, and fusi ble, and does not undergo decomposition at any degree of heat to which it may be subjected; but it is deliquescent, and, when exposed to the air, absorbs the carbonic acid of the atmosphere, and will consequently effervesce by the application of any of the stronger acids, such as sulphuric, nitric, or chlorohydric. It is one of the most powerful bases, and so caustic as to alter all organic substances'with which it comes in con tact, and it is hence used as an escharotic in surgery. Not only does it dissolve many animal substances, but also changes the nature of vege table products, particularly when its action is aided by heat. Potash is never found pure in nature, being always combined with acids, such as carbonic, sulphuric, chlorohydric, nitric, tar taric, oxalic, etc. That which is extracted from the ashes of vegetables is mixed with divers other salts, varying according to the vegetables from which the ashes have been procured, the nature of the soil, and the kinds of manure used in their production. In preparing caustic potash,
regard must be had to the substance used for the carbonate. That produced by reducing to ashes the tartrate of potash is the most pure. By suc cessive crystallizations any degree of purity may be gradually attained. The carbonate of potash is decarbonized by the application of caustic lime to a solution of the carbonate in boiling water, the boiling being continued for a time. The car bonate of lime, formed by the absorption of the carbonic acid from potash, precipitates, and may hence be easily separated by decantation or by filtration. To ascertain when all the carbonic acid has been removed, it is only necessary to add a few drops of acid to an equal quantity of the clear solution, when any effervescence will indicate the incompleteness of the operation. The decomposition being effected, the solution is allowed to settle, the clear liquid is decanted, and the residuum is thrown upon a filter, which may be of straw, clean sand, cloth, or paper. The evaporation should be rapid until the water is dissipated, when the product may be run into moulds, as may be desired, or allowed to cool on the sides of the evaporating pan. It should then be broken into fragments and secured in glass vases with emery stoppers. Potash thus obtained is known in commerce as potash prepared with lime. It is not absolutely pure, but contains salts, such as chlorides, sulphates, silicates, and aluminates of potash. By dissolving this potash in alcohol, and evaporating first in a still, to econ omize the/ alcohol, and finally in a silver vase, a product is obtained known as potash zi l'alcohol, which is used in analyses, and may be con sidered the purest found in commerce. Pot- . ash, if not the strongest, is at least one of the strongest of the bases, and forms salts that are very permanent—all of which are soluble in water; such as arc but slightly so being rare exceptions. In agriculture it is never used alone, but is combination with substances produced in the arts or found in certain localities, as geologi cal formations, such as green sand, occurring along our eastern littoral, (sea shore between high and low water), varieties of feldspar, lavas, etc. Potash is widely diffused throughout nature. It enters into the composition of animals and plants, and of all the soils which support vegetation ; and it forms one of the constituents of the predominant rocks of which the earth is composed, such as granites, mica-schists, the sienites, lavas, basalts, etc. Where the soil is formed from a rock in which there is no potash, it would be useless to seek it, or to anticipate fertility without supplying this element. (See Manures.)