Pearl-Ash, a kind of fixed alkaline salt, prepared in various parts of Europe, and also in America, by melting and extracting the salts from the ashes of burnt vegetables ; and, after evaporating the jnoisture, and reducing them to dryness, by calcining such ashes for a considerable time in a furnace moderately heated.-r-See Alkalies.
The best pearl-ashes are obtained from weeds, the ashes of which yield a larger proportion of salt than most kinds of wood. And it appears from the numerous experiments of Mr. Kirwan, that, among weeds, the fumitory produces the greatest quantity of salt; and next to it, wormwood ; though he observes, that if we attend only to the proportion of salt in a given weight of ashes, those of wormwood contain the. most.—The Tre-foil-BucKBEAN (Menyanthes trifo-liata, L.) also produces a larger quantity of ashes, and salt, than fern.
Pure pearl-ashes should possess a very acrid, caustic taste, and be uniformly white; though such criterion is not always to be relied upon, as they are frequently adulterated with lime and salt; impositions, not easily discovered by the eye. In order to detect this fraud, let a small portion of the suspected pearl-ash be exposed to the air till it become soft, when it should be held over the fire in a shovel: if the alkali contain any Common salt, the latter will crackle, and a slight explosion will take place, as soon as it becomes hot.
Pearl-ashes are very generally employed in the manufacture of glass ; for they combine with earths in a proper degree of heat, and form a vitreous mass : they are also used for domestic purposes, in washing linen, etc. ; and are subject to a duty of 2s. 51/2d. per cwt. on importation: but, by the 24 Geo. II. c. 51, § 2, 3, both pearl, and pot-ashes, may be imported duty-free from the British colonies of America.
In 1791, a patent was granted to Mr. George Glenny, for his method of obtaining a larger proportion of pearl and pot-ashes from those of wood, than that which is usually procured.—The patentees process consists in calcining the common wood-ashes in a furnace ; previously to which, a smal quantity of lime is to be sifted among them, to prevent the mass from vi-tretying; though, if the latter be continually stirred during the cess of calcination, the addition of lime will be unnecessary, When the ashes are calcined into a fine powder, they may be treated in the usual manner; but he observes, that it will be better to boil them in large vessels, especially during frosty weather.