ALU covering ; in order to prevent the blossoms from being killed by the frost, during the months of Fe- bruary and March. When the fruit is set, and the leaves are suf- ficiently long to cover it, such shel- ter ought, if the weather be warm, to be removed toward the end of April, or early in May ; by which expedient an abundant supply of almonds may be obtained for the dessert, both in autumn and in the winter. The fruit of the almond-tree is chiefly valued on account of its kernels: it may be preserved either in dry bran, or in sand ; but it ought previously to be dried on shelves or boards in an open situa- tion ; as it is otherwise apt to be- come mouldy, and consequently the kernels will be unfit for use. ALOE. — According to M. Fab- B^ONi (Annales de Chimie, vol. 25), the leaves of the Socotrine Aloe afford a beautiful violet co- lour, which resists the a6tion of ojfygen, acids, and alkalies. He direfts the juice to be extra«5ted from the fresh leaves, and then ex- posed to the air : thus, the liquid will become gradually red, and at length be converted into a deep violet purple, which is peculiarly cal- culated for dyeing silk, a stuff that readily imbibes the colour without the aid of mordants, — M. F. ob- serves, that such juice may also be inspissated ; in which state it fornis a beautiful transparent colour, for painting in miniature, ALUM. — Beside the methods of detecting alum in bread, already stated, there is a chemical prpcess, that consists in combining a little chalk with a small portion of aqua- fortis, and pouring the mixture on water, in which the suspeded bread )ias been immersed for some time. AMB [391 If there be any aluminous acid, it* presence will become evident, by a gypseous or chalky mass deposited at the bottom of the vessel : in the contrary case, no sediment will be formed. In Odtober, 1794, a patent was granted to the Earl of D UNDO NALD, for his method of preparing alum, vitriol of argil, and other saline substances. He direds aluminous, vitriolic, or pyrituous schist, to be mixed with sea-water, or with so- lutions of sea-salt, kelp, sandiver, soap-boilers ashes, or any saline matter, containing mnriat of soda. The liquor, resulting from such mixture, is then boiled till it be sufficiently concentrated for crys- tallization ; after which it is mixed with a due proportion of alum- schist, clay, or other argillaceous ingredient. The materials are next dried, pulverized, and submitted to the a dion of heat, till the mu- riatic acid be expelled : the result of these various processes, is alum. The substance remaining may, by repeated washing and drying, be used as a pigment} and, by col - leding the muriatic acid in proper vessels, and combining it with vo- latile alkali, Lord D. procures jcZ ammoniac. — A more diffuse ac- . count of his iiiventions, is inserted in the 41 h volume of the " Repcrr tory of Arts," Sec. » AMBER. — ;A method of making artijicial amher has lately been dis- covered by Prof. Hermbstaedt, oi B«riii]. He placed reftified pe- troleum, abopt one line in thick- ness, on water, in a china saucer, which was exposed to the rays of the sun, for several months, be- neath a glass-bell, containing oxy- gen. At lengtli, the petroleum had absorbed the oxygen, and sunk a little beneath the surface : tlig glas& C C 4 was
