Page:Willich, A. F. M. - The Domestic Encyclopædia (Vol. 1, 1802).djvu/385

353&#93; Bfei i3 obtained by soaking fragments of bricks in olive oil, and after- wards distilling them in the usual manner. In the present improved state of chemistry, it has been found that, by this fanciful pro- cess, the oil of olives, so far from being impregnated with healing" in- gredients, is necessarily corrupted. Brick-water, or water impreg- nated with the contents of bricks, i-. possessed of properties so pecu- liarly striking, and at the same time so pernicious in their effects, when used for culinary purposes, that we cannot, in justice to our readers, withhold from them the following various experiment made by Dr. Percival, and stated in the first volume of his Essays. He steeped two or three pieces of common brick, four days in a bason full of distilled water, which he after- wards decanted oft", and examined by various chemical tests. It was not miscible with soap ; struck a lively green with syrup of violets ; became slightly lactescent by the volatile, alkali ; but entirely milky by the fixed alkali, and by a solu- tion of sugar of lead. No change was produced on it by an infusion of tormcntil-root. Hence the Doc- tor justly concluded, that the lilting ofweits with /ricks, a practice very commori in many places, is ex- tremely improper, as it cannot fail to render the water hard and un- wholesome. Clay generally contains it ty of heterogeneous matters ; and coloured loams often partici- pate of bitumen, and the ochre of iron. Sand and lime-earth are still more common ingredients in their composition' ', and the experiments of Mr. Geoffrey and Mr. Pott prove, that the earth of alum also may in considerable quantity be se- parated from clay. As therefore xo. ni. — ol. i. BR i [353 clay is exposed to the open air for a long space of time, before it is moulded into bricks and burnt, this process in many respects resembles that by which the alum stone is prepared. And it is probable, that the white efflorescence, which is frequently observable on the sur- face of new bricks, is of an alumin- ous nature : indeed the combina- tion of the vitriolic acid with the earth of alum, may be sufficiently accounted for, partly from the long exposure of clay to the air, before it is moulded into bricks, and partly from the sulphureous exhalations of the pit- coal used for burning them, together with the suffocat- ing, bituminous vapour arising fromi the ignited coal. BRIDGE, a construction of stone, timber, or iron, consisting of an arch or arches, and built over a river, canal, &e. for the convenience of passengers. A bridge built of stone is evidently the strongest and most durable: the proper situation, for it is easily known ; and the only circumstance necessary to be ob- served is, to make it cross the stream at right angl s, that boats may readily pass through the arches with the current of the river. Those bridges built for a com- munication between high roads, ought to be so strong as to resist all accidents, and afford an easy passage to the waters : they should therefore be at least as long as the river is wide at the time of its greatest flood ; because, by the ac- cumulation of the waters above, too great a fall may be occasioned, and the foundation of the piers and abutments may thus be under- mined. The necessary requisites in a bridge are, that it be well designed, commodious, durable, and suitably A a ornamented.