7S] LEA •Keeling, for his contrivance of a substitute, both for re J and white- lead, in gla/in^ earthen-wares, glass, enamel, &c. He direfts any quantity or lead-ore, to be pat into a reverberatory or other furnace, and to be roasted till it become of a ivhite-heat, daring which pro- cess the metal will emit a con- siderable portion of fumes. The j5re must be continued till about an hour after the vapour is dissi[)ated ; and, when the mass grows cool, it is to be removed from the furnace, and ground with water to a tine liquid state, when the other ingre- dients, usually employed in makin-y glazes, may be added ; and the preparation will be complete. Thus the injuries occasioned to the work- men, by the dusty particles which settle upon their skin and lungs, will be etfeftually prevented ; but this sitccedaiieum does not remove tlie poisonous qualities of the metal in the glazing" of earthen-ware. White-lead is emploj-ed in paint- ing, and furnishes a tolerable white. — See vol. ii. p. 3o ; and also Paint. Cerusse is likewise used in sur- gery ; and, on account of its cool- ing, dr}'ing, and astringent pro- perties, is of considerable service wl5tn sprinkled over running sores or ulcers. Black-Le.ad, or Phimlago, a genus of inflammable sul.stances, found in various parts of the world; but most abundantlv atBorrowdale, in Cumberland ; whence Britain, as well as the greater part of Eu- rope, are suppHed with this article. Pure black-lead is of a very deep colour : when newly cut, it pre- sents a blueidh-white cast, and shines like common lead. It is insoluble in acids ; but, if it be put into a vessel placed over a strong LEA fire, and exposed at the same tirne to the air, it is almost entirely vo- latilized, depositmg only a little iron, and a small pordon of sili- ceous earth. Black-lead is chiefiy used in the manufafture of pencils for draw- ing ; and thouj^n paper can be marked with them for a time, yet evnry trace may afterwa^ds be to- ta'.y ruboed out by means of .sojft bread, or elastic gam. In fojming such pencils, the lead is divided into long pieces, and fix d into s(,uare grooves, cut in ced-ir or other soft wood : another p ece is then glued over, and the whole worked into thm cylinders. A coars..r kmd oi penoii.i is ma- nufactur-.d, by miXiUg pu'ver/zed biack-lead wan sulphur ; w ich, however, are calculate'.: only for carpenters' mirks, or very -t.-oarse drawings. — T!i(^ powder of black- lead also serves to cover nizor- straps ; and con iderable quantities of it are used for imparting a bright gloss to CList-iron grates or .-toves - It may also be advautageoubly applied to smoothen the inner surface pf wooden - screws, packi ng - presses, and other wood- ork that is sub- je6t to frequent fritStion, fur which purpose it is far superior to greasy, soapy, or oily matters. LEAD-W'OHT, or Plumhago, L. a genus of exotic plants, con- si.sting of four species ; the most remarkable of which is the Euro- paed : its root is perennial, strikes deep into the ground, and grows natnrally in the southern parts of Europe. This very acrid and poisonous vegetable may be propagated either by parting the roots, or by the seeds 3 as it will grow in__ the open air of our climate, and is far from being an useless plant. Its root was
