A supplement to Ures Dictionary of Arts, Manufactures, and Mines, : containing a clear exposition of their principles and practice. . tances it is necessary to continue the operation during three or fourweeks. The charge of hard lead varies from eight to eleven tons. When the metal is thought to be in a fit state for tapping, a small portion taken outwith a ladle, and poured into a mould used for this purpose is found on cooling to assumeat the surface a peculiar crystalline appearance, which when once seen is readily agiin rec-ognized. As soon as this appearance presents itself, an iron plug
A supplement to Ures Dictionary of Arts, Manufactures, and Mines, : containing a clear exposition of their principles and practice. . tances it is necessary to continue the operation during three or fourweeks. The charge of hard lead varies from eight to eleven tons. When the metal is thought to be in a fit state for tapping, a small portion taken outwith a ladle, and poured into a mould used for this purpose is found on cooling to assumeat the surface a peculiar crystalline appearance, which when once seen is readily agiin rec-ognized. As soon as this appearance presents itself, an iron plug is withdrawn from thebottom of the pan, and the lead run oif into an iron pan, from which it is subsequentlyladed into moulds. The items of cost attending the calcination of one ton of hard Spanish lead iii thenorth of England are about as follows:— Wages Coals, 2-7 , &c. d. 11-2 4-7 0-5 2 4-4The coBstruction of a furnace of this description requires 5,000 common bricks, 3,500fire-bricks, and i tons of firc-:lay. Figs. 380 and 381 represent an elevation and vertical section of the calcining furnace. E m E E 3S1. A is the fire-place ; b, ash-pit; c, fire-bridge; d, cast-iron pan; e, flue; r K F, channels for allowing the escape of moisture; g, one of the working doors; b, spout for running off calcined metal. Fi^. 382 represents the pan removed from the masonry, and shows a groove in the hp for the introduction of a sheet-iron dam tightened with moistened bone-ash, for keeping in the fused metal. In the more modern furnaces of this de-scription, the corners are usually rounded toprevent breakage from expansion, whilst thetapping is effected by means of a hole throughtiie bottom near one of the sides. This, whenclosed, is stopped by means of an iron plug keptin its place by a weighted lever. Concentration of the silver.—This processis founded on the circumstance first noticed in the year 1829, by the late H. L. Pattinson of Newcastle-on-Tyne, that when lead con-tai
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Keywords: ., bookcentury1800, bookdecade1860, bookpublishernewyo, bookyear1864
