COPPER.

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running off the liquid slag; /, a small wall; g, iron curb for keeping the coalstogether.

The hearth being heated with a bed of charcoal, J cwt. of darrlinge ai^ laid over it,and covered with more fuel: whenever this charge is melted, another layer of the coaland darrlinge is introduced, and thus in succession till the hearth become full, orcontain from 2J to 2J cwt. In Neustadt cwt. of darrlinge have been refined in onefurnace, from which 5 cwt. of gahrcopper has been obtained. The blast oxydizes theforeign metals, namely, the lead, nickel, cobalt, and iron, with a little copper, formingthe gahrslag: which is, at first, rich in lead oxyde, and poor in copper oxyde ; but, at theend, this order is reversed. The slag, at first blackish, assumes progressively a copperred tint. The slag flows off spontaneously along the channel e, from the surface of thehearth. The gahre is tested by means of a proof-rod of iron, called gahr-eisen, thrustthough the tuyere into the melted copper, then drawn out and plunged in cold water.As soon as the gahrspan (scale of copper) appears brownish red on the outside, andcopper red within, so thin that it seems like a net-work, and so deficient in tenacitythat it cannot be bent without breaking, the refining is finished. The blast is thenstopped; the coals covering the surface, as also the cinders, must be raked oflf the copper,after being left to cool a little; the surface is now cooled by sprinkling water upon it,and the thick cake of congealed metal ( rondelle ) is lifted off with tongs, a process calledschleissen (slicing), or sheibenreissen (shaving), which is continued till the last convex cakeat the bottom of the furnace, styled the kingspiece, is withdrawn. These rondelles areimmediately immersed in cold water; to prevent the oxydation of the copper; whereuponthe metal becomes of a cochineal red color, and gets covered with a thin film ofprotoxyde. Its under surface is studded over with points and hooks, the result oftearing the congealed disc from'the liquid metal. Such cakes are called rosette copper.When the metal is very pure and free from protoxyde, these cakes may be obtained verythin, one 24th of an inch for example.

The refining of two cwts. and a half of darrlinge takes three quarters of an hour, andyields one cwt. and a half of gahrcopper in 36 rosettes, as also some gahrslag. Gahr-copper generally contains from 1J to 2| per cent, of lead, along with a little nickel,silver, iron, and aluminum.

Smelting of the Mannsfeld copper schist, or bituminous Mergelschiefer. —The cupreousore is first roasted in large heaps, of 2000 cwts., interstratified with brush-wood, andwith some slated rich in bituminous matter, mixed with the others. These heaps are3 ells high, and go.on burning 15 weeks in fair and 20 in rainy weather. The bitumenis decomposed ; the sulphur is dissipated chiefly in the form of sulphurous acid ; the metalgets partially oxydized, particularly the iron, which is a very desirable circumstancetowards the production of a good smelting slag. The calcined ore is diminished onetenth in bulk, and one eighth in weight; becoming of a friable texture and a dirty yellowgray color. The smelting furnaces are cupolas (schachloferi) , 14 to 18 feet high ; thefuel is partly wood charcoal, partly coke from the Berlin. gas-works, and Silesia. Theblast is given by cylinder bellows, recently substituted for the old barbarous Blasebdlgen,or wooden bellows of the household form.

The cupreous slate is sorted, according to its composition, into slate of lime, clay, iron,&c., by a mixture of which the smelting is facilitated. For example, 1 post or charge mayconsist of 20 cwt. of the ferruginous slate, 14 of the calcareous, 6 of the argillaceous, with3 of fluor spar, 3 of rich copper slags, and other refuse matters. The nozzle at thetuyire is lengthened 6 or 8 inches, to place the melting heat near the centre of thefurnace. In 15 hours 1 fodder of 48 cwts. of the above mixture may be smelted,whereby 4 to 5 cwts. of matte (crude copper, called Kupferstein in Germany ) and alarge body of slags are obtained. The matte contains from 30 to 40 per cent, of copper?and from 2 to 4 loths (1 to 2 oz. ) of silver. The slags contain at limes one tenth theirweight of copper.

The matte is composed of the sulphurets of copper, iron, silver, zinc, along with somearsenical cobalt and nickel. The slaty slag is raked off' the surface of the melted mattefrom time to time. The former is either after being roasted six successive times,smelted into black copper; or it is subjected to the following concentration process. Iis broken to pieces, roasted by brushwood .and coals three several times in brick-wallskilns, containing 60 cwts., and turned over after every calcination; a process of f°“‘weeks’ duration. The thrice roasted mass, called spurrost, being melted in the cup°fig. 313, with ore-cinder, yields the spurstein, or concentrated matte. From 30 to 40 cw s.of spurrost are smelted in 24 hours ; and from 48 to 60 per cent., of spurstem are obtamea,the slag from the slate smelting being employed as a flux. The spurstein contains Iro50 to 60 per cent, of copper, combined with the sulphurets of copper, of iron, a

The spurstein is now mixed with dimnstein (a sulphuret of copper and iron pioducedin ihe original smeltings) roasted six successive times, in the quantity of 60 cwts., '