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of the flue should be from one-sixth to o the fireplace. Defective draught very ofte bad construction of the flues, for when th from several furnaces open into a comm currents, being continued beyond their orif other. Figs. 7 to 12 show in plan and elev large sized furnaces with their flues opening stack.

Furnaces for melting metals, heated w of solid fuel, have been adopted in some shows an arrangement formerly used in the Manufactory, and in the mint. A is a chan - having an ordinary flat grate, composed of another grate in which the bars are placed i a grate of this kind small free-burning coa which would in a great measure drop throu grate. The surface of the grate, by this st ment of bars, is considerably increased, an allowed for admission of air. The two ope closed by iron doors. A blast of air is intro grates by the pipe f. The fuel is charge opening g, which is closed with an iron a sliding damper h. The gases generated, oxide, pass through the pipe k, provided wi valve l, and escape at m. Immediately i opening m, and extending across the furn pipe n, from which air issues. The carbo burns, and the heat is communicated to the fu the crucible is placed. In order to represent producer and the melting furnaces in the section, it has been necessary to deviate fr position of these furnaces at the mint, wher furnace is at the side of the gas furnace. Th by a small fan through the pipes ƒ and n, whi with regulating valves.1

Great improvements in the constructio
Percy's Metallurgy, p. 201.

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furnaces heated by gaseous fuel have been made during th last thirty years, notably through the labours of Messr Siemens. By the use of gas-producers fuel may be use which is too inferior for ordinary furnaces, and a highe temperature attained by the combustion of the gas formed than by using solid fuel directly. A gas-producer is generall a somewhat rectangular chamber, in which fuel is burn for the formation of carbonic oxide as already explained Siemens's producer, Fig. 14, is lined with fire-brick; the sid A is formed of iron plates lined with fire-bricks, and has step-grate B, with wrought-iron bars C. The fuel is charge

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C

FIG. 14.

E

FIG. 15.

through the hopper D. The gas passes up the pipe E, which is cased with iron, and issues into a horizontal wrought-iro pipe, which conveys it to the regenerator, where it is highl heated before entering the furnace in which it is burnt, thu producing a much higher temperature. The waste heat o the furnace is not lost, but utilised in heating the regenerators The arrangement of a Siemens's crucible furnace is show in Fig. 15, where the pots are heated by the combustion of hot gas and hot air. The regenerators are chamber of open refractory brickwork, built in pairs, two pairs bein required for each furnace; each pair being used alternatel for absorbing the heat of the gaseous products from th furnace, and heating the gas and air required for com bustion. By means of a reversing valve, the waste gase

pass to the right or left pair at will. When are passing down through the right pair, th producer gas are passing up through the direction being reversed when sufficient hea sorbed. It will be observed that the combust enter the furnace alternately at the right and to which pair of regenerators is being us them. By using gas for melting metals a oxidising flame can be obtained, which preve by oxidation, a manifest advantage in cas necessary to preserve the composition of an a should be of great advantage in the manufactu as brass.

Reverberatory furnaces are only used for t of brass where large quantities require to be case of ingots of yellow metal used for ships' The furnace commonly employed, Figs. 16,

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of holding about a ton of metal. It is somew in shape, with flat sloping bed, which incl bridges and back towards the front, or worki bed is formed of fire-brick carefully set edge rammed sand bottom is used.

It is advisable that the copper should be

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an atmosphere of flame, so as to exclude the air as much a possible. Then the scrap and zinc, previously heated, ar introduced, and the mixture thoroughly stirred as rapidly a possible, to prevent loss of zinc. Another plan, which find favour with some manufacturers, is to melt the copper i

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the furnace, tap it into a large iron ladle, and add the heate scrap and zinc to the ladle, so that the metal may b poured into the moulds immediately after the necessar stirring required to mix the contents is effected.

The alloys of copper and zinc are easily formed, bu when the zinc is added to the copper in the furnace th damper of the chimney should be nearly closed, and the fir should not be too brisk, since by having too high a tempera ture at this stage much zinc will be wasted. Moreove when the metals are thoroughly mixed the surface shoul be covered with charcoal or sand, especially when it i necessary to raise the temperature before tapping. Whe the metal is ready for tapping the tap-hole is opened wit an iron bar, and the metal run into a ladle. The surface c

the metal is covered with charcoal, which keeps in the heat and preserves the metal from oxidation by the air. The tem perature of molten brass and bronze becomes rapidly lowered

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