This mixture, intimately blended, is compressed into a crucible of the form of fig. 3. Plate XXXV I.* One of these crucibles holds about 100 lbs. of brass, when the process is finished ; but as this con sists of the pure copper and zinc,. pot, when charged, will contain of copper 66.31bs., of calamine 63. lbs., and of charcoal powder 13 lbs. When the crucible is filled, the contents should be covered .with a mixture of clay sand and horse-dung, in order to defend the metals and charcoal from the action of the air. When this covering is strictly attended to, less charcoal powder might be employed, and a larger dose of the other ingredients might be put in its place, but it is generally the most defective part of the process. Having charged the pots, we will now describe the furnace which has to receive them.
Fig. 1. Plate XXXVI.• is a plan of the furnace. The part AB is taken at the level EF, showing the opening into the furnace on the ground floor at a and 6 : c and d are horizontal flues leading to the chim neyf, and can be cut off from the same by the dam pers seen in the dark part of the flue. CD, in the same figure, is a plan on the level GH, where the pots rest upon the cast iron plate on bottom x, y.
Fig. 2. is an elevation and section of the same fur nace. AB shows a front view of the pyramidal chim ney, and the archway opening into it. CD is a sec tion of the same, through the middle of the fire-place II. R,P,Q, is a vaulted passage going across the building, and open at both ends, for the admission of air, which passes through the openings in therirch, through the fires. The bottom of the furnace is not a common grate, but a thick plate of cast metal, perforated with holes for the air to pass through ; one hole being between each pot, as they are seen arranged in fig. 1. at I, I, and also in the section at y. When the pots are placed upon the plate, the fire is not placed immediately upon them, as it would not only derange them, but it would displace the co vering. To prevent this, the pots are first cover
ed by some dried heath, or common brambles. This lying on the pots, defends them for a time, when the fuel is thrown in. By the time the brambles are consumed, the coal will have coked upon the pots, and will act as a defence for the rest of the process. The fire is kept up from twelve to twenty hours at the Cheadle Brass Works in Staffordshire, where these drawings were taken from. They cast twice in the twenty-four hours.
The melted brass, after the refuse is skimmed off, is cast into ingots, if sold for melting over again, and into plates, if intended to be rolled into sheets, or made into wire. The plates are cast between large blocks of Cornwall stone. The lower stone is fixed, and the face made even and smooth, by filling up the recesses of the ruff stone with fine send. The upper stone is similarly prepared, and is suspended over the fixed one. The height and breadth of the place to receive the metal is limited by iron bars laid on the lower stone. The upper stone is then let down upon the bars. The lower stone is a little longer than the upper one, and projects to the front. Being a little higher in that part, it forms a lip, or mouth-piece, to pour the metal. into. The flat sides of the cast plate are therefore bounded by the sur face of the stones, and the edges of the same by the bars above-mentioned. The ingot moulds are re cesses in blocks of cast-iron, open on one• side.
The most certain and correct method of forming brass and the other compounds expressed in the table above-given, is by immediately uniting the me tals in given weights. It should, however, be ob served, that it will be found difficult to introduce zinc into melted copper. The best way of uniting it with copper, in the first instance, will be to introduce the copper in thin slips to the melted zinc, till the alloy requires a tolerable heat to fuse it, aniFthen to unite this alloy with the melted copper. (r.)