Having traced the formation of various kinds of moulds for brass work, we must now return to the furnace to see if the metal is in condition to be poured, which is indicated by the slight wasting of the zinc from its surface with a lambent flame. When this condition is observed, the large cokes are first removed from the mouth of the pot, and a long pair of crucible tongs are thrust down beside the same to embrace it securely, after which a coupler is dropped upon the handles of the tongs: the pot is now lifted out with both hands and carried to the skimming-place, where the loose dross is skimmed off with an iron rod, and the pot is rested upon the spill-trough, against or upon which the flasks are arranged.

The temperature at which the metal is poured must be proportioned to the magnitude of the works; thus large, straggling, and thin castings, require the metal to be very hot, otherwise it will be chilled from coming in contact with the extended surface of sand before having entirely filled the mould: thick massive castings if filled with such hot metal would be sand-burned', as the long continuance of the heat would destroy the face of the mould before the metal would be solidified.

The line of policy seems therefore to be, to pour the metals at that period when they shall be sufficiently fluid to fill the moulds perfectly and produce distinct and sharp impressions, but that the metal shall become externally congealed as soon as possible afterwards.

For slight moulds the carbonaceous facings, whether meal-dust, charcoal, or soot, are good, as these substances are bad conductors of heat, and rather aid than otherwise by their ignition: it is also proper to air these moulds for thin works, or slightly warm them before a grate containing a coke fire. But in massive works these precautions are less required, and the facing of common brick-duet, which is incombustible and more binding, succeeds better.

Many beautiful brass castings of vegetable bodies, as ears of wheat, and thick fleshy plants, such as cockscombs, etc, have been frequently exhibited during the last few years, and appear to have been thus produced, or with the previous composition.

The founder therefore fills the moulds having the slightest works first, and gradually proceeds to the heaviest; if needful he will wait a little to cool the metal, or will effect the same purpose by stirring it with one of the ridges or waste runners, which thereby becomes partially melted. He judges of the temperature of the united brass, principally by the eye, as when out of the furnace and very hot, the surface emits a brilliant bluish-white flame, and gives off clouds of the white oxide of zinc, a considerable portion of which floats in the air like snow the light decreases with the temperature, and but little zinc then fumed away.

Gun-metal, and pot-metal, do not flare away in the manner of brass, the tin and lead being far less volatile than zinc; neither should they be poured so hot or fluid as yellow brass, or they will become sand-burned in a greater degree, or rather the tin and lead will strike to the surface as noticed at page 295. Gun-metal and the much used alloys of copper, tin, and zinc, described at page 272, are sometimes mixed at the time of pouring; the alloy of lead and copper is never so treated, but always contains old metal,* and copper is seldom cast alone, but a trifling portion of zinc is added to it, (sec page 207,) otherwise the work becomes nearly full of little air-bubbles throughout its surface.†

Some persons judge of the heat proper for pouring, by applying the skimmer to the surface of the metal; which when very hot has a motion like that of boiling water; this dies away and becomes more languid as the metal cools. Many works are spoiled from being poured too hot, and the management of the heat is much more difficult when the quantity of metal is small.

The mixture and temperature of the metal being found to be proper, it is poured in the manner represented in fig. 138, p. 306: the tongs are gradually lowered from the shoulder down the left arm, and the right hand is employed in keeping back the dross from the lip of the melting pot. A crucible containing the general quantity of 40 or 50 lb. of metal, can be very conveniently managed by one individual, but for larger quantities, sometimes amounting to one hundred weight, an assistant aids in supporting the crucible, by catching hold of the shoulder of the tongs with a grunter, an iron rod bent like a hook.

* When the founder is in doubt as to the quality of the metal, from its containing old metal of unknown character or that he desires to be very exact, he will either pour a sample from the pot into an ingot mould, or extract a little with a long rod terminating in a spoon heated to reduces. The lump is cooled and tried with the file, saw, hammer, or drill, to learn its quality.

† The engraved cylinders for calico-printing are required to be of pure copper, and their unsoundness when cast in the usual way was found to be so serious an evil that it gave rise, in 1819, to Hollingrake's patent for casting the metals under pressure.

Whilst the mould is being filled, there is a rushing or hissing sound from the flow of the metal and the escape of the air, the effect is less violent when there are two or more passages as in heavy pieces, and then the jet can be kept entirely full, which is desirable. Immediately after the mould is filled, there are generally small but harmless explosions of the gases, which escape through the seams of the mould, they ignite from the runners, and burn quietly: but when the metal blows, from the after-escape of any confined air, it makes a gurgling, bubbling noise, like the boiling of water but much louder, and it will sometimes throw the fluid metal out of the runner in three or four separate spirts: this effect which mostly spoils the castings, is much the most likely to occur with cored works, and with such as are rammed injudiciously hard, without being, like the moulds for fine castings, subsequently well dried.

The moulds are generally opened before the castings are cold, and the founder's duty is ended when he has sawn off the ingates or ridges, and filed away the ragged edges where the metal has entered the seams of the mould; small works are additionally cleaned in a rumble, or revolving cask, where they soon scrub each other clean.

Nearly all small brass works are poured vertically, and the runners must be proportioned to the size of the castings that they may serve to fill the mould quickly, and supply at the top a mass of still fluid metal, to serve as a head or pressure for compressing that which is beneath, to increase the density and soundness of the casting. Most large works in brass, and the greater part of those in iron, are moulded and poured horizontally, and the process being exactly alike for both metals, we must refer the reader to the following chapter.