slightly warm, as otherwise on cooling it has an increased affinity for damp; but the mould when hot is more or less filled with aqueous vapor, which is equally prejudicial.

When a figure, such as a bust, is required to be cast hollow from a solid model, it is first moulded exactly as above. The core is now produced as follows: at the foot of the bust a large space, nearly equal in length and bulk to the bust, is cut away in the sand, to serve for fixing the core in the mould, or for the balance, as it is called, as the core cannot be propped up at both ends. The entire hollow, that is for the bust and the balance, is filled with a composition of about one part of plaster of Paris and two of sand or fine brick-dust, mixed with a little water and poured in fluid, a few wires being placed amidst the same for additional support.

The mould is now taken to pieces to extract the core, which is then dried, thoroughly burned, and allowed to cool slowly (which the founder calls annealing, from a similar method being employed in annealing or softening the metals and glass): the core is then returned to the mould, to see that it has not become distorted. If needful the fitting around the balance is made good to suit the reduced magnitude of the core, which latter is then so far pared away as to leave room for the thickness of metal; this is frequently regulated by boring holes at many parts of the core with a stop-drill, having a collar to prevent its penetrating beyond the determined depth; the surface of the core is now pared down to the bottoms of the holes, as uniformly as possible. When the mould has been faced, dried and smoked, the whole is put together for pouring, for which purpose the figure is inverted and filled from the pedestal.

Equestrian and other figures are sometimes cast in two, three, or more pieces, and joined together by solder, screws, or wires; but in all such works, the aim of the founder is to leave little or nothing for the finisher or chaser to do.

Some objects which are either exceedingly complex in their form, or soft and flexible in their substance, and which do not therefore admit of being moulded in sand, in the ordinary manner of figure casting, may be moulded for a single copy, provided the originals consist of substances which may be either readily melted or burned into ashes.

A cavity is made in the sand of the moulding-trough, a little larger and longer than the object, or else a wooden box of appro. priate size is procured, in the midst of which the wax model may be placed; to the end of the model is added a piece to represent the runner, which will be required for introducing the metal. The composition of one-third plaster of Paris and two-thirds brick-dust, mixed with water, the same as for the core of the bust, is then poured in, entirely to surround the model. The mould is first slowly dried, it is then inverted and made warm to allow the wax to run out, after which it is annealed, or burned to redness, and lastly, when cooled, it is buried in sand and filled with metal. The

method necessarily throws the chance of success upon a single trial, as the model is destroyed.

Should the face of the casting be required to be particularly smooth, a small quantity of brick-dust is washed, (in the manner practised with emery, and to be explained,) and mixed with very fine plaster a coat of this is brushed over the model, which ex cludes air-bubbles, the model is quickly placed in its cavity, and the coarser mixture is poured in as before.

The above method exactly corroborates a mode long since described as being suitable to casting copies of small animals or insects, parts of vegetables and similar objects; these are to be fixed in the centre of a small box, by means of a few threads attached to any convenient parts, one or two wires being added to make airholes, and ingates for the metal. A small quantity of river silt or mud, which had been carefully washed, was first thrown in and spread around the object by swinging the box about; and when partly dry, successive but coarser coats were thrown in, so as ultimately to fill up the box. When it had become thoroughly dry, the wires were first removed from the earthy mould; it was then burned to reduce the object to ashes, and when every particle of the model had been blown out, it was ready to be filled with metal.

FILLING THE MOULDS.-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-dustcharcoal, or soot, are good, as these substances are bad conductors,

CASTING AND FOUNDING.

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of heat, and rather aid than otherwise by their ignition; it is 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-/ dust, which is incombustible and more binding, succeeds better..

RY

1.

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 melted 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 is then fumed away.

OF

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 212. Gun-metal and the much used alloys of copper, tin, and zinc, 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, otherwise the work becomes nearly full of little air-bubbles throughout its surface. 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 redness. 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 to casting the metals under pressure.

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. 119, p. 221. 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 lbs. 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.

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 where 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 gener ally 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 inless judiciously 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.

IRON-FOUNDERS' FLASKS, AND SAND MOULDS. The process of moulding works in sand is essentially the same both for brass and iron castings; but the very great magnitude of many of the latter gives rise to several differences in the methods: it will suffice, however, to advert to the more important points in which the two practices differ, or to those which have not been already noticed; I shall therefore commence with a few remarks upon the flasks and the sand.

In the greater number of cases the iron-founder moulds and casts his work horizontally, with the flasks lying upon the ground; frequently the top part only is lifted; and in the largest works the lower part of the flask is altogether omitted, such pieces being moulded in the sand constituting the floor of the foundry; in these cases the position of the upper flask is denoted by driving a few iron stakes into the earth, in contact with the internal angles of the lugs, or projecting ears of the flasks.

The sand would drop out of such large flasks, if only supported around the margin; they are consequently made with cross-bars or wooden stays a few inches asunder, which, unless the entire flask is

made of wood, are fixed by little fillets cast in the solid with the sides of the iron flasks. A great number of hooks in the form of the letter S, but less crooked at the ends, are driven into the bars, and both the bars and hooks are wetted with thick clay water, so that the sand becomes entangled amidst them, and is sustained when the flask is lifted. Some flasks require the force of either two or several men, who raise them up by iron pins or handles projecting from the sides of the flask; they are then placed upon one edge, and allowed to rest against any convenient support whilst they are repaired, or they are sustained by a prop.

The very heavy flasks are lifted with the crane, by means of a transverse beam and two long hangers, called clutches, which take hold of two gudgeons in the centres of the ends of the flask; it can be then turned round in the slings, just the same as a dressing-glass, to enable it to be repaired.

The modern iron-founder's flasks are entirely of iron, and do not require the wooden stays, as they are made full of cross ribs nearly as deep as the flask itself, and which divide its entire surface into compartments four or five inches wide, and one to two feet long. On the sides of every compartment are little fillets, sloping opposite ways, so as to lock in the small bodies of sand very effectually. When these top flasks are placed upon middle flasks without ribs, as in moulding thick objects, the two parts are cottered or keyed together, by transverse wedges fixed in the steady pins of the flask; lifters or gaggers are then placed amidst the sand; these are light T shaped pieces of iron, wetted and placed head downwards, the tails of which are largest at top, so as to hold themselves in the sand, the same as the key-stone of an arch is supported. The gaggers are placed at various parts to combine the sand in the two flasks, and they fulfil the same end as the iron hooks and nails driven into the wooden stays of the old-fashioned flasks.

The bottom flask or drag has sometimes plain flat cross-ribs two inches wide (like a flat bottom with square holes), that it may be turned over without a bottom board; and unless the flasks have swivels for the crane, they have two cast-iron pins at each end, and one or more large wrought-iron handles at each side, by which they may be lifted and turned over by a proportionate number of

men.

The sand of the iron-founder is coarser and less adhesive than that used by the brass-founder. The parting sand is the burned sand which is scraped off the castings; it loses its sharp, crystalline character from being exposed to the red heat. The facingsand is sometimes only about equal parts of coal-dust and charcoaldust, ground very fine; at other times, either old or new sand is added, and for large thick works a little road-drift is introduced. All these substances get largely mixed with the sand of the floor. and lessen its binding quality, which is compensated for by occasional additions of new sand, and by using more moisture with the sand; as before extracting the patterns, the iron-founder wets the