TEMPERATURE OF THE METAL.

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massive works these precautions are less required, and the facing of common brick-dust, which is incombustible and more binding, succeeds better.

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.

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, (see page 267,) 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:

* 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, in 1819, to Hollingrake's patent for casting the metals under pressure.

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 the 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 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 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 gates 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.

CHAPTER XVII.

CASTING AND FOUNDING CONCLUDED.

SECT. I. —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 works 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 slips 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; 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 stood 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

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IRON-FOUNDERS' FLASKS.

a transverse beam and two long hangers, called clutches, which take hold of two gudgeons in the centers 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 each compartment are little fillets, sloping opposite ways, so as to lock in each small body 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 in the sand, the same as the keystone 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 are 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; much of the former, used about London, is procured at Lewisham. 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 facing-sand is sometimes only about equal parts of coal-dust and charcoal-dust, ground very fine; at other times, either old or new sand is added, and for large thick works a little roaddrift 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

MOULDS OF VARIOUS KINDS.

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more moisture with the sand; as before extracting the patterns, the iron-founder wets the edges of the sand with a sponge, sometimes having a nail tied to it to direct the water in a fine stream; for heavy works a watering pot is used.

The green-sand moulds, are made as in the brass-foundry, of the ordinary stock of old moist sand; these are often filled as soon as they are made.

The dry-sand moulds, are made in the same manner, but with new sand containing its full proportion of loam; these moulds are thoroughly dried in a large oven or stove, and then blackwashed or painted, with thin clay water containing finely-ground charcoal; this facing is also thoroughly dried before the moulds are poured.

The loam-moulds, which are much used for iron castings and somewhat also for those of brass, are made of wet loam with a little sand, ground together in a mill to the consistence of mortar; the moulds are made partly after the manner of the bricklayer and plasterer, as will be explained: the loam moulds also are thoroughly dried, and then black-washed, as from their greater compactness they allow less efficient escape for the vapour or air, and therefore they must be put into the condition not to generate much vapour when they are filled.

Iron moulds are also employed for a small proportional number of works, which are then called chilled castings; these were referred to at pages 258 and 259; and occasionally the methods of sand casting and chilling are combined, as in some axletreeboxes, which are moulded from wooden patterns in sand, and are cast upon an iron core. To form the annular recess for oil, a ring of sand, made in an appropriate core-box, is slipped upon the iron mandrel, and is left behind when the latter is driven out of the casting.

It would be a useless repetition to enter into the details of moulding ordinary iron-works; but from the horizontal position of the flasks it is necessary that the part of the work which is required to be the soundest, and most free from defects, should be placed downwards, as the metal is more condensed at the lower part, and free from the scoria or sullage, which sometimes renders the upper surface very rough and full of minute holes. As the flasks almost always lie on the ground, it is also found the most convenient to retain them in contact by placing heavy