heats of common brass work would be considered a fair day's work. The number of moulds constituting a heat is regulated, however, by the size of the crucibles and weight of the castings.

Before the molten metal is poured in, the impressions from the patterns in the sand must be connected by the principal ingates or channels by which the metal is run into the mould, the sand being scooped out by a special tool, termed a "drawer." This operation, although apparently simple, really requires much judgment and experience, especially in large work, in order to obtain the requisite amount of metal to feed the impressions. The runners are generally made on the "she-side," but sometimes they are employed on both the "she-side" and "peg-side.' The "" cores are generally laid in the peg-side. For common work the metal is poured into the moulds while in the damp state, the impressions having been previously dusted with flour or charcoal.

§ 59. Fine Work.-For fine castings the moulds, after being made, are dried before a fire, previous to dusting, and then dusted with powdered charcoal. For single-face only one side of the mould is dried. For very delicate work the face of the mould is smoked with a torch composed of pitch. In this case, after drying and torching, the moulds must be again brought in contact with the patterns before being screwed up, and the soot being in a very finely-divided state, the impression is brought out clear and sharp. The caster uses a clayey sand, termed "loam," to mix with his ordinary sand for fine work, and for that reason the moulds must be well dried. By the use of loam the chased and sharp corners of the impressions hold together better. When loam is used facing sand is necessary, and this being of a more porous nature than loam sand, permits the gases more freely to escape when pouring, and thus prevents blowholes in the work.

When moulding thin scrolls, or when the pattern has a

thin part, the moulds must not be rammed too hard, for, as the metal contracts on cooling, if the sand does not give way the metal will crack and the castings become what is termed seared. The caster overcomes this difficulty by damping the thin part of the impression with charcoal and water, which renders that part of the mould soft and yielding when the metal cools.

§ 60. Cores. When the objects to be cast are required to be hollow, they are then "cored," as it is termed. It is advisable in all cases, wherever possible, to allow the pattern to deliver its own core. This can be done by making the pattern to "leave" half-way, or by turning it taper all through. For example, in Fig. 26 a to c, the light shaded

B

d

FIG. 26.

portion marked d represents the core. In many cases this method cannot be adopted. Sometimes the pattern is moulded as though for a solid casting, and the sand core pushed out of the pattern, and fixed on the face of the mould with a splint of wood or a nail, before pouring in the metal. For many articles core-prints have to be made on the pattern, and these imprint in the mould the places where the ends of the core will subsequently be supported. The core bearing must always be of the same diameter as the prints in the pattern.

Core-stocks. These are core-boxes, generally made of plaster of Paris or wood, the interior of which contains a cavity, of the desired shape of the interior of the object to be cast. Core-stocks are made as follows: The core-bearing is placed half-way in the sand, and pieces of metal or wood placed round to form an enclosure. Plaster of Paris is then

poured over the bearing in this enclosure, and left until it has completely set. The plaster cast along with the bearing is then removed from the sand, trimmed up, and hollows cut out of the sides, and left to dry, when the bearing becomes loose. This forms one-half of the core-box. The plaster cast is then well oiled, placed in sand, an enclosure made as before, and plaster of Paris poured in. When the whole is set and dry the two parts are separated, and the bearing removed. The core-stocks are then ready for use. Should

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any difficulty be experienced in getting the parts asunder, the stocks are placed in an oven and heated, when the parts are readily separated. These stocks are then generally used to cast from in brass or iron, so as to form permanent core-boxes.

In casting from a pattern which has a hole at one end only, the core requires to be balanced—that is, it must be heavier at one end than at the other, the light end projecting into the part which is to be hollow. Very often the core is balanced in the middle, one core being made to do duty for two castings. This principle is taken advantage of in patterns which are undercut, as in the flange of a pulley. This process is called false coring.

§ 61. Figure Casting, etc.-This most complex part of the founders' art is done by the false-coring process, the patterns being generally solid. The figure to be cast is laid as far into the sand as will enable it to leave properly, and when the caster comes to an undercut part, he dusts it with parting sand, and fits in a piece of sand. When he comes to another undercut part he uses more parting sand, and rams more sand in as before. In this way piece after piece is successively laid on the pattern, until he comes to a part which will leave the sand without breaking any portion of it. This part is then moulded, removed, and each separate piece of core taken out with two needles, in order to remove the pattern. The moulds and pieces of core have to be dried and carefully replaced, and mended if required. The im

pression after dusting, etc., is then ready to receive the metal. The pieces of sand are removed with two needles stuck in a piece of wood. The relative position of the cores are readily recognised by their irregular forms.

Birds, insects, and parts of plants may be cast by fixing the object to be cast in the centre of a box by means of pieces of cotton. China clay mud, plaster of Paris, or any substance which is not combustible is thrown into the box, and the object covered. Plaster of Paris crumbles to powder when heated, but if it be mixed with a little potassium sulphate, alum, or borax, the plaster can be heated to redness without crumbling. When the object is covered with the non-combustible matter, sand is added until the box is full. It is then dried, and the box and its contents heated sufficiently to burn the object to ashes, which are carefully blown out. A place is left as usual for the metal to be poured in.

Dr. Branson's Method.-This method was devised for taking copies of ferns, seaweed, etc. A sheet of gutta-percha is softened in boiling water, put upon a warm metal plate, and dusted over with bronze powder; this dries the surface, makes it smoother, and prevents the specimens sticking to the plaster. A fern is then laid on the top of the guttapercha, then a smooth plate, and pressure applied. The plate is removed when cold, and from the beautiful impression thus prepared a cast is taken in plaster of Paris, and a casting may be obtained in type-metal, brass, etc.

Some articles, such as a pattern for a paraffin lamp-stand, are moulded as follows: The pattern is moulded in wax or plaster, laid upon a board, and an impression of the outside taken. The mould is then inverted and the pattern removed. Parting sand is dusted in, a frame fixed on the top, and an impression taken of the sunken sand-mould. The thickness of the casting is then determined by placing a layer of clay between the two moulds. Each part of the casting is, in this case, of the same thickness throughout.

DIPPING AND PICKLING BRASS

§ 62. The layer of oxide on the surface of brass, which has been heated in contact with air, is removed by dipping in acid liquids and finally swilling in water. The corrosion may be also due to sulphur and other bodies derived from the fuel, and with soldered articles from the fluxes used. It often happens that the incrustation is very persistent, and if it is attempted to remove it rapidly by using strong and hot aqua-fortis, much of the brass is also dissolved producing a very rough surface. For this reason it is preferable to employ at first a weak liquid containing salts of copper and zinc from previous operations, and termed pickle, which slowly removes the surface coating and leaves the metal smooth. Dilute sulphuric acid is also used as a pickle for sheet copper, being slower and more uniform in its action in proportion to the degree of dilution. Nitric acid, which is the chief constituent of aqua-fortis, exerts a more powerfully solvent action on zinc than on copper, so that the surface of dipped brass assumes a warmer tone, shading more or less into a reddish-yellow. To some extent the colour may be varied by using aqua-fortis of different strengths, probably depending on the component metals being dissolved in different ratios by acids of varying densities.

Nitric acid, containing a certain quantity of nitrous acid, is capable of producing different shades of colour. To obtain such a mixture small quantities of organic substances are used for the purpose of generating nitrous fumes, by the action of concentrated nitric acid upon them. Thus saw-dust added to strong nitric acid imparts an orange-yellow colour, due to the partial decomposition of the acid and the formation of nitrous acid.

Dead dipping is the name applied to the process of producing a dead yellow surface on brass-work by dipping in suitable liquids. The work is first pickled in dilute or spent acid until the scale can be removed by rubbing. It is then well swilled and placed in stronger acid, which acts much