magnesia, is too weak or too close-that is t retain its form, or it will cause the metal closeness, the gases not having a free means o the oxide of iron is greater than the above sand is liable to fuse, and unite with and bl of the casting, generate gases, and cause b metal. Different kinds of castings require

of sand.

One class necessitates the use o yet adhesive sand; in another the sand mu free from grit, and very adhesive, so as to finest parts of the pattern.

The best moulding sand is often found a of large rivers, in the vicinity of granite or sl or in coal districts, where the river flats are la of sand. In such localities it sometimes con oxide of iron, and is liable to melt; but this m by mixing it with coke-dust. Kampmann sta sand for moulds may be artificially made from mixture:

A valuable casting sand is obtained from sandstone at Birmingham. The value of this sand at the Old Cemetery was estimated sterling.

Core-sand. This sand should be coarse, pc adhesive, such as rock-sand, the fine material rocks; free-sand from river-banks, or from and pounded blast-furnace cinder, etc., are oft fine, strong sand, and a little clay to make it each case fresh sand must be used for a core. burnt sand, or sand mixed with coal is not ad part of clay mixed with nine parts of free-sand strong for small and simple cores, but for la plicated ones a stronger sand is required.

Parting-sand.-A substance which does not retain moisture is required for this purpose. Red brick-dust i preferred, but free-sand, sea and river sand, and blast-furnace cinder are also used.

Facing-sand.-If molten metal is allowed to come ir immediate contact with some kinds of fresh sand, a surface fusion of the sand takes place, with consequent roughness of the casting. If the raw sand is too coarse the metal wil penetrate the sand to some extent, and also produce a rough casting. To avoid this defect the sand is coated with carbon or carbonaceous matter in the form of fine dust. Carbon and coal dust do not adhere well to old sand, so that in such a case the mould is first dusted with pea-flour and then with charcoal. Charcoal powder is also mixed with one-tenth of its volume of fine sand, and used as a facing for small castings.

The success in casting is not only dependent on the manipulative skill of the founder, but also on that of the pattern-maker. If a wood-pattern is required, pine, mahogany, oak, and other kinds of wood are sometimes used. In the brass trade boxwood is most commonly employed. The pattern is made larger than the size of the required casting, about inch per foot being allowed for shrinkage and finishing. Patterns with their edges at right angles do not leave the sand without disturbing the impression, so that they are made to taper in the parts which enter the sand. Sharp angles in a pattern should be avoided as much as possible, as they leave an edge of sand which is liable to break off on removing the pattern, and produce a defect in the casting. Such a defect in the mould is remedied by mending the broken places with sand before pouring. Wood patterns should either be varnished or brushed with black-lead to prevent absorption of moisture, and enable them to part from the sand more freely. Bees-wax o plaster of Paris is used for stopping up holes and cracks in the wood. It often happens, when a permanent pattern is required, that a metal pattern is cast from a wooden one

and the former then used as a pattern fr In such a case the wood

are obtained. made much larger than the finished art sequently produced, are required. This is double shrinkage, and for the dressing of Sometimes patterns must have pegs of enable the caster to lift them easily o Besides wood and metal, casting patterns a clay, plaster of Paris, or wax.

Moulding-sand is kept in position by

parts, as represented in Fig. 25, where A is B the lower frame; or they may be term and the eye-side respectively. In addition shown in the figure, a third frame is often u odd-side, which is subsequently described.

§ 58. To make the odd-side.-The sand i with water, and passed through a rough si five meshes to the linear inch. It should be black or old sand does not hold together sand, the black sand containing burnt flour brick-dust; and probably the sharp edges of sand are partly worn off by frequent use, wedged so firmly together. If black sand o castings are liable to be blown, the mate sufficiently porous to allow the air and other

The moulding is commenced by placing one often termed the she-side, on the top of a f dusting the inside with parting sand, then ad

The sand is ramm hands, then with t

sand, and filling up with black sand. down tightly with the palms of the knuckles, and finished with a mallet. The surface is ne scraped level with a straight-edged piece of wood, a boa placed on the top, and the whole frame with its conten inverted.

The patterns are now carefully laid on the mould and t dust bag shook over them; this will leave a clear outline the patterns upon the sand, which is then cut away in ord to let them in half-way. The "odd-side," which is alwa the "peg-side," is now fixed to the lower frame, parti sand added, and then a mixture of raw sand and bla sand, and finally black sand to complete the mould as befor The facing-sand, which is sometimes mixed with black san half and half, must be pounded in a mortar and pass through the meshes of a fine sieve. The odd-side must rammed down as tightly as possible, as upon the compactne of the sand the future success of the operations depends. board is then placed on the top and the "flask” turned ove The board which now forms the top is hammered to loos the patterns, and the "she-side" taken off and broken up. The "odd-side" contains the patterns, and is now read to mould from. A frame is fixed to the "odd-side," sa pressed in as before, then covered with a board, and t whole inverted. The patterns are then loosened hammering the top board, and the odd-side, which no contains perfect impressions of half of each of the pattern is removed, leaving the patterns in the she-side. A fram containing pegs is now fixed to the she-side, sand added a pressed as before. This peg-side is then removed and plac aside, leaving the patterns in the "she-side." The "odd-side is then placed on the "she-side," the flask again inverte the patterns loosened with the hammer, and the she-si removed, leaving the patterns in the "odd-side" ready start again. It will thus be seen that the "odd-side " used over and over again to make other moulds from, group of five to six moulds constituting a heat. About s

heats of common brass work would be cons work. The number of moulds constit regulated, however, by the size of the cru of the castings.

Before the molten metal is poured in, from the patterns in the sand must be d principal ingates or channels by which the the mould, the sand being scooped out by termed a "drawer." This operation, alth simple, really requires much judgment especially in large work, in order to obta amount of metal to feed the impressions. generally made on the "she-side," but son employed on both the "she-side" and " cores are generally laid in the peg-side work the metal is poured into the moulds wh state, the impressions having been previous flour or charcoal.

§ 59. Fine Work. For fine castings th being made, are dried before a fire, previous then dusted with powdered charcoal. For one side of the mould is dried. For very de face of the mould is smoked with a torch con In this case, after drying and torching, the again brought in contact with the pattern screwed up, and the soot being in a very finel the impression is brought out clear and shar uses a clayey sand, termed "loam," to mix wi sand for fine work, and for that reason the m well dried. By the use of loam the cha corners of the impressions hold together better is used facing sand is necessary, and this be porous nature than loam sand, permits the gas to escape when pouring, and thus prevents blo work.

When moulding thin scrolls, or when the