While this is doing, a deep pit is dug, and into this the core is let down by a crane; when this is done, the mould is lowered over the core; as soon as the adjustment is perfected, sand is thrown in and rammed round about it, to about the half of its height; after which a flat cover of dried loam is put on the top of the mould and core, and pieces of rounded wood are put into the holes, which had been before made for pouring in the metal. The plugs which keep open these holes are carefully taken out, and small channels prepared for the metal to run through from the furnace. Before the metal is run into the mould, the latter should be carefully examined, to ascertain that it is quite dry, and in other respects in a perfect condition to receive the metal. Sand, or open casting, is used for such articles as will allow of cutting into two pieces, or even more, the models of which are indented in the sand, and the metal is run in between flasks.

A patent for an improved mode of casting metallic cylinders was taken out in 1826 by Mr. William Church, of Birmingham, the object of which was to produce perfectly sound castings of uniform solidity. The process consists in exhausting the air from the moulds by means of an air-pump, and afterwards in forcing the fluid metal, from an air-tight reservoir beneath, upwards into the mould by the aid of a condensing pump. As the apparatus for this purpose may be constructed in a variety of ways, and be adapted to the description of articles to be cast, the patentee has described only one arrangement, which he adopts and recommends for the purpose of casting large cylinders, rollers, cannon, etc. The mould prepared for casting is enclosed in a cast-iron airtight casing, and suspended in a vertical position, by means of chains, to the jib of an ordinary crane, over the vessel containing the fluid metal; to the lower end of the mould, an earthen tube (the materials similar to the crucible ware,) descends and forms the channel for conveying the metal upwards into the mould at the proper period of time; this earthen pipe is covered with a cap at its lower extremity, which is luted to it so as to be air-tight, and the material and thickness of the cap is such that it will melt a short time after being immersed in the fluid metal.

As soon as the metal has arrived at the proper temperature the suspended mould, with its appendage, as before mentioned, is lowered by means of the crane, so that the earthen tube is immersed into the liquid metal in the chest beneath; this metal chest is then closed air-tight with a flange fixed on the upper part of the earthen tube, by proper contrivances for that purpose, such as a conical rim, an elastic metal hoop and luting; the perfect closing of which is effected by the pressure of the mould in its descent to its seat on the top of the metal chest. The apparatus so far prepared is next connected by short pipes with union joints, to pipes leading from an air-pump of large dimensions, which both exhausts and condenses. First, the air is exhausted from the mould, and from above the surface of the melted metal in the chest; by this time the cap of metal at the lower end of the earthen tube becomes fused, the fluid metal ascends that tube, and is then forced by the condensing operation of the air-pump into the mould above, which, being previously exhausted, the metal is uniformly pressed into every cavity.

As the vacuum in the mould is of course imperfect, from the previous exhausting operation, and the remaining portion of air becomes condensed by the rising of the metal, to prevent any ill effects from its pressure, a stop cock, communicating with the exhausting end of the air-pump, is opened, by which it is withdrawn. For the purpose of rapidly cooling the mould after being filled with the liquid metal, the cast-iron mould case is surrounded with an outer case or jacket, with a vacant space between, which is charged with cold water whenever desired, as in some castings this application must be of great utility in hardening their surfaces.

In 1825 a patent was taken out by Messrs. White and Sowerby for an air furnace for melting iron, for the use of founders, in which the requisite degree of heat is obtained without the necessity of resorting to mechanical aid, but simply by the production of natural currents of air through lateral openings or passages, with the further advantage of causing a body of flame to be conducted over that portion of the metal lying in a fluid state at the bottom of the furnace, by which it is kept from solidifying prior to the whole contents being discharged. On these principles the patentees state that the furnaces may be made square, round, oval, octagonal, or any other convenient form, with passages for the admission of atmospheric air in various parts and in different directions, according as they may be required to direct the heat. The annexed figures are intended to illustrate one convenient mode of carrying it into effect a represents the body of the furnace, in which the coke and metal is deposited; b and c are flues leading from the same into the vertical chimney d; the capacity or depth of the flues is regulated by dampers e e; f f show the situation of two of the lateral air chambers, (of which there may be any number;) one of these is shown as opening into the outside of the structure, and the other into an open archway or passage between the chimney and the body of the furnace; a man hole, for clearing out the bottom or bed of the furnace whenever required, is situated at g.

To set the furnace to work, the cover h is removed, and coke or other fuel thrown in, which may be lighted, if required, at either of the air passages f f; when the heat has been raised to the proper degree for the fusion of the iron, the metal and coke are thrown in alternately, in such quantities and proportions is may be required for the casting, when the furnace is again to be closed by the cover h. When the whole of the metal is reduced to the fluid state, it is run off from the bed by means of a tap hole in the lower part By the arrangement of the furnace, it will be perceived that a body of flame is made to operate upwards in melting the metal, and another takes a downward course, passing over the bed of the furnace, preserving that portion of the metal which has been already melted, and lying upon it, in a fluid state, until the whole contents of the furnace are melted.