When the casting is completed it is of course allowed to remain undisturbed until the iron has had time to cool, and then the whole mass is to be dug out of the pit in which it is imbedded. So much heat, however, still remains in the iron and in the sand surrounding it, that the mould itself and the twenty or thirty men engaged in disinterring it, are enveloped in dense clouds of vapor which rise all around them while the operation is proceeding. [Illustration: DIGGING OUT THE CYLINDER.] It is necessary that the sand which surrounds these moulds should be rammed down in the most compact and solid manner to sustain the sides of the mould and enable them to resist the enormous pressure to which it is subject, especially in the lower portions, while the iron continues fluid. In the case of iron, the weight of four inches in height is equivalent to the pressure of a pound upon the square inch. In a pit, therefore, eighteen feet deep, as some of the pits at this foundry are, we should have a pressure at the bottom of fifty-four pounds to the inch. Now, in the most powerful sea-going steamers, the pressure of steam at which the engines are worked, is seldom more than _eighteen_ pounds to the inch; that of the Cunard line is said to be from twelve to fifteen, and that of the Collins line from fifteen to eighteen. In other words there is a pressure to be resisted at the lower ends of these long castings equal to three times that at which the most powerful low pressure engines are worked, and which sometimes results in such terrific explosions. When the cylinder is freed from the pressure of the sand around it, in its bed, the great iron cross by which the mould was lowered into the pit, as seen in the engraving of the Casting, is once more brought down to its place, and the stirrups at the tops of the iron rods seen in the engraving below, are brought over the ends of the arms of the cross. The lower ends of these rods take hold of a frame or platform below, upon which the whole mould, together with the cylinder within it, is supported. The arm of the crane is then brought round to the spot. The hook pendant from it is attached to the ring in the centre of the cross, and by means of the wheels and machinery of the crane, the whole is slowly hoisted out, and then swung round to some convenient level, where the ponderous mass is freed from its casing of masonry, and brought out at last to open day. It is then thoroughly examined with a view to the discovery of any latent flaw or imperfection, and, if found complete in every part, is conveyed away to be the subject of a long series of finishing operations in another place,--operations many and complicated, but all essential to enable it finally to fulfill its functions.