When every part is moulded, the box is taken to pieces, and the parts of the pattern are carefully taken out of the sand, for which purpose they are first struck with'a wooden mallet. Each part of the mould is then carried separately to the stove to dry. The stove is a room 12 or 15 feet square, with large iron doors on one side ; the fire is made in a large conical grate placed on the middle of the floor; the smoke issues by an aperture in the brick ceiling. The heat in this stove is considerable, but it mug not be so great as to make the boxes red-hot, for then, by the expansion of the iron, the mould would be 'injured ; the moulds take about 15 hours to dry in this situation. When the moulds are taken out of the stove, their interior surface is painted over with a coat'of blacking, that there may be no adhe. sion between the mould and the metal.
The pieces of the gun-box containing the mould are then taken to the pit, and being carefully placed the one upon the other by the crane, they are put together and secured by their bolts. The mould is placed with the breech undermost ; the axis of the mould is made perpendicular to the horizon by a plumb-line, that the weight of the melted metal may press equably, and not more on one side of the mould than on another. It is not necessary that sand should be rammed round the mould, the box being strong, and its paits firmly bound together, so as to require no additional support. The mould is now in a position for the metal to flow into it through its open end, which is the extremity of the head. Whether the gun is to be of Cie-iron or brass, the construction of the mould is the same.
The pig iron from which the gun is to be made is melted m a furnace, called an air-furnace in the iron-fonnderies, and termed by some authors a re verberatory furnace. The flame of pit coal is car ried by a current of air, so as to play upon the pig iron. The stack of the chimney is 40 feet high. By the pressure of the unrarified external air on the lower part of the rarified column of air in the fur nace and chimney, the current of air through the furnace is produced. The grate G is larger than any other transverse section of the furnace. (See figure next page.) The furnace has three open. ings, one C, for introducing the coals ; the se cond P, which has it„ sliding brick door, with a counterpoise, serves for introducing the p* ire. The third I is for the purpose of stirring the tal, and taking out the melted iron for small cut.
logs by iron ladles coated with clay, and made red-hot. This third opening has a door of fire brick, the joints between the door and the door-frame are lnted. In the middle of the door is a hole, through which the state of the melted metal may be sr. There is likewise a smaller opening T for letting out the melted metal.
The furnace and stack are of brick. The ieterior of the furnace is a coating of fire brick, 9 mho thick, detached and separate from the outer cog, and the other parts of the building, in order that the heat may not melt the common brick of which the outer parts are composed. The fire-brick is made of refractory clay, which, containing little iron, and lit tle or no calcareous matter, burns white, and sustains a great heat without melting. These bricks are made of Stourbridge clay, or of a light blueish grey stratified clay found in the strata that accompany coal. The clay is first ground, the pieces of iron stone picked out, and then made into bricks. In making the interior coating of the furnace, the bricks must be built with moistened fire-clay, and not with lime mortar. The quantity of metal put into the furnace should be equal to the weight of the solid unbored gun with its head, and something more in case of need. It requires a large air-furnace to con tain metal enough for one large gun.
The pig-iron for guns should be grey, that kind having most tenacity.; white pig-iron is too brittle, and so hard that the head cannot be cut off, Tier the gun bored.
A bed of sand N is made in the furnace on which the pig-iron is to be laid. The furnace is heated to a white heat, till the sand is vitrified, which is known to have taken place by touching the surface of the Sand with an iron ringard. The brick door is then lifted up, and the pig-iron is laid on the bed of sand. The heat should be applied so as to produce a spee dy fusion, for if the iron is long exposed to heat be fore melting, a portion of its carbonaceous matter is and it passes from the state of grey cast-iron to that of white. In situations where pit-coal can not be had, wood may be used in the air-furnace, but the heat given by wood is not so great as that produced by pit-coal. To obtain the most heat that the wood is capable of affording, it should be well dried, cut into small logs, and the logs should 'be placed with their end upon the grate.