considered impossible to use iron moulds for plate-casting, as, through inexperience and ignorance of the conditions necessary for success, the castings very frequently turned out to be failures. Loam moulds were sometimes used, but, as they readily break, much trouble was experienced. For small work moulds of sand, thoroughly dried, were employed in some foundries; but sand is liable to crack and injure the plate of metal. For the most part granite moulds were used, and were considered to yield the best results. The preparation of granite moulds requires great care; it is requisite to line them with a thin coating of clay, which must be kept in such a condition as to insure the greatest uniformity of surface of the plates. The clay coating was covered with a thin layer of cow-dung to prevent it cracking. Brannt gives the following description of the method: "The prepared granite moulds are arranged in the following manner. The upper plate is suspended over the lower one, the space or mould between the two being limited by iron bars laid on the lower stone, which is a little longer than the upper one, and projects to the front, so as to form a lip or mouthpiece for receiving the metal. The plates are bound together with iron, and raised on one side so that they stand at an angle of 45° while the metal is run in. As soon as the casting is finished, and the metal is supposed to be solidified, the sheet of brass is carefully taken from the mould. With sufficient precautions such granite moulds can be used for a long time without the coating of clay being damaged, and the sheets turn out very uniform after the mould has once been heated by several castings. One and the same mould is frequently used continuously in order to keep it warm, and if it has to stand empty for some time, it is enveloped in a bad conductor, such as a coarse carpet, to prevent its cooling. If the mould is damaged it must be carefully mended, and the mended places sharply dried to prevent cracking." Plate brass after casting is carefully inspected, and subjected to a mechanical cleansing previous to rolling. During the rolling process the brass becomes hardened, and requires occasional annealing. As annealing blackens the metal, due to the formation of oxide, it is advisable to cleanse it in a bath of dilute sulphuric acid and scour with sand if necessary, and lastly to well swill in water. Sheet brass is annealed in a reverberatory furnace represented in section and plan, Figs. 21, 22. The furnace is so constructed as to prevent oxidation of the metal as much as possible. The fire-bridge a is high, and the charging door b is at the front. The waste gases and heat are drawn off by the flue c. To facilitate the introduction and withdrawal of the sheets a roller d is arranged at the front of the charging door, and on the bed itself are movable cast-iron bars e e, which favour the sliding in of the sheets. They also assist in the heating by isolating the sheets from the brickwork of the bed. Annealing furnaces, heated by gas from Wilson's gas producers, have been worked for some years in Lancashire with economical and advantageous results. Experience has now been gained, and it is stated that the sheets come out admirably in colour and condition of surface. After passing through the rolls, sheet brass may require to be left soft and flexible, or hard and elastic. For soft brass the sheets are finally annealed. For hard brass the metal is passed through the rolls two or three times after the last annealing. Plate brass intended for wire is first rolled to a certain gauge to obtain the requisite thinness. This preliminary rolling is not only advantageous in obtaining metal of a certain thickness, but the mechanical treatment imparts to the brass greater strength and ductility than if the metal were cast of the desired size for the slitting rolls, without first passing through the flat rolls. The sheet metal is first cut into strips, and then the strips are cut into rods by means of slitting-rolls. These consist of spindles carrying steel discs, fixed at suitable intervals. They are so arranged that the discs on the upper spindle project into the spaces of the lower series, and when revolving form a rotatory shearing-machine. On inserting one end of the brass strip between the guides it is drawn forward by the shearing discs, and cut into rods, which, if necessary, are afterwards cut to length. The exceedingly thin sheet-metal or leaf, known as Dutch metal, is not produced entirely by rolling, but by a combination of rolling and hammering. The metal is cast in thin plates and reduced to a certain thickness by rolling until a thin ribbon is obtained, frequent annealing being requisite. The ribbon is then cut into portions about one inch square, and a large number of these are piled on the top of each other, each piece being separated by a sheet of specially prepared tough paper, the whole forming a packet enclosed in parchment. The packet is then hammered on a block for some time with a heavy hammer, until each piece of metal is extended to sixteen times its former dimensions. These sheets are each cut into four, and the pieces so obtained made into a packet as before, except that a layer of goldbeaters' skin is placed between each sheet, and the beating repeated as before until the requisite degree of thinness is obtained. Careful annealing at certain stages of the process is requisite to prevent the sheets of metal cracking. § 55. Ingot Casting.-In casting ingots of brass, which have to be subsequently remelted, less care is required than with plate-casting, but when the metal is employed for casting various articles in sand moulds, equal care is absolutely necessary. Crucibles are invariably used for mixing and melting brass for the above uses, and the metal poured directly from the crucibles into the moulds. Brassfounders' melting-pots are made of plumbago mixed with fire-clay and coke-dust in varying proportions, a description of which has already been given. These crucibles, although more expensive than clay ones, are much more durable and stand a greater number of meltings, so that they are now most generally used. § 56. Air-drying Stove. The flue from the casting furnaces is generally used for heating the stove, and so constructed as to pass underneath the drying stove, Fig. 23. Where such an arrangement is not convenient an ordinary fire-grate is employed. The flue in both instances passes under the stove, and the arch is constructed of specially shaped fire-bricks, as shown in Fig. 24. The size of drying stoves varies according to the requirements. Those used for drying cores for tube-casting are generally 6 feet long, 4 to 5 feet wide, and not less than 6 feet high. The bottoms are made of cast-iron plates, 1 inch thick, and |