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.

Shee

brass is annealed in a reverberatory furnace represented in section and plan, Figs. 21, 22. The furnace is so con structed as to prevent oxidation of the metal as much a possible. The fire-bridge a is high, and the charging doo b is at the front. The waste gases and heat are drawn of by the flue c. To facilitate the introduction and withdrawa

of the sheets a roller d is arranged at charging door, and on the bed itself are n bars e e, which favour the sliding in of th also assist in the heating by isolating the brickwork of the bed.

Annealing furnaces, heated by gas from producers, have been worked for some year with economical and advantageous results. now been gained, and it is stated that the s admirably in colour and condition of surface.

After passing through the rolls, sheet bra to be left soft and flexible, or hard and ela brass the sheets are finally annealed. For metal is passed through the rolls two or th the last annealing.

Plate brass intended for wire is first rolle gauge to obtain the requisite thinness. Th rolling is not only advantageous in obtainin certain thickness, but the mechanical treatme the brass greater strength and ductility than were cast of the desired size for the slitting first passing through the flat rolls. The sheet cut into strips, and then the strips are cut means of slitting-rolls. These consist of spin steel discs, fixed at suitable intervals. They a that the discs on the upper spindle project in of the lower series, and when revolving for shearing-machine. On inserting one end of th between the guides it is drawn forward by discs, and cut into rods, which, if necessary, a cut to length.

The exceedingly thin sheet-metal or lea Dutch metal, is not produced entirely by rolli combination of rolling and hammering. The in thin plates and reduced to a certain thickne until a thin ribbon is obtained, frequent ann requisite. The ribbon is then cut into portions

inch square, and a large number of these are piled on the to of each other, each piece being separated by a sheet specially prepared tough paper, the whole forming a packe enclosed in parchment. The packet is then hammered o a block for some time with a heavy hammer, until each piec of metal is extended to sixteen times its former dimension These sheets are each cut into four, and the pieces so obtaine made into a packet as before, except that a layer of gold beaters' skin is placed between each sheet, and the beatin repeated as before until the requisite degree of thinness obtained. Careful annealing at certain stages of the proces is requisite to prevent the sheets of metal cracking.

§ 55. Ingot Casting.-In casting ingots of brass, whic have to be subsequently remelted, less care is required tha with plate-casting, but when the metal is employed fo casting various articles in sand moulds, equal care is al solutely necessary. Crucibles are invariably used for mixin and melting brass for the above uses, and the metal poure directly from the crucibles into the moulds. Brassfounder melting-pots are made of plumbago mixed with fire-cla and coke-dust in varying proportions, a description of whic has already been given. These crucibles, although mor expensive than clay ones, are much more durable and stan a greater number of meltings, so that they are now mo generally used.

§ 56. Air-drying Stove. The flue from the castin furnaces is generally used for heating the stove, and constructed as to pass underneath the drying stove, Fi 23. Where such an arrangement is not convenient a ordinary fire-grate is employed. The flue in both instance passes under the stove, and the arch is constructed specially shaped fire-bricks, as shown in Fig. 24. The siz of drying stoves varies according to the requirements. Tho used for drying cores for tube-casting are generally 6 fe long, 4 to 5 feet wide, and not less than 6 feet hig The bottoms are made of cast-iron plates, 1 inch thick, an

perforated with inch holes to allow the wards from the flue.

The stoves for drying ordinary brassfound similar in construction, with this difference, th

also arranged in them, upon which the cores to

placed.

MOULDING AND CASTING

§ 57. The valuable property of moderate fusibility, whic many metals possess, enables articles of various kinds to b produced from a pattern, by impressing upon sand or othe mobile material a copy of the pattern, and subsequentl pouring molten metal into the cavity thus obtained. Th solidified metal will be an exact counterpart of the impression in the sand.

The term "moulding" is used to signify the various opera tions concerned in preparing the impression to receive th metal, and the term "casting" is applied to the whole opera tion of producing the object, and includes both the moulding and running in the metal. The principal materials used in moulding are:-sand of various kinds, loam, plaster of Paris blackening, pea-flour, etc.

Sand is by far the most common, and certainly the mos perfect and convenient moulding material. The propertie which make it so valuable are its porosity, adhesiveness mobility, practical infusibility, and unalterability. By mean of its porous nature the gases generated during pouring o the metal can freely escape; by its adhesive property perfect impression is produced from any given pattern; the metal is firmly retained when run into the mould; by it mobility it gives way sufficiently, and flows into the fines markings of the pattern when pressure is applied; and in virtue of its non-fusibility and chemical unalterability, the heat of the molten metal does not fuse it, or change it chemical composition. The best kinds of moulding sand employed for casting brass have been found to have a almost uniform chemical composition, varying only in siz of grain or aggregate form. It contains

Sand containing other metallic oxides, such as lime and

L