These casts, or jets, are all terminated with a kind of plugs, which are kept .close, that, upon opening the furnace, the brass, which gushes out with violence, may not enter any of them, till the basin be fiill enough of matter to run into them all at once. Upon which occasion, they pull out the plugs, which are long iron rods, with a head at one end, capable of filling the whole diameter of each tube. The whole of the furnace is opened with a long piece of iron, fitted at the end of each pole, and the mould filled in an in stant. This completes the work in rela tion to the casting part ; the rest being the sculptor's or carver's business, who, taking the figure out of the mould and i earth wherewith it is encompassed, saws the jets with which it appears cover i ed over, and repairs it with chisels, gra vers, puncheons, &c. FOUNDERY of bells. The metal for bells has already been described. See BELL. The dimensions of the core, and the . wax, for bells, W a ring of bells especially, are not left to chance, but must be mea sured on a scale, or diapason, which gives the height, aperture, and thickness ne cessary for the several tones required. It is on the wax that the several mould ings, and other ornaments, are formed, to be represented in relievo on the outside of the bell.
The business of bell-foundery is re ducible to three particulars : the propor tion of a bell ; the forming of the mould; and the melting of the metal.
The proportions of our bells differ much from those of the Chinese : in ours the modern proportions are, to make the diameter fifteen times the thickness of the brim, and twelve times the height.
There are two kinds of preparation, viz. the simple and the relative : the for mer are those proportions only that are between the several parts of a bell, to render it sonorous ; the relative propor tions establish a requisite harmony be tween several bells.
The particulars necessary for making the mould of a bell, are, 1. The earth ; the most cohesive is the best : it must be well ground and sifted, to prevent any chinks. 2. Brick-stone ; which must be used for the mine, mould, or core, and for the furnace. 3. Horse-dung, hair, and hemp, mixed with the earth, to render the cement more binding. 4. The wax for incriptions, coats of arms, &c. 5. The tallow, equally mixed with the wax, in order to put a slight lay of it upon the outer mould, before any letters are ap plied to it. 6. The coals to dry the mould.
For making the mould, they have a scaffold, consisting of four boards, ranged upon tressels. Upon this they carry the earth, grossly diluted, to mix it with horse dung, beating the whole with a large spatula.
The compasses of construction is the chief instrument for making the mould, which consists of two different legs, join ed by a third piece. And last of all, the founder's shelves, on which are the en gravings of the letters, cartridges, coats of arms, &c.
They first dig a hole of a sufficient depth to contain the mould of the bell, together with the case, or cannon, under ground ; and about six inches lower than the terre-pleine, where the work is per formed. The hole must be wide enough for a free passage between the mould and walls of the hole; or between one mould and another, when several bells are to be cast. At the centre of the hole is a stake erected, that is strongly fastened in the ground. This supports an iron peg, on which the pivot of the second branch of the compasses tarns. The stake is encompassed with a solid brick-work, perfectly round, about half a foot high, and of the proposed bell's diameter. This they call a mill-stone. The parts of the mould are the core, the model of the bell, and the shell. When the outer surface of the core is formed, they begin to raise the core, which is made of bricks that are laid in courses of equal height upon a lay of plain earth. At the laying each brick they bring near it the branch of the compasses, on which the curve of the core is shaped, so as that there may re main between it and the curve the dis tance of a line, to be afterwards filled up with layers of cement. The work is con tinued to the top, only leaving an open ing for the coals w bake the core. This work is covered with a layer of cement, made of earth and horse-dung, on which they move the compasses of construction, to make it of an even smoothness every where.
The first layer being finished, they put the fire to the core, by filling it half with coals, through an opening that is kept shut during the baking, with a cake of earth, that has been separately baked. The first fire consumes the stake, and the fire is left in the core half, or sometimes a whole day : the first layer being tho roughly dry, they cover it with a second, third, and fourth ; each being smoothed by the board of the compasses, and tho roughly dried before they proceed to another.
The core being completed, they take the compasses to pieces, with intent to cut off the thickness of the model, and the compasses are immediately put in their place, to begin a second piece of the mould. It consists of a mixture of earth and hair, applied with the hand on the core, in several cakes that close toge ther. This work is finished by several layers of a thinner cement of the same matter, smoothed by the compasses, and thoroughly dried, before another is laid on. The first layer of the model is a mixture of wax and grease spread over the whole. After which are applied the inscriptions, coats of arms, &c. besmeared with a pencil dipped in a vessel of wax in a chafing-dish : this is done for every let ter. Before the shell is begun, the com passes are taken to pieces, to cut off all the wood that fills the place of the thick ness to he given to the shell.