It is then removed, and placed on a rest or casher-box, when a small purity of melted glass at the end of a poirdel is is brought by a boy; this the workman applies to one side of the cylinder, just below the shdulder formed at the blow pipe end ( fig. 4, g), and drawing it out to a thin string, wraps it quickly so as to draw a line round the cylinder; after a second or two; he withdraws this line of red-hot glass, and touching it quickly with his cold shears, the shoulder and neck drop off as neatly as if cut with a diamond.
The cylinder (fig. 4, It) is now placed for a short time in the annealing oven (b, fig. 3), where it is prepared for cutting; it is next placed in a groove lined with green baize, and a diamond fixed to a sliding rule makes a perfectly straight cut from end to end. The split cylinder is then taken to the flattening arch or furnace, where it is laid on the bottom, with the diamond-cut upwards. The bottom is a perfectly smooth stone, kept constantly free from dust by the workman; here the beat is sufficient to soften without melting the glass, and the as it softens, opens the two edges of the crack until they fall outward that on the stone: he then takes an implement in the form of a rake. made by placing a piece of charred wood transversely at the end of a long handle, and this is gently rubbed over the glass, producing a very smooth surface. At the back of the flattening arch is an annealing oven, communicating with the arch by a narrow horizontal slit, through which the sheet of glass is now pushed on to a plate of iron, which receives it; and as this plate is one of a series linked together so as to form an endless band, which can be turned round, the sheets more forward into the annealing oven, where the workman gently lifts them on edge until the oven is filled, when, as in the case of crown-glass, the heat is allowed to decline until perfectly cool, the sheets are then ready for use. Very much larger sheets are obtained by this process than by the former one, hence it is becoming of great importance; but it is not easy to obtain workmen sufficiently powerful and dexterous to blow and twirl the largest-sized cylin ders; at present, we obtain almost all the operatives so employed from Belgium.
Glass-shades are made in the same manner as above described; indeed, they are nothing more than the rounded ends of the cylinders before being burst. When wanted oval or square, these forms arc produced by boxes of wood charred inside, of the size the shades are required, through which the cylinder is passed when being blown, until the soft glass touches, and receives shapes from the inside of the box or mold: they are afterwards annealed, and cut to the lengths required. If of large diameter, they require immense strength and great' skill in the 'operator, who sometimes aids the power of his breath by taking into.his mouth a little spirit, which he blows down the pipe; tins is instantly coverted into vapor when it reaches the red-hot cylinder, and aids iu distending the glass. Mechanical blowers have been tried successfully in Belgium.
is made in a totally different mariner; and, as its value depends chiefly on its purity, the greatest possible care is taken to procure materials of the best quality, and almost every manufacturer has his own private formula for the mixture. It may, howevei, be said to consist chiefly of sand and alkaline salts, as in other kinds of glass, and the following is one receipt known to be in use: Fine white sand well washed, to free it from impurities, 720 lbs.; sulphate of soda, 450 lbs.; slacked lime, 80 lbs. nitrate of potash, 25 HA ; and millet of plate-glass. 425 ibs. These ingredients, when melted and skimmed, should yield about lbs. of perfectly clear metal, which is the quantity usually required for a casting. When melted and ready for use, the pot is lifted out of the furnace by means of the forceps, and wheeled up to the casting-table; here it is seized by a crane and tackle, by which it is lifted, and so nicely poised over the table, that it can be easily tilted so as to pour out its contents. All this requires so much care and steadiness, that the men impressed with the great danger of carelessness, usually preserve perfect silence during .their "work. The table is of large size-20 ft. or more in length, by 8 or 10 ft. in When the red-hot liquid glass is poured on, it immediately begins to spread; two bars of iron, a little thicker than the plate is intended to be, are quickly laid on each side of the table, and a steel roller is laid across, resting on these bars; this roller is worked by hand, and rapidly spreads the glass all over the table, the bars preventing it from running over the sides, and regulating its thickness: In a very short time it begins to cool; the men then seize the end of it with pincers, and pull it forward with great dexerity on to an endless band of wire-gauze, which, being made to revolve, moves the immense plate forward to a slit-like opening to•the anneal ing oven, where it is worked on to another table on wheels, which is pushed forward to make room for another. The annealing oven is usually of immense length, as, in the case of plate-glass, the sheets cannot be set on edge. At the works at St. Helen's in Lancashire, where glass of all kinds is extensively made, there are usually two annealing ovens to each 'shed, the furnaces being placed between them; each oven runs to the end of the shed, and these sheds are usually over BOO ft. in length. The main building is a shed, with the doors at each end, and both doors and windows are made so as to exclude drafts of air, which, if admitted during the operation of casting, are highly injurious to the quality of the manufacture.