The tube drawn for thermometers and barometers is cut into suitable lengths, and passed on to the lamp-worker, who inserts the mercury and seals the ends. The " lamp " is a combination of a gas-jet, an air-jet, and a foot-bellows, or of a gas-jet and a mouth blow pipe. Tube or cane is speedily rendered ductile by the intense heat of the blow-pipe flame, and can be readily manipulated. The lamp-worker prepares from tube some of the most delicate apparatus used in scientific research. A variety of goods for domestic and medical purposes, e. g. syringes, globule-bottles, vaccine-tubes, breast-glasses, &c., are made at the lamp from the same source. Cane is used in oonj unction with tube in the manufacture of many useful and ornamental objects. Coloured canes are used to a considerable extent for imitating the decoration so common in Venetian vases. From cane, or in fact any solid glass, rendered dnotile by the heat of the blow-pipe flame, a thread may be drawn out, which, if attached to a rapidly revolving wheel, may be indefinitely extended. In this way, spun glass is made. In order to render the thread more durable, it is annealed by heating the wheel upon whioh it is being wound!' In Austria, spun glass has been pressed into the service both of science and of decorative art ; it is used in the laboratory for filtering acids, and appears in the drawing-room as a permanent substitute for silk and feathers. Some ornamental processes during manufacture are :—(1) Upon the surface of a vessel in course of manufacture, small drops or seals of molten coloured glass may be fixed, and may he pressed hy moulds into the form of stars, gems, &c. (2) A small quantity of molten glass is gathered upon the end of a working-rod, and allowed to lengthen by the force of gravity ; the free end is attached to some point on the body of a vessel in course of manufacture, and the vessel is rapidly rotated, thus a thread is evenly coiled around the vessel. A machine is uow being used for causing the vessel attached to the blow-pipe to revolve more evenly and rapidly than can be effected by the unaided skill of the workman. (3) If, after the first gathering, the bulb of white glass be dipped into a crucible containing coloured glass, a vessel may he formed with a coloured casing. In preparing coloured glasses for casing, great care must be taken that they shall neither be harder nor softer than the white metal, or the vessel formed is sure to crack. (1) If a bulb of molten glass be rolled upon variously coloured powdered glasses, flakes of mica, or leaves of gold, silver, or platinum, it will adhere to them, and, by continuous rolling, will amalgamate with them. Very beautiful effects of colour may be obtained in vessels made from glass prepared as described. (5) Iridescence, which is due to inequality of surface, may be produced by the action of an acid, or of the fumes of chloride of tin, upon the surface of glass. The glass, whilst hot, is subjected to the fumes of chloride of tin, during manufacture. Any acid process must take place after the glass is annealed and cold. To effect iridescence, weak solutions of hydrofluoric or hydrochloric acids may be used. In the latter case, the process takes place in heated air-tight vessels. (6) Glass vessels may be frosted hy plunging them, whilst still red-hot, into cold water, and afterwards reheating them. (7) Etchings in gold-leaf may be introduced into the substance of a vessel in the following manner. The gold-leaf is floated on to a thin plate of glass, and etched. The plate of glass is heated, and a mass of molten glass is dropped upon the surface of the gold-leaf, and adheres to the thin plate of glass through the pores in the gold. The molten mass may be fashioned in the glass-house, or by the cutter.
Cutting.—Annealed glass vessels may be subjected to a variety of processes after they have become cold. The mark of fracture left at the base of a blown-glass vessel by the working-iron, is removed by pressing it upon the edge of a swiftly-revolving stone wheel. After the inequality is removed, the roughness is polished away by substituting a wooden wheel for the stone one. Cutting and engraving are modified forms of the same process. The difference of effect lies in the greater depth of incision produced in cutting. In either process, lathes are used, in which the glass is pressed against the cutting-tools, instead of the cutting-tools being pressed against the glass. The cutting-tools are wheels revolving rapidly in a perpendicular plane. In cutting, the lathes are driven by steam, and the cutting-wheels are of considerable dimensions. The actual cutting is performed by iron wheels supplied from hoppers with sand and water. The incisions produced by iron wheels are smoothed by stone wheels supplied with water, and are polished by wooden wheels supplied with water and emery-powder, putty-powder, pumice, or rouge. For engraving, the lathes
are usually worked by foot-treadles, and the wheels are of copper, and in some cases do not measure more than I- in. in diameter. In engraving, it is customary to leave the pattern rough, and the ground clear ; this arrangement, however, may be reversed, by polishing the pattern with leaden wheels supplied with oil and rouge, and by previously roughening the ground. Specimens have lately appeared with polished patterns upon a clear ground, and the effect is decidedly pleasing.
Stoppering.—In stoppering a bottle, there are two processes : (1) The mouth of the bottle is opened to the required size by a steel cone revolving in a lathe; (2) the stopper is fixed in a wooden chuck, reduced to proper dimensions, and finally ground into the mouth of the bottle.
Roughening.—This may be produced by the recently invented sand-blast process, based upon the principle that if a stream of sand be made to fall through a vertical tube open to the air at the top, and the falling sand and air he received in a suitable closed vessel below, a jet or current of com pressed air can be obtained. The entire surface of a vessel may thus be roughened, or, if parts are protected by a suitable medium, only tbe exposed portions will be abraded. By this means, very delicate patterns may be produced. Glass may be etched by the action of hydrofluoric acid, either in solution or in the form of gas. The parts of the vessel which are required to remain clear must ho coated with wax, and the vessel be exposed to the fumes of the gas, or dipped into the solution. The variety in depth of incision, which gives the chief beauty to engraved glass, cannot be gained by either of these processes.
In the British Section at the Paris Exhibition, 1878, were exhibited some specimens of carved glass composed of two layers of glass, namely, a white upon a darker base. The carver had removed with his chisel parts of the upper white orust, and discovered, or partially discovered, the dark ground below ; in this manner, were produced designs of the greatest beauty.
Imitation Jewels.—The property of glass to display a variety of tints by the addition of metallio oxides, is made use of for the production of artificial gems (see Gems—Artificial). The percentage composition of the base used is 38.10 ; 7.90 ; PbO, 53.00 ; . For the colouring agents used in imitation of precious stones, compare Coloured Glass.
Bottle-Glass.—The manufacture of moulded bottles depends upon the principle that a mass of moulded glass, expanded by the breath, will take the shape, externally as well as internally, of a resisting environment. It is essential that a moulded bottle shall he cheap, strong, and capable of resisting tbe corrosive action of any liquid which may be placed in it for preserva tion. Those essentials may be gained by great economy in manufacture, great care in mani pulation, and by a scientific) combination of the raw materials. Economy of manufacture depends on the position of the manufactory, on the power of obtaining the greatest result from the consumption of the smallest quantity of fuel, and on the utilization of waste products in the com position of the glass. Bottle-manufactories are, as a rule, placed within a short distance of coal bearing strata, and have easy access to water-carriage. It is also a considerable advantage if sand, suitable for glass-making, can be obtained in the vicinity of the works. The consumption of fuel is mainly regulated by the construction of the furnace. The ordinary furnace for bottle-making is oblong, with openings at the angles, to allow the flame to pass from the main structure into four subsidiary ovens, containing the mixture of the raw materials. By this arrangement, the mixture will have already undergone partial fusion, before it is placed in the working-crucibles. The absence of oxide of lead from the composition of common bottle-glass permits the use of open crucibles, in which fusion is effected more quickly than would be the case if the crucibles were even only par tially covered. The form of the crucibles, except in this particular, varies in different manufac tories. Large reservoirs or tanks seem, however, to be best suited. The combination of gas-furnace and tanks, introduced by Dr. C. W. Siemens, is in every respect admirably adapted for the produc tion of bottle-glass. On the old system, a crucible, when emptied and recharged, is useless for all working purposes, until the fusion of the fresh charge is completed, i. e. for some 18 hours.