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Street, Blackfriars, London. The term "flint glass was originally given to this kind of glass, because flints were formerly employed as the silicious material. The materials of flint glass are nearly as follows:-1 part of alkali, carbonate, or nitrate of potash; 2 parts of oxide of lead; and 3 parts of sea-sand. The sand employed is obtained from the sea-shore at Lynn, in Norfolk, and at Alum Bay, in the Isle of Wight. The carbonate of potash is obtained from Canada and the United States; the oxide of lead from our own lead-works.

The most important part of the operations of a glass-house is the crucible or melting pot. These instruments are made from a particular kind of clay, which is found at Stourbridge, in Worcestershire. This is first pounded fine, then sifted moistened, and worked into a thin dough. Some old crucibles are also used, broken into powder, in combination with some red clay. The pots are not moulded, but built up with clay by the hands of the workman, and the quantity of clay used in each is about 1,000 lbs. ; they are, when finished, about 3 feet in height, 2 feet in diameter, and from 2 to 3 inches thick. The shape is nearly cylindrical, with an arched top and a flat base, and the only opening is at the upper part on one side. The furnace houses for the manufacture of plate glass are similar in construction, and of various dimensions. They generally consist of a circular dome, about 15 feet in diameter, and the same in height. All are constructed with brick, and lined with clay, capable of sustaining the greatest heat.

The fuel for these furnaces is laid underneath, on an iron grating, and the flame and heat pass up through arches between the pots towards the dome, roof, and chimney.

Each pot is so placed in the furnace that the mouth shall

be directed outwards; and this projecting mouth is so bricked and clayed round as to prevent the escape of flame. The ingredients to form the glass being dug, mixed, and put into the pots by means of shovels, through the openings already mentioned, about 4 cwt. is put into each pot, the mouth is closed, and the fire is kept burning strongly; but the bulk of the mixture soon decreases by the melting, and, therefore, in about four or five hours, more of the mixture must be added; the mouths of the pots are again opened, and a fresh supply thrown in. This is repeated four times, until the pot becomes fully charged with melted glass. When this is full, the opening through which the charge was introduced is materially essened with wet clay, so that only a narrow hole remains, through which the impurities may be removed, and small portions of the contents may from time to time be drawn for examination. To get at the mouths of the pots, semicircular holes, of about a foot in diameter, are left opposite to and a little above the top of each pot, called working holes, by which the workmen shovel in the materials, and take out the plastic glass.

Immediately upon the materials being placed in the crucibles, the heat of the furnace is raised to its highest point. The contents, after a time, sink down into a soft paste, and become perfectly melted. The glass does not, however, become transparent at first, but loses its opacity by slow degrees; a white porous scum, called sandover, or glass-gall, arises through the mass, which is removed. It is necessary that the whole of this substance should come away before the glass is withdrawn from the pots for use, otherwise articles formed with it will appear cloudy and filled with bubbles. As the process advances,

the glass becomes exceedingly flexible, heavier, and less brittle, and at last the whole is seen to be translucent and colourless, and the vitrification is complete. The temperature is now gradually lowered in the furnace, till the mass is cooled to the heat most proper for its being wrought.

It is almost impossible to enumerate the vast quantity of articles made from this description of glass. Bottles, decanters, glass ornaments of every kind, from the chandelier to the glass button, are made by the operations of blowing or pressing, or by the union of both. The method of blowing glass may be well illustrated by the formation of a wine bottle. Six people are employed in this task. One, called a gatherer, dips the end of an iron tube, about four feet long, previously made red hot, into the pot of melted metal, turns the rod round so as to surround it with glass, lifts it out to cool a little, and then dips and turns it round again, and so in succession till a ball is formed on its end sufficient to make the required bottle. He then hands it to the blower, who rolls the plastic lump of glass on a smooth stone or cast-iron plate, till he brings it to the very end of the tube. He next introduces the pear-shaped ball into an open brass or cast-iron mould, shuts this together by pressing a pedal with his foot; and holding his tube vertically, blows through it, so as to expand the cooling glass into the form of the mould. Whenever he takes his foot from the pedal lever, the mould spontaneously opens out into two halves, and falls asunder by its bottom hinge. He then lifts the bottle up at the end of the rod, and transfers it to the finisher, who, touching the glass tube at the end of the pipe with a cold iron, cracks off the bottle smoothly at its mouth ring.

In a similar manner an infinite variety of glass articles are manufactured. Water pitchers, claret jugs, drinking glasses, decanters, lamp shades, cruets, and vases of various kinds, are often fashioned, with the exception of the cutting, in the space of a few minutes, and with the aid of a very few instruments, and the glass is worked with all the ease of the most plastic clay or putty-indeed, with far greater ease than either of these substances, from the greater tenacity of the molten glass, which enables the workman to wind, to twist, to draw it out, to cut it, to compress it, and to mould it, with extreme ease—and the rapidity with which all these manual operations are performed is such as to baffle the eye of the spectator.

In all vessels provided with a leg and foot, such as wineglasses, the leg is formed of one dip of glass, and the foot of another, each in turn being attached to the body of the vessel, and worked into shape. Vessels requiring handles have them most dexterously put on. A lump of soft glass is drawn out and attached to one part of the vessel, turned, modelled, and attached at another part in a few seconds, the workman having no guide but the accuracy of his eye in the process. Glass tubing is formed in a manner equally simple and equally wonderful. A workman, having collected a quantity of glass on the end of his tube, rolls it on an iron plate into a cylindrical form, blows into it so as to form an internal cavity; he then holds the mass to a second workman, who attaches a heated rod to the other end, and the two recede from each other, the glass tube lengthening between them, until a tube fifty or sixty feet long is produced, the bore of which is perfect throughout its whole length.

Various ornamental forms are given to the surface of glass

vessels by metallic moulds. The mould is usually of copper, with the figure cut on its inside, and opens with hinges to permit the glass to be taken out. The mould is filled by the workman, who blows fluid glass into its top. The chilling of the glass, when it comes in contact with the mould, impairs the ductility, and, in some inferior kinds of glass, prevents the impression of the figure from being sharp. Moulds are now, however, made in pairs, which can be so suddenly and evenly brought together on the inside and outside of the glass vessel, that specimens are produced that can scarcely be told from cut glass by the uninitiated. A vast number of articles of every description are moulded in this manner, and afterwards slightly cut, which are sold at a cheap rate.

ANNEALING OF GLASS.

Before glass can be of any essential service to those who use it, it has to undergo the process of annealing; for, without this, it would be liable to fly with the smallest change of temperature, and would break with the slightest touch. The reason of this brittleness arises, in all probability, from the sudden cooling of the external particles of glass, which are thus forcibly contracted, while the inner ones remain soft and expanded; and a constant strain being thus kept up between the different parts, a very slight shock is sufficient to separate the entire mass, and the article is broken. Hence it is necessary to cool glass in an oven, called the annealing oven.

The annealing oven has a fire at one end only, and articles newly-made are placed on shallow trays in the part of the oven most exposed to the heat of the fire, and are gradually pushed forward towards the colder end, whence they are

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