THE GLASS-BLOWER.

Glass is a transparent, solid, brittle substance, formed by the combination of flint or silex, with alkaline salts and metallic oxydes. It is applicable to innumerable purposes of ornament and comfort, as well as of scientific investigation and research.

The invention of glass is very ancient : the books of Moses and of Job make mention of it. Aristophanes, Aristotle, and Pliny, speak
of it in their works. Aristotle, who flourished three centuries and a half before the Christian era, proposes two problems concerning glass : one is, why we see through it, the other, why it will not bend. Theophrastus, who flourished about three hundred years before Christ, describes glass as having been made of the sand of the river Belus : and the sphere of Archemides is a remarkable instance of the perfection to which the art of glass making had been brought at that early period, namely, two hundred and nine years before Christ. For the sake of our young readers, we may remind them that Virgil, in his fifth Eneid, compares the clearness of the water of the Facine lake to glass ; and Horace, in his third book of the Odes, mentions glass in such terms, as shew that its transparency was brought to great perfection, lu the time of Strabo, the manufacture of glass was well understood, and had become a considerable article of trade. Seneca seems not only to have been well acquainted with glass, but also understood its magnifying powers when formed into a convex shape. Pliny relates the manner of the discovery of glass : it was, he says, first made from sand found in the river Belus ; a Phoenician merchant ship, laden, with mineral alkali (now understood to be some preparation of soda), being driven on the coast, and the crew going ashore for provisions, and dressing their victuals on the sand, made use of some lumps of alkali to support their kettles. Hence a vitrification of the sand beneath the fire was produced, which afforded a hint to the manufacturer.

The earliest positive authority, relating to the use of glass in windows, is said to be in a passage of Lactantius, one of the Fathers of the Christian church, in the third century.

Bede mentions, that artificers skilled in .making glass, were brought over to England in the year 1674: glass windows did not begin to be used before 1180: for a long time they were very scarce, and considered as a sort luxury, and as signs of great magnificence.

Painted glass is supposed to have been introduced in the reign of John, although we have no know specimens earlier than the time of Henry the third. The regular glass manufacture was begun in England, in 1557.

As it would be impossible , in the small limits to which we are confined, to enter at large into the composition of glass, we shall merely state, that flint-glass is made by melting over a very strong fire, onfe hundred and twenty pounds of white sand, fifty pounds
of red lead, forty pounds of the purest pearl- ash, twenty pounds of nitte (nitrate of potash), and five ounces of magnesia. Crown, or Window glass, contains no lead ; it consists of soda and fine sand. Bottle glass is the coarsest of all, and is composed of kelp and common sand, or sand and the refuse of the scoap-boiler. Of these, the most fusible, is the flint glass, and the least fusible, the
bottle glass.

The farriace in which the glass is melted, is round, and has several apertures, in one of which the fuel is introduced ; the others serve to lade out the melted metal. When the ingredients are perfectly fused, and have acquired the necessary degree of heat, part of the melted matter is taken out at the end of a hollow tube, about two feet and a half long, which is dipped into it, and turned about till a sufficient quantity is taken up ; the workman then rolls it gently upon a piece of iron to unite it more intimately. He then blows through the tube till the melted mass at the extremity swells into a bubble; after which, he again rolls it on a smooth surface to polish it, and repeats the blowing till the glass is brought as near the size and form of the vessel required, as he thinks necessary.

There are three principal kinds of glasses,distinguished by the form or manner of working them, viz. round glass, as bottles, drinking-glasses, &c. table or window-glass ; of this, also, there are several kinds, and plate glass.

If a bottle is to be formed, the melted glass, at the end of the tube, is put into a mould of the exact size and shape of its body, and the neck is formed on the outside, by drawing out the ductile glass.

If it be a vessel with a wide orifice, the glass, in its melted state, is opened and widened with an iron tool after whicl, being again heated, it is whirled about by a circular motion, till it is extended to the size required. If a handle, foot, or any thing else of the kind, be required, these are made separately, and stuck on in the melted state.

Window-glass is formed in a similar manner, except that the liquid mass is blown into large globes, and detached from the first iron tube by the assistance of a second person, who fixes his iron tube at the opposite side of the globe ; and the man who originally blew it, then separates his tube from it; the mouth of the globe is gradually w idened, till it ulti'mately becomes, in the hand of the workman, a circular planisphere. The best window-glass was, till within these few years, made at Radcliffe : but this manufactory is now abandoned, and the crown, as well as the green and black bottle glass, is brought principally to London from Newcastle-upon Tyne.

Plate-glass, for looking-glasses, and some superior windows, is made by suffering the mass in a state of complete fusion, to float
upon a table covered with copper, with iron ledges to confine the melted matter, and as it cools, a metallic roller is passed over it, to reduce it to an uniform thickness.

Glass is sometimes coloured, by mixing it, while in a fluid state, with various metallic oxydes. It is coloured blue by the oxyde of
cobalt ; red, by the oxyde of gold ; green, by the oxyde of copper or iron ; yellow, by. the oxyde of silver or antimony; and violet, by the oxyde of magnesia.

Although glass, when cold, is brittle, it is one of the most ductile bodies known in its melted state ; if a thread of melted glass be drawn out, and fastened to a reel, the whole of the glass may be wound off; and by cutting the threads of a certain length, there is obtainecl a sort of feather glass. A thread of glass may be drawn, or spun so fine, as to be scarcely visible to the naked eye. Glass is very elastic and sonorous ; fluoric acid dissolves it ; it is by this acid, that engravings are made upon glass ; and the alkalis act upon it when in a melted state.

Articles made of glass, require to be gradually cooled in an oven ; this operation, called annealing, is necessary to prevent them
from breaking by change of temperature, wiping, &c.

Plate-glass comes from the manufactory in a very rough state ; it is scarcely transparent. It is then ground with sand, and polished with emery, and putty, formed of lead and tin, calcined together. This last substance is the principal thing used in forming white enamels and glazings for earthenware.

Glass-makers usually work in the cold months, owing to the great heat of their furnaces : their wages are large in proportion to the disadvantages attending their labours.

Glass-grinders and polishers work by the piece, and may get a good living, considering .that little more ingenuity is required thau
that which is necessary for common labours.