FORMATION OF OLASS.

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When these substances are completely fused and have acqulr^ed a certain degree of heat, which is known by the fluidify - of*the mass, part of the melted matter is taken out at the end ofa long hollow tube, which is dipped into it, and turned aboutuntil a sufficient quantity is taken up; the workman at each turnrolling it gently upon a piece of iron, to unite it more intimately.He then blows through the tube, till the melted mass at the ex-tremity swells like a bubble, after which he rolls it again on asmooth surface to polish it, and repeats the blowing, until theglass is brought as near the size and form of the vessel required,as he thinks necessary.

If it be a common bottle, the melted matter at the end of thetube 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 ductileglass.

If it be a vessel with a large or wide orifice, the glass in itsmelted state is opened and widened with an iron tool; afterwhich being again heated, it is whirled about with a circularmotion, and by means of the centrifugal force thus produced isextended to the size required. Should a handle, foot, or anything else of the kind be required, these are made separately,and stuck on in its melted st3te.

Window-glass is made in a similar manner, except that themass at the end of the tube is formed into a cylindrical shape,which being cut longitudinally by scissors or shears, is graduallybent back until it becomes a flat plate.

Large plate-glass for looking-glasses, &c. is made by sufferingthe mass in a state of complete fusion to flow upon a casting-ta-ble, with iron ledges to confine the melted matter, and as itcools a metallic roller is passed over it to reduce it to an uniformthickness. There are different kinds of glass manufactured fordifferent purposes; the principal of these are flint-glass, crown-glass, and lottle-glass.

Flint-glass is the densest, most transparent, colourless, andbeautiful. It is often called crystal. The best kind is said to be

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