GLASS-MAKING.

HE Art of Glass-Making is one of the most useful that we possess. Like many other of the great discoveries which have proved of service to man, the manufacture of glass from sand and soda was the result of accident. The story goes, as told by Pliny, the Roman historian, that a company of mariners who had a cargo of nitrum

(probably soda or salt) on board, landed on the banks of a river in Palestine, and finding no stones to rest their pots on when they wished to prepare their dinner, took some pieces of the nitrum, and so placing them in a little heap, made a fire on the sand. The nitrum being fused or melted by the heat with the sand, a clear transparent stream of molten glass ran from beneath the pot. Thus was

the union of sand, soda, and chalk found to produce a new substance-Glass.

"It might dispose us to a kinder regard for the labours of one another," writes Dr. Johnson, "if we were to consider from what unpromising beginnings the most useful productions of art have probably arisen. Who, when he first saw the sand or ashes, by a casual intenseness of heat melted into a metallic form, rugged with excrescences and clouded with disparities, would have imagined that in this shapeless mass lay concealed so many conveniences of life as would, in time, constitute a great part of the happiness of mankind?"

The manufacture of glass soon became well known, and the production of drinking vessels and other domestic utensils in glass was carried to great perfection by the Venetians, the Bohemians, and other nations. It appears that the making of glass was known to the ancients, for we find glass ornaments and vases among the ruins of Herculaneum, Pompeii, and Egypt; and there is little doubt that the production of articles in glass has been known in China and India for many

centuries.

You may ask-What is glass? Well, then, glass is a transparent, solid, homogeneous substance, more or less brittle; and is formed by the fusion of siliceous and alkaline substances. I will explain the meaning of the terms I have used: A "homogeneous" substance is one that is of the same nature throughout; "fusion" is the capability of being melted by heat; "siliceous" is flint-like, from the word "silex," flint; and an "alkaline" means the fixed salt of any natural body. Flint, sand, quartz, rock, crystal, &c., are siliceous substances;

and soda is a fixed salt, or alkaline. These earths being melted together form glass.

Many opaque (dark, cloudy, not transparent) substances are capable of assuming a form more or less vitreous, or glasslike; such are the earths (simple substances found in the earth), some acids and salts, and the metallic oxides or rusts. The principal kinds of glass in use-crown (for windows), plate (for picture frames, &c.), bottle (green rough glass), and flint (for table utensils)—have all one common origin; sand as the silica, and soda or potash as the solvent, or fluid, that dissolves and mixes with the silex,

If you understand these explanations you will have little difficulty in following the processes adopted in all glass-houses in the making of glass. I will now endeavour to explain to you how glass is made:

First, the sand, cullet (broken glass), &c., are bruised and ground down to a fine powder, and then mixed with the proper proportion of alkali. They are then placed in a pot in the furnace and submitted to a great heat till they are melted into one great red, glowing mass, which the glassmakers call metal. Now, look at the engraving. In the centre is the furnace with the pots full of melted glass. At the left and right hand holes the workmen are taking out a portion of glass at the end of iron rods, called blow-pipes. As soon as a sufficient mass of the melted glass is attached to the blow-pipe, the workman withdraws it from the pot, gives it a swing in the air, and then rolls it on the cast-iron slab, called the marvre, so as to give it a smooth outer surface, at the same time blowing gently through the pipe till he has

made the glass thin enough for his purpose.

We will suppose

a decanter is the article to be made. The blow-pipe, with

INTERIOR OF A GLASS-HOUSE, SHOWING THE DIFFERENT PROCESSES
USED IN GLASS-MAKING.

the lump of hollow glass attached, is then taken to the chair, and another workman shapes and fashions the yet red-hot