Page:Popular Science Monthly Volume 36.djvu/172

160 year. Every three hours during the entire twenty-four a charge of a ton and a half of the batch is added to the melting tank. In an atmosphere so intensely heated as this, it does not take very long for the crude materials to fuse and form a glass quite as liquid as water.

Picture for a moment the white-hot caldron in which this transformation of the opaque into the transparent takes place. It is an oblong tank, some eight by ten feet, in which the glass in various stages of fusion stands to a depth of nearly three feet. Above this seething mass there is a low arch which deflects the long, curling flame as it comes over the bridge from the generators, until it bathes the entire contents of the tank in its Plutonic breath. As the materials of the batch unite and melt alone, they would be for the most part entirely infusible the liquid glass sinks to the bottom of the tank and flows through small openings into the gathering chamber beyond. The glass resulting from the union of sand and alkaline bases is heavier than the crude materials from which it is formed, and consequently seeks the lowest level. In this way the tank, although filled with material in all stages of transformation, has always at the bottom a bath of thoroughly fused glass. The communication between tank and gathering chamber is arranged at such a level that the fluid glass alone can pass from one to the other.

This central gathering chamber and the busy life surrounding it are the points of chief interest to the visitor who wishes to see the scenic part of bottle-blowing, and is willing to take the chemistry and some of the more occult parts of the process on faith. The chamber itself is circular, usually about sixteen feet in diameter, and contains a bath of molten glass nearly two feet deep. The temperature of this fiery lake is kept above the fusing-point by the hot gases which come from the melting tank and rise into the high shaft immediately over the gathering compartment. It takes only from two and a half to three hours for the crude materials of the batch to pass to the condition of perfectly fused glass. This is pretty quick glass-making.

A little sand, a little alkali, a little limestone, and considerable heat have so far been expended, and the result is fluid glass. It is that greater amount of skill which is now needed to transform the glass into a bottle.

There is a series of openings, some sixteen in number, around the sides of the gathering chamber and a little above the level of the molten glass. Through these the glass-blower draws his supply, but he does not dip his blowpipe directly into this glowing reservoir. Such an arrangement would cause too great a loss of heat, besides interrupting the furnace-draught, and would be a source of constant annoyance to the gatherer on account of the