any interruption to the flow, a coal fire could be started in six or eight minutes. In the glass furnaces themselves greater changes were necessarily made. As the supply of gas became more abundant and assured, the tendency was toward the evolution of distinct apparatus for its utilization. At the present time the glass furnaces burning natural gas are models of simplicity and efficiency. In the melting furnaces the gas is admitted at each end of the furnace and mixes with air which has previously been heated by passing through flues in the brickwork. The combustion thus takes place in the melting chamber directly above the crucible pots, and produces an intense and easily regulated heat. The blowing furnaces are even simpler. They merely provide a chamber of brickwork with suitable openings in the sides, and immediately under each opening a large Bunsen burner supplied with natural gas and drawing the requisite air directly from the atmosphere.
Under the stimulus of the new fuel the development of the glass industry since 1885 has been without precedent. The greatest growth took place first in the flint-glass works, because in these the advantages of the gas were most manifest. The absence of coal smoke and dust, and the tendency to reduce the lead oxide to the metallic state, were in themselves sufficient to bring about the substitution of the gas for the coal, had there been no other reasons. But the economic advantage was also in favor of gas. Thus, a factory which was run by coal in 1883 at a weekly cost of $175.17 was operated by natural gas in 1885 for $94.96, effecting a saving of forty-six per cent. In addition to this the repairs were less costly and the product was more salable.
The introduction of natural gas into window-glass factories was held for some reason to be less advantageous than in flint-glass works, but the tradition rapidly melted away in the face of a larger experience. By 1885 and 1886 natural gas had made its way into all departments of glass-making, and everywhere turned out to be an immense improvement. Now it is the universal fuel, and up to the present year it has been the cause of that concentration of the industry of which we have already spoken. It has not only given a better product and more economic working, but it has made possible the carrying out of operations on a scale hitherto undreamed of. In plate glass and window glass the product is now measured by the acre, and even by the square mile, where formerly it was reckoned in feet. Hollow ware is shipped by the ton in place of pound lots. One hundred and twenty thousand dozen lantern globes are turned out as a summer's work. With the more complete organization of the industry it is no longer necessary for large plants to grow out of small ones. The conditions need-