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tank on their way to the chimney. The raw materials, called the "batch," are shovelled into compartment A, where they melt. They then pass under bridge a, to compartment B, where the "metal" is purified; and under bridge b to compartment C, the walls of which are perforated with "working holes" W. In some bottle factories the tank is not divided in this manner, and there are working holes all along the sides of the tank. In order to prevent the scum from interfering with the quality of the bottles, a fireclay pot, perforated at the lower end, runs from each hole to the bottom of the tank (Fig. 53), where the metal is pure.     For the manufacture of plate-glass the "batch" is melted in huge fireclay pots, which are removed bodily from the furnace to be poured. SHAPING GLASS.     Glass is shaped in three ways-- (1) blown; (2) rolled; (3) pressed. GLASS-BLOWING is used for fashioning bottles, lamp-glasses, bowls, and other objects, and in the making of window-glass.     Bottle-making consists of expanding a bulb of