Fire-bridge
The Encyclopedia of Founding (1892)
A hollow cast frame, encased in fire-brick, which is built between the hearth and the grate of a reverberatory furnace. See REVERBERATORY FURNACE. Fire-clay is the kind of clay which, when mixed with other refractory ingredients, is used for the manufacture of fire-bricks, crucibles, glass pots, retorts, etc., which require to withstand intense heat. It is found abundantly near the surface of the ground, but chiefly in the coal measure. Fire-clay to be of value should be comparatively free from ferrous oxide (or combination of iron with oxygen), calcium carbonate (or substances such as limestone, chalk, marble, etc.), and iron pyrites, because at very high temperatures these bodies would combine with the silica of the clay with the formation of fusible vitreous silicates. See REFRACTORY MATERIAL. Fire-sand is the name given to all foundry sands that are composed principally of coarse grains of quartz, intermixed with more or less alumina or clayey sand. Because of the highly refractory nature of these siliceous sands they are usually termed "fire-sands." See FACING-SAND; REFRACTORY MATERIAL. Flame is the luminous phenomenon produced by the combustion of gases and is, hence, fire in motion. Substances which burn with flame are either gases already or they contain a gas which is set free by the heat of combustion. But flame does not necessarily produce light. In the burning of pure oxygen and hydrogen there is intense flame, but the light is so weak that it can scarcely be seen. If we sift a little charcoal-dust into this non-luminous flame, the particles of solid carbon are instantly heated to incandescence, a bright flash of light resulting. Therefore the conditions of illumination are, first, an intense heat, and, second, a solid placed in the midst of it, which remains fixed and gives out the light. The lighting power of a gas depends upon the proportion of carbon it contains, the particles of which become glowing hot before being consumed. See COMBUSTION; HEAT; CARBON.
What Has Changed in the Last Century
When the Encyclopedia of Founding described this in 1892, the fire-bridge was a routine piece of ironwork: a hollow cast frame faced with fire-brick separating the coal grate from the hearth of a reverberatory furnace, so that flame passed over the charge without the fuel touching it. That geometry has largely vanished with the solid-fuel grate. Reverberatory furnaces that survive today — chiefly for melting secondary aluminium and some copper work — burn oil, natural gas or oxy-fuel through burners, and need no bridge wall to keep coals off the bath, while most foundry and steel melting has moved to cupolas, electric arc and induction furnaces. The entry's companion notes on fire-clay and fire-sand hold up better: low iron, lime and pyrites content is still what makes a clay refractory, though modern refractories run heavily to high-alumina, magnesia and silicon carbide rather than natural clay alone.
Written for this edition, 2026.