Fireplace

(-plās.) (Arch.) The square opening in the wall of an apartment for the reception of ag rate or stove; its upright sides are termed the jambs; and the head, or arch, the mantel. The stone under the jambs is sometimes called the slab, and the stone or stones immediately in front of the latter, the hearth. However much they may be improved, fireplaces will always remain the most imperfect and costly mode of heating, for they only render available 13 per cent. of the total heat yielded by coal or coke, and 6 per cent. of that by wood. Their enormous lo of temperature arises from the fact, that the current of air nece ary for combustion always carries with it a large quantity of heat produced, which is lost in the atmosphere. Hence 13 it was that Franklin said fireplaces should be adopted in cases where the smallest quantity of heat was to be obtained from a given quantity of combustibles. Notwithstanding their want of economy, however, they will Fig. 325. FIRE-PLACE. always be preferred as the healthiest and pleasantest mode of heating, on account of the cheerful light which they emit, and the ventilation which they insure. The draught of a fire is the upward current in a chimney caused by the ascent of the products of combustion; when the current is rapid and continuous, the chimney is said to draw well. The draught is caused by the difference between the temperature of the inside and that of the outside of the chimney; for, in consequence of this difference, the gaseous substances which fill the chimney are lighter than the air of the room, and consequently equilibrium is impo ible. The weight of the column of gas CD, Fig. 325, in the chimney being le than that of the external column of air A B of the same height, there is a pre ure from the outside to the inside which causes the products of the combustion to ascend the more rapidly in proportion as the difference in weight of the gaseous ma es is greater. [s. 366] Fire -proof. [Eng.fire Fire -proof. [Eng.fire, and proof.] Designating that which is incombustible; as, afire-proof building. Fire'- works. See PYROTECHNY. Fire'- worshippers. See GUEBRES. [s. 366]