CHIMNEY. (Fr. cheminee.) The place in a room where the fire is burnt, and from which the smoke is carried away by means of a conduit called a flue. Chimneys are usually made by projection from a wall, and recess in the same from the floor, ascending within the limits of the projection and recess. That part of the opening which faces the room is properly the fire-place, the stone or marble under which is called the hearth. That on a level with, and in front of it, is called the slab. The vertical sides of the opening are called jambs. The head of the fore plate resting on the jambs is called the mantel; and the cavity or hollow from the fire-place to the top of the room is called the funnel. The part of the funnel which contracts as it ascends is termed the gather*, or by some the gathering of the wings. The tube or cavity of a paral lelogrammatic form on the plan, from where the gathering ceases up to the top of the chimney, is called the fine. The part between the gathering and the flue is called the throat. The part of the wall facing the room, and forming one side of the funnel parallel thereto, on the part of the wall forming the sides of the funnels, where there are more than one, is the breast. In external walls, that side of the funnel opposite the breast is called the back. When there is more than one chimney in the same wall, the solid parts that divide them are called wills. And when several chimneys are collected into one mass, it is called a stack of chimneys. The part which rises above the roof for discharging the smoke into the air, is called a chimney shaft, whose horizontal upper surface is termed the chimney top.
The covings were formerly placed at right angles to the face of the wall, and the chimney was finished in that manner; but Count Rumford showed that more heat is obtained from the fire by reflexion when the covings are placed in an oblique position. He likewise directed that the fire itself should be kept as near to the hearth as possible, and that the throat of the chimney should be constructed much narrower than had been practised, with a view to prevent the escape of so much heated air as happened with wide throats. If the throat be too near the fire, the draught will be too strong, and the fuel will be wasted ; and if it be too high up, the draurrht will be too languid, and there will be it'danger of the smoke being occa sionally beat back into the room. Beforo Count Rumford directed his attention to this subject, smoky chimneys were very common ; but by studying his principles, these at present seldom occur.
Lieut. Mason, in a letter to the London Becilcler on the subject of smoky chim neys, writes : " I have built many chim neys in all possible sitaations, and have found one simple plan everywhere suc ceeded, the secret being only to construct the throat of the chimney, or that part of it just above the fire-place, so small that a man or a boy can barely pass through it. Immediately above this the chimney should be enlarged to double its width, like a ioarse, to the extent of about two feet in height, and then dimin ished again to its usual proportions. No chimney that I ever constructed thus, smoked."