AND VENTILATING APPARATUS.
The objects named in the heading take rank among the most important in the whole domain of building construction, and their consideration in volves peculiar difficulties, as it must involve other departments of science. This treatise will be restricted, however, particularly iu reg-ard to the apparatus for heating, to the proper selection of methods, and to a general inquiry into the conditions demanded for successful application. Chim neys are, indeed, parts of heating apparatus, but a separate consideration of them is justified for the reason that their arrangement does not depend upon the special purpose for which they are built, and because the chimney forms an integ-ral part of the entire building, while heating apparatus is frequently a separate adjunct. The means employed for heating, and ventilation will be considered together, on account of the close natural connection between them, and also because they are generally in actual uuion.
Chimneys are built for the purpose of carrying- off the products of com bustion, such as carbonic oxide, carbonic acid, steam, the incombustible portions of fuel, etc., and also of introducing the necessary amount of at mospheric air, or oxygen, needed in the process of combustion. The quantity of product to be carried off must regulate the inner dimensions, or cross-section in the clear, and also, indirectly, the height of the chilli ney. The outer dimensions, however, must depend entirely upon con siderations of construction, such as stability, material, relative position, safety against fire, and architectural elegance.
upward tendency of the air current within the chimney— called the "draught "7—is caused by the direct effect of a column of specif ically heavier atmospheric air of equal height on the outside of the chim ney upon the column inside, which is rarefied by the heat, and is therefore specifically lighter. Apart from such hindrances to its passage as the fric tion of the walls, etc., the draught is increased in force by the additional height of the chimney and the difference in temperature between the in side and the outside column of air. The product of the speed of the draught and the size of the cross-section will give the volume carried away in a given unit of time, and, inversely, the size of the cross-section must depend upon the speed or strength of the draught and the quantity of smoke to be carried away. If the chimney has a cross-section larger than
the smoke-flues of the heating apparatus or of the opening for atmospheric air, the force of the draught will be proportionally retarded. In other words, narrow chimneys draw better than wide ones.
The distinction between factory chimneys and those in ordinary build ings must be clearly marked. The latter have cross-sections of regulated size, and a height also regulated by the character of the building; so that the number of chimneys must be proportioned to the volume of the prod uct to be carried away. In factories, on the contrary, the dimension of the chimney is varied according- to the demand made upon the boiler fur naces for steam-power.
Chimneys for Ordinary Buila'engs are usually of two kinds, one being of such width that it can be entered, the other being the narrow, or Rus sian, chimney. In the former, the cross-section is at least 1534 inches in the clear and the walls one brick, or 4.7 inches, thick. The Russian chim ney is generally preferred, as the air can be more quickly and uniformly heated, and as it can be introduced into the walls without occasioning a projection or chimney breast. It also requires less framing in the floor joists and beams, takes less space, and is easily cleaned, a broom weighted by a ball and suspended to a line being used for the purpose. The cross section of the Russian chimney is generally circular and 7% inches in diameter. In many countries—as in Saxony', for instance—the bond of the courses is arranged as in Plate io (fig. The bricks employed are of the size used in the walls—that is, 9.8 inches long by 4.7 inches wide and 2.5 inches thick. A circular notch of inch depth is made on one of the long sides of the brick, as seen in the Figure, reducing the wall to a mini mum thickness of 3.7 inches. A chimney built in this manner can carry off the smoke of three ordinary stoves, and can be built without a chimney breast in a brick wall 15 inches thick, a slight departure from the vertical direction being- admissible.