Chimney Factory

Chimney, Factory. The intensity of the draught through a fire may be increased in two ways. A blast of air may be forced through it by bellows, fan, or other pumping machinery; or a greater current of air may be induced to pass through by the use of a high chimney. This second method is much employed in factories, for, besides producing greater draught, the products of combustion, which in many cases are objectionable and injurious to animal and vegetable life, are discharged at a sufficient height to render them less harmful. Inside the chimney there is a column of hot gases; outside the air is colder, and a column of this cold air of the same length and sectional area as the chimney would be heavier, and would exert a greater pressure at the base of the chimney. Hence the difference in the pressures of these two columns will force the inside gases upwards, this force depending on the temperatures of the burnt gases and of the surrounding air, and on the height of the chimney. Other things being equal, the draught is increased by lengthening the chimney; also the draught is greater on a cold day than on a hor, day, greater at night than in the daytime. The Townsend shaft in Glasgow has a height of 468 feet; St. Rollox shaft, Glasgow, 456 feet; and Mechernich shaft, Cologne, 441 feet. These are among the highest chimney-shafts.