OPERATING THE DAMPERS.
According to the mechanical dictionary, a damper is a device for regulating the admission of air to a furnace, with which the fire can be stimulated, or the draught cut off, when necessary. Some runners regard locomotive dampers in a very different light. They seem to think the openings to the ash-pan are merely holes made to let air in, and ashes out; that doors are placed upon them, which troublesome rules require to be closed at certain points of the road to prevent causing fires. Those who have made their business a study, however, understand that locomotive dampers are as useful, when properly managed, as are the dampers of the base-burner which cheers their homes in winter weather. To effect perfect combustion in the fire-box, a certain quantity of oxygen, one of the constituents of common air, is required to mix with the carbon and carbureted hydrogen of the coal. The combination takes place in certain fixed quantities. If the quantity of air admitted be deficient, a gas of inferior calorific power will be generated. On the other hand, when the air-supply is in excess of that needed for combustion, the surplus affects the steam-producing capabilities of the fire injuriously; since it increases the speed of the gases, lessening the time they are in contact with the water-surface, and a violent rush of air reduces the temperature of portions of the fire-box below the heat at which carbureted hydrogen burns.