Page:Encyclopædia Britannica, Ninth Edition, v. 9.djvu/246

236 FIRE The boilers are tubular, of sufficient capacity to work the pumps 500 strokes per minute. The usual working pres sure of steam is 80 to 100 Ib per square inch. The weight as drawn to fires is about 8000 Ib. Chemical Engines are of several forms and sizes. The size most used consists essentially of two cylindrical copper or steel tanks, each holding 80 gallons of water (fig. 3). The charge for each tank is 28 Ib bicarbonate of soda and FIG. 2. Steam Fire-Engine. 141b sulphuric acid. The soda is dissolved in the water, and the acid is held in a leaden jar within the tank, which is securely closed. At the moment of using the sulphuric acid is mixed with the water, and instantly combining with the soda causes carbonic acid to be given off with a pressure FIG. 3. Chemical Engine. of 140 Ib on the square inch. The tanks are used inde pendently and charged separately, so that a continuous stream of water, usually ^-inch jet, may be maintained. 300 feet of f-inch rubber hose is carried. The whole ap paratus, charged and carrying three men, weighs about 5000 ft), and is drawn by two horses. The hose is rarely carried upon the engine ; it is usually on a separate car riage drawn by one horse. The reel carries about 1000 feet of 3i-inch rubber hose. Six hosemen ride on the car riage. The total load is about 3000 Ib. 1 Ladder Carriages carry from 20 to 25 ladders of various lengths (see fig. 4). Two ladders spliced reach 70 feet. The carriage fully equipped and carrying 12 men weighs from 7000 to 8000 tt>, and is drawn by two horses. The " aerial ladder " (so-called) reaches when fully extended a height of 100 feet, and is self-supporting: it is readily moved, when raised. It is made in 8 sections, each being a ladder about 1 2 feet long, and is put together and raised in six minutes. It is available as a fire-escape. The total load with its carriage is about 6000 Ib. Electric Fire-Alarm Telegraph. Time is a most import ant element in all fires, and the purpose of this telegraph is to put it in the power of any one discovering a fire to make known the locality of it to the fire department in the shortest possible time. Throughout the town or city "alarm boxes" are placed, connected by telegraph wire 1 A combined manual and chemical fire-engine is made by Dick of Glasgow, which consists of an iron tank on wheels, divided into two galvanized compartments. It has two pumps, with vertical motion, connected with the suction pipes, to fill the compartments with water where the chemicals are dissolved, and two pumps to project the chemical liquid from each compartment into the air-chamber, where they combine and generate carbonic acid gas. The gas is held in solu tion by the water, and is conveyed direct to the fire, upon which it exercises its fire-extinguishing power. The engine can be worked by four or five men, and is capable of throwing 30 gallons of water per minute, containing 250 gallons of carbonic acid gas, a distance of 75 to 90 feet.