This change did not come all at once. The fire extinguisher has been developing ever since man learned to fear fire. Devices for extinguishing fire are almost coeval with that element itself. In the second century before Christ, the Egyptians had pumps worked by levers to put out their fires. The Roman, Pliny, refers to fire extinguishers but gives no account of their construction. Apollodorus, architect of the Emperor Trajan, speaks of leathern bags with pipes attached. Water was projected by squeezing the bags. Medieval Europe used various forms of water pumps, and it was not until the opening of the nineteenth century that chemicals were used to combat fire. [Illustration] There are two classes of chemical fire extinguishers: the soda and acid tank or three-gallon type, and the one-quart pump type. The latter came when the efficiency of carbon tetrachloride as an extinguishing agent became known. All the extinguishers of this type use a liquid which has carbon tetrachloride as a base. The liquid is a combination of organic materials with an aromatic odor and high specific gravity. When subjected to a temperature of 200° F. or over, it changes to a heavy, cohering, non-poisonous gas blanket which surrounds the burning material and cuts off the air supply necessary for the life of the fire. The first one-quart pump type of extinguisher appeared in the United States in 1907. There was little resemblance between it and the extinguisher of today. A cylindrical tube with a perforated end contained the liquid. The user was expected to sprinkle the liquid over the fire just as salt is sprinkled from a saltcellar over meat. One company applied the idea of pumping the liquid on the fire in 1909. They introduced a single-acting pump. The user inserted the nozzle in the liquid, drew it into the pump, and then ejected it on the flames. This company substituted a double-acting pump early in 1910. The container for the fluid and the pump were thus combined and the extinguisher had the general appearance of those now on the market. Brass construction was substituted for tin in the latter part of 1910, and in 1911 all brass construction was adopted. The extinguisher has remained practically unchanged since 1911. This was the only one-quart type extinguisher on the market until 1911. Since then several others have been marketed. All use an extinguishing liquid with carbon tetrachloride as a base. They differ principally in the manner of its ejection. The original type pumps the liquid out by hand. Others eject it by air pressure or by a combination of the two methods. The objection made by some people to the use of air pressure is that it demands attention and the use of a complicated mechanism which more readily gets out of order. [Illustration]