FIRE CHIEF or MARSHAL, an officer in some of the larger American cities who has the supreme command of the fire department of the municipality, and who directs the work of extinguishing fires. He is generally clothed with large powers of discretion, and has also police authority.
is distinguished from ordinary clay by its refractoriness and infusibility, which i render it an excellent material for bricks, cru cibles, glass pots, retorts and similar vessels which are to be exposed to a constant and very high temperature, at which ordinary bricks and clay vessels would fuse and become vitri fied. This difference is due to the purity of fire-clay, or at least to the absence from it of iron, lime, magnesia and alkalis, In appre ciable quantities. It consists of hydrated sili cate of aluminum almost entirely, but may con tain traces of organic matter, and of some of the bases mentioned above. Fire-clays are com monly found associated with the coal forma tions, and usually form a stratum immediately below the coal. It seems, indeed, to be part of the soil on which the coal vegetation flourished and died. Fire clays are generally plastic, but the United States furnishes a variety known as flint clay, which is non-plastic. In the United States fire-clay is found in the Carboniferous rocks of Pennsylvania, Missouri, Kentucky and Ohio; in the Cretaceous of New Jersey, Colo rado and other States and in the Tertiary formations of the Gulf States. Flint clay, which is non-plastic, resembles flint in appearance; ganister is a refractory clay with a high per centage of silica; pot clay is used in the manu facture ofglass pots and burns dense at a low red heat; fire mortar is a sandy fire clay used for making mortar to set fire bricks; retort clay is very plastic and is used in the manu facture of as retorts. About 1,750,000 tons
are produced annually in the United States and are valued at about $2,375,000. Consult Bischof, (Die feuerfesten Thone) (Leipzig 1895), and Ries, (Clays: Occurrence, Properties and Uses) (New York 1908). See also CLAY; COAL the name given by coal miners to carburetted hydrogen or marsh-gas, CH.. It is an inflammable gas, lighter than air, and is often found in coal mines, it being one of the products of the retarded decay of plant remains. A mixture of fire-damp and air in certain proportions is highly explosive; hence many frightful disasters with great loss of life mark the history of coal mining. The lowest explosive limit is a mixture of one part marsh gas with 5)/2 parts of air. The explosive violence increases with the addition of air, reaching a maximum with parts air ; beyond this the explosive violence decreases and with 13 parts air to 1 part gas becomes inert. White Damp is carbon monoxide; Stink Damp or sulphur gas is hydrogen sulphide; Black Damp is carbon dioxide. Afterdamp is the mixture of gases formed by an explosion. See COAL MINING; GASES, MINE; METHANE; SAFETY LAMP.