producing iron, the top is usually sealed by a bell closing against a hopper, to distribute the stock in the wide throat of the furnace and to control the gases which are the result of the smelting operation, so as to employ the calorific value of these gases for heating the blast or for generating steam in boilers to operate machinery. The practicability of using these gases in engines, where the gas, in exploding, gives impetus to a piston, has also been demonstrated. The blast is heated in hot blast stoves, generally cylinders from 14 to 25 feet in diameter and from 50 to 115 feet high, filled with checker work of fire brick. These stoves are placed in series; the gas being admitted to and burned in a stove raises the temperature of the masonry, when the gas is shut off and the blast forced through the highly heated checkers. By alternating a series of stoves on gas or blast, at intervals of one or two hours, uniform temperature is maintained.
The blast, after passing through the hot blast stoves, is conveyed in iron or steel conduits, lined with fire brick, to tuyeres, set in the walls of the crucible. These tuyeres are formed of an inner and outer shell with closed ends, water circulating between the two shells. The tuyeres are mostly made of bronze or copper and are set in larger tuyere blocks (also water cooled) of iron or bronze. Nozzles connect the lined air conduits to the tuyeres. The cooling water required by a modern blast furnace amounts to millions of gallons daily. A large furnace requires a boiler equipment of from 3,000 to 3,500 horse power for its blowing, pumping and elevating machinery, electric plant, etc.
There were on Jan. 1, 1920, 262 blast furnaces in operation in the United States. See Iron and Steel.
BLASTOIDEA (so called from their oval or globular form, like that of a bird), an order of echinoderms, called also pentremites. They are found only in Palæozoic rocks.
BLATCHFORD, SAMUEL, an American jurist, born in New York City, March 9, 1820; was graduated from Columbia College in 1837; became private secretary to William H. Seward, when the latter was elected Governor of New York; practiced law in New York City; became Judge of the District Court for the Southern District of New York in 1867; Circuit Judge of the Second Judicial Circuit in 1878; and Justice of the Supreme Court of the United States in 1882. He died in Newport, R. I., July 7, 1893.
BLATTA, a genus of insects, the typical one of the family blattidæ. It contains the various species of cockroaches. B. orientalis is the common species in houses in the southern portions of the United States, though, as its name implies, it is believed to have come first from the East. In the higher latitudes of the United States B. orientalis is rarely or never seen, its place being taken by B. americana, or the kakerlac, as it is called.
BLAVATSKY, HELENE PETROVNA, a noted theosophist, born in Yekaterinoslav, Russia, in 1831; founded the Theosophical Society in New York in 1875, and wrote "Isis Unveiled" (1876); "The Secret Doctrine" (1888); "Key to Theosophy" (1889), etc. She died in London, May 8, 1891.
BLAZON, or BLASON, a heraldic term which originated in the custom of blowing a trumpet to announce the arrival of a knight, or his entrance into the lists at a joust or tournament. The blast was answered by the heralds, who described aloud and explained the arms borne by the knight.
BLAZONRY, the art of describing a coat of arms in such a way that an accurate drawing may be made from the verbal statements given.
BLEACHING, the art of rendering materials colorless. This is done by exposing them to the actinic rays of the sun, or by the action of bleaching agents. The chief of these is called bleaching powder. It is chloride of lime, and is prepared by exposing moistened quick-lime to the action of chlorine, when hypochlorite and chloride of calcium are formed, the former being the bleaching agent. By the action of an acid on good bleaching powder 30 per cent. of chlorine is liberated. Substances are bleached by alternately dipping them in dilute solutions of bleaching powder and of dilute sulphuric acid. Bleaching powder is also used to purify an offensive or infectious atmosphere.
BLEAK, a fish, the leuciscus alburnus of Cuvier, belonging to the family cyprinidæ. It is a river fish five or six inches long, and is found in Great Britain.
BLEB, a blister, a thin tumor filled with a watery liquid arising upon the surface of the body. If idiopathic, it is called pemphigus. If produced by external irritation, or some similar cause, it is a vesicle.
BLEEDING, or HEMORRHAGE, one of the most serious accidents which can
