173 



DEFINITION OF TERMS. 



with limestone, and with this the ex- 

 periments of Levasseur correspond. 

 There are a great many varieties ol iron, 

 which artists distinguish hy particular 

 names; but all of them may be reduced 

 under one or other of the three following 

 classes : cast iron, wrought or soft iron, 

 and steel. Cast iron, or pig iron, is the 

 name of the metal when first extracted 

 from its ores. The ores from which iron 

 is usually obtained are composed of oxide 

 of iron and clay. The object of the 

 manufacturer is to reduce the oxide to 

 the metallic state, and to separate all the 

 clay with which it is combined. These 

 two objects are accomplished at once by 

 mixing the ore reduced to small pieces 

 with a certain portion of limestone and 

 of charcoal, and subjecting the whole to 

 a very violent heat in furnaces construct- 

 ed for that purpose. The charcoal ab- 

 sorbs the oxygen of the oxide, flies off in 

 the state of carbonic acid gas, and leaves 

 the iron in the metallic state; the lime 

 combines with the clay, and both together 

 run into fusion, and form a kind of fluid 

 glass; the iron is also melted by the 

 violence of the heat and being heavier 

 than the glass, falls down and is collected 

 at the bottom of the furnace. Thus the 

 contents of the furnace are separated into 

 two portions ; the glass swims at the 

 surface, and the iron rests at the bottom, 

 A hole at the lower part of the furnace is 

 now opened, and the iron allowed to flow 

 out into moulds prepared for its reception. 

 The cast iron thus obtained is distin- 

 guished by the follovving properties: it 

 is scarcely malleable at any temperature. 

 It is generally so hard as to resist the file; 

 it can neither be hardened nor softened 

 by ignition and cooling. It is exceedingly 

 brittle. It melts at 130° Wedgewood. 

 It is more sonorous than steel. For the 

 most part it is of a dark-gray or blackish 

 color ; but sometimes it is whitish, and 

 then it contains a quantity of phosphuret 

 of iron, which considerably impairs its 

 qualities. A great number of utensils 

 are formed of iron in this state. To con- 

 vert it into wrought iron, it is put into a 

 furnace, and kept melted, by means of 

 the flame of the combustibles, which is 

 made to play upon its surface. While 

 melted every part of it is stirred by a 



workman, that every part of it may be 

 exposed to the air. In about an hour the 

 hottest part of the mass begins to heave 

 and swell, and to emit a lambent blue 

 flame. This continues nearly an hourj 

 and by that time the conversion is com- 

 pleted. The heaving is evidently pro- 

 duced by the emission of an elastic fluid. 

 As the process advances, the iron gradu- 

 ally acquires more consistency; and at 

 last, notwithstanding the continuance of 

 the heat, it congeals altogether. It is 

 then taken while hot and hammered 

 violently, by means of a heavy hammer 

 driven by machinery. This not only 

 makes the particles of iron apj roach 

 nearer to each other, but drives away 

 several impurities which would other- 

 wise continue attached to the iron. In 

 this state it is the substance described 

 under the name of iron. As it has never 

 yet been decomposed, it is considered at 

 present, when pure, as a simple body; 

 but it has seldom or never been found 

 without some small mixture of foreign 

 substances. These substances are either 

 some of the other metals, or oxygen, car- 

 bon, or phosphorus. When small pieces 

 of iron are stratified in a close crucible, 

 with a sufficient quantity of charcoal 

 powder, and kept in a strong-red heat for 

 eight or ten hours, they are converted 

 into steel, which is distinguished from 

 iron by the following properties : It is 

 so hard as to be unmalleable while cold, 

 or at least, it acquires this property by 

 being immersed while ignited into a cold 

 liquid; for this immersion, though it has 

 no effect upon iron, adds greatly to the 

 hardness of steel. It is brittle, resists 

 the file, cuts glass, affords sparks with 

 flint, and retains the magnetic virtue for 

 any length of time. It loses this hard- 

 ness by being ignited and cooled very 

 slowly. It melts at above 130° Wedge- 

 wood. It is malleable when red-hot but 

 scarcely so when raised to a white heat. 

 It may be hammered out into much thin- 

 ner plates than iron. It is more sonorous, 

 and its specific gravity, when hammered, 

 is greater than that of iron. By being 

 repeatedly ignited in an open vessel, and 

 hammered, it becomes wrought iron, 

 which is a simple substance, and if per- 

 fectly pure would contain nothing but 



