Page:The American Cyclopædia (1879) Volume IX.djvu/385

 IRON 371 properties, and generally accompanies it in its ores. The amount in spathic iron ores is often large, in other ores usually small. Manganese is reduced from its oxide with much more diffi- culty than iron. When the manganese forms an integral part of the iron ore, it is reduced to a large extent together with the iron ; but when the oxide as such is present in the charge, it passes mainly into the slag, unreduced. The effect of manganese on cast iron is peculiar. Specular iron, generally known by its German name Spiegeleisen, made from spathic ores rich in manganese, contains from 4 to 12 (exception- ally as high as 20) per cent, of the latter metal, and also nearly 5 per cent, of carbon, all chem- ically combined, and but a fraction of 1 per cent, of silicon. On its freshly fractured sur- face it is white and resplendent, with large crystalline faces. It is very hard. Gray pig iron may contain as much as 6 per cent, of manganese without showing any tendency to whiteness ; the effect of manganese may here be counteracted by the silicon. Pig iron con- taining manganese is preeminently adapted for conversion into wrought iron and steel. The part that manganese plays in these processes is not well understood. It replaces silicon as a heat producer in pig iron employed in the Bes- semer process. Spiegeleisen is generally very pure, and is almost exclusively used in steel- making. The effect of the other substances mentioned above on the physical properties of pig iron is not known definitely. II. WROUGHT IKON. By far the largest amount of wrought iron in the arts is made from pig iron by the removal of the carbon, silicon, &c., through oxidation in a reverberatory furnace. (See IBOST MANUFACTURE.) The iron is removed from the furnace in the form of a white-hot ball or bloom, composed of small particles of soft iron, intimately mingled with cinder. The cinder is expelled and the particles of iron are united by squeezing, hammering, or rolling. Slabs of iron thus made are welded by exposing them to a white heat and rolling them out to- gether. The homogeneity of the product de- pends on the thoroughness of the working, and this in turn on the temperature and the fusi- bility of the cinder. The fibrous character of wrought iron is due to the elongation of the granules or crystals of iron by rolling with in- termingled cinder. Fibre, however, is not a condition inherent in iron, nor is it necessarily characteristic of good or strong iron, as is often supposed. Iron from which the cinder has been removed by thorough working, or by fusion, exhibits the granular crystalline fracture prop- er to the metal itself ; and such iron is, other ( things being equal, stronger than that showing well developed fibre. But fibrous structure is evidence of good quality in iron, in so far as it shows the absence of substances (notably phosphorus) which tend to make it crystalline and brittle. It is to be observed that all iron, even the most fibrous, shows a crystalline char- acter when broken short off; and that some varieties of crystalline iron may appear fibrous when bent and broken slowly. The specific gravity of wrought iron differs according to treatment. The following determinations are by Kirkaldy : rolled, 7'7626 to 7'2898 ; ham- mered, 7-8067 to 7-7206 ; angle iron, 7'7310 to 7-5297; sheet iron, 7'7419 to 7-5381. The physical properties of wrought iron are inti- mately connected with its chemical composi- tion. Carbon is almost always present in mi- nute quantity ; without it, iron is liable to take up oxide of iron and become rotten or " burnt." In the analysis of wrought iron it is often diffi- cult to determine whether a substance is pres- ent in the iron itself or in the cinder. This is especially the case with silicon. The amount of silicon in wrought iron is never large (dis- regarding cinder), as it is the element most readily removed by oxidation in the operation of puddling. It is supposed to render the iron weak and brittle. Sulphur and phosphorus are frequently met with in wrought iron, and their effects have been tolerably well determined. Sulphur makes iron "red short " or " hot short," that is, brittle at a red heat. Phosphorus, on the contrary, makes iron " cold short," that is, brittle when cold. A red short iron can be worked cold, and a cold short iron hot. Ac- cording to Eggertz, iron with 0'04 per cent, of sulphur can still be punched hot. More than this amount renders iron perceptibly red short. The effect of phosphorus on wrought iron differs according to the treatment it has received. Its tendency, even in proportions as low as 0-1 per cent., is to make iron coarse- ly crystalline in texture; this tendency is in- creased by prolonged heating. The strength and extensibility are thereby decreased and the hardness increased. If however the phos- phorus is in not too large quantity and the iron is drawn out to such an extent that on slow fractur^ it exhibits a fibrous structure, the metal becomes both strong and tenacious. The presence of cinder facilitates the forma- tion of fibre; and iron with an abundance of cinder (2 to 3 per cent.) has been found by Knut Styffe to be tenacious with 0'25 to 0'35 per cent, of phosphorus. He considers that phosphorus, like carbon, raises the elas- ticity and strength within the crystalline par- ticles of the iron (whence results its superior hardness), but that it does not increase the cohesion between the separate crystals. The general impression among iron workers is that phosphorus and sulphur neutralize each other in iron, so that a " neutral " iron can be made from a mixture of cold and hot short irons. Whether the effect produced by such a mix- ture is one of neutralization, strictly speaking, or merely of dilution, remains to be deter- mined. Little is known of the effect of other elementary substances on wrought iron. Man- ganese, if present in pig iron, is almost entire- ly removed on conversion into wrought iron. Chromium, titanium, tungsten, manganese, and other substances are sometimes added to