1022 IRON 



metal will have completely molted down, and in dropping through the blast from the 

 tuyere, have become partially oxidised ; by the action of the oxide of iron thus formed, 

 and of the basic silicate of protoxide of iron remaining in the hearth at the close of 

 the last operation upon the molten pig-iron, the latter is decarburized to a considerable 

 extent, and, in consequence, becomes less fusible and more pasty. After perfect 

 fusion of the metal, the refining process begins ; this consists in incessantly breaking 

 up the metal with an iron bar, and carrying towards the tuyere the raw portions, 

 which being more highly carburised and more fusible than the rest, always run down 

 to the bottom and there harden. The metal, which has thus more or less solidified, 

 is Broken up and submitted to the action of the blast, until all is sufficiently refined ; 

 this operation lasts about half an hour. Subsequently, all the metal is brought up to 

 the top of the hearth, and again melted down with a lively heat to form the ball, fresh 

 charges being thrown into the hearth, and the unmelted portions being kept up at 

 intervals with an iron bar to prevent their adhering to the ball before having been 

 melted. The ball is then taken out and hammered into a prismatic shape, which is 

 cut into pieces to be welded in another fire. The whole process lasts from l to 1J 

 hour. 



The blast is frequently used at a temperature of 100 C., and at a pressure of 2 

 inches of mercury. 



The cut-up pieces to be drawn out under the hammer are welded and heated in 

 hearths much resembling in size and construction the charcoal finery itself, or in 

 an Ekman's furnace, now extensively used for this purpose. 



The quality of the iron is tried in various ways : as, first, by raising a bar by one 

 end, with the two hands over one's head, and bringing it forcibly down to strike 

 across a narrow anvil at its centre of percussion, or one-third from the outer extre- 

 mity of the bar ; after which it may be bent backwards and forwards at the place of 

 percussion several times ; 2, a heavy bar may be laid obliquely over props near its 

 end, and struck strongly with a hammer with a narrow pane, so as to curve it in op- 

 posite directions ; or while heated to redness, they may be kneaded backwards and 

 forwards at the same spot, on the edge of the anvil. This is a severe trial, which the 

 hoop L. Swedish iron, bears surprisingly, emitting as it is hammered a phosphoric 

 odour, peculiar to it and to the bar iron of Ulverstone, which also resembles it in fur- 

 nishing a good steel. The forging of a horse-shoe is reckoned a good criterion of the 

 quality of iron. Its freedom from flaws is detected by the above modes ; and its 

 linear strength may be determined by suspending a scale to the lower end of a hard- 

 drawn wire, of a given size, and adding weights till the wire breaks. The treatises 

 of Barlow, Tredgold, Hodgkinson, and Fairbairn may be consulted with advantage 

 on the methods of proving the strength of different kinds of iron in a great variety 

 of circumstances. 



Dry Assay of Iron-ores. The object of a dry assay of an iron ore is to ascertain 

 by an experiment on a small scale the amount of iron which the ore should yield 

 when smelted on the large scale in the blast-furnace. For this purpose the metal 

 must be deoxidised, and such a temperature produced to melt the metal and the 

 earths associated with it in the ore, so that the former may be obtained in a dense 

 button at tho bottom of the crucible, and the latter in a lighter glass or slag above it. 

 Such a temperature can only be obtained in a wind furnace connected with a chimney 

 at least 30 feet in height, and when made expressly for assaying the furnace, is gene- 

 rally built of such a size that four assays may be made at the same time, viz., al>ont 

 14 inches square, and 2 feet in depth from the under side of the cover to the moveable 

 bars of iron which form the grate. In order that the substances associated with the 

 iron in the ore should form a fusible compound, it is usually requisite to add a flux, 

 the nature of which will depend upon the character of tho ore under examination. 

 Berthier divides iron-ore into five classes : 1. The almost pure oxides, such as the 

 magnetic oxide, oligistic iron, and the haematites ; 2. Ores containing silica, but free or 

 nearly so from any other admixture ; 3. Ores containing silica and various bases, but 

 little or no lime ; 4. Ores containing one or more bases, such as lime, magnesia, alinnina, 

 oxide of manganese, oxide of titanium, oxide of tantalum, oxide of chromium, or oxide 

 of tungsten, but little or no silica; 5. Ores containing silica, lime, and another base, and 

 which are fusible alone. Ores of the first class may be reduced without any flux, 

 but it is always better to employ one, as it greatly facilitates tho formation of tho 

 button ; borax may be used, or better, a fusible earthy silicate, such as ordinary flint- 

 glass. Ores of the second class require some base to serve as a flux, such as carbonate 

 of soda, a mixture of carbonate of lime and clay, or of carbonate of limp and dolomite. 

 Ores of the third class are mixed with carbonate of lime in tho proportion of from one 

 half to three-fourths of the weight of the foreign matter present in tho ore. Ores of 

 the fourth class require a flux of silica in tho form of pounded quartz, and generally 

 also some lime; tho manganesian spathic ores which belong to this class may be 



