IRON. 



regulated, in order to obtain iron of any 

 desired quality; and this quality must 

 likewise, in the first product, be necessa- 

 rily different, according to the nature of 

 the parts which compose the ore. 



The iron which is obtained from the 

 smelting furnaces is not pure, and may 

 be distinguished into three states: white 

 crude iron, which is brilliant in its frac- 

 ture, and exhibits a crystallized texture, 

 more brittle than the other kinds, not at 

 all malleable, and so hard as perfectly to 

 withstand the file : grey crude iron, 

 which exhibits a granulated and dull tex- 

 ture when broken ; this substance is not 

 so hard and brittle as the former, and is 

 used in the fabrication of artillery, and 

 other articles which require to be bored, 

 turned, or repaired : and black cast iron, 

 which is still rougher in its fracture ; its 

 parts adhere together less perfectly than 

 those of the grey crude iron; this is 

 usually fused again with the white crude 

 iron. 



Whenever crude iron,especially the grey 

 sort, is used again in contact with air, it 

 emits sparkles, loses weight, and becomes 

 less brittle. In order to convert it into 

 malleable iron it is placed on a hearth, 

 in the midst of charcoal, urged by the 

 wind of two pair of bellows. As soon as 

 it becomes fused, a workman continually 

 stirs it with a long iron instrument. Dur- 

 ing the course of several hours it be- 

 comes gradually less fusible, and assumes 

 the consistence of -paste. In this state it 

 is carried to a large hammer, the repeat- 

 ed blows of which drive out all the parts 

 that still partake of the nature of crude 

 iron so much as to retain the fluid state. 

 By repeated heating and hammering, 

 more of the fusible iron is forced out ; 

 and the remainder, being malleable, is 

 formed into a bar or other form for sale. 

 Crude iron loses upwards of one fourth 

 of its weight in the process of refining ; 

 sometimes, indeed, one half. 



Purified, or bar iron, is soft, ductile, 

 flexible, malleable, and possesses all the 

 qualities which have been enumerated 

 under this article as belonging exclusive- 

 ly to iron. When a bar of iron is broken, 

 its texture appears fibrous ; a property 

 which depends upon the mechanical ac- 

 tion of the hammer while the metal is 

 cold. Ignition destroys this fibrous tex- 

 ture, and renders the iron more uniform 

 throughout; but hammering restores it. 



If the purest malleable iron be bedded 

 in pounded charcoal, in a covered cruci- 

 ble, and kept for a certain number of 

 hours in a strong red heat, (which time 

 must be longer or shorter, according^ 



the greater or less thickness of the bars 

 of iron) it is found that by this opera- 

 tion, which is culled cementation, the 

 iron has gained a small addition of weight, 

 amounting to about the hundred and fif- 

 tieth, or the two hundredth part, and is 

 remarkably changed in its properties. It 

 is much more brittle and fusible than be- 

 fore. Its surface is commonly blistered 

 when it comes out of the crucible ; and 

 it requires to be forged to bring/its parts 

 together into a firm and continuous state. 

 This cemented iron is called steel. It 

 may be welded like bar iron, if it have not 

 been fused or over-cemented : but its 

 most useful and advantageous property is 

 that of becoming extremely hard when 

 ignited and plunged into cold water. The 

 hardness produced is greater in propor- 

 tion as the steel is hotter, and the water 

 colder. The colours which appear on 

 the surface of steel slowly heated are yel- 

 lowish-white, yellow, gold colour, pur- 

 ple, violet, deep blue ; after which the 

 ignition takes place. These signs direct 

 the artist in tempering or reducing the 

 hardness of steel to any determinate 

 standard. If steel be too hard, it will 

 not be proper for tools which are intend- 

 ed to have a fine edge, because it will be 

 so brittle thai, the edge will soon become 

 notched ; if it be too soft, it is evident 

 that the edge will bend or turn. Some 

 artists ignite their tools, and plunge them 

 into cold water ; after which they bright- 

 en the surface of the steel upon a stone : 

 the tool being then laid upon charcoal, or 

 upon the surface of melted lead, or , 

 placed in the flame of a candle, gradually 

 acquires the desired colour ; at which in- . 

 stant they plunge it into water. If a hard 

 temper be desired, the piece is dipped 

 again, and stirred about in the cold water 

 as soon as the yellow tinge appears. If 

 the purple appear before the dipping, > J 

 the temper will be fit for gravers, and 

 tools used in working upon metals; if. 

 dipped while blue, it will be proper forj 

 springs, and for instruments used in the 

 cutting of soft substances, such as coi 

 leather, and the like ; but if the last pa 

 colour be waited for, the hardness of th< 

 steel will scarcely exceed that of iror 

 When soft steel is heated to any one 

 these colours, and then plunged into 

 ter, it does not acquire nearly so great 

 degree of hardness as if previously made 

 quite hard, and then reduced by tem- 

 pering. The degree of ignition required 

 to harden steel is different in the dif- 

 ferent kinds. The best kinds require 

 only a low red heat. The harder the 

 steel, the more coarse and granulated its 



