164 Forging of Irm. [Book VI. 



which is contained in the crude iron, and which it ' is 

 commonly fuppofed to acquire from the fuel during the 

 procefs of fmelting * 



The iron, by this mode of refining, lofes, befides 

 the plumbago, a quantity of fiderite, which Bergman 

 luppofed to be a peculiar metal, but which is now 

 found to be a combination of iron and phofphoric 

 acid. 



After the iron has been kept in this fituation a cer- 

 tain time, it is carried to a large hammer, generally 

 moved by water, where it is formed into bars. The 

 hammering, by bringing the particles of the iron 

 nearer together, prefles out the impurities, and thus 

 completes what was left deficient by the fufion. This 

 keating and hammering are repeated a number of 

 times, till the iron has acquired the defired degree of 

 perfection. Crude iron loles from a quarter to a third 

 of its weight by the procefs of refining, and is then 

 called forged iron. 



Steel is made by furrounding the bars of iron with 

 a compofition of which charcoal is the chief and only 

 elTential ingredient, and by keeping them in an iutenfe 

 heat a longer or fhortcr time, according to their thick- 

 'nels. They are then taken from the furnace, and 

 plunged in cold water. The metal is now found to 

 be more fufible than it was before, but to have lefs duc- 

 tility and foftnefs. Its texture is finer j it breaks fhorfji 

 its fracture is always grey, and it has gained a fmall irt- 

 Creafe of weight. 



With refped to the chemical ftates of the metal, 

 in the three forms of caft iron, forged iron, and fteel, 

 it appears that they chiefly depend on the quantities 



* Plumbago confifts of carbon, with about one tenth of its weight 

 of iron. 



Of 



