54 Obfervations on Iron and Steel. 



Bergman, but which have been more perfectly explained by 

 Vandermonde, Berthollet, and Monge, that crude iron is a 

 regulus, the reduction of which is not complete ; and which 

 confequently will differ according as it approaches more or 

 lefs to the metallic (late. Forged iron, when previoufly well 

 refined, is the purefl metal ; for it is then the moft malle- 

 able and the moft ductile, its power of welding is the greateft, 

 and it acquires the magnetic quality fooneft. Steel confifts 

 of iron perfectly reduced and combined with charcoal ; and 

 the various differences in bliftered fteel, made of the fame 

 metal, confift in the greater or lefs proportion of charcoal 

 imbibed. Iron gains, by being converted into fteel, about 

 t^ part of its weight. In order to harden fteel, it muft be 

 put into a clean charcoal, coal or cinder fire, blown to a 

 fufiicient degree of heat by bellows. The workmen fay, 

 that neither iron nor iteel will harden ptoperly without a 

 blaft. When the fire is fufficiently hot, the inftrument in- 

 tended to be hardened muft be put in, and a gradual blaft 

 from the bellows continued until the metal has acquired a 

 regular red heat : it is then to be carefully quenched in 

 cold water. If the fteel be too hot when immerfed in wa- 

 ter, the grain will be of a rough and coarfe texture j but if 

 of a proper degree of heat, it will be perfectly fine. Saws 

 and fome other articles are quenched in oil. Steel is tem- 

 pered by again fubjecting it to the action of the fire. The 

 inftrument to be tempered we will fuppofe to be a razor 

 made of caft fteel. Firft rub it upon a grit (tone until it is 

 bright, then put the back upon the fire, and in a fhort time 

 the edge will become of a light ftraw colour, whilft the back 

 is blue. The ftraw colour denotes a proper temper, either 

 for a razor, graver, or pen-knife. Spring knives require a 

 dark brown ; fciffars a light brown or ftraw colour ; forks or 

 table-knives a blue. The blue colour marks the proper tem- 

 per for fwords, watch-fprings, or any thing requiring elafti- 

 city. The fprings for pen-knives are covered over with oil 

 before they are expofed to the fire to temper. 



Expla- 



