1 66 Caft StecL [Book VI. 



it acquires a deeper yellow and more toughnefs, with 

 fcarcely any diminution in the degree of hardnefsj 

 when brought down to the colour of watch fprings-, it 

 is of the fitted temper for cutting wood. Steel, by 

 being heated in this manner, becomes fucceffively 

 white, yellow, orange, red, violet, and laftly blue, 

 which colour remains a confiderable time 3 but if the 

 heat is raifed it becomes whitifh. 



Steel ftrongly heated while in the fire, a flumes a 

 red and fparkling appearance, it next becomes very 

 white and dazzling, and then burns with a fenfible 

 flame. 



Ca(l fteel is nothing more than fteel refined by 

 fufion. During this procefs it throws up fcoria, whilft 

 the metallic matter which remains is much harder than 

 before, and its texture more uniform. 



Iron is one of the metals which is acted on moft 

 powerfully by acids. But not only acids, but all fa- 

 line fubftances feem to affect it, and even water is ca- 

 pable of acting on it fo as to acquire from it a peculiar 

 tafte. The tendency, indeed, which this metal has to 

 combination with other bodies, particularly with oxy- 

 gen, which occafions mil, renders it incapable of per- 

 manencyj and for this defect no fufficient preventative 

 has yet been difcovered. 



M. Lavoifier, having expofed iron with water in a 

 glafs vefiel over mercury, obferved that the iron be- 

 came rufty, and that the water was diminifned in quan- 

 tity. The iron was increafed in weight, and there was 

 a production of inflammable gas, fo that in this experi- 

 ment the water was decompofed by the iron, even 

 without the prefence of air. 



Iron is acted on by the vitriolic, muriatic, and ni- 

 trous acids, with nearly the fame phenomena as zinc. 

 The products, however, are very different. The fo- 



lutioi), 



