Observations on Iron and Steel. 47 



<>f iron to be about twelve hours ; but it is difficult to difco- 

 ver whether he alludes to call or to bar fteel : for he fays, 

 that fhort bars of iron are to be put into an earthen box 

 with a cement, and clofed up. Now fteel is made from bars 

 of iron ©f the ufual length and thicknefs : but caft fteel is 

 made according to the procefs defcribed by Fourcroy, with 

 this eflential difference— the operation is begun upon bar 

 fteel, and not bar iron. 



Mr. Nicholfon is equally unfortunate in the account given 

 in his Chemical Dictionary. He fays that the ufual time 

 required for the cementation of iron is from 6 to i o hours, 

 and cautions us againft continuing the cementation too 

 long ; whereas the operation, from the beginning to the end, 

 requires 1 6 days at leaft. In other parts of the operation he 

 is equally defective, confounding the making of bar with 

 that of caft fteel, and not fully defcribing either. In fpeak- 

 ing of the ufes of fteel, or rather of what conftitutes its fu- 

 periority, Mr. Nicholfon is alfo deficient. He obferves that 

 " its moft ufeful and advantageous property is that of becom- 

 ing extremely hard when plunged into water." He has here 

 forgotten every thing refpe&ing the temper and tempering 

 of fteel inftruments, of which, however, he takes fome no- 

 tice in the fame page. " Plunging into water " requires a 

 little explanation : for, if very hot fteel be immerfed in cold 

 water without great caution, it will crack, nay fometimes 

 break to pieces. It is however neceflary to be done, in order 

 to prevent the fteel from growing foft, and returning to the 

 ftate of malleable iron ; for, were it permitted to cool in the 

 open air, the carbon which it holds in combination Would 

 be diffipated*. I fhall at prefent confine my remarks to 

 the operations performed on iron in Sheffield and its neigh- 

 bourhood, from whence various communications have been 

 tranfmitted to me by refident friends, and where I have my- 

 felf feen the operations repeatedly performed. The iron 



* It is the opinion of fome mm'lurgifts, that a partial ?.bflra<ftion of 

 «ygcn takes place, by plunging hot metal into cold water. 



nrudt 



