Steel. 
gular to observe how very imperfectly the cementation 
of iron has been described by men of great eminence in 
the science of chemistry . Fourcroy states the length of 
time necessary for the cementation of iron to be about 
twelve hours ; but it is difficult to discover whether he 
alludes to cast or to bar steel : for he says, that short bars 
of iron are to be put into an earthen box with a cement, 
and closed up. Now steel is made from bars of iron of 
the usual length and thickness : but cast steel is made 
according to the process described by Fourcroy, with this 
essential difference— the operation is begun upon bar 
steel, and not bar iron. 
Mr. Nicholson is equally unfortunate in the account 
given in his Chemical Dictionary. He says, that the 
usual time required for the cementation of iron is from 6 
J to 10 hours, and cautions us against continuing the ce- 
mentation too long ; whereas the operation, from the be- 
ginning to the end, requires 16 days at least. In other 
parts of the operation he is equally defective, confound- 
ing the making of bar with that of cast steel, and not fully 
describing either. In speaking of the uses of steel, or 
rather of what constitutes its superiority, Mr. Nicholson 
is also deficient. He observes that “ its most useful and 
advantageous property is that of becoming extremely hard 
when plunged into water.” He has here forgotten every 
thing respecting the temper and tempering of steel instru- 
ments, of which, however, he takes some notice in the 
same page. u Plunging into water” requires a little ex- 
planation : for if very hot steel be immersed in cold wa- 
ter without great caution, it will crack, nay sometimea 
break to pieces. It is however necessary to be done, in 
order to prevent the steel from growing soft, and return- 
ing to the state of malleable iron ; for, were it permitted 
to cool in the open air, the carbon which it holds in com- 
