On hardening and tempering Steel. 95 
and, with the precautions already noticed, giyen it the pro- 
per form, it may be hardened; but the fame method will 
not anfwer for all. purpofes. Some pieces, from, their fize 
and figure, are very difficult to be hardened ; if they are 
large, they heat the water in immediate contact with them, 
and the heat is communicated to the reft of the water, fo 
faft that it prevents the pieces from. being cooled quick 
enough to produce the defired effect: this is in part pre- 
vented by continually moving the piece about in the water ; 
but when too large to be hardened by this method, a ftream 
of watér mut “a4 employed ; and for fuch pieces as the face 
of large anyils, a birch broom is, ufed with advantage, to 
break the bubbles that are formed by the continual difen- 
gagement of air, and which, if not {wept away, would’ prevent 
that intimate contact and.uniform fucceflion of the ftream 
neceflary to produce the degree of hardnefs requized.. Other 
articles, from their length, are difficult, and almoft impof- 
fible to be made hard without bending, or otherwile altering 
their figure: this circumftance oceafions a. great deal of 
trouble ; end many a piece of work is fpoiled, after a good 
deal of labour has been beftowed upon it. The method that 
has fucceeded belt with me is, either to inclofe the piece or 
pieces intended to be hardened in an iron cafe or box, open 
at one end (for the more ready dropping the pieces into the 
water), and giving it a flow, yet regular heat; then to take 
the cafe out of the fire, and drop the pieces into the water 
in fuch manner as will allow them to. come as little as_pof- 
fible in contaét with the air. This method anfwers two 
good purpofes.at once, caufing the heat to be more equally 
applied, and preventing the contaét of the air, and of courfe 
any {caling ; and when the work has been polithed and well 
defended from the air, it comes out nearly as.clean as it 
was before. When the greateft poffible hardnefs is re- 
guired, it may be obtained by ufing quickfilver inftead of 
water; but this can only be employed for fmall articles. 
For a La fteel is required to have a fuperior degree 
of 
