43 $ 
Cast Steel. 
it, it gives what clock-makers mostly use for their work. 
Farther tallow is useless; a small degree of heat more 
would just be seen in a dark place, or the lowest degree 
of a red heat : such is the temper given to the springs 
1 for coaches, &c. Thus I have given a reason why oil or 
tallow is made use of, and given you the parallel degrees 
of temper which by a dry heat are observed by the change 
of colour only. The method of hardening in quicksil- 
ver is of great use where a superior degree of hardness is re- 
quired ; and good steel so hardened, when the precautions 
before mentioned are duly attended to, will cut glass like 
a diamond, and turn or cut other steel at so high a temper 
I as to differ but little from quite hard.-— Perhaps at a future 
time I may give you a method by which this hardest of 
i steel may also be worked with considerable ease, and the 
cases in which I have applied it to advantage. 
As steel is always found more compact and strong 
! bodied when hardened with a low heat, and as that effect is 
best obtained the colder the water is which is employed 
hardening it, provided the water is clean, (a circumstance 
which should always be attended to,) — -it appeared proba- 
ble, that if water was cooled down to the freezing point, 
or even lower, which it may be, and retain its fluidity by 
being kept in a state of perfect rest, the effect might be 
heightened. I caused a large heap of snow to be collected 
together at a time when the thermometer stood at 22° of 
Fahrenheit, and making a deep hollow in the middle, I set a 
glass of clean water in the bottom of the hollow, and co- 
vered the whole with a board to prevent the air from dis- 
turbing or causing any motion in the water. I heated 
some pieces of steel in the breech end of a gun barrel to 
a low red heat ; and bv means of an assistant to take off 
the board at the instant I arrived with the heated barrel 
and its contents, I quickly dropped the pieces into the 
water ; which having stood all the preceding night in the 
