Cast Steel, 
427 
The excellence and uniformity of a fine edge may be 
ascertained, by its mode of operation when lightly drawn 
along the surface of the skin, or leather, or any organized 
soft substance. Lancets are tried by suffering the point 
to drop gently through a piece of thin soft leather. If 
the edge be exquisite, it will not only pass with facility, 
but there will not be the least noise produced, any more 
than if it had dropped into water. This kind of edge can- 
not be produced, but by performing the last two or more 
strokes on the green hone. 
The operation of strapping is similar to that of grinding 
or whetting, and is performed by means of the angular par- 
ticles of fine crocus, or other material bedded in the face of 
the strap. It requires less skill than the operation of set- 
ting, and is very apt, from the elasticity of the strap to 
enlarge the angle of the edge, or round it too much. 
Letter on the Properties of tempered Steel, 
To Mr. NICHOLSON. 
SIR, 
In one of your Journals, I do not recollect which, you 
signified your intention of giving in a future number, 
some ideas upon certain singular properties of tempered 
steel. A number of unexplained facts have for some 
time been known to the workers of steel-plate. As I am 
concerned in a manufactory of the kind, and in the daily 
habit of witnessing those curious and anomalous appear- 
ances, I thought you might in some measure profit by the 
following description of the changes which take place in 
the various processes of hardening, tempering, hammer- 
ing, burnishing, 8cc. 
I took a steel-plate 30 inches long, 12 broad, and about 
,04 thick ; I hardened it in a composition of oil and tal- 
low, and afterwards tempered it down to a spring temper ; 
it was now so elastic as to recover its position after being 
