128 Remarks on the Cutting of Steed by Soft tron. 
steel is broken or separated by fracture,* with much less force 
than when heated less or more, the requisite temperature va- 
rying probably in proportion to the carbon contained in the 
el. 
The result of the copper wheel mentioned by MM. Da- 
fier and Colladon having no action on the steel, goes far to 
prove that the effect depends at least as much on heut soft- 
ening the steel, to a certain degree, as on percussion, copper 
having but little disposition to generate heat under any eir- 
cumstances, a fact duly appreciated by the manufacturers of 
u " 
‘he veo reason why. “the heat should be nearly all concen- 
trated in the steel and scarcely perceptible in the iron,” I 
think to be this; the percussion against the steel is continual, 
but against any one part of the iron cutter, perhaps not more 
than from 34, to ste part of the time ; consequently the 
leat received by each would be in an inverse proportion of 
the thickness of the steel to the circumference of the irom, 
making the proper allowance for what may be thrown 
off from: the circular cutting iron in its egesae trough the 
ay which must be considerable 
P. Se bs evidence: of ’ the ae ate of “see it is fainted in 
the of MM. Darier and Colladon that the smail 
— -of steel adhering to the edge of the cutter, “seen 
hrough a lens, did not appear as if untempered, and when 
ished with a file, were found as hard as: the best tempered: 
steel.’” 
I have never observed the appearance of the particles, or 
examined their temper, but have examined the: burr: raised 
incu @ plate of steel, which before the operation was 
sufbein soft to file with ease, but in the operation beeame 
hardened on the outer edge much harder than before, which 
was evidently caused by the great heat and by being sudden- 
ly-cooied by the current of air caused by the motion of the 
cutter; the same would be the case with particles disen- 
seged se or when hot, Wwe! adhering to som edge * ~ 
acmeneel 
Ave disposition to be eas separated yacture at a particuley 
hanlsadvcneoute carbonized or oy pny fw 3 at and of tim, 
is very perceptible in flint glass, and perhaps’ in all factitious : ee 
compounds ; some requiring a moderate, and others a plore intense heat 
7 
