Remurks og the Cutting of Steel by Soft Irew. 127 
Arr. XV. gaflererie, on the cutting of stecl by soft iron, in u 
letter to the Editor, Bid om Tomas Kenpatu, Je. 
As the subject of cutting steel by ‘soft iron, has excited 
considerable attention, and seems not yet to be exhausted, 
I take the liberty to communicate such facts connected with 
the subject, as have come under my own observation, to- 
gether with some remarks, which ere at your disposal. In 
the cutting of revolving tron by tempered steel, experience 
proves that there is a certain velocity beyond which it can- 
not be well and freely done. Much depends on the purity 
and state of ren iron, much on the form, temper, and sharp- 
ness of the cu instrument, much whether the work is 
performed 8 a ept constantly wet with water oroil, and 
also much on the disposition of the particles of tron to ehip. 
There is a great aeron in different samples of iron in that 
respect, but much more difference in copper and its alloys, 
some of which, although sufliciently soft, can ‘scarcely be 
wrought by. turning, filing, drilling. or grinding. Whenever 
the steel or cutting tool, from any cause, ceases to act on 
the iron, and the heat is perhaps at the maximum, the iron 
if revolving will act on the steel; the greater the velocity 
the more freely it acts, and the progress is marked by differ- 
comes heated be ecaaail the cutting tool to a blue clout if 
moving with ter sign 
gaged. These become ignited because, 9 connected 
with, and forming a part of the plate, they are by the motion 
disengaged with a velocity that does not admit of the trans- 
mission of the heat to the other parts of the steel. Perhaps 
the ignition is commenced and carried to that degree de- 
nominated biack heat, before the particles are separated, 
and is completed by the friction attending the separation. 
It is a fact, perhaps not generally known to those who have 
written on the subject, that at the heat called black heat, 
(but which is in fact nearly or quite a red heat in the dark ) 
