423 OF ENGINEEBING FORMULÆ.
Tempering Steel.
Colour. Purpose, Tempe- rature. Alloy whoso Fusing Point is of tne same Temperature.
Light straw Dark straw . ßrown yellow Dark purple f Turning tools for i ( metal .. ,. j J Wood tools, taps, ) t and dies ,. J J Hatchets, chip- ( t ping chisels .. | Springs, &c. i. J’ah. 430° 470° 500° 550° tia. lead. 1 to if 2 >. 3 ‘U 1 „ 12
Brazing.
The edges filed or scraped clean and bright,
coveted with spelter and powdered borax and ex-
posed in a clear fire to a heat sufficient to melt
the solder.
To Test Steel and Iron. (4 Scientific American.’)
Nitric acid will produce a black spot on steel,; the
darker the spot the harder the steel. Ii;ou, on ths
contrary, remains bright if touched with nitric acid.
Good, steel in its soft state has a curved fracture
and a uniform grey lustre; in its hard state a
dull, silvery, uniform white. Cracks, threads, or
sparkling particles denote bad quality.
Good steel will not bear a white beat without fall-
ing to pieces, and will crumble under the hammer
at a bright red heat, while at a middling heat it may
be drawn out under the hammer to a fine point.
Care should be taken th;it before attempting to
draw it out to a point the.fracturø is not concave, and
should it be so the end should be filed to an obtuse
point before operating. Steel should be drawn out
to a fine point and plunged into cold water; the frac-