The Princeton union. [volume] (Princeton, Minn.) 1876-1976, 1913-08-21
BATTLES SCIENCE.
Why Hot Steel Is Tempered by
a Sudden Cooling.
SLOW COOLING KEEPS IT SOFT

Vet the Busy Brain of Man Cannot
Succeed In Reasoning Out Why This
Is So-The Mysterious Properties
Exhibited by Water. Tin and Glass.
Here is fact, known 10 everybody.
which is as mysterious as would be
the actual appearance of a ghost. by
which mean that the fundamental ex-
PLANTATION of the phenomenon is about
as far beyond our reach in the one
case as in the other.
The fact to which refer is the pro-
duction of tempered steel by quenching
in cold water. If hot steel is cooled
very slowly it becomes soft and cannot
take cutting edge, but if it is cooled
suddenly: it becomes very hard and can
be ground into keen swords. knives
and cutting tools.
Now, why the difference? Have you
ever thought about that question? If
you have not, many a man Of science
has, and has been puzzled over it.
Here is another related mystery If
you heat an old Japanese sword, which
for centuries has retained it's capacity
to slice off head at a blow. or to
open a swift passage for the soul of
the victim Of the harakiri mania. to
the temperature Of boiling water it
gradually softens and loses the keen
ness that once made it so formidable.
It is the same steel, but it. too, seems
to have lost it's soul. At a tempera-
ture of $50 degrees centigrade the
few minutes. Surely there is some
thing strange in that.
Then consider this: At zero tempera-
ture water changes from liquid and
suddenly becomes solid. But if you put
the water in vase and carefully pro-
tect it from dust you may cool it as
much as 20 degrees below zero and yet
it will not freeze! But now shake the
vase or drop in bit Of ice, and the
water Immediately solidifes!
owe the collection of these facts to
a paper by Professor James II. Wal
ton, Jr., of Wisconsin university. The
explanation which he gives is that sub
stances like the hardened steel and the
unfreezing water are in state of
suspended change" That accounts
for the phenomena. but in a certain
sense they remain mysterious, just as
life is mysterious
Many substances possess the same
curious characteristics. Professor WAL
ton says that if a flask containing So
dunn acetate, which has been cooled
below its natural freezing point with
out solidifying, is opened in a room
containing dust of the solid acetate the
fine particles of the latter dropping into
the flask will cause the whole contents
to solidify.
lin is very strange metal with re-
gard to this state of suspended change
or "metastability." A severe winter cold
will sometimes cause it to lose it's
hardness and crumble.
Objects made Of tin sometimes un.
dergo such change and are then said
to be suffering from 1.-The tin disease
The contact of "diseased" tin with
bright, hard tin is capable Of setting
up the transformation.
Glass, Professor Walton informs US.
is IAN undercooled substance"-that is.
it is in metastable condition. If old
glass tubes through which water has
frequently passed are heated the glass
crystallizes and loses its transparency.
All substances in this state are liable
to change. and the change, under prop
er conditions, may be sudden. Hard
ened steel is in similar category. If
it were as perishable as tin it could not
be safely used for many purposes for
which it is habitually employed For
tunately steel exhibits great resistance
to change OF state after it has been
tempered. Transformation is retarded
or arrested.
docs steel slowly return to the sta
bic form and thus grow softer?" asks
Professor Walton. and then answers:
THAT we do not know: we can only
say that if such a change does take
place. hundreds of years are necessary
to bring it about
The same ancient Japanese swords,
which. when heated, as before describ-
ed. become soft. retain all their hard
ness if carefully preserved.
1t is evidently Of the highest i'm
portance to the practical world that
science is investigating these things
and discovering the way and the cir
cumstances in which the changes come
about, even If it has not unveiled the
Underlying mystery of their cause
Garrett P. Serviss in New York Jour-
nal.
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