The Durham recorder. [volume] (Durham, N.C.) 1879-19??, 1910-01-27
PROPERTIES OF ice.
Why Skating Is Easier When the Tenn.
perature Is Not Too Low.

WHY CAN We SKATE more eaSll'
when the weather is not too cold
Why do our skates sbitev or tax,
hold of the ice better when the tenn
perature is not far below the freez
ing point? The explanation Of THU
simple and universally recognized
fact will enable us also to see til,
reason for another. the truth Of
which is recognized BY every school
boy-namcly, that snow<will pacl
better into snowballs when nearl,
at its melting point.
The explanation of both these
facts lies in an almost unique prop,
erty OF water or, rather, ice, which
causes it to melt or tend to melt
when pressure is applied to it. When
the pressure is relieved, if it is still
below its normal freezing tempera-
ture. il at once solidiEes again.
This property is beautifully illus
trated in familiar experiment in
which a LARGE cake of Ice is used,
supported at eachend. II a loop OF
fine wire il passed around it and
a weight attached to the end it will
soon be noted that the wire is slow
~ cutting its way through the ice,
but curiouslv enough without caus-
ing any division Of the cake, for the
ice is melted into water by the
pressure directly beneath the wire,
which water at once freezes into ice
again above the wire, so that per-
haps after IN hcar's time the wire
will have cut its way completely
through tive CAKE. leaving it, how
ever, rs solid and whole as ever.
In the case of the skater, then,
the weight of his body carried on a
narrow skate may produce a pres
sure on the ice sufficiently great to
melt a snail groove under the edge
Of the runner. This enables it to
take hold Of the ice more readily,
and, furthermore, the water acts as
a lubricant on the ice and makes it
slippery. Since considerable pres
sure Is necessary to produce melting
even when the temperature is only
a degree or 50 below the normal
melting point. this effect will not
take place on a very cold day, for,
as is we'll known. very cold ice is not
Slipper. The szne explanation
holds Tor snowballs. But the pres
sure DEVELOPED in tbs case Is much
less, 81 that melting enough to
''pal" vel VII not occur unless
tie lsos i nearly warm enough to
Iil eees is ns.ea W q Grand
feale u tha etre 81 el0ie-s. which
flow siev, casn 4 pso-nsain SIDE
mWt IA y ne IVES vicioss fuii.
The i. ase dcu.opel aloag
TIE bottom IS rel At TIE turns
and oaer points cases a siieht
me.tu Which i Immediately fol-
IDTca IN frcesing 'n "a soan is
The pressure is T0 I'D. Thu -
ables lie iee 70 apt itself to ine
shaFa q taa Yal.c as it proceeds on
is vas.
Ice j. oae 81 tie few sab tances
that shbw this e.eet Al melting nm
der pressure. ard il ice . because
Of the fact that water expands On
freezing. The great majority OF
substances contract on solidifying
ard hence would show the reverse
eifect-that IS. pressure applied 10
them IN the molten state would tend
TO cause qualification.
Thi~ i ore reason for believing
that tie Interior 81 our earth as a
whole j. solid rather than molten,
for, while sc believe that the tenn
perature Ct tire interior NAV be
much To-n than cnoagh t. melt
rock nn,lsT ordinary coalitions
and indeed volcanoes show that
there j. plcrty Of molten rock not.
50 yery fat below the surface-the
enormous pressU-c- that exist deep
down IN the earth are caonrh to
keep the material in q solid condi-
tion.-ilinneagoli4 journal.