Evening star. [volume] (Washington, D.C.) 1854-1972, 1891-03-07
QUEER THINGS ABOUT HEAT.
Prof. searie Tells Some Things People Gen.
orally DO Not Know.

erolty do NOT AnOW.
DIFFICULTY OF DISTINGUISHING BErwkRx Ex-
IRENE HEAT AND EXTREME coLp-oN CANNOT
wAEN ICE ABOVE rHIRry-rwo DEaRKKs-HARD
To WARN wArER-AcTIoN or HEAT ON GAsEs.
At the Catholic University yesterday after
noon Rev. Geo. NJ. Searle, c. q. p, delivered
the first of q course of public lectures on
Heat We suppose, he said. that we can tell
the difference between hot object and cold
one. but we have to acknowledge that the
heat or cold is very considerable we cannot ex-
actly tell which it is, and general feeling Of
pain is all that we can distingu ish. In moderate
temperatures sometimes a thing seems warm to
one person and cold 10 another, and the same
temperature effects the same person differently
at different times. But does not the Their
mometer show how much heat there is in the
object? Let us experiment little. Put to-
gcther equal parts of alcohol at 80 degrees
and water somewhere near the boiling point
say at 200 degrees. This. am given to under
stand, is rather n familiar experiment. with
some people. especially on festive occasions
What will the temperature OF the mixture
be? Most people win say 125 degrees, half way
between so and 200 degrees. bat if We put in q
thermometer we find it il $50 degrees In other
words, the water has thus been cooled only 30
degrees, while the alcOnOl has Deem warmed Dy
100 degrees. or twice az much.
A second experiment: Take pound Of mer-
curry at 100 degrees and u pound of water at
40 degrees stir up the mixture. Will the tenn
perature then be 20 degrees, half way between
40 and hundred? No. by no means, 1t will
only be AZ degrees: the water has hardly
warmed perceptibly. Now, we begin to see
why water puts out fires.
CANNOT WARN ICE.
Again, take pound of ice and try to warm
it When the ice is very cold we shall succeed,
but when it gets up to 80 the warming will
stop and we can warm it no more until it is all
melted. The same thing when 1t begins to
boil When it has started boiling You can put
in enough heat to raise it q thousand degrees
in temperature, but il will still stay at 202.
Another reason why water puts ont fires.
One more experiment.: Take air in an air
tight cylinder with movable piston in 1t, but
at first fasten the piston so il cannot move.
Let us heat the air for while and note the
Thermometer. Wait now till it cools off and
then set free the piston. Now, let US heat the
air again under the same circumstances and
just as long as before. Now, the piston will
move, the air will press it out, but the thermom-
eter will not rise near SO much % it did be-
fore.
By these experiments We see that the ther-
mometer does not measure heat. even in the
popular sense. What does it measure? 1t
be able to define temperature clearly until our
third lecture. Two bodies are said to be at the
same temperature when no heat will pass from
one TO the other when they are broughtint con-
tact. A q rule the rise and fall of temperature
is measured quantitatively by the amount Of
heat which passes from one to the other. For
every quantity of heat that comes in we have q
corresponding rise in temperature. But rise
in temperature Of the thermometer will be
altogether different according to the substances
into which the heat is going. This il what Is
called specific heat. 1t takes more heat to
warm water than almost anything else. By
the combination Of the theory Of heat with the
science Of chemistry We can not only figure out
why the specific heat of water is 80 great, but
we can figure out in advance pretty exactly
what the specific heat of body will be IL we
know its chemical composition.
ACTION OF HEAT on GASES.
After describing the different kinds Of scales
in Thermometers Prof. Sesrle went on to speak
Of the action of heat on gases. We find by the
air thermometor that air and all gases expand
automatically by an equal amount to every de-
gree Of Temperature. end that this amount 10
one Northumberland Q492) Of
the volume Of the gas at freezing point. 1t
would seem then that II we substract 492 de-
grees from air at the freezing point it should
shrink TO nothing at all. We cannot perform
this experiment., for We have no means of get
ting out all the heat. II we could we should
find that after while the gas would suddenly
change 70 liquid, shrinking good deal at the
time. Then the contraction would not 60 on
at the regular rate. Finally the gas would be-
come a solid and would remain %. It would
refuse to shrink to nothing at all Still. the in
dication Il believed to be true one that 492
times the amount Of heat We would have to take
out Of it to make it shrink from 81 degrees to
81 degrees Fahrenheit Is all the heat there IL in
it. and that there il such thing an absolute
zero Of heat, and this zero is 460 degrees below
that of the Fahrenheit scale. This il probably
realized pretty nearly in the small meteors
which ny through the planetary and stellar
spaces. in which the substances has not only
no power Of warming anything else, which Is
the idea of temperature, but no warmth or heat
even for itself. Now. the distinction between
heat which appears in q body rs temperature
and that which does not involves the CONVEX
sion of heat into something else. This will be
treatedof at the next lecture.