The Houston daily post. [volume] (Houston, Tex.) 1886-1903, 1900-04-17
cr,,,cnI temperature.

rrtticaI TempeFoa"N
=, ,,e substances familiar to everxpod5'
- occur under ordinary conditions IN
~. ,,ro. states OF gas. liquid and SOLO
,uater for example, under the usual pres
sure Of the atmosphere, passes mic steam
Mt 100 degrees centigrade or zlS oes'e.'
Fahrenheit, and freezes at degrees seN''-
vraae and % degrees Fahrenheit. the
pressure is increased the boiling po'u'
rises and II the pressure is lowered the
boiling point falls accordingly. Inc pres
sure and the temperature must botn Dc
,ahen into account. II the temperature y
Len, high as in steam boiler, sIel',si
nressure must be exerted to MAINTAIN tne
water in the LIQUID state and II the CT
dinary temperature were, on the aVel'e
400 degrees centigrade higher tnsn II -
water should be known TO us oniy az tssc
That is. steam at 4 temperature aooYe goo
degrees centigrade, or about 81 degrees
! Fahrenheit can not be changeu 10 HUN
by any pressure, however great
The researches of Andrews showed clear
Nv that a similar state of things exists LOT
every substance. That is, there Is ior
every substance some point OF tenlpetatuis
shove which Il can not become Liquid, ana
this temperature is called the criscai
Temperature His most instructive %,
periments we're made with "carbon!c acio
gas" or carbon dioxide. which has q eriti-
cal temperature easily reached. Inc hrst
sfen, then. in the liquefaction OF any Ses
must evidently be to reduce its tempeTa
lure below the critical point. Then, anu
not before then. will pressure become et-
fective in reducing It to Liquid. WI
IDENTIFY. also, any gas will be easy or dlih,
cult TO liquefy according as its crilcal
Temperature is high or low. OXygeA
whose critical temperature Is ll6 beloW
zero. centigrade, resisted all efforts az
liouefaction for many years; nitrogen, WAN
a critical temperature OF lit degrees cen
Upgrade. was still more refractory ana
hydrogen, whose critical Temperature mas
not been exactly determined, had 10 ot
cooled to about 1886 degrees or more below
the zero of the centigrade scale before II
yielded.
The attainment of these extremely low
Temperatures was matter OF great aim
Guilty and was accomplished only graz
ually, through years of experiment az
means upon which chief reliance has oee'
placed until recently is the heat chahg'
occurring when a substance wn;ch melt'
or hollis at low temperature Is allo"e'
to change from the solid to the llquld @
from the liquid 10 lne GHseouo SNS'NS'
Heat Changes in Melting and Botitni
When a solid is melted heat must b
continually supplied to it until the mel I'M
ia completed This heat is used in doinl
the work of separating the particles Icon
the close bonds which make 1t SOLO,. !
produces no change in temperature ana
therefore called latent" heat. The use Q
Ice in drinking water Is common illust a
ton Of this action, or the freezing OF 10
cream by the melting of mixture oil c
! and salt. In the latter case part OF Ii
: necessary heat Is applied to the meltin
mixture by the cream which is frozen. IN
Q freezing point OF the cream being hlghe
than the melting point OF the mixture
4 Similarly, when a liquid is changed to
gas, steady supply of heat is necessary
: much greater than is needed to melt III
S same quantity of the substance. It
e possible to evaporate water so rapid
: under reduced pressure that the watt
i. Itself is frozen. The heat is used II wor
at rapid rate and is taken FROM The bod
of water which is evaporating. Small POI
! tions OF substances which are usa7lly gas
, eous have been solicited in this way.
, BY means of this action, and by q prop'