The Salt Lake herald. [volume] (Salt Lake City [Utah]) 1870-1909, 1900-02-27

body, some occur, under ordinary con-
ditiohs. in the three states Of gas, liquid
and solid. Water, for example, under
the usual pressure of the atmosphere,
passes into steam at 100 degrees cent?
grade or 212 degrees Fahrenheit, ana
freezes at 0 degrees centigrade or 81
degrees Fahrenheit. If the pressure is
increased the boiling point rises, ana
if the pressure is lowered the bOlllng
point falls accordingly. The pressure
and the temperature must both De
taken into account If the temperature
is kept shigh, as in a steam boiler
greater pressure must be eXerteu 70
maintain the water in the hqulu sld1e
and if the ordinary temperature WelS'
on the average. 400 degrees cenCSraue
higher than il is water would be known
10 MS only as a gas. That is, steam at
a Temperature above 35S degrees cent?
grade. or about 81 degrees Fahrenhelt'
cannot be changed to LIQUID Dy any
pressure, however great
The researches of Andrews showed
clearly that a similar state OF IhlhsS
exists for every substance. mat II,
there is for every substance some PoIlit
of tenperature above which 1t cannot
become LIQUID. and this temperature is
called the critical temperature his
most instructive experiments were
made with "carbOniC acid gas, or car
bon dfoxide, which has a critical tenn
perature easily reached Inc IlIdI sIep'
then, in the liquefaction or any gas
must evidently be to reduce us IeIli-
perature below the critical point LNl-
IDENTIFY, also, any gas Will De easy VI
difficult TO liquefy according as Us cIllI
cal temperature is high or low OAS ssH'
whose critical temperature IS 10 De
Z gTdOe, EeSAStEA
| All efforts at liduefaction for many
wears: nitrogen, with a critical tenn
nerat1re of -146 degrees centSrade'
was still more refractory, ana hSuIo-
gen whose critical temperature Hds
NOT bpen exactly determined, had 10
/ be cooled to about 235 degrees or more
/ below the zero of the centigraue scSie
/ before it yielded, .-1,.
The attainment of these extremely
/ low tenoneratllres was a matter OF
/ great difficulty, and was accomplished
only gradually, through years OF eA-
pertinent. The means upon Wnlch chlSI
| reliance has been placed until recently
/ is the heat change occurring Mheh
substance which melts or Dolls at
! low temperature is allowed 10 chanse
/ from the solid to the liquid or from tHe
! liquid to the gaseous state
Heat Changes In Melting and Boiling
When a solid is melted heat must
| be continually supplied TO II until the
melting is completed. TINS neat Is
used in doing the work OF separating
/ the particles from the close Donds
which make it solid. 1t produces no
/ change in temperature, anc IS there
] fore called latent" heat. The use or
ice in drinking water is a common IL
lustration Of this action, or the freezing
Of ice cream by the melting OF mix
ture of ice and salt In TIE latter case
part of the necessary heat is supplied
to the melting mixture by the cream
which is frozen. the freezing point OF
! the cream being higher than the melt
/ ing point Of the miXture.
| Similarly, when a liquid IS changed
/ to q gas. a steady supply or neat IS
I necessary. mucn greater than IS need
| ed to melt the same quantity OF the
| substance. IT is possible 20 evaporate
water so rapidly under a reduced pres
sure that the water itself iS frozen me
heat Is used in work at rapid rate
and is taken from the BODY OF water
which is evaDorating. Small portions
Of substances which are usually case
1 Gus have been soiidifed in this way.
( by means Of this action, and by
proper choice Of substances. very low
/ temperatures have been produced, The
method is still used and must continue
to be. In the past it has been an eX-
peEsive method because the substances