The sun., 1900-12-30

porcelain. at known temperature, closing
the bulb while still hot and weighing IL
after IL is cold. knowing the capacity OF
the bulb. the weight Of hydrogen necessary
to Ill it at the desired temperature can be
calculated and the density of the vapor
thus arrived at. A second method was
devised by Gay-Lussao and perfected by
A. W Hofmann us8s,. and third. prefer
able for It's simplicity and ease of execu-
tion. is due to Victor Meyer assn.
In 1883, as already remarked, Canniz-
Nrro showed the connection between these
known facts. and for the first time atten-
ton was called to the true atomic weights.
which were. up to that time. confused with
equivalents, or weights of elements re-
qured 10 replace one unit weight Of hydro
gen. These were generally regarded "a
atomic weights by Dalton and his con-
temporaries.
EXCEPTIONS TO THE LAW.
Some exceptions had been observed to
the law Of Dulong and Petit. viz. beryllum
or glucinium. an element occurring in
emcralds: boron, Of which borax is a COM
pound; silicon, tho component of quartz
and flint, and carbon. II was found by
Weber that at high temperatures the spe-
Cfc heats of these elements are higher.
and the atomic heats approximate TO the
number OF 90: but this behavior ia not
peculiar TO these elements. for IL appears
that the specific heat of all elements in
crcascs with rise of temperature.
4 certain number Of exceptions have also
been noticed to the law Of Gay-Lussac,
which may be formulated The molecular
weight of a compound in a gaseous state is
twice its density referred to hydrogen.
Thus. equal volumes of ammonia and ny
drogen chloride unite 10 form ammonium
chloride II was 10 be expected that the
density should be half the molecular weight,
thus:
Nh, HCl-NTI.Cl; and So c=25 rs density.
"a g. 1850 SO
But the density actually found is only
half that number, viz, 1897; and for long
this and similar cases were supposed To be
exceptions 10 the law of Gay Lussac, viz,
that equal volumes Of gases at the same
pressure expand equally for equal rise Of
temperature. In other instances the grad
ual decrease in density with rise Of tenn
pcrature can be followed. rs with Chloral
hydrate, the products of which are choral
and water
1t was recognized by ST. Claire Deville
Gs57l that the decrease in density of such
mixtures of gaSoS was due. not To their being
exceptions q AvOgairo'S law. but To the
gradual decomposition of the compound
body with rise OF temperature. To this
gradual decomposition he gave the name
dissertation This conception has proved
Of the utmost importance to the science. ~
will be seen in the sequel To take the above
instance of ammonium chloride. irs abnormal
density il due to It's dissertation into am
monia and hydrogen chloride; and the gas
which is obtained on raising its temperature
consists, not of gaseous ammonium chic
ride. but of mixture Of ammonia and
hydrogen chloride. which. as is easily seen.
occupy. when separate, twice the volume
that would be occupied by the gaseous COM
pound. OF recent wears it has been shown
by Brereton Baker that il perfectly free
from moisture. ammonium chloride CASTLES
as such, and that its density In the state Of
vapor is in fact 2675.
thus gradually become comprehended. and
the truth Of Avogadro's law has gained
acceptance And as a means of picturing
the behavior Of gaseous molecules the kinefic
theory OF gases has been devised by Joule,
Causus Maxwell, Thomson lord Kelvin
and others. On the assumption that the
pressure OF a gas on the walls of the vessel
which contains il is due to the continued
impacts of its molecules, and that the tenn
perature Of gas Is represented by tho
product Of the mass OF the molecules, or
the square of their velocity. it has been
possible 10 offer a mechanical explanation
Of Boyles law, that at constant temperature
the volume OF gas diminishes in proportion
as the pressure increases; OF Gay-Lussac's
law, that all gases expand equally for equal
rise Of temperature, provided pressure Is
kept constant; the condition being that equal
volumes Of gases contain equal numbers
Of molecules. A striking support is lent
To this chain Of reasoning by the facts dis
covered by Thomas Graham usO5-lS6M.
professor az University College, London,
and subsequently, master OF tie Royal Mint.
Graham discovered that the rates Of
diffusion Of gases into each other is in
vcrsely a. the square roots of their densities
For instance. the density of hydrogen being
taken as a unity that Of oxygen " 10 times
as great: If vessel containing hydrogen
be made to communicate with one contain
ing oxygen. the hydrogen will pass into
the oxygen and mix with it; and, conversely.
the oxygen will pass into the hydrogen
vessel. This is due to the intrinsic motion
of the molecules Of each gas. And Graham
found experimentally that for each volume
Of oxygen which enters the hydrogen vessel
four volumes OF hydrogen will enter the
oxygen vessel Now, 4=Nls: and as these
masses are relatively l and 10. and their
temperatures are equal. the squares Of their
yelooities are respectively and 10.
CoMPLENITY OF LIQUID MOLECULES.
The question of molecular compeyity
Of gases being thus disposed OF, 1t remains
to be considered what are the relative com
pleNity ~ liquid molecules. The answer
is indicated by a study ~ the capillary
phenomena Of Equids, one method of meas
nrinu which 1. tho bni,,n, ,f th,ir ..,1..