The times., 1900-12-30

monium chloride. It was to be expected
that the density should be half the mo
lecular weight, thus:
(NHa+H U=NH.c i.nd 5s.5 s.5se=2e.75=densit,
H+9u 1859 5a5.
But the density actually found Is only
half that number, viz. 1881: and for lone
this and similar cases were supposed to be
| exceptions TO the law of Gay-Lussac, viz
that equal volumes of gases at the same
pressure expand equally for equal rise oi
temperature. In other instances the grad
ual decrease in density with rise of tenn
perature can be followed, as with chloral
hydrate, the products of which are choral
and water.
1t was recognized by st. Claire DevilIe
| QS5D that the decrease in density of such
mixtures of gases was due, not to their
being exceptions to Avogadros law, bu,
to the gradual decomposition of the COM
pound 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, as will be seen in the sequel. To
take the above instarce of ammonium
| chloride, its abnormal density is due to
| its dissertation into ammonia and hydro.
| gen chloride: and the gas which is OBJ
| tained on raising its temperature consists,
not of gaseous ammonium chloride. but of
a mixture of ammonia and hydrogen chlo-
ride, which, as is easily seen, occupy.
when separate, twice the volume that
would be occupied by the gaseous COM
pound of recent years II has been shown
by Brereton Baker that If perfectly free
=
ifies as such. and that its density in the
state of vapor is in fact 26.75.
| The molecular complexity OF gases has
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
kinetlc theory of gases has been devised
by Joule, Clausius, Maxwell Thomson
Qord Kelvin) and others. On the as
sumption that the pressure of a gas on
the walls of the vessel which contains it
is due to the continued impacts OF its
molecules, and that the temperature of
gas is represented by the product of the
mass of the molecules, or the square Of
their velocity, it has been possible to offer
a mechanical explanation of Boyle's law.
that at constant temperature the volume
of gas din1lnishes 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 discovered by Thomas Graham
I-p;x
London. and subsequently master of the
Royal Mint. Graham discovered that the
rates of diffusion of gases into each other
is inversely as the square roots Of their
densities. For instance, the density of hy-
drogen being taken as unity, that of oxy-
gen is 16 times as great; If vessel con-
tanning hydrogen be made TO communicate
with one containing 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 molecule of each
gas. And Graham found experimentaIly !
that for each volume of oxygen which En-
ters the hydrogen vessel four volumes of
hydrogen will enter the oxygen vessel
Now. 4=T16; and as these masses are rela-
lively and 10. and their temperatures
are equal, the square of their velocities
are respectively and 16.
The question Of the molecular complex
ity of gases being thus disposed of, ii re-
mains to be considered what are the rela-
tive complexity of liquid molecules. The
answer is indicated by n study of the ca
pillary phenomena Of liquids, one method
of measuring which is the height of their
Iarr- t,,r,o
is impossible in the space at our disposal
te enter into detail as to the method and
arguments necessary; suffice ii to say that
the Hungarian physicist Eotvos was the
first to indicate the direction of research,
and that Ramsay and Shields succeeded in |
proving that the conplexity of the laoie- |
cules of most liquids is not greater than |
that of the gases which they form on be- |
ing vaporized; and also that certain |
liquids, e. g., water, the alcohols, and |
ether liquids, are more or less "asso- !
ciaied;" /. e., their molecules occur in |
coupllces of two, three, four, or more. and !
as the temperature is raised the complex
ity of molecular structure diminishes.
AS regards the molecular complexity of |
solids, nothing definite is known, and. !
moreover, there appears to be no method /
capable of revealing 1t.
While the researches of which a short /
account has now been given have led to
knowledge regarding the nature of mole
cules, the structure of the molecule has
excited interest since the early years OF ]
the century, and its investigation has led |
to important results. The fact OF the de-
of acidified water by an eiec-
Carlisle and of salts into bases and
"acids" by Berzelius and Hisinger in
1893, led to the belief that a close connec-
ton exists between electric energy, or, as
ii was then termed, electric force" and
the affinity which holds the constituents
of chemical compounds in combination. |
In 1907 Davy propounded the theory that
all compounds consist of two PORTIONS, one |
and the other clectro-neg-
ative. This idea was the result of expert
ments on the behavior of substances such,
for example, as copper and sulphur. II
portions of these elements be insulated
and then brought into contact they be-
come oppositey electrified. The degree of
is intensified by rise of tenn
perature until, when combination ensucs,
The electrification vdnishes. Combination.
therefore, according to Davy, is c..ncur-
rent with the equalization of potentlals
In 1872, Berzelius brought forward an elec-
tro-chemical theory which for the follow
ng twenty years was generally accepted.
His primary assumption was that the
atoms of clements, or, in certain cases.
groups of atoms, are themselves electri-
led: that each atom, or group of atoms,
possesses two poles, one positive, the other