The sun., 1900-12-30

u2.l2) given by Berzelius as the atomic
weight OF carbon; and with his collaboration.
Stas, undertook the redetermination OF the
atomic weights OF the commoner elements.
for example. carbon, oxygen. chlorine and
calcium. This line Of research was subse-
auently pursued alone by Stas. whose name
will always be remembered for the precision
and accuracy OF his experiments. At first
Dumas and Stas inclined to the view that
Prouts hypothesis was just one. but 1t
was completely disproved by Stas's subse-
quent work IA well as by that Of numerous
other observers 1t is nevertheless curious
that much larger proportion of the atomic
weights approximate to whole numbers
than would be foretold 10y the doctrine OF
chances. and perhaps the last has not been
heard Of Prout's hypothesis. although in its
original crude form it is no longer worthy OF
credence
ATOMS AND MOLECULES.
One OF the most noteworthy Of the dis
coveries Of the century was made by Gay
Lussao Q77s-ls5o) in the year 1893. In
conjunction with Alexander Won Humboldt.
Gay-Lussao had rediscovered about three
years before what had previously been
established by Cavendish. namely, that.
as nearly az possible. two volumes Of hydro
gen combine with one volume Of oxygen
to form water. the gases having been meas
ured at the same temperature and pressure.
Humboldt suggested TO Gay-Lussao that
Il would be well TO investigate whether
similar simple relations exist between the
volumes Of other gaseous substances when
they combine with each other This turned
out to be the case: it appeared that almost
exactly two volumes Of carbonio oxide
unite with one volume of oxygen TO form
carbon dioXide; that equal volumes OF
chlorine and hydrogen unite TO form hydro
Chloric acid gas: that two volumes of am
Inonia gas consist OF three volumes of
hydrogen, in union with one volume Of
nitrogen and so on. From such facts.
Gay-Iussao was led to make tho state
ment that: The weights Of equal volumes
OF both simple and compound gases, and.
therefore, their densities, are proportional
10 their empiricqlly found combining
weights. or TO rational multiples of the latter.
Gay-Lussac recognized this discovery Of
his to be a support for the atomic theory;
but it did not accord with many OF the
then received atomic weights. The as
sumption that equal volumes OF gases
contain equal numbers o! particles. or. as
they were termed 10y lin. molecules tn
tfgrGntcs. was made in 1911 by Avogadro.
professor of physics at Turin (l77G-lsjGl.
This theory. which has proved of the ut
most importance TO the sciences both Of
physics and OF chemistry, had no doubt
occurred to Gay-I I.ussac, and had been
rejected by him for the following reasons
4 certain volume of hydrogen, say one
cubic inch, may be supposed 10 contain
an equal number Of particles tatoms) as
an equal volume Of chlorine. Now. these
two gases unite in equal volumes. The
deduction appears so far quite legitimate.
that one atom of hydrogen has combined
with one atom of chlorine. But the re-
sulting gas occupies two cubic inches, and
must therefore contain the same number
of particles Of hydrogen chloride, the COM
pound Of the two elements as one cubic
inch originally contained of hydrogen
or OF chlorine. Thus We have two cubic
inches containing. Of uncombned gases.
twice as many particles as is contained
In that volume after combinations. Avo-
Gadro's hypothesis solved the difficulty.
BY promising two different orders Of par
ticlcs. now termed atoms and molecules,
the solution was plain. According TO him.
each particle. or moleculc. of hydrogen
is a complex. and contains two atoms; the
same is the case with chlorine. When
these gases combine. or rather reoct. TO
form hydrogen chloride. the phenomenon
Is one Of a change of partners; the mole
cule the double atom, Of hydrogen splits:
the same Is the case with the molecule of
chlorine: and each liberated atom of hydro
gen untCs with liberated atom Of chlorine.
forming a compound. hydrogen chloride.
which equally consists Of a molcCule, or
double atom. Thus two cubic inches Of
hydrogen chloride consist of a definite
number Of molecules, equal in number TO
those contained in n cubic inch Of hydrogen
plus those contained in a cubic iuch Of
chlorine The case IL precisely similar if
other compounds Of gases be considered.
Ber2elius was at first inclined 10 adopt
this theory and indeed went so far rs TO
change many Of his atomic weights 10
make them ft II. But later lie somewhat
withdrew from his position. for it appeared
TO him that il was hazardous to extend
10 liquids and solids theory which could be
held only of gases. Ayogadro's suggestion.
therefore. rested in allowance until the
publication, in 1858. by Cannizzaro. now
professor of chemistry In Rome, Of an
essay in which all the arguments in favor
ut the hypothesis were collected and stated
in a mastery manner. II will be advisable
To revert 10 this hypoth, sis at a later point
and to consider other guides for the de-
termination of atomic weights.
EQUAL CAPACITY PoR HEAT.
In 1919. Dulong i7s5-ls3s). director of the
Ecole Polytechnique at Paris. and Petit
u791-is2W. professor Of physics there. made
the discovery that equal amounts Of heat
are required 20 raise equally the tempera-
ture OF solid and liquid elements. pro-
vided quantities are taken. proportional
to their atomic weights. Thus TO raise
the temperature Of SO grammes OF iron
through one degree requires approximately