Year: 1874


many chemists ',ave abstaned from it as too purely
hypothetical, and the fundamental idea OF the
science has lfen that Of ratios or equivalents OF
combination expressible on any scale starting from
hydrogen. as one, or oxygen as one hunuieu' INC
equivalents proportions of combination oelne
equally indicated in either case. But the new start
ing point the mOlecule, is something more uenhI'e
and fixed. that the physicist and the chemist eau
now begin to entertain It IN common. ohe"'suS
now plants itself upon the foundation whlch waslau
for il by the Italian physicist Avogadro fifty years
ago Ii was proposition of determlnate qnahuuos
IN relation to molecules. Avogadro enunciated the
following law in 1871: Equal rOhtmes Of all sub
stances rheu in the state Of gas and under IKE cOndo"s
contain the same number Of molecules"


This principle is arrived at by the following con-
siderations: cubic inch Of water, for example, is
assumed TO consist of certain number OF definite
water particles or molecules, and these are mann
tanned through all the physical changes OF the
LIQUID When sufficiently heated, this cubic men OF
water becomes q cubic foot of steam. The neat,
tberefora separates the molecules to greater dis
tances from each other, that the spaces between
them become enormously increased. lhe steam'
With IFS definite number of particles greatly sepa-
rated. may thus be taken to represent the general
constitution of gases. --a'~-


That these large interspaces do exist is proved
in the following manner: A globe is filled with
steam at the temperature of boiling water, ana no
more steam can be introduced at that temperature
But that the space cannot be continuously occupied
or packed close with water molecules Is proved Dy
the fact that the vapor of boiling alcohol will enter
it, and that the globe will contain just as much OF
this yapor as if no steam were present. If, now
that the globe is filed with aqueous yapor and alco-
hol yapor at one and the time, each acting III
all respects as if it occupied the space alone, we add
a ouantity of ether we shall have the same phe-
nomena repeated The ether will expand and fill
the space with It's vapOr and the globe viii hold
lust as much ether vapor if neither OF the other
two were present"


The following experiment has a still further sig
nifcance II water, alcohol, and ether, IN the h9u'd
state be heated they all expand but with the same
amount of heat, they expand aheQadty Zach has
its own rate of expansion, which seems to he con-
| nected with the nature of the substance. But II
| now these liquids be converted into vapor ana a
higher temperature applied, two things will be OBJ
| served. First. they expandsfar more rapidly than
before; and second, they all expand at the same
rate The influence of the nature of the substances
| has wholly disappeared. and they come under the
operation of q common law which pertains to the
aerform state. Upon this point Prof Cook remarks:
| Why now this difference between the states OF
matteri II material fills space completely In the
not conceive why the nature OF the substance should
have the same influence on the phenomena OF e1,
gate Of definite small masses or molecules, %hlcl, WINE
widely separated when the liquids are converted into
vapor then 1t obvious that tue action OF the particles
on each other which might be considerable in the first
state would become less and less the molecules were
separated, until at last it inappreciable aud ~
| further Avogadros law assumes the number OF
these particles in given space Is the same for a gases
under the same conditions then 1t is equally obvious
that there being no action between the particles All
yapors may be regarded as aggregates OF the same
should expect that the action OF heat on such similar
masses would be the same.


How this simple physical principle was found TO
underle the whole fabric of modern chemistry, 1t
is the purpose of Professor Cooks book to explain.
! OF one of its bearings he says:


II not then without that we take this law as
the basis of the modern system OF chemistry; and,
starting from it, let what it leads In the first
directly the relative weight Of OF All such
substances as are capable OF existing ~ the serfoTm @
gases contain the same number Of noieele ne retdtpe
peights Of equal 9ds-roiones Thus. cubic foot OF


weighs sixteen times as much as cubic foot OF
hydrogen under the same conditions IT, then; there
in the cubic foot OF each gas the same number OF
molecules each molecue OF oxygen must weigh sixteen
times as much as each mOlecule 0I hydrogen.


This clearer and more definite conception OF mole
! cules that has been concurrenuy reached by the
chemists and physicists has led them TO undertake
the problem of measuring the actual dimensions OF
| molecules OF course the quantities with which we
have here to deal, at natures extreme Of minute
ness are excessively inconceivably small. But
Prof Cook paves the way to the infntesimal scale
on which nature operates by first showing how
art can approach il. While the smallest of


light those of the violet ray $4,000 of an inch
in SIZE the German Optican Nobert makes plates for
testing microscopes which ruled at the rate of
ll2 900 lines to the inch, and he is said TO have car
ried his ruling as far as 224,OOO lines to the inch.
Prof Cook is not confident as to the existence of
luminiferous ether but he regards the undulatory
! theory of light an established fact. He says:
whether there are such things as waves Of ether
! or not, there is something concerned in the phe-
nomena of light which has definite dimensions that
| have been measured with as much accuracy az the
! dimensions Of astronomy" These dimensions he
! employs to measure the thickness of soapbubble
films and we will let him tell in his own lucid Ian
guage how the result bears upon the question of the
| size of molecules:


You thus that the theory light enables 20
the thickness OF the m and we know that where that
gray tint appeared in experiment the thickness OF
the film was less than of the length OF "a OF red
jght less than 1l5eo0 OF an inch, aud DO wonder
that the film broke when 1t reached such degree Of


But having followed me thus far. and being assured,
as hope you are. safe ground, and talk
lug about hat do know. your curiosity will lead
you 70 inquire whether We can stretch the hIm any


The facts are that after the appearance OF the gray
tint, although the film evidently STRETCHES to limited
extent 10 very breaks. Practically then, we can
not stretch II beyond this point 20 any great ex-
tent but why mott theoretically IL the material OF
water is perfectly homogeneous there would 10 he
no good why Ii should not be capable OF al
indefinite extension, and why this film could not be
stretched TO indefinite degree OF attenuation Assume,
however that water consists OF molecules OF definite
size, then II is evident that limit would be reached
the thickness Of the film reduced to the
stretch the film beyond this without increasing the dis
tance between the molecules and thus increasing the
~ fha