10 .
1.
CHARGE OF THE ELECTRON
'
eQuation, rst derived by Laplace, which
the number of
particles per
cubic centirheter at different he1ghts 1s
_
_
d
_
71 = 710€"
_
(1_17) .
in which 710 is the number per
cubic centimeter at a given distance
& below the plane in which 71 is measured, 772 is the true mass, D is
the density of the particle, while of is the density of the uid, g is
the acceleration of gravity, R is the universal gas constant, T is
the absolute temperature
and N is the quantity sought, i.e.,
Ayogadro’s number. Perrin, after extensive tests with colloidal
suspensions, found N '= 6.82 X 1023
which is surprisingly
close to the accepted value considering the diiculties of the experiments.
Substitution in the equation Ne _= 9649, gives a reasonable,àlthough not an_ accurate value of 6 (4.24 X 10*10 e.s.u.).
Einstein has derived an equation for the average—squared—
_
distance
through which a suspended particle moves in a given
=
direction in a time-[.
This is
Ü
-
ZÎ2 =
(1—18)
NK
-
‘
in which R_ is" the gas constant per gram-molecule, T is the absolute
temperature, Nis Avogadro’s number and K (which is the same
‘
as
in equation 1—1) is the resistance to the motion. Perrin
_
tested ;this equation with colloidal suspensions and found
N=688 X1023.
T0gether
with
Ne = 9649, this
gives
1VeS € =
>< 10“10 e.s.u., again in approximate agreement
Value.
'
.
_
'
1-9 ;AVOgadÿ0’s‘ Number from Brownian
Emste1n’s
motion equation may besolved for Avogadro’s
numberNThus
Ï,
_
.
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_
.
.
.
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'
,
.
“hthand81de°ftheequat10nmaÿbedetermmedbytheuseOf-the '
—
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