.
EXPERIMENT 3—1
65
a shallow dish with the gold side on the platinum, carefully add
amyl acetate, wait until the lacquer is dissolved, wash in the sol—
vent several times and nally Withdraw with care.
lt need hardly
be stated that the preparation of the thin foil is one of the most
difcult parts of the experiment and that several attempts may be
made before a successful foil is obtained.
The observation chamber has a brass tube, T, 12 to 15 centimeters long and about 6 centimeters in diameter. A glass plate,
P, not less than 3 or 41 millimeters thick is sealed on the end with
wax, or with a rubber gasket and stop-cock grease.
There is a
coating of luminescent material on the inner surface of P. To
form this
“
screen,” the glass is placed horizontally, moistened
with saliva and sprinkled With a mixture of nely powdered phosphorescent zinc sulphide (20%) and calcium tungstate (80%). If
desired, photographic records of the diffraction patterns may be
obtained.
Descriptions of various cameras for this purpose will
be found in the references 9
or may
be designed by the student.
The potential may
be supplied by a large induction coil and
condenser, a large static machine or a transformer—rectier-con—
denser unit.
An x—ray power supply serves nicely. Potentials from
10,000 to 60,000 volts will be found satisfactory, although consider—
able heating will be encountered at the higher potentials. The
wave-length of the electrons and hence the radii of the diffraction
rings depend on the applied potential. Sharper rings are, therefore, obtained when the potential is maintained at a constant value.
Good ltering equipment is needed when a hot lament is used as
the electron source.
With the cold discharge tube, however, the
potential drop across the tube depends to a large extent on the
residual gas pressure, as regulated by the leak, and to a lesser
extent
on
the current passing through the tube. A suitable
voltage supply may therefore be made up
of a transformer, half—
wave rectier tube, an 0.01 microfarad condenser and a series diode
operating under saturation conditions to maintain constant current to the discharge tube.
The potential may be measured by means of a sphere gap, by
means of a milliammeter in series with a high resistance or with
an
electrostatic voltmeter across a portion of a high resistance.
See chapter 19.
EXPERIMENT 3—1
65
a shallow dish with the gold side on the platinum, carefully add
amyl acetate, wait until the lacquer is dissolved, wash in the sol—
vent several times and nally Withdraw with care.
lt need hardly
be stated that the preparation of the thin foil is one of the most
difcult parts of the experiment and that several attempts may be
made before a successful foil is obtained.
The observation chamber has a brass tube, T, 12 to 15 centimeters long and about 6 centimeters in diameter. A glass plate,
P, not less than 3 or 41 millimeters thick is sealed on the end with
wax, or with a rubber gasket and stop-cock grease.
There is a
coating of luminescent material on the inner surface of P. To
form this
“
screen,” the glass is placed horizontally, moistened
with saliva and sprinkled With a mixture of nely powdered phosphorescent zinc sulphide (20%) and calcium tungstate (80%). If
desired, photographic records of the diffraction patterns may be
obtained.
Descriptions of various cameras for this purpose will
be found in the references 9
or may
be designed by the student.
The potential may
be supplied by a large induction coil and
condenser, a large static machine or a transformer—rectier-con—
denser unit.
An x—ray power supply serves nicely. Potentials from
10,000 to 60,000 volts will be found satisfactory, although consider—
able heating will be encountered at the higher potentials. The
wave-length of the electrons and hence the radii of the diffraction
rings depend on the applied potential. Sharper rings are, therefore, obtained when the potential is maintained at a constant value.
Good ltering equipment is needed when a hot lament is used as
the electron source.
With the cold discharge tube, however, the
potential drop across the tube depends to a large extent on the
residual gas pressure, as regulated by the leak, and to a lesser
extent
on
the current passing through the tube. A suitable
voltage supply may therefore be made up
of a transformer, half—
wave rectier tube, an 0.01 microfarad condenser and a series diode
operating under saturation conditions to maintain constant current to the discharge tube.
The potential may be measured by means of a sphere gap, by
means of a milliammeter in series with a high resistance or with
an
electrostatic voltmeter across a portion of a high resistance.
See chapter 19.