184
8.
ELECTRICITY THROUGH GASES
,—
Precoutiom.——1. Turn ol/ stop rocks slowly so
to Strip
.
the _stopcock grease
and introduce a leak into the system. 2. Turn
'
the stopcock (81) to the outside air before rhutz‘ing of the motor of
’
_
thefore pump, and especially at the end of the day. Otherwise,
oil Will be drawn out of the fore pump by the continued suction of
the evacuated system and considerable effort will be required to —
clean and re-assemble the equipment. 3. Raise the
in
.
the McLeod gauge (P3) slowly, particularly as it enters the capillary tube. It may be lowered rapidly. Do not leave the mercury
raised above the
“
cut-off” point at the end of the day. 4. Be
'
_
sure. that water is running through the cooling jacket of the pump '
'
(P) before turning on its heater.
If this has been neglected, do
not try to rectify your error by turning on the water until after
the pump has had time to cool down. Turn the water off at the
end of the day for, if left running and a break occurs in the rubber
tubing, the oor of the room will be ooded. Only a small stream
of water need run continuously through the pump
while it is in use.
5. Let the current run through the discharge tube as long as
you wish while studying the phenomena, but turn it off while you
‘_
proceed with other work. Reason: a hard, colored deposit forms
on the inner walls
long use of the tube, masks the dis—_
charge and requires removal or a new tube.
Ï
Experiment—(1) Tabulate the following characteristics of the
'
glow discharge for, say, ten different pressures from several cent1'
meters down to the point where the tube no longer conducts
length, intensity and color of the positive column, Faraday dark
space, negative glow, cathode dark space and cathode glow.
ï
At a given pressure, increase R until the discharge no longer
“
occurs.
decrease R and note the voltage Vs on the electro—
J.-___
voltmeter V at which the discharge may just
’
start
in the tube. Repeat at different pressures. This’workmay
be carried out simultaneously‘fwüh (1), at the same pressures
Vs as ordinates and of pressure as absCissae. Alog—
anthmlcscalemay be used ro;— the latter, if desired, in ordert0
';g::},äÎ
:
:
-
,
s—
(3)Atag1venpressure andw1th Constant electron curren'cln
themmzatmngauge() (section16—11) record'the
current 1nP4andtheMcLeodgaugepressure readmg Repeat
8.
ELECTRICITY THROUGH GASES
,—
Precoutiom.——1. Turn ol/ stop rocks slowly so
to Strip
.
the _stopcock grease
and introduce a leak into the system. 2. Turn
'
the stopcock (81) to the outside air before rhutz‘ing of the motor of
’
_
thefore pump, and especially at the end of the day. Otherwise,
oil Will be drawn out of the fore pump by the continued suction of
the evacuated system and considerable effort will be required to —
clean and re-assemble the equipment. 3. Raise the
in
.
the McLeod gauge (P3) slowly, particularly as it enters the capillary tube. It may be lowered rapidly. Do not leave the mercury
raised above the
“
cut-off” point at the end of the day. 4. Be
'
_
sure. that water is running through the cooling jacket of the pump '
'
(P) before turning on its heater.
If this has been neglected, do
not try to rectify your error by turning on the water until after
the pump has had time to cool down. Turn the water off at the
end of the day for, if left running and a break occurs in the rubber
tubing, the oor of the room will be ooded. Only a small stream
of water need run continuously through the pump
while it is in use.
5. Let the current run through the discharge tube as long as
you wish while studying the phenomena, but turn it off while you
‘_
proceed with other work. Reason: a hard, colored deposit forms
on the inner walls
long use of the tube, masks the dis—_
charge and requires removal or a new tube.
Ï
Experiment—(1) Tabulate the following characteristics of the
'
glow discharge for, say, ten different pressures from several cent1'
meters down to the point where the tube no longer conducts
length, intensity and color of the positive column, Faraday dark
space, negative glow, cathode dark space and cathode glow.
ï
At a given pressure, increase R until the discharge no longer
“
occurs.
decrease R and note the voltage Vs on the electro—
J.-___
voltmeter V at which the discharge may just
’
start
in the tube. Repeat at different pressures. This’workmay
be carried out simultaneously‘fwüh (1), at the same pressures
Vs as ordinates and of pressure as absCissae. Alog—
anthmlcscalemay be used ro;— the latter, if desired, in ordert0
';g::},äÎ
:
:
-
,
s—
(3)Atag1venpressure andw1th Constant electron curren'cln
themmzatmngauge() (section16—11) record'the
current 1nP4andtheMcLeodgaugepressure readmg Repeat