182
8.
ELECTRICITY THROUGH GASES
.
a gas as the pressure
is gradually diminished, (2) to plot a striking
‘
potential—pressure curve and (3) to calibrate an ionization gauge by
'
means of a McLeod gauge.
'
Âppamz‘us.——An oil pump, discharge tube and induction coil
will show many of
but a more elaborate system,
‘such as that in gure 8—16, is to be preferred. Here B is a dis—
charge tube (say one meter long and 5 centimeters in diameter)
containing the aluminum electrodes 1% and C
.
A low power transformer (T) may be used and is to be controlled by the rheostat (R).
The alternating current is partially rectied by the use of a pointed
Ï
anode (Â) and a large area cathode (C). The voltage drop is
read on the,electrœstatic voltmeter (V); range 200 to 2000 volts._
,
The discharge tube may be evacuated in steps by use of the ‘
stopcocks 82 and 83 and the large ask (F).
83 is closed and F
evacuated by the pump (P). Then 82 is closed and 83 opened.
Air may be admitted to the system through the capillary tube (1).
It is dried as it enters by the phosphorus pentoxide, P205. The
use of the P205 tube here, as well as the one near the fore pump,
.
is necessary, especially if the refrigerant in the trap (D) is C02
(solid pieces of carbon dioxide, slowly added to acetone) since the
_
_
.,
vapor pressure of ice (frozen in D) at the temperature of freezing
-
carbon dioxide is comparatively high. Other gases than air may
be introduced at 84.
(This stopcock is Shown backwards in
8—16 and should be reversed.)
'
“.
'
Pressures above one millimeter are determined from the differ—‘
ence between the barometric height and the difference of level of
the mercury
in the two arms of the open tube manometer (P1)—_
_
Forlower pressures, the McLeod gauge (P3) is used. A
_
tion Will be found in Chapter 16. A gauge of this type design?d
’
f0r use at higher pressures, Will not be accurate at lower values,
'.
and vice versa. Hence, it is suggested that a McLeod gauge be
_
,
used which covers
the range from, say
to 10”5 millimeterof
mercury, “With good accuracy and that the Pirani type (P2)(See
,
section 16”—8) =be‘ used_in the intermediate region from, say,0ne
t0
millimeter. .»P4 is the ionization gauge
to »be cahbrated
from 0.005“ “_m'illi‘r‘neter ‘ d0w11.
that the gauges =P2 andP4
may
on the opposite side of theCOz or liquid air tra()
of "the
and
measuring
8.
ELECTRICITY THROUGH GASES
.
a gas as the pressure
is gradually diminished, (2) to plot a striking
‘
potential—pressure curve and (3) to calibrate an ionization gauge by
'
means of a McLeod gauge.
'
Âppamz‘us.——An oil pump, discharge tube and induction coil
will show many of
but a more elaborate system,
‘such as that in gure 8—16, is to be preferred. Here B is a dis—
charge tube (say one meter long and 5 centimeters in diameter)
containing the aluminum electrodes 1% and C
.
A low power transformer (T) may be used and is to be controlled by the rheostat (R).
The alternating current is partially rectied by the use of a pointed
Ï
anode (Â) and a large area cathode (C). The voltage drop is
read on the,electrœstatic voltmeter (V); range 200 to 2000 volts._
,
The discharge tube may be evacuated in steps by use of the ‘
stopcocks 82 and 83 and the large ask (F).
83 is closed and F
evacuated by the pump (P). Then 82 is closed and 83 opened.
Air may be admitted to the system through the capillary tube (1).
It is dried as it enters by the phosphorus pentoxide, P205. The
use of the P205 tube here, as well as the one near the fore pump,
.
is necessary, especially if the refrigerant in the trap (D) is C02
(solid pieces of carbon dioxide, slowly added to acetone) since the
_
_
.,
vapor pressure of ice (frozen in D) at the temperature of freezing
-
carbon dioxide is comparatively high. Other gases than air may
be introduced at 84.
(This stopcock is Shown backwards in
8—16 and should be reversed.)
'
“.
'
Pressures above one millimeter are determined from the differ—‘
ence between the barometric height and the difference of level of
the mercury
in the two arms of the open tube manometer (P1)—_
_
Forlower pressures, the McLeod gauge (P3) is used. A
_
tion Will be found in Chapter 16. A gauge of this type design?d
’
f0r use at higher pressures, Will not be accurate at lower values,
'.
and vice versa. Hence, it is suggested that a McLeod gauge be
_
,
used which covers
the range from, say
to 10”5 millimeterof
mercury, “With good accuracy and that the Pirani type (P2)(See
,
section 16”—8) =be‘ used_in the intermediate region from, say,0ne
t0
millimeter. .»P4 is the ionization gauge
to »be cahbrated
from 0.005“ “_m'illi‘r‘neter ‘ d0w11.
that the gauges =P2 andP4
may
on the opposite side of theCOz or liquid air tra()
of "the
and
measuring