CARE REQUIRED
'
TO PRODUCE VACUA
371
VACUUM TECHNIQUE
'
16—12. Gare Required to Produce Vacua.—The lower the
_
-
pressure
to be obtained, the greater the care needed in the assembly
of the vacuum system.
For comparatively high pressures, above
say
0.1 mm., rubber tubing, greased stop cocks, waxed joints, etc.,
may be satisfactorily used. But for lower pressures, all connec_
tions should be made of glass while metal parts, waxed joint—s, stop
cocks and other sources of vapor pressure should be elimi‘hâted
wherever possible. For very low pressures, allparts must be
baked out for long periods of time to drive out the occluded gases.
With mercury condensation pumps or mercury gauges, it is neces—
sary to freeze out the mercury vapor with liquid air or carbon
dioxide snow if the pressure is to be lowered below 10”3 mm.
16—13.
Hunting for Leaks.—Dœpite great care in the assembly of a vacuum system, it is usually found that there remain small
-
_
holes or cracks too small to be visible._ When these are
>
tively large, blow into the system through a drying tube or apply
.
a few pounds of compréssed air and
over the outside with soap
suds.
Bubbles appear
at the leak.
'
_
,
'
When the pressure can be reduced so that a discharge passes
through, the leaks may be located with a…spark coil. This should
have a spark gap
in parallel with its
«to prevent high
‘
potentials which would spark through lweak spots intheglass._ _
_
_
Connect one terminal of the
theçoil to an ”electrode
sealed in the System. If there
Stick-a pin through
_
the rubber tùbing of the jfore vacuum lmeand war; arbund 1t‘. A_
_
wire‘fiom
allongglass rod and
care—
—
fully moved
oftheêystïem—ÿ
The
bem—g low
'
enough, & brightSparkoœursthrwgh
thehole
th€
lightsrup WhentheexplormgWirelsneaftheïeak _…=_}
.
.
‘
TheGe1ssierchschargeatthe10W6fPŒSSWËSIHanalr =t‘%‘b° ',
.
.:
«
'
._
tunesTh1s1sduetoasurface1aYÜ©fWaœr©nthemlde
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'
'
'
TO PRODUCE VACUA
371
VACUUM TECHNIQUE
'
16—12. Gare Required to Produce Vacua.—The lower the
_
-
pressure
to be obtained, the greater the care needed in the assembly
of the vacuum system.
For comparatively high pressures, above
say
0.1 mm., rubber tubing, greased stop cocks, waxed joints, etc.,
may be satisfactorily used. But for lower pressures, all connec_
tions should be made of glass while metal parts, waxed joint—s, stop
cocks and other sources of vapor pressure should be elimi‘hâted
wherever possible. For very low pressures, allparts must be
baked out for long periods of time to drive out the occluded gases.
With mercury condensation pumps or mercury gauges, it is neces—
sary to freeze out the mercury vapor with liquid air or carbon
dioxide snow if the pressure is to be lowered below 10”3 mm.
16—13.
Hunting for Leaks.—Dœpite great care in the assembly of a vacuum system, it is usually found that there remain small
-
_
holes or cracks too small to be visible._ When these are
>
tively large, blow into the system through a drying tube or apply
.
a few pounds of compréssed air and
over the outside with soap
suds.
Bubbles appear
at the leak.
'
_
,
'
When the pressure can be reduced so that a discharge passes
through, the leaks may be located with a…spark coil. This should
have a spark gap
in parallel with its
«to prevent high
‘
potentials which would spark through lweak spots intheglass._ _
_
_
Connect one terminal of the
theçoil to an ”electrode
sealed in the System. If there
Stick-a pin through
_
the rubber tùbing of the jfore vacuum lmeand war; arbund 1t‘. A_
_
wire‘fiom
allongglass rod and
care—
—
fully moved
oftheêystïem—ÿ
The
bem—g low
'
enough, & brightSparkoœursthrwgh
thehole
th€
lightsrup WhentheexplormgWirelsneaftheïeak _…=_}
.
.
‘
TheGe1ssierchschargeatthe10W6fPŒSSWËSIHanalr =t‘%‘b° ',
.
.:
«
'
._
tunesTh1s1sduetoasurface1aYÜ©fWaœr©nthemlde
°fthe
'
'