366
.
-
16.
VACUUM TECHNIQUE
where K is a constant (=7r7'2/ /7 ). Then a scale calibrated for
pressure may be placed along the central capillary tube. The
'
instrument may be built to cover ranges extend1ng from 1 mm.
10*6 mm.
With a bulb of 200 cc. capacity and a capillary whose
reidiusis 0.5 mm. and length is 20 cm., K = 3.93 X 10—6 and the
gauge
reads conveniently from 10"5
Two ranges
of pressure may be measured by the same instrument 1f constructed
with the larger tube E of (4). - This gure also shows a d1fferent
!”B
"
'
î
'
'
'
G
""”
M
F-—
|-P
‘9’
I
‘
_
.
F1Gi16—10.
Pressure gauges.
‘
theressurethegreatertherateatwhlchheatlsCOHducœdawaÿ