-
_
376
*
16.
VACUUM TECHNIQUE
_
.
;
from leaks.
It may
then be sealed into the walls of the vacuum
chamber, glass to glass.
_
In gure 16—12, a copper tube E has been ared at its end and
thinned down by
“
spinning
”
in a lathe. This is rst fused to the
.
glass at F, after which the fusion is extended to G by blowing out
‘
_the__ glass as the ame is advanced. The joint is then carefully
'annealed by cooling slowly.
Either hard or soft glass may be used.
,
At H in the same gure, a copper
foil is placed between the
ends of two
tubes.
The glass is fused, then the right tube (dotted)
is blown out and drawn away leaving a ring of glass on the face
J
D
E
F
a
'
_H__-____
&
|
1
=
,
—
0
L
A
,
.
.
[|
_
‘
76cms
7Gcms
_
_
-Ll
1|
'
M
_
_
_
Fm. 16—12.
Vacuum
_
of the copper which is now fused to the other tube. Various
electr0des may be put through this
soldered in place. .
,
An alloy of iron, nickel and cobalt, called
“
F ernico,” is used
,
as an 'intermediary metal between the iron shell of radio tubes
and
special glass
beads through which the lead—in Wirespass.
-
Sealing
a Chamber is to be sealed—off from
—
the system, a narrow
made in the tubing as close as
possible tothe chamber, as at ] in gure 16—12. After pumpîng
.
out, this const'riction is warmed all over, the pumps
m
operation
to remove
giVen o" by the heated Walls. Then a … '