372
16.
VACUUM TECHNIQUE
in the system itself.
Phosphorus pentoxide (PgO5) in a side arm
or in a bottle as in gure 16—4 is very effective in absorbing water
vapor.
The oil in a fore pump
should be freed from moisture by
removing and boiling whenever the pump fails to operate at its
normal rate.
Another method for hunting leaks is to pass a discharge through
the system and sponge over it with ether or water.
With air in
the tube, the color changes from a pinkish to a bluish when the
water passes through the hole.
When the leak has been found, let in the air and fuse the hole.
For quick repair, the leak may be eliminated by covering it with
one of the low vapor pressure waxes; but this method cannot be
used for very low pressure work, especially on parts which are
to be heated.
Stop cocks should be tested for leaks before sealing into the
system by holding in a vertical position, pouring & drop or two of
ether or alcohol into the tube (the cock being greased and closed),
quickly sucking on the same tube, putting the tongue on the end
and watching if any bubbles come through the liquid.
Turn a
stop cock leisurely when using it and as seldom as possible for the
grease is ultimately squeezed out, leaving rings which leak. Never
twist the stopper unless the grease is present or the glass walls will
be scratched and leak.
Cast iron leaks badly and should be avoided. Brass, aluminum,
copper, steel, nickel, etc., may be used but must be baked out
when dealing with very low pressures.
Pyrex has a great tendency to contain minute pin holes where
it has been fused, even though carefully worked in an oxygen
ame.
Rubber tubing connections to glass should be made as follows.
The glass is warmed gently so that a ring of wax can be melted
around it a short distance from the end.
The rubber tubing is
slipped over this and gently Hamed at its end. Rubber tubing,
even of the thick walled
“
pressure
”
type, permits the passage
of
air through its walls at low pressures and should be used only in
the fore-pressure lines. Red sealing wax may be used or a good waX
may be made of about 10 parts rosin and 90 parts beeswax. The
beeswax is melted in boiling water to free it from sugar granules.
When cooled, it forms a cake on top of the water and is taken o”
and dried, then melted with the rosin.
A pan
of this mixture is
16.
VACUUM TECHNIQUE
in the system itself.
Phosphorus pentoxide (PgO5) in a side arm
or in a bottle as in gure 16—4 is very effective in absorbing water
vapor.
The oil in a fore pump
should be freed from moisture by
removing and boiling whenever the pump fails to operate at its
normal rate.
Another method for hunting leaks is to pass a discharge through
the system and sponge over it with ether or water.
With air in
the tube, the color changes from a pinkish to a bluish when the
water passes through the hole.
When the leak has been found, let in the air and fuse the hole.
For quick repair, the leak may be eliminated by covering it with
one of the low vapor pressure waxes; but this method cannot be
used for very low pressure work, especially on parts which are
to be heated.
Stop cocks should be tested for leaks before sealing into the
system by holding in a vertical position, pouring & drop or two of
ether or alcohol into the tube (the cock being greased and closed),
quickly sucking on the same tube, putting the tongue on the end
and watching if any bubbles come through the liquid.
Turn a
stop cock leisurely when using it and as seldom as possible for the
grease is ultimately squeezed out, leaving rings which leak. Never
twist the stopper unless the grease is present or the glass walls will
be scratched and leak.
Cast iron leaks badly and should be avoided. Brass, aluminum,
copper, steel, nickel, etc., may be used but must be baked out
when dealing with very low pressures.
Pyrex has a great tendency to contain minute pin holes where
it has been fused, even though carefully worked in an oxygen
ame.
Rubber tubing connections to glass should be made as follows.
The glass is warmed gently so that a ring of wax can be melted
around it a short distance from the end.
The rubber tubing is
slipped over this and gently Hamed at its end. Rubber tubing,
even of the thick walled
“
pressure
”
type, permits the passage
of
air through its walls at low pressures and should be used only in
the fore-pressure lines. Red sealing wax may be used or a good waX
may be made of about 10 parts rosin and 90 parts beeswax. The
beeswax is melted in boiling water to free it from sugar granules.
When cooled, it forms a cake on top of the water and is taken o”
and dried, then melted with the rosin.
A pan
of this mixture is