The pump in the first instance is to be inclined at
an angle of about 10 degrees, the tube of the gauge being supported by
a semicircular piece of thick pasteboard fitted with two corks into the
top of the cylinder. This seemingly awkward proceeding has in no case
been attended with the slightest accident, and owing to the presence of
the four leveling-screws, the pump when righted returns, as shown by the
telescope of the cathetometer, almost exactly to its original place. In
the inclined position the exhaustion of the vacuum bulb is accomplished
along with that of the rest of the pump. The exhaustion of the
vacuum-bulb when once effected can be preserved to a great extent for
use in future work, merely by allowing mercury from the reservoir to
flow in a rapid stream at the time that air is allowed to re-enter the
pump. During the first process of exhaustion the tube of the gauge is
kept hot by moving to and fro a Bunsen burner, and is in this way
freed from those portions of air and moisture that are not too firmly
attached. After a time the vacuum-bulb ceases to deliver bubbles of
air; it and the attached tube are now to be heated with a moving Bunsen
burner, when it will be found to furnish for 15 or 20 minutes a large
quantity of bubbles mainly of vapor of water. After then production
ceases the pump is righted and the exhaustion carried farther. In spite
of a couple of careful experiments with the cathetometer I have not
succeeded in measuring the vacuum in the vacuum bulb, but judge from
indications, that is about as high as that obtained in an ordinary
Geissler pump.
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