5.
The air is expelled from the tube by filling with mercury. This
may be done by making a paper funnel and pouring the mercury
slowly into the tube through the funnel. When the tube is filled
to within 1/2 in. of the funnel remove the funnel and tap the side
of the tube gently in order to remove any small air bubbles that
may be clinging to the sides of the tube. The air bubbles will
rise and come to the top. The tube now must be filled completely,
expelling all the air. Place a finger over the end of the tube to
keep the mercury in and invert the tube and set the end in the
bowl of mercury. The mercury in the tube will sink until the level
will be at about 30 in., leaving 8 in. of vacuum at the top. The
next operation is to seal the tube at the half-way point between
the lower platinum wire and the mercury level.
As the lower end of the tube must be kept at all times in the bowl
of mercury until the tube is sealed, an assistant will be
necessary for this last operation. Have the assistant hold the
tube in the mercury at a slight angle, using care to always keep
the lower end in the mercury, while you hold the burner in the
left hand and allow the flame to strike the tube at the stated
point.
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