Both tubes should be
pointed at the bottle end so that they may enter the cork easily. Make the
top of the cork air tight with sealing-wax. The purpose of the bottle is to
catch any mercury that might be sucked out of the tube; one does not wish
mercurial poisoning to result from the experiments. Also it prevents any
saliva entering the mercury tube.
When the latter has been secured to the standard by a couple of slips of
tin nailed to the front, connect it up with the bottle, and fill it up to
the zero mark with mercury poured in through a small paper funnel.
The open end of the tube should be provided with an inch of tubing. Clips
placed on this and on the rubber connection between tube and bottle will
prevent the escape of mercury should the apparatus be upset when not in
use.
The average blowing pressure of which the lungs are capable is about 1-1/2
lbs. per square inch; inspiration pressure without mouth suction about 1
lb. per square inch; suction pressure 2-1/2 to 3 lbs. per square inch.
Caution.--Don't ask people with weak lungs to try experiments with the
apparatus described in this chapter.
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