XLII
an air-pump. After the air has been exhausted the sphere sinks.
This instrument is termed: a Baroscope.
The chief applications of this principle are Balloons, 221;
and the flight of birds. 222.
CHAPTER VII.
Chemical and physiological properties of air.
223-241.
§ 95. Composition of air and the relation of its consti
tuents to the processes of vegetation, respiration, and combus
tion. 223.
§ 96. 1) The necessity of Oxygen. 224.
1) For Combustion. A lighted taper under the receiver of
an air-pump, 225; a light put under a bell-jar, in such a man
ner that no fresh air has access, will be gradually extinguish
ed, 226; a lamp without cylinder smokes, 227; in a cellar,
in which wine ferments, a light is extinguished, 228; wind
increases a fire, 229; similarly we blow a fire to revive it, 230;
but (see: 231); a current of fresh air causes iron to melt in fire,
232; when the chimney is covered by a wet sack-cloth, the fire
becomes extinguished, 233; when in the bottom of a large
chimney sulphur is burned, the fire goes out, 234; fire some
times goes out by itself in a burning room, if the doors and
windows are carefully shut up. 235.
2) For Respiration: Animals die in vacuo, 236; (fishes and
reptiles can bear it for a much longer time, insects live several
days in a vacuum). The diver's bell must be drawn out of
water from time to time, 237; it is unhealthy, if a room is
crowded. 238.