I make it close for a little time,
and by means of a pipe I get my mouth over it so that I can inhale the
air. By putting it over water, in the way that you see, I am able to draw
up this air (supposing the cork to be quite tight), take it into my lungs,
and throw it back into the jar.
[Illustration: Fig. 33.]
We can then examine it, and see the result. You observe, I first take up
the air, and then throw it back, as is evident from the ascent and descent
of the water; and now, by putting a taper into the air, you will see the
state in which it is, by the light being extinguished. Even one
inspiration, you see, has completely spoiled this air, so that it is no
use my trying to breathe it a second time. Now, you understand the ground
of the impropriety of many of the arrangements among the houses of the
poorer classes, by which the air is breathed over and over again, for the
want of a supply, by means of proper ventilation, sufficient to produce a
good result. You see how bad the air becomes by a single breathing; so
that you can easily understand how essential fresh air is to us.
To pursue this a little further, let us see what will happen with
lime-water. Here is a globe which contains a little lime-water, and it is
so arranged as regards the pipes, as to give access to the air within, so
that we can ascertain the effect of respired or unrespired air upon it.
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