ng lime water, used to show
that breath makes lime water milky]

You can also show that breathing is going on in the soil even after you
have picked out every living thing that you can see. First of all you
must do a little experiment with your own breathing so that you may
know how to start. Shake up a little fresh lime with water and leave
it to stand for 24 hours. Pour a little of the clear liquid into a
flask or bottle fitted with a cork and two tubes, one long and one
short like that shown in Fig. 27. Then breathe in through the tube _A_
so that the air you take in comes through the lime water: notice that
no change occurs. Next breathe out through the tube _B_ so that your
breath passes through the lime water; this time the lime water turns
very milky. You therefore alter in some way the air that you breathe:
you know also that you need fresh air.

Now we can get on with our soil experiments. Take two small flasks of
equal size fitted with corks and joined by a glass tube bent like a U
with the ends curled over. Put some lime water into each flask and a
little water in the U-tube. Now make a small muslin bag like a
sausage: fill it with moist fresh garden soil, tie it up with a silk
thread and hang it in one of the flasks by holding the end of the
thread outside and pushing in the cork till it is held firmly (see Fig.
28). Fix on the other flask, and after about five minutes mark the
level of the liquid with a piece of stamp paper; leave in a warm place
but out of the sun. {61} In one or two days you will see that the
water in the U-tube has moved towards the soil flask, showing that some
air has been used up by the soil; further, the lime water has turned
milky. But in the other flask, where there is no soil, the lime water
remains quite clear.

This proves, then, that some of the tiny creatures want air just as
much as we do. The air readies them through passages in the soil,
through the burrows of earthworms and other animals, or by man's
efforts in digging and ploughing.

[Illustration: Fig. 28. A bag of soil is fixed into a flask containing
lime water. In a few days some of the air has been used up, and the
lime water has turned milky]

Now try the experiment with very dry garden soil: little or no change
takes place. As soon as you add water, however, breathing begins
again, air is absorbed and the lime water turns milky just as before.
Water is therefore wanted just as much as air.