Fig. 27. Bottle containing 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. 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.
