After breathing two or three times, you will notice that the lime-water begins to look milky.

In a short time it becomes almost as white as milk.

This is because the lime-water catches the carbonic-acid gas which escapes from our lungs with each breath, while the pure water does not.
~10.

Why we Breathe.~--By this experiment we learn another reason why we breathe.

We must breathe to get rid of the carbonic-acid gas, which is brought to the lungs by the blood to be exchanged for oxygen.