How Does An Aqualung Work?

Aqualung is a modern aid to diving. It makes it possible for a diver to go on berating underwater. He carries his own air supply with him, strapped to his back. He is a free diver.
For air supply the aqualung has two or more sturdy steel bottles filled with compressed air. A special valve gradually lets the air out of the bottles. A hose from the valve goes to a mouthpiece. The diver has to breathe through his mouth because; his nose is covered with a face plate.
With the aqualung strapped to his back and a heavy belt to keep him down, a man can swim almost as freely as a fish. He uses big flippers on his feet, so he does not need his hands for swimming. He can even hold a camera or a fishing spear. In shallow water he may be able to stay down for half an hour or more.
There is a problem in deep diving. The compressed air in the aqualung bottles is about four-fifths nitrogen and about one-fifth oxygen, like ordinary air. We need oxygen to stay alive. Ordinary the nitrogen we breathe in is breathed out again. But as the pressure of the air increases, some of the nitrogen dissolves in blood and tissues.

As the diver comes up, the nitrogen must leave his blood and tissues. If it cannot come out fast enough through his lungs, it turns into tiny bubbles inside his body. The bubbles squeeze nerves and block blood vessels and the diver is overcome by the ‘bends’. The diver feels great pain. A bad case of the bends may kill him or cripple him for life.
This is why diver must come up quite slowly when he is down to a depth of two hundred or three feet. And he must stop often on the way up.