The pressure of the air on the cider in the barrel.
To what height will water rise in a tube to fill a vacuum?
The water will rise to the height of thirty-four feet.
To what useful purpose is this applied?
It is applied to making pumps.
Of what material are pumps made?
Either of wood, or of metal, such as lead or iron.
What is necessary in regard to the tube or pump-tree?
It must always be air-tight.
Why must the tube or pump-tree be air-tight?