Articles Required : One round-bottom flask with a tight-fitting cork, water and arrangement to heat it.
We all know that water boils at 100° C. But this fact is not true in all the conditions. So we can say that the boiling point of water is 100° C at the sea-level under normal conditions. So higher you go, the air pressure decreases correspondingly, and as a result the water boils at a much lower temperature. By the same principle, deeper one goes the boiling point of water increases correspondingly.
So, if you want to prove this fact through experiment just fill your flask with water and put on fire to heat. Now when the water begins to boil, and the flask is full of steam produced by the boiling water, tighten the cork on its mouth. Remove it from the fire and hang the flask upside-down as shown in the figure here and make sure that the water is not boiling now. Once the water surface-is quiet, just squeeze some cold water on its top with the help of a cloth piece. But wt at's this? With little sprinkling of cold water, the water inside the flask starts boiling again! Do you know its reason?
By sprinkling cold water on the flask, some of the steam inside gets converted into water. This leads to a decrease in pressure and so water starts boiling once again and that even without fire!