Normal solids, e.g. iron, copper and wax, expand when they change into liquids. When pressure is applied on the surface of a normal solid, expansion is suppressed and melting is delay. Thus, the melting point of a normal solid is raised.
Abnormal solids, like ice and bismuth, contract on melting into liquids. When pressure is applied on the surface of such a solid, the change into the liquid is assisted. Thus, the melting point of ice is lowered by the application of pressure.
Application of pressure
1. If two blocks of ice are pressed together and released, they stick to each other. This is because when pressure is applied, the ice at the common surface of joining melts, as the melting point is raised and so the water formed re-solidifiers and the two pieces join together.
2. The regelation experiment:
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You will observe that the wire cuts through the ice, but the ice does not break into two pieces.
The pressure of the wire lowers the melting point of the ice below it, and thus the ice melts.
The wirer therefore cuts through. As the pressure is released, the melting point is again raised and the water formed resolidifies. Therefore, the block remains intact.