Because a current of cold air from a window or a door, blows upon them.

Does quicksilver expand when heated?

Like other metals, quicksilver expands as it grows warmer, and contracts as it grows cooler.

Is quicksilver in the form of a solid or a fluid?

It is a fluid as we usually see it.

For what is quicksilver used?

It is used for filling the tubes of thermometers.

What is a Thermometer?

It is an instrument used for measuring the degree or quantity of heat in any substance.

How does heat affect the quicksilver?