heat
Heat them.
The process of melting.
liquids turn into gas and solids don't and gas evaporates
with some you can ex) water can turn into ice
All solid can be liquified if the temperature is high enough.
Liquids can through evaporation, and solids can through combustion.
When a liquid looses enough energy (heat), it turns into a solid.
water
water
water
water
Solids turn into liquids at their melting point.