Which describes the process or processes in which freezing nuclei play a role?

In 2002, the rare earth elements mine in mountain pass, california was closed because

The msds for glacial acetic acid says that it is a flammable liquid that can severely burn any human tissue it comes in contact with. it reacts with bases, various metals, and strong oxidizing agents. its vapors can form explosive mixtures with air.

Which change to the system wood cause the freely-moving piston to lower?