what was the discovery made by the alchemist that was part liquid and part soil?

Well, you could mean what was called "The Soul of the World" also called the Master Work- boiling metals down until only pure liquid is left (called the Elixir of Life) and knowing that the solid part is the Philosopher's Stone which alchemists believed could transform metal into gold.

The goal of alchemy is the Master Work. The Master Work is part liquid and part solid; the liquid is called the Elixir of Life and the solid is called the Philosopher's Stone.