A direct quote:
"This is called a liquid-liquid extraction, and takes advantage of the different solubilities of polar (salts) vs nonpolar (hydrocarbons) compounds in polar (water) vs nonpolar (oil) solvents." (Stinkyattic)

I've used this recipe and love how it works. The taste of the butter improves with each boiling session.

http://boards.cannabis.com/medicated...-tutorial.html