Quicksilver contains information about the ThaumCraft_2 mod.
Quicksilver is a metal which can be obtained in balls by cutting Silverwood leaves (drops at a rate similar to apple drops in normal trees). It can also be obtained by smelting Cinnabar Ore. You must make discoveries (lost type) in order to use quicksilver.
Quicksilver's only confirmed use is to make a quicksilver core.
The recipe for infusing a Quicksilver Core
In order to infuse a quicksilver core, you must research at a Quaesitum until you form a theory of it, you must then research the theory until you get a discovery. Right-clicking while holding the discovery shows you the menu on the right, and also makes you actually able to infuse one. A quicksilver core is essentially just a speed upgrade to any of your thaumic machines.