Alchemy
The Beginner's Laboratory
The Kabbalistic Tree of Life
Within the last few hundred years, some alchemists have adopted the Tree of Life from the Kabbalah. This knowledge is not used by all alchemists, which is fine, but a basic working knowledge of it can go very far for one's progress, of this I am certain.
The Tree of Life serves as a sort of spiritual road map between the physical world and the Absolute, or God. There are different levels of consciousness, each associated with a particular rate of vibration (slower vibrations for lower levels, higher rates for higher levels, eventually reaching to infinity or the Absolute), a planet, and a metal. You can apply this to work both in spagyrics and mineral alchemy, as you can see for yourself just where on the Tree these particular plants or ores/substances are located.
As another application, the Tree of Life can be stretched out into a line, levels 1 through 10, ten on the bottom, 1 at the top. Level 10, our physical reality, is the most mundane. Between it and the higher worlds is the first Veil, guarded by our own Guardian of the Threshold, our own morality. Based on the state or evolution of that morality, we can access higher worlds through mysticism (one avenue of which is alchemy). If our intent is noble, our Guardian will allow us access to the higher worlds, the level accessible based on our spiritual evolution. Levels 9 to 7 constitue the Lunar Astral world; Levels 6 to 4 constitute the Solar Astral world; and Levels 3 to 1 constitute the Buffer between the Created worlds and the Absolute.