Alchemy is the ancient "science" that sought to combine elements of magic and chemistry to produce such things as gold from lead, the elixir of life, or the legendary philosopher's stone. Alchemy was practiced for thousands of years, in Egypt, Greece, Rome, and Medieval Europe, and is in many ways a precursor to modern science, especially chemistry. During its long tradition, alchemists created a special system that used symbols.
Paracelsus, a Swiss German alchemist from the early Renaissance, listed the three primes of alchemy:
Salt was the base matter of the universe, sulfur was the fluid connection between low and high matter, while mercury was the spirit of life. Each element had its own symbol, salt represented by a circle with line running through it, sulfur as a triangle on top of a cross, and mercury with the astrological symbol for the planet, which resembles a circle topped by a short u sitting on a small plus sign.
Classical alchemy also used the four basic elements of the universe, first described by the ancient Greeks. These elements are:
Alchemists devised triangular symbols to represent these elements. Fire is a simple triangle; water is an upside down triangle. Air is a triangle with a line running through the top, while earth is the inverse of water. There are, of course, hundreds of other alchemy symbols.