Hermetic Rose Cross
On page 18 of the Book of Thoth, Crowley states:
"Sulfur is Acitivity, Energy, Desire
Mercury is Fluidity, Intelligence, the power of Transmission
Salt is the vehicle of these two forms of energy, but itself possess qualities which react on them."
"The symbols for these three alchemical principals occupy different lobes on each arm of the Cross. Mercury is placed in the central lobe of the top and bottom arm, indicating dominance in air/Swords and earth/Disks. The symbol of salt dominates on the right arm (water/Cups), and the symbol of sulfur dominates the left arm (fire/Wands).
The secondary lobes of each arm are occupied with symbols of hte not-so-dominant alchemical principals arranged in a logical and balanced manner. This is very important because, when these three principles are combined and balanced, they create the alchemical substance known as "vitriol," the universal solvent. It is the initials of the alchemical motto: Visita interiora terrae rectificando invenies occultum lapidem (Visit the interior parts of the earth: by rectification thou shalt find the hidden stone).
Crowley identifies three cards with the alchemcial elements:
The Magus - Mercury
The Empress - Salt
The Emperor - Sulfur
Other trumps also have alchemical significance:
Art - Vitriol
The Lovers, the Hermit, Death, and the Devil all have vital roles to play in the alchemy of the tarot." -Duquette, Thoth Tarot, 53
On page 83 of the Book of Thoth, Crowley speaks of one more alchemical symbol called the Orphic egg: "This egg represents the essence of all life that comes under the formula of male and female."