Ancient alchemists were wise in coding their texts with words that can be so easily mistaken for their elementary counterparts (sulfur, mercury, salt, etc.). Even today many fall short of the authentic alchemical experiments described in these old manuscripts due to this confusion. Of all of the multifaceted words found within alchemy, it seems that none are more commonly misunderstood than Mercury.
In the alchemical perspective, Mercury was considered the spirit of any given material. Paracelsus explained it simply as such, saying:
"For Mercury is the spirit, sulfur is the soul, and salt is the body." 
Exploration of the word spirit, featured in the article Truth of the Matter, helped to define spirit as the mind - an inherent power of consciousness. It is the part of any given material that organizes the Logos, which inherently exists within consciousness - our alchemical sulfur. To the Greeks, Logos was considered to be a divine dialogue that God had within himself. This dialogue, in effect, was the beginnings of the creation of matter and our known reality.
"In beginning was the Word, and the Word was with God, and God was the Word." John 1:1
It is found then that Mercury is intimately tied to Sulfur - Consciousness and the mind acting as one to manifest nature. Frater Albertus pointed to this relationship, noting:
"Sulfur, that is, the alchemical sulfur, is usually found in its oily form adhering to the Mercury."
Made for one another, alchemists viewed these two aspects - Sulfur and Mercury- as lovers, intimately bound together in union. These principles embodied archetypical patterns of masculinity & femininity, existing in a natural state of union unless separated by art. Manfred M. Junius wrote:
"Mercury... Represents the feminine and passive principle. Sulfur is the...masculine or active principle."
These general archetypes of masculine and feminine inspired alchemists to use words that were synonymous with these terms, once again further coding the alchemical principles of Mercury & Sulfur. Junius, describing these literary synonyms saying:
"Mercury is occasionally called the Moon, the Lunar, or Diana, Sulfur is the Sun, the Solar, Apollo, the original potency, the formative principle, the active, the principle of the "invisible fire" and also of love."
These principles, being so closely tied, made it difficult at times for alchemists to distinguish between one or the other, and many times these principles were considered to be two sides of the same coin. The image of two snakes, wrapped in a circle, biting each others tails served as a symbol to describe this and helped paint a picture of the motion going on within the realm of consciousness.
Recognition of the affinity that the principles of Mercury and Sulfur have towards each other, gave rise to another crucial observation: Sulfur coagulates Mercury. When brought together, the union of Sulfur and Mercury has the power to create salt, or a body. Francis Bacon starts out his essay- Experiments Touching Sulfur and Mercury- by saying:
"There bee two Great Families of Things; You may terme them by severall Names; Sulphureous and Mercureall, which are the Chymists Words: (as for their Sal, which is their Third Principle, it is a Compound of the other two;) Inflammable, and Not Inflammable; Mature and Crude; Oily and Watry."
Sulfur and Mercury - consciousness and Mind - existing together, naturally gave birth to the third principle - Salt.
Sulfur is the soul, the consciousness in matter. Consciousness being the actuating cause of an individual life. The Spirit is the mind, an inherent power of consciousness - this is our sulfur and mercury bound together - consciousness and mind. Consciousness, using the power of the mind, organizes and embodies thoughts, giving concrete reality to these thoughts, which have no concrete existence - it births Salt. This in turn makes all forms of matter, a matter of Soul and Spirit. Paracelsus defines this precisely, explaining in his book Concerning the Nature of Things:
"It should be known that the life of things is none other than a spiritual thing. On this account there is nothing corporeal but has latent within itself a spirit and life, which as just now said, is none other than a spiritual thing. But not only the lives which move and act, as men, animals, worms in the earth, birds under the sky, fishes in the sea, but also all corporeal and substantial things. For here we should know that God, at the beginning of the creation of all things, created no body whatever without its own spirit, which spirit contains after an occult manner within itself. For what is the body without the spirit? Absolutely nothing. So it is that the spirit holds concealed within itself the virtue and power of the thing, and not the body."
Confirmed to us by Paracelsus, all matter, and the alchemical Salt, are a manifestation of Spirit. All things have been made real by and through the Spirit, and the Spirit is made real by the Soul, Our Sulfur. This Spirit is our Mercury, the Mercury of the 3 principles. The mind of matter.
Mercury is the bridge or the medium through which invisible and immaterial consciousness can be placed within and reside in matter.
Applying the knowledge that Sulfur and mercury in union together gave rise to the third principle, Salt, alchemists employed these philosophical understandings in pursuit and finalization of every alchemists Magum Opus, the confection of the philosophers stone.
In Search of the stone, alchemists often referred to Mercury as Argent Vive. Another code word further mystifying the materials they were harnessing in their laboratories. Under this pseudonym -Argent Vive - Mercury was recognized in its metallic form as quicksilver. It's union with the masculine metallic seed/Sulfur, would in time coagulate into a Salt if incubated properly. Copulation between the masculine and feminine gave birth to a new form of metallic matter, a red powder - the famed philosophers stone.
At times, alchemists would also refer to quicksilver as Our Mercury, as if to show their own intimate philosophical understanding of the secrets hidden within this amazing and luminous liquid metal - this water which does not wet the hands. Prefacing mercury with the word Our pointed to the relationship the alchemists had with this matter. It showed possession, and a depth of understanding - One of knowing a material, inside and out, for its true nature and not just its surface level appearances. Much like how referring to a specific person as my wife or my husband shows others your intimate connection and understanding with that person, alchemists too had Our Mercury and Our Gold.
References to this relationship that Mercury facilitated between the soul and the body are prevalent amongst Greek and roman mythology as well. The name Mercury originally comes to us from the God Mercury that existed within the roman pantheon. Often considered one of the most favorited gods, Mercury was known as the son of Maia and Jupiter (Maia and Zues). It is believed that the name Mercury comes from a Proto-Indo-European root - merĝ- which stands for "boundary or border."
In Greek mythology Mercury was known as Hermes and similar to the etymological meaning of Mercury in the roman language, Hermes gets his name from the Greek word Herma which meant a heap of stones, or a boundary marker.
In the mythical stories of Ancient Greece and Rome, Mercury/Hermes was known as a messenger between the realm of immortal gods and the realm of mortal man. Mercury bridged this gap between creator and created - God and Man. He resided within the gap between the two and facilitated contact between their borders. He was the boundary marker.
Mercury's mother Maia is also of particular interest in these stories, and helps illuminate much of the nature that is attributed to Mercury. Maia was one of the seven Pleiades, all of which were considered sea-nymphs and daughters of the Titan Atlas, who was associated with the Moon. This watery nature of his sea-nymph mother and the lunar nature of her father Atlas seem to have been passed along to Mercury/Hermes.
Also of interest, is the linguistic similarity that Mercury's mother Maia has to the Vedic god of Illusion, Maya. Taking into consideration the fact that earthly matter and reality is an embodiment of thoughts - imagination taken as reality - produced by the Spirit/Mind, a thread connecting illusion to Mercury begins to be revealed. Mercury/Hermes was recognized as a trickster god, outwitting other gods for the satisfaction of mankind. This makes the thread between Mercury and illusion become even more apparent. What more is an illusion than a fancy trick? And certainly it can be seen that the Mind can play tricks on us all. Mind, being of course synonymous with Mercury, the connection of illusion thickens.
In ancient symbology, water embodies the moon, the feminine and the mercurial nature; alchemical mercury often being called Luna, or the feminine. Alchemy also considered Mercury to be composed of the elements air and water, And when found within any given material (plant, animal, mineral, metal) it was recognized by its watery consistency and Airy volatile nature. Mercury was always any humidity, moisture, or fluid found within different materials. For plants it was their inherent water, and liquor if fermented, in minerals and metals it was their acetones, and in animals it was their blood and semen. Physically, Mercury was always a liquid substance.
In many ancient traditions there is a great sea that separates the realm of immortality from the realm of mortality - Men from Gods. The ancient Egyptians spoke of this ocean as the "sea of death", a place that no mortal man could venture past and return from. In Greek/Roman mythology Mercury/Hermes was known to be a conductor of souls between these two abodes, helping to ferry individuals into the afterlife. Mercury himself was seen as this medium, this water/sea, spreading far and deep between the two lands of mortality and immortality.
Mercury was, and is, always the water, in all facets of study. The messenger and communicator standing between these two lands. Mercury bridged the gap between what appeared to be two separate worlds. The Presence of Mercury, Mind, or Spirit, unified and made what appears to be separate, whole, placing soul into Body - Mind into matter - immortal into mortal.
 Concerning the Nature of Things: Book One - Concerning the Generation of natural Things
 The Alchemists Handbook
Avery is the lead Alchemist at Kymia Arts and routinely shares information on general alchemy topics as well as our methods and products.