The number 3 can be seen when the candidates are being placed in the room of reflection, where they are being presented with elements like Sulfur, Mercury and Salt, can you elaborate on the esoteric meaning there of?

The Chamber of Reflection is a feature of the French and Scottish Rites rather than the Craft Lodge 1. Within Craft Masonry, numbers such as three serve as symbols representing sacred objects or ideas, rather than carrying mystical or occult virtues 1.

The supplied passages do not provide an esoteric or alchemical reading of Sulfur, Mercury, and Salt in connection with Craft initiation. While Rosicrucian tradition used the initials I.N.R.I. to represent salt, sulfur, and mercury 1, and high-degree Hermetic rites introduced alchemical symbolism surrounding Mercury 2, these interpretations belong to other systems and are not part of the Craft degrees.