Sulfur represents the soul in Alchemical philosophy. It is a volatile principle that relates to the individual essence of a being and expresses itself through unique compounds that are typically found in the oil of any given substance.
In plant works it is expressed as the essential oil of any plant, which would be held similarly true for mushrooms. However it can be represented in any oily portion of the being, such as the alkaloids. Again this principle denotes the individuality of any given being.
When, for example, you have an essential oil of lavender or peppermint, you can tell which plant you are working with through the scent of the essential oil, because that oil contains the individual properties of that plant, which are recognized as chemical compounds in modern chemistry (terpenes, lipids, etc.).
Each plant has a unique profile corresponding to its individual constituency, and the same is true for mushrooms. Mushrooms do not always yield an essential oil through steam distillation, although some do, it is my theory that it would require a different set of solvents to get a more fully expressed Sulfur from the mushroom realm.
Distillation for the essential oil is seen as a spiritualization of the material into the celestial realm, and holds philosophical significance in that regard. It is my suggestion that mushrooms be processed primarily through steam distillation, with secondary and tertiary processing through means of other solvents to get a wholistic expression of the essential nature.
In a more philosophical sense, the Sulfur represents the individual expression of the mushrooms as they are being worked with. This is explored through understanding the naturally occurring compounds and constituency of an individual mushroom. This section will relate to that exploration as some of these unique preparations are tested to reveal the inherent compounds.
As with each of the other sections there is much exploration to be done in discovering the constituency of particular mushrooms, especially related to Spagyric extraction. There are scholarly articles available that explore specific constituency, and Robert Rogers book Fungal Pharmacy is a great starting point to begin delving into this work.