I find these things quite interesting. It seems to provide a different emphasis to the concerns of contemporary science.
These ‘alchemical’ elements appear to describe ‘things’ more in terms of connection, and relationship, rather than modern sciences search for ‘what a thing is, of itself’, in isolation and stasis.
The alchemical elements take unity and wholeness as a starting point and sub-divide from that. Logically all that issues from ‘unity’ must carry these ‘flavours’, but in different proportions. This appears quite mutable though. Like the taiji symbol, no phenomena is static; All is in the process of being transformed; Becoming the opposite of itself.
Alchemy also has the three principles: Salt, sulphur and mercury.
I get the feeling that the four alchemical elements: earth, water, fire and air have more to do with the outpouring from ‘unity’ and the stream into greater complexity and ‘ever-new’ combinations. (One becoming two)
The three principles are then an opposite, recombining, ‘return to source’ mechanism.
Sulphur, the active fire principle, clashes with salt, the passive earth principle; The ensuing friction, tension and ‘suffering’ creates mercury, the unifying air principle. (Two becoming one)