They were originally conceived as part of alchemy or proto-science (pre-science), which later evolved into chemistry. Until the 18th century, the aforementioned symbols were used to denote certain elements and compounds. The symbols varied slightly in the markings of the alchemists, so the ones we know to this day are the result of the standardization of these marks.
According to Paracelsus, these signs are known as the First Three:
salt - denoting the base of the substance - marked in the form of a circle with a clearly marked horizontal diameter,
mercury, meaning the liquid bond between high and low, is a circle with a semicircle at the top and a cross at the bottom,
sulfur - the spirit of life - a triangle connected by a cross.
The following are the symbols for the elements of earth, all in the form of triangles:
Metals marked with symbols of planets and celestial bodies:
Alchemical symbols also include:
Ouroboros is a snake that eats its own tail; in alchemy, it symbolizes a constantly renewing metabolic process; it is the twin of the philosopher's stone.
Heptagram - means the seven planets known to alchemists in ancient times; their symbols are shown above.