The Gnostic Science of Alchemy:
According to Zosimos of Panopolis, a fourth century alchemical apologist, the “sons of God” mentioned briefly in Genesis taught the alchemical arts to their human lovers in gratitude for having sex with them. Tertullian, an early Church Father, agreed with this and thought that these “fallen angels,” or nephilim, had the evil intention of seducing human woman with the joys of “mundane pleasures.”
Zosimus was just repeating the accepted wisdom of the Jewish and Christian sages of that era. As he warmed to his subject though, Zosimus related the story of the first alchemist, Chemes, who wrote the teachings of the fallen angels in a book called Chema. The nephilim used this book to instruct the daughters of men in the spagyric arts and therefore the art itself came to be called Chemia. This was indeed the Greek word for alchemy, to which the Arabs added the article, al, of their own language.