By cross referencing with other books, they reaslie that the passage in question in the book was about the Opus Magnum and the Albedo (Oeuvre au Blanc) which is the second step of the realisation of the philosopher's stone, after the Nigredo (oeuvre au noir)

More infos about the Book of the Acts of Solomon who is a biblical lost text : https://en.wikipedia.org/wiki/Acts_of_Solomon