Rare first (and only early) edition of a Dutch Hermetic textbook by the medical doctor Herman Follin, who was born in Friesland at the end of the sixteenth century and died of the plague in Cologne around the middle of the 17th century. Follin had a successful medical practice at s-Hertogenbosch and became professor of medicine at Cologne. His present work in Dutch, one of his first publications, presents alchemists and occult knowledge in clear and easy language for pharmacists and physicians. It is composed like a schoolbook, treating each subject succinctly in short chapters. The first chapter is devoted to alchemists knowledge of metals, presented in short propositions followed by their proofs. The second chapter, "Die const Hermetis, ofte chymie", treats chemistry. In the third chapter, "Van de eerste materie der philosophen, en van sijn ontallijcke vruchten", Follin gives a survey of the Hermetic-philosophical thought concerning the quintessence of matter.
Den Nederlandtsche sleutel is a rare book, not recorded in the standard occult-chemical subject bibliographies, but found in some medical collections. It is a great example of how a medical doctor spread alchemical and occult knowledge among medical practitioners by presenting it in an understandable manner.
With an owner's inscription of the Jesuit College at Brussels, dated 1647, at the head of the title-page. In good condition. BMN, p. 528; Krivatsy 4149; Simoni F47; STCN (4 copies); not in Brüning, Caillet; Duveen; Ferguson; Wellcome.