The Pass-Keys to Alchemy: The Lost Book of Lapidus by Lapidus (David Curwen), from Salamander and Sons, is due to be available directly and via Weiser Antiquarian. It’s a little confusing because, as I write this, although the publisher has stated that the volume is available now, their own shop has it still listed as pre-order and the volume does not appear at Weiser Antiquarian yet. In theory, at least, the volume can now be ordered, or will soon be. This follows the previous work In Pursuit of Gold: Alchemy Today in Theory and Practice [also] which was re-issued, in a revised and expanded edition, in 2011.

“Lost for more than three decades, the companion volume to In Pursuit of Gold has been found.
For decades students of alchemy have believed that In Pursuit of Gold – hailed upon its 1976 publication as a rare work by one of the few practicing laboratory alchemists writing in English during the mid-to-late 20th century – constituted the sole alchemical text penned by the enigmatic alchemist Lapidus. The truth is that Lapidus – real name David Curwen – wrote a second text which, unknown to most, he secreted away with at least one trusted Brother in the Art. Throughout the intervening years this remarkable book, The Pass-Keys to Alchemy, has passed through just a few select and trusted hands.
Each of the chapters of The Pass-Keys to Alchemy details one pass-key to the successful confection of the Philosophers’ Stone, as identified by Lapidus. Drawing upon the writings of Eirenæus Philalethes and Ali Puli, The Hermetic and Alchemical Writings of Paracelsus the Great, Bendictus Figulus’ A Golden and Blessed Casket of Nature’s Marvels, Sir Edward Kelly’s Book of St. Dunstan, and Michael Maier’s Atalanta Fugiens among other canonical texts, this lost alchemical masterpiece includes the kind of profound insights into alchemical theory, laboratory processes and practical methods that only derive from a lifetime of quiet alchemical work.
A rare alchemical gem in print for the first time, The Pass-Keys to Alchemy also includes an introductory essay by Tony Matthews, grandson of Lapidus, and 16 of Theodor de Bry’s masterful engraved emblems from Atalanta Fugiens with accompanying commentary by Lapidus.” [via]