British Library MS. Sloane 2558. Paper. Quarto. 66 folios. 17th Century. 'The Marrow of Alchemy, being an experimental Treatise discovering the secret and most hidden mystery of the Philosopher's Elixir; divided into two parts' by Eirenaeus Philoponos Philalethes. ff.1-66. [Printed in octavo, London, 1654-5.] 'It is supposed, Eireneus Philalethes' name was Bartlet, who was acquainted with Dr Child'.