London, Wellcome Institute MS. 4593. 499 pages + 1 folio. 200x140mm. Mid 18th Century. [Sias. Letter-book containing transcripts of his letters on alchemical matters and 'secrets' to M. Chevalier, Ingénieur du Roi, amateur des Sciences, between 29 October, 1719 and 15 March, 1723.] [From the Julius Kohn library.]