Extract of a letter, from Monsieur Geoffroy [Claude Joseph] to Hans Sloane, dated at Paris Concerning the discovery of Pierre Seignette's 'Sal polychrestus Rupellensis' (potassium sodium tartate or Rochelle salt) and other salts eg salt of Kali, Glauber's salt Printed in 'Philosophical Transactions', vol 39, no 436, p 37 4 May 1732