Martin Heinrich Klaproth (1801), Analytical Essays Towards Promoting the Chemical Knowledge of Mineral Substances . T. Cadell, Jr. & W. Davies, London. His finding of potassium in leucite appears on pp. 353-354.
George Ernst Stahl (1703), Specimen Beccherianum. Johann Ludwig Gleditsch, Leipzig. From p. 269: "CVII. Vitriolum, Creta præcipitari potest, ut omissa metallica sua substantia, aluminosum evadat." (107. Sulfuric acid [and] chalk can [form a] precipitate, as its liberated metallic substance, alum, escapes.)
Andreas Sigismund Marggraf (1754), "Expériences faites sur la terre d'alun" (Experiments made on the earth of alum), Mémoires de l'Académie des sciences et belles-lettres de Berlin. стр. 41—66.,