Note 16 — BOOK VII.

Dried lees of aqua which separates gold and silver. (Siccae feces aquarum quae aurum ab argento secernunt. German translation, Der scheidwasser heffe). There is no pointed description in Agricola's works, or in any other that we can find, as to what this material was. The "separating aqua" was undoubtedly nitric acid (see p. 439, Book X). There [Pg 235]are two precipitates possible, both referred to as feces,—the first, a precipitate of silver chloride from clarifying the aqua valens, and the second, the residues left in making the acid by distillation. It is difficult to believe that silver chloride was the feces referred to in the text, because such a precipitate would be obviously misleading when used as a flux through the addition of silver to the assays, too expensive, and of no merit for this purpose. Therefore one is driven to the conclusion that the feces must have been the residues left in the retorts when nitric acid was prepared. It would have been more in keeping with his usual mode of expression, however, to have referred to this material as a residuus. The materials used for making acid varied greatly, so there is no telling what such a feces contained. A list of possibilities is given in note 8, p. 443. In the main, the residue would be undigested vitriol, alum, saltpetre, salt, etc., together with potassium, iron, and alum sulphates. The Probierbüchlin (p. 27) also gives this re-agent under the term Toden kopff das ist schlam oder feces auss dem scheydwasser.