Note note 10, p. 443 — BOOK X.

[10] In this description of parting by nitric acid, the author digresses from his main theme on pages 444 and 445, to explain a method apparently for small quantities where the silver was precipitated by copper, and to describe another cryptic method of precipitation. These subjects are referred to in notes 11 and 12 below. The method of parting set out here falls into six stages: a—cupellation, b—granulation, c—solution in acid, d—treatment of the gold residues, e—evaporation of the solution, f—reduction of the silver nitrate. For nitric acid parting, bullion must be free from impurities, which cupellation would ensure; if copper were left in, it would have the effect he mentions if we understand "the silver separated from the gold soon unites with it again," to mean that the silver unites with the copper, for the copper would go into solution and come down with the silver on evaporation. Agricola does not specifically mention the necessity of an excess of silver in this description, although he does so elsewhere, and states that the ratio must be at least three parts silver to one part gold. The first description of the solution of the silver is clear enough, but that on p. 445 is somewhat difficult to follow, for the author states that the bullion is placed in a retort with the acid, and that distillation is carried on between each additional charge of acid. So far as the arrangement of a receiver might relate to the saving of any acid that came over accidentally in the boiling, it can be understood, but to distill off much acid would soon result in the crystallization of the silver nitrate, which would greatly impede the action of subsequent acid additions, and finally the gold could not be separated from such nitrate in the way described. The explanation may be (apart from incidental evaporation when heating) that the acids used were very weak, and that by the evaporation of a certain amount of water, not only was the acid concentrated, but room was provided for the further charges. The acid in the gold wash-water, mentioned in the following paragraph, was apparently thus concentrated. The "glass" mentioned as being melted with litharge, argols, nitre, etc., was no doubt the silver nitrate. The precipitation of the silver from the solution as a chloride, by the use of salt, so generally used during the 18th and 19th Centuries, was known in Agricola's time, although he does not mention it. It is mentioned in Geber and the Probierbüchlein. The clarity of the latter on the subject is of some interest (p. 34a): "How to pulverise silver and again make it into silver. Take the silver and dissolve it in water with the starckenwasser, aqua fort, and when that is done, take the silver water and pour it into warm salty water, and immediately the silver settles to the bottom and becomes powder. Let it stand awhile until it has well settled, then pour away the water from it and dry the settlings, which will become a powder like ashes. Afterward one can again make it into silver. Take the powder and put it on a test, and add thereto the powder from the settlings from which the aqua forte has been made, and add lead. Then if there is a great deal, blow on [Pg 444]it until the lead has incorporated itself ... blow it until it plickt (blickens). Then you will have as much silver as before."