Volume 1

The elements of materia medica and therapeutics / by Jonathan Pereira.

  • Jonathan Pereira
Date:
1849-1853
Catalogue details

Licence: Public Domain Mark

Credit: The elements of materia medica and therapeutics / by Jonathan Pereira. Source: Wellcome Collection.

Provider: This material has been provided by King’s College London. The original may be consulted at King’s College London.

    922/934 (page 892)
    Water, fjj. [grs. 1600, E.] Dissolve the nitrate of silver in the water, and strain; then, the access of light being prevented, keep it in a well-closed vessel.)—This solution is employed as a test of chlorine, chlorides, or hydro- chloric acid. 2. SOMJTIQ ARGENTI AMMONIATI, E.; Solution of Ammonio-Nitrate of Silver; Hume’s Test for Arsenious Acid. (Nitrate of Silver, grs. xliv.; Distilled Water, f5j.; Aqua Ammonite, a sufficiency. Dissolve the salt in the water, and add the aqua ammonite gradually, and towards the end cautiously, till the precipitate at first thrown down is very nearly, but not entirely, re- dissolved.)—Employed as a very delicate test for arsenious acid (see ante, p. 645). Order XXXI. GOLD AND ITS COMPOUNDS. 178. AURUM.-GOLD. Symbol Au. Equivalent Weight 199. History.—Gold has been known from the most remote periods of antiquity. It was in common use 3,300 years since,1 and was probably the first metal with which mankind was acquainted. The alchemists termed it Sol, or Rex- metallorum, 0. Natural History.—It is found only in the metallic state, commonly alloyed with other metals, especially with silver, tellurium, copper, and iron. It occurs in veins in primitive rocks, and is also found in alluvial deposits in small lumps or particles, called gold dust. It is found in several parts of Europe, Asia, and Africa, but principally in America, especially the southern part. Preparation.—The mode of extracting gold varies in different places, principally according to the nature of the gangue. The ore is freed as much as possible from foreign matters by mechanical processes (stamping, washing, &c.), and sometimes by roasting, and is then smelted with some flux, as borax, to separate the stony matters. Or it is fused with lead, and afterwards submitted to cupellation; or amalgamated with mercury, and, after straining, distilled. The separation of gold from silver {parting) may be effected in the dry way by fusion either with sulphur, by which metallic gold and sulpliuret of silver are procured,—or with tersulphuret of antimony, by which sulpliuret of silver and an alloy of gold and antimony are procured : the last-mentioned metal may be separated by heating the alloy in the air, as well as by other methods. Gold may also be freed from silver in the wet way by the process of quartation ; that is, by treating an alloy of three parts of silver and one of gold with nitric acid, which dissolves the silver,—or by action of sulphuric acid (see cupri sulphas). Properties.—The crystalline forms of native gold are the cube, the regular octohedron, and their modifications. Pure gold has a rich yellow colour,—a sp. gr. of 19‘2 to 19'4; is soft, very ductile, and malleable; fuses at a bright 1 Exodus, xi. 2.