Licence: Public Domain Mark
Credit: The elements of experimental chemistry (Volume 2). Source: Wellcome Collection.
Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)
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![of tin. A solution of platina, so dilute as to be scarcely distin- guishable from water, assumes a bright red colour, on the addi- tion of a single drop of the recent solution of tin. 14. Platina has been discovered by Dr. Wollaston to be a re- markably slow conductor of caloric. When equal pieces of sil- ver, copper, and platina, were covered with wax, and heated at one end, the wax was melted 3-J inches on the silver ; 2-£- on the copper ; and 1 inch only on the platina. Its expansion by heat is considerably less than that of steel; which, between the tempera- tures of 32* and 212° is expanded about 12 parts in 10,000, while the expansion of platina is only about 10. From trials made by Mr. Scott of Dublin, it appears to possess sufficient elasticity to be applicable to the making of pendulum springs for watches. (Nicholson's Journal, xxii. 148.) SECTION III. Silver. Silver is a metal, which admits of a degree of lustre, inferior only to that of polished steel. Its specific gravity, after being hammered, is 10.51. In malleability, ductility, and tenacity, it ex- ceeds all the metals, except gold. Its fusing point, as determined by Dr. Kennedy, is 22° of Wedgwood's pyrometer. By consider- ably raising this heat, it may be volatilized ; and, by slow cooling of the fused mass, it may be made to assume a regular crystallized form. Its chemical properties are the following : I. Silver is difficultly oxidized by the concurrence of heat and air. The tarnishing of silver is owing not to its oxidation merely, but to its union with sulphur, as Proust has satisfactorily shown. II. It is acted on by sulphuric acid, which, when assisted by heat, oxidizes and partly dissolves it. The sulphate of silver, however, which is very useful as a test, is better prepared by dissolving in sulphuric acid the carbonate of silver, precipitated from the ni- trate by carbonate of soda. It forms small brilliant and needle- shaped crystals, which require for solution a large quantity of water. III. Nitric acid diluted with from two to four parts of water, dissolves silver with a disengagement of nitrous gas. If the sil- ver be pure, the solution is colourless, otherwise it has a green hue. [See note 33, at the end of this vol.] According to Proust,](https://iiif.wellcomecollection.org/image/b21128169_0039.jp2/full/800%2C/0/default.jpg)
