Platinum is the heaviest of all metals, gold being next. Platinum is practically infusible, and quite indifferent to reagents. It is therefore very useful in certain manufactories, and in the laboratory. It can be dissolved by aqua-regia. The stills for sulphuric acid are made of platinum, and the metal is used for Russian coinage, but must be very difficult to work on account of its infusible property.
Fig. 419.—Döbereiner’s lamp.
In the finely-divided state it forms a gray and very porous mass, which is known as spongy platinum, and possesses the remarkable property of condensing gases within its pores. Hence, when a jet of hydrogen is directed upon a piece of spongy platinum, the heat caused by its condensation suffices to inflame the gas. This singular power has been applied to the construction of a very beautiful apparatus, known as Döbereiner’s lamp, which consists of a glass jar, a, covered by a brass lid, e, which is furnished with a suitable stop-cock, c, and in connection with a small bell jar, f, in which is suspended, by means of a wire, a cylinder of metallic zinc, z. When required for use, the outer jar is two-thirds filled with a mixture of one part sulphuric acid and four parts water, and the stop-cock opened to allow the escape of atmospheric air, the spongy platinum contained in the small brass cylinder, d, being covered by a piece of paper. The stop-cock is then closed, and the bell jar, f, allowed to fill with hydrogen, and after it has been filled and emptied several times, the paper is removed from the platinum and the cock is again opened, when the gas, which escapes first, makes the metal red-hot and finally inflames. This property of platinum is also used in the “Davy” lamp.
The remaining metals do not call for detailed notice.
In conclusion, we may refer to the following statement, which in general terms gives the properties of the metals, their oxides and sulphides for ordinary readers.
General Classification of the Metals.
The metals admit of being really distinguished by the following table, in which they are presented in several groups, according to their peculiar properties, and each distinguished by a particular name:—
| Metals. | Properties of the | |
|---|---|---|
| Oxides. | Sulphides. | |
| (A.) Light Metals. Specific gravity from 0·8 to 1; never occur in the uncombined state. | Powerful bases; possessing a strong affinity for water, and form with it hydrates. They yield their oxygen to carbon only at a white heat. | Powerful bases, which oxidize in the air, and form sulphates; when treated with acids evolve hydrosulphuric acid. |
| (a.) Alkaline Metals. 1. Potassium. 2. Sodium. (Ammonium.) | Highly caustic; powerful bases, separate all other oxides from their combinations with acids; are very soluble in water, and do not lose their water of hydration at the highest temperatures; attract carbonic acid rapidly from the air. | Caustic; strong bases; very soluble in water, and dissolve a large quantity of sulphur, which is separated on addition of an acid as a white powder, termed milk of sulphur; they were formerly termed liver of sulphur. |
| (b.) Metals of the Alkaline Earths. 3. Calcium. 4. Barium. 5. Strontium. | Caustic; strong bases; slightly soluble in water; lose their water of hydration at a moderate heat, and powerfully absorb carbonic acid. | Caustic; strong bases; dissolve sulphur, and are partly soluble in water, and partly insoluble. |
| (c.) Metals of the Earths proper. 6. Magnesium. 7. Aluminium. | Weak bases, Feebly caustic, or not caustic. insoluble in water. | Insoluble in water. |
| (B.) Heavy Metals. Specific gravity from 5 to 21; are found chiefly in combination with oxygen, and frequently with sulphur and arsenic; some are native. | Feebler bases than the foregoing, some are acids; insoluble in water, and lose their water of hydration at a moderate heat. | Neutral compounds; insoluble in water; antimony and several of the rarer metals produce compounds with sulphur, which deport themselves as acids. |
| (a.) Common Metals. Become oxidized in the air. 8. Iron. 9. Manganese. 10. Cobalt. 11. Nickel. 12. Copper. 13. Bismuth. 14. Lead. 15. Tin. 16. Zinc. 17. Chromium. 18. Antimony. | With few exceptions, are soluble in acids, and, when ignited with carbon at a red heat, yield their oxygen; are, for the most part, fusible and non-volatile. | Those occurring in nature are somewhat brass-like in appearance, and are termed pyrites and blendes. Those which are artificially prepared have peculiarcolours; by heat they are converted into sulphates. |
| (b.) Noble Metals. Unchangeable in the air. 19. Mercury. 20. Silver. 21. Gold. 22. Platinum. | Have more the properties of acids than of bases; are decomposed by ignition into oxygen and metal. | With the exception of sulphide of mercury, they leave the pure metal when ignited. |