Many of them are what is called malleable, that is, may be extended or spread out by rolling, or beating them with a hammer; and ductile, or have the property of being drawn out into wire. Gold, silver, copper, and iron, are the most remarkable in this respect.
All the metals are fusible, but some require very different degrees of heat to render them fluid,—platinum requiring the heat of the oxy-hydrogen blowpipe, while tin melts in the flame of a candle, and mercury is fluid at all temperatures in this climate, but becomes solid at 40° Fahr. below 0,—a temperature occasionally experienced in the Arctic regions, where the mercurial thermometer is useless, the mercury becoming solid.
They are all excellent conductors of heat and electricity, and have the property of reflecting light and forming mirrors; for looking-glasses owe their power of reflecting objects principally to what is called the “silvering;” that is, a mixture of mercury and tin spread over the back of the glass, which being transparent, allows the image reflected from the metal to pass through it.
The following classification is most instructive, because it suggests to the young student that there must be identical properties in the metals thus placed together:—
Class 1. Ammonium, cæsium, lithium, potassium, sodium.
Class 2. Calcium, barium, strontium.
Class 3. Aluminium, cerium, didymium, erbium, glucinium, lanthanum, thorium, yttrium, zirconium.
Class 4. Zinc class: cadmium, magnesium, zinc.
Class 5. Iron class: cobalt, chromium, indium, iron, manganese, nickel, uranium.
Class 6. Tin class: niobium, tantalum, tin, titanium.