432 METALLIC ELEMENTS. 



Of the physical properties of metals and their combinations 

 with each other, the most characteristic is their lustre and 

 power to reflect much of the light which falls upon them, a 

 property exhibited in a high degree by burnished steel, spec- 

 ulum metal, and the reflecting surface of mercury in glass 

 mirrors. Metals are also remarkable for their opacity, although 

 they have a certain degree of transparency in a highly atten- 

 uated state, as fine gold-leaf allows light of a green colour to 

 pass through it. They are peculiarly the conductors of elec- 

 tricity, and also the best conductors of heat, The most dense 

 substances in nature are found among the metals, gold, for in- 

 stance, being upwards of nineteen, and platinum nearly twenty- 

 one times heavier than an equal bulk of water. But some of 

 the metals, notwithstanding, are very light, potassium and so- 

 dium floating upon the surface of water. 



Certain metals possess a valuable property, malleability, de- 

 pending upon a high tenacity with a certain degree of soft- 

 ness; particularly gold, silver, copper, tin, platinum, palla- 

 dium, cadmium, lead, zinc, iron, nickel, potassium, sodium, and 

 solid mercury. These metals may all be hammered out into 

 plates, or even into thin leaves. In zinc this property is found 

 in the highest degree between 300 and 400, and in iron at a 

 degree of temperature exceeding a red heat. The same metals 

 are likewise ductile, or may be drawn into wires, although the 

 ductility of different metals is not always proportional to their 

 malleability, iron being highly ductile, although it cannot be 

 beaten into very thin leaves. By a peculiar method, Dr. Wol- 

 laston formed gold wire so small that it was only l-5000th of 

 an inch in diameter, and 550 feet of it were required to weigh 

 one grain. He also obtained a wire of platinum not more 

 than l-30,000th of an inch in diameter*. The tenacity of differ- 

 ent metals is determined by ascertaining the weight required 

 to break wires of them having the same diameter. Iron ap- 

 pears to possess that property in the greatest, and lead in the 

 least degree. It has been observed by M. Baudrimont that the 

 tenacity of wires of iron, copper, and brass is much injured by 

 annealing themf. A few of the malleable metals can be 

 welded, or portions of them joined into one by hammering them 

 together. Pieces of iron or platinum may be united in this 



* Phil. Trans. 1813. f An. dc Ch. et de Ph. t. GO, p. 78. 



