4 METALS AND THEIR PROPERTIES. PART i. 



metal of a bronze colour. Magnesium, which is a bril- 

 liant silver-white hard brittle metal, is obtained from 

 magnesium limestone or dolomite. Although the ores 

 of calcium and magnesium cover vast areas of the 

 globe, the metals form a very small comparative pro- 

 portion of them. 



The metals derived from non-alkaline earths are 

 glucinum, yttrium, thorinum, zirconium, and aluminium, 

 which is the only one of any interest : it is now be- 

 coming a very useful metal. It combines readily with 

 ^oxygen to form clay. The ruby, sapphire, and oriental 

 topaz are merely coloured varieties of corundum, which 

 is nothing but crystallised clay. Rubidium, csesium, and 

 thallium were discovered by spectrum analysis. 



The avidity of some of these metals for oxygen 

 is quite remarkable : potassium and rubidium inflame 

 when they touch ice or cold water ; they decompose the 

 water and combine with its oxygen. Calcium becomes 

 luminous in warm water, and burns with intense light 

 when heated to redness ; but a magnesium wire burns 

 with such intense brilliancy that it has been employed 

 for photography, and will probably become useful for 

 household purposes, as two ounces and a half of mag- 

 nesium wire when burnt give a light equal to that of 

 twenty pounds' weight of stearine candles. 



The metals whose oxides are not reducible by heat 

 without the aid of some form of carbon include nearly 

 all the useful metals. They are all polyatomic, that is, 

 they combine with other elements in the number of 

 atoms varying from two to eight, and are divided into 

 seven groups in regard to this property. For in- 

 stance, zinc, copper, and cadmium are diatomic. Zinc 

 is invaluable as a source of electric light and heat in 

 the voltaic battery, and its vapour burns brilliantly. 

 Copper is one of the most useful of metals, while cad- 

 mium is of no value at all. Nickel, cobalt, and uranium 



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