COMMON ELEMENTS OF THE EARTH 155 



to form soft alloys called amalgams. An amalgam of 

 silver and mercury is used by dentists in filling cavities in 

 teeth. , 



172. Uses of other Metals. Nickel is used as a plat- 

 ing material and in coins. Zinc, tin, and lead, in thin sheets, 

 are used to cover wood and to line tanks. Iron coated with 

 zinc is called galvanized iron; covered with tin, it is called 

 tin plate. Ordinary tinware is thin sheet iron coated with 

 tin; the coating makes the ware brighter and prevents 

 rusting. The flexibility of lead makes it useful in pipes 

 which must be bent to turn corners. Ordinary water pipes 

 and gas pipes are made of iron, plain or galvanized. Coil 

 pipes are frequently made of copper. 



Platinum is one of the rarest and most expensivt metals. 

 Its principal use is in scientific apparatus and in the setting 

 of precious stones. Magnesium burns with a brilliant light 

 of great chemical energy and is therefore used in photo- 

 graphic flashlight work. 



173. The Specific Gravity of Metals. Most of the 

 metals have a greater specific gravity than the common rocks. 

 The specific gravity of common rocks varies from about 2.5 

 to 3.5. Below are given the specific gravities of some of the 

 metals in the pure state: 



174. Chemical Symbols. In scientific work, abbrevia- 

 tions are used to represent the elements. As many of the 

 elements have Latin names, the abbreviations or sym- 

 bols may be unlike their English names; for instance, Au 

 stands for gold, from the Latin word for gold, aurum. 

 In every language the symbols used in scientific work are 

 the same. 



