THE UNFAMILIAR METALS 181 



The familiar metals answer to the above description, but other 

 metals, like sodium, potassium, and calcium, do not. We need 

 some chemical guide to determine what is and what is not a metal. 



Any element which will combine with oxygen and hydrogen 

 to form a base is a metal, no matter what its physical appear- 

 ance may be. Metal sodium when put into water unites with 

 oxygen and hydrogen to form the base sodium hydroxide, or 

 caustic soda. The metal potassium unites with oxygen and 

 hydrogen to form the base potassium hydroxide, or lye. 



The unfamiliar metals. The metal sodium is never found 

 free, but it is found almost everywhere in combination. Its 

 most abundant compound is common salt. Large deposits of 

 another compound, sodium nitrate or Chile saltpeter, occur in 

 Chile, and sodium silicate is present in many rocks. The un- 

 familiar metals, potassium and calcium, are little used in the 

 pure state, but their compounds are very important. 



The most important compound of the metal calcium is cal- 

 cium carbonate, of which marble and limestone are good ex- 

 amples. Marble and limestone are used as building stones, and 

 limestone is also used in the manufacture of lime, without which 

 we could have no whitewash, cement, or mortar. Limestone is 

 heated in strong furnaces until it is transformed to quicklime. 

 Water is then placed on the lumps of quicklime, which swell and 

 finally crumble to a powder called slaked lime. The greatest use of 

 slaked lime is the making of mortar and cement, and the removing 

 of hair from skins which are to be tanned and made into leather. 



If a small quantity of the slaked lime is dissolved in water 

 and the solution is filtered, it forms the lime water often pre- 

 scribed by physicians for sour stomach. If a large quantity 

 of the slaked lime is placed in water, much of it does not dis- 

 solve, but remains suspended in the water. Water full of 

 suspended lime particles is called whitewash and is used to coat 

 the walls of cellars and sheds. 



