138 APPLIED SCIENCE 



passes off. Ordinary commercial nitric acid has a specific gravity 

 of 1.42 and contains about 68% of acid. 



Sulphuric acid, often called oil of vitriol, is the most im- 

 portant chemical used in manufacturing operations. Its 

 symbol is H 2 S0 4 and in a diluted or weak form it acts on 

 metals. When concentrated or strong it forms on the metal 

 a coating of a salt which prevents further action. 



The action of the acid on a metal may be represented by the 

 following equation : 



Fe + H 2 SO 4 FeSO 4 + H 2 



Iron Sulphuric Iron Hydrogen 



Acid Sulphate 



Muriatic" or hydrochloric, acid is generally made by the 

 action of sulphuric acid on salt. 



The action may be represented by the following equation : 



2NaCl + H 2 SO 4 = Na 2 SO 4 + 2 HC1 

 Common Salt Sulphuric Sodium Hydrochloric 



Sodium Chloride Acid Sulphate Acid 



148. Formation of Salts. A salt is a compound of metal- 

 lic and non-metallic elements or radicals. It is formed by the 

 action of: (1) an acid on an alkali or base (a base is a compound 

 of a positive, i.e., a metallic element, or a group of them 

 called a radical, and OH, the hydroxyl group); (2) an acid 

 and a metal; (3) an acid and a salt. 



In forming a salt, the hydrogen of the acid is replaced 

 by the metal or metallic radical. If there is an excess of 

 acid that is, if the base is only sufficient to combine with 



