LESSONS IN CHEMISTRY. 119 



Acids change litmus blue to red, while a basic solution changes 

 the red to blue again. 



When a base and an acid are mixed in solution they neutralize 

 or change the properties of each other, forming water and a com- 

 pound called 3, salt. If we mingle hydrochloric acid and sodium 

 hydroxide the salt, sodium chloride will be formed, together with 

 one molecule of water, according to the following equation, HC1 

 -j-NaHO=NaCl, common salt,-hH 2 0. The hydrogen of the acid 

 exchanges places with the metal of the base, as shown in the 

 equation. The following equation shows the same exchange. 

 Sulphuric acid, H 2 S0 4 -f-2NaHO, sodium hydroxide, Na 2 S0 4 , 

 sodium sulphate, H-2H 2 0. 



The names of the stronger acids end in ic, as nitric, sulphuric 

 and hydrochloric. If an acid containing the same elements has 

 a less proportion of oxygen the name ends in ous, as nitrous 

 acid, sulphurous acid. In the case of acids of which chlorine is 

 a distinguishing element we have a hypo or subchlorous acid 

 and a perchloric acid; the former contains less oxygen than 

 the ous acid, the latter more than the ic acid. 



The bases are metallic hydroxides, and the metal of the com- 

 pound is the distinguishing part of the name, as sodium hydrox- 

 ide, potassium hydroxide and calcium hydroxide. Such com- 

 pounds are sometimes called hydrates, as they may have been 

 formed by the metal replacing one atom of hydrogen in water, as 

 H 2 0+K KOH-f-H, one atom of free hydrogen. 



Salts are named from the acids forming them, as nitrates, 

 sulphates, chlorates, etc., and they are further distinguished by 

 the name of the metal of the base, as potassium nitrate, sodium 

 sulphate, etc. The salts formed by nitrous acid are called nitrites 

 and those by sulphurous acid are called sulphites, etc. If the 

 name of the acid ends in ic, the name of the salt ends in ate, if the 

 name of the acid ends in ous, the name of the salt ends in ite. The 

 reciprocal action of chemical agents, as in the case of an acid and 

 a base, or the action of some form of energy causing chemical 

 changes, is called a reaction, and a substance capable of producing 

 with another substance a chemical reaction is called a reagent. 



