Chemical Classification 315 



different form from the same materials, and further 

 investigation of the properties and composition of the 

 two sorts of crystals would show that they are, in fact, 

 two totally different substances. The crystals last 

 obtained are those of a substance called potassium 

 hydrogen sulphate. 



Equations : 

 Magnesium + hydrogen chloride 



= magnesium chloride + hydrogen. 

 Lead oxide + hydrogen nitrate 



= lead nitrate + hydrogen oxide. 

 Sodium carbonate + hydrogen chloride 

 = sodium chloride + hydrogen oxide + carbon dioxide. 

 Potassium hydroxide + hydrogen sulphate 



= (1) potassium sulphate -f hydrogen oxide. 



= (2) potassium hydrogen sulphate + hydrogen oxide. 



217. Potassium hydrogen sulphate belongs to a 

 class of substances termed " acid " salts. This term 

 bears no reference to their reaction, when in solution, 

 with litmus, but is intended to emphasise the presence 

 of some of the hydrogen the typical element of acids 

 in the salt, this hydrogen being derived from the acid 

 used in preparing the salt, and being capable of replace- 

 ment by a metal, just as was the hydrogen already 

 so displaced. Other names for such an acid salt as 

 potassium hydrogen sulphate are potassium acid 

 sulphate and potassium bisulphate. A familiar example 

 of an acid salt is afforded by baking-soda, or sodium 

 bicarbonate. 



Exercise for Student. 



Write down other names for baking-soda. Test the reaction upon 

 litmus of solutions of baking-soda and potassium bisulphate. 



218. Another class of salts is known, in which 

 a portion of the base remains in combination with the 



