CHAPTER XXII 



ACIDS, BASES, AND SALTS 



Acids and Salts. It has already been shown that from 

 hydrochloric acid there can be obtained common salt and other 

 allied compounds, called chlorides, while from sulphuric acid 

 we get a series of compounds called sulphates. It will be 

 necessary to consider a little more fully the formation of these 

 compounds. 



Besides the two acids mentioned above, a third is very 

 frequently employed in the laboratory, viz., nitric acid, HNO 3 . 

 Examine this acid, and notice that it gives off pungent, choking 

 fumes, especially on heating, being then coloured yellow. By 

 the action of copper, red fumes and a blue liquid result ; this 

 forms a good means of recognising the acid. If the blue liquid 

 be evaporated and allowed to crystallise, a salt which closely 

 resembles the copper sulphate is obtained, which is called copper 

 nitrate, consisting of nitric acid in which the hydrogen has been 

 replaced by copper. 



We may therefore consider acids as compounds containing 

 hydrogen which is capable of being replaced by a metal 

 with the formation of salts. They have usually a sour 

 taste and change the colour of blue litmus to red. Salts 

 may be evidently denned as compounds resulting from acids 

 by the replacement of their hydrogen by a metal. 



Preparation of Salts. We can frequently prepare salts by 

 the action of the acid directly on the metal, and numerous 

 examples of such action have been studied. In the first place 

 hydrogen is liberated, and this hydrogen may either pass off as 

 a gas or may react again with the acid to form various products. 

 An example of the first case has been seen in the action of 

 sulphuric acid on zinc, and of the second case in the action of 



