450 APPENDIX. 



685. 



NEUTRAL, ACID, AND BASIC SALTS. In general, salts con- 

 taining an equivalent of base to an equivalent of acid are 

 called neutral. The composition fixes the name, whether ex- 

 actly neutral to the taste and in their action or vegetable 

 colors, or not. Salts containing more acid in proportion 

 are called super-salts or acid salts, and those containing 

 mere base, sub-salts or basic salts. 



There are two exceptions to the above rules. The first 

 is that of certain classes of acids which have double and 

 treble neutralizing power, and require, therefore, the first two 

 atoms, and the latter three atoms of base, to make them 

 neutral salts. Such acids are bibasic and tribasic, in contra. 

 distinction from the mono-basic or ordinary salts. Phospho- 

 ric acid is one of the latter class of tribasic acids, and the 

 neutral phosphates have therefore three atoms of base and 

 is called a tribasic phosphate. Phosphates containing more 

 acid or base than their proportion, are acid or basic accord- 



ing 1 y- 



The second exception is that of salts or bases which con- 

 tain more than one atom of oxygen to an atom of metal. 

 In proportion as they contain more, they neutralize more acid. 

 Alumina or oxide of aluminium, for example, contains three 

 atoms of oxygen. Its neutral sulphate, therefore, is a salt 

 containining 3 atoms of acid. A salt of aluminium containing 

 more or less than their proportion, is acid or basic accord. 



DOUBLE SALTS. There are also double salts or compounds 

 of salts with each other. They are generally of the same 

 acid. Thus alum is a double sulphate of potassa and alu- 

 mina and the bisulphate of potassa may be regared as a 

 double sulphate of potassa and water. Such double salts 



