NATURE OF SALTS. 67 



acid and the base lose their caustic and corrosive 

 qualities. 



111. These compounds of acids and bases are 

 usually called Salts, or saline compounds, and are 

 very numerous ; for there are many acids, and many 

 bases. Most of the acids combine with bases in two 

 or three different proportions, forming sub-salts, neu- 

 tral salts, and acid, or super-salts. In the sub-salts, 

 the proportion of acid is not enough to more than 

 half neutralize the base; in the super-salts it is twice 

 as much as is required to neutralize the base; and in 

 the neutral salts, as the name indicates, the acid and 

 base are combined in single proportionals, or per- 

 fectly equal quantities (139, 141). 



112. There is also a great number of salts called 

 double salts: these are compounds of two similar 

 salts; thus there are double sulphates, like alum, the 

 sulphate of alumina and potash (25T) ; and double 

 phosphates, like the phosphate of ammonia and mag- 

 nesia (253). These double salts are distinct com- 

 pounds of the salts of which they consist, and possess 

 perfectly different properties from either of their 

 constituents; they may generally be made by merely 

 mixing together solutions of their two components. 

 The number of double salts is very considerable, but 

 there is also an immense number of salts which do 

 not thus combine together. 



113. Acids have a curious property of changing 

 certain vegetable colors. The greater number of 

 vegetable blue colors are by acids changed to red, 



