CLASSIFICATION OF ALTERATIONS. 205 



iron oxide. Carbonic acid may replace any of the other ternary rock- 

 forming- acids, including silicic, titanic, and phosphoric, and thus become 

 united with any of the important bases. The carbouation of the silicates 

 is of fundamental importance. The carbonation of the titanates and phos- 

 phates is unimportant. 



(6) Decarbonation is the separation of carbonic acid from a base with • 

 out the addition of other compounds, or with the substitution of another 

 acid for the carbonic. The most frequent substituted acid is silicic. 



(7) Silication is the union of silicic acid and base, or the substitution 

 of silicic acid for a combined acid, in either case producing silicates. The 

 only important oxide with which silicic acid unites as a rock-forming con- 

 stituent is iron oxide Silicic acid may replace carbonic, titanic, or phos- 

 phoric acid, thus becoming united with any of the bases with which it can 

 combine. The silication of the carbonates is of fundamental importance. 

 The silication of the titanates and phosphates is unimportant, 



(8) Desilication is the separation of silicic acid and bases without the 

 addition of other compounds, or with the substitution of another acid for 

 the silicic acid. The most frequent acid substituted is carbonic. 



(9) Silicification involves the addition of silica without union with 

 bases. The added silica may or may not replace other compounds. 



(10) Desilicification involves the subtraction of free silica. The sub- 

 tracted silica may or may not be replaced by other compounds. 



(11) Sulphidation is the union of sulphur with a metal forming- 

 sulphides. Added sulphur may be substituted for another element, usually 

 oxygen. 



(12) Desulphidation involves the subtraction of sulphur. Generally 

 the subtracted sulphur is replaced by another element, usually oxygen. 



(13) Sulphation is the union of sulphuric acid with base or the 

 substitution of sulphuric acid for another combined acid, in either case 

 producing sulphates. 



(14) Desulphation is the separation of sulphuric acid and base, or the 

 substitution of another acid for the sulphuric. 



(15) Titanation is the union of titanic acid with base, or the substitution 

 of titanic acid for another combined acid, in either case producing titanates. 



(16) Detitanation is the separation of titanic acid and base, or the 

 substitution of another acid for the titanic. 



