206 A TREATISE ON METAMORPHISM. 



(17) Phosphation is the union of phosphoric acid with base, or the 

 substitution of phosphoric acid for auother combined acid, in either case 

 producing- phosphates. 



(18) Dephosphatiou is the separation of phosphoric acid and base, or 

 the substitution of another acid for the phosphoric acid. 



(19) Chloridation is the addition of chlorine, forming chlorides. 



(20) Dechloridation is the subtraction of chlorine, destroying chlorides. 



(21) Fluoridation is the addition of fluorine, forming fluorides. 



(22) Defluoridation is the subtraction of fluorine, destroying fluorides. 



(23) Boration is the union of boric acid with base, or the substitution 

 of boric acid for another combined acid, in either case producing borates. 



(24) Deboration is the separation of boric acid and base, or the 

 substitution of another acid for the boric. 



GENERAL STATEMENTS. 



The foregoing processes are seen to be in pairs, in each case one of a 

 pair being the reverse of the other. That is, deoxidation is the reverse of 

 oxidation, dehydration is the reverse of hydration, etc. Moreover, one of 

 the processes of a pair is in several of the cases frequently the complement 

 of that of another pair. To illustrate, the processes of the following pairs 

 are often complementary of each other, viz, oxidation and desulphidation, 

 sulphidation and deoxidation, carbonation and desilication, silication and 

 decarbonation. By complement is meant that one takes place simultaneously 

 with the other, and that the two may really be one chemical reaction. In 

 such a case the change may be considered from either of two points of view. 

 To illustrate, the process of carbonation may be also a process of desilication, 

 and tlie process of silication may be also a process of decarbonation. 

 In general the process is named on the basis of the substance added rather 

 than that subtracted, for such substance is the active agent which drives 

 off the other and takes it place. It has been shown (pp. .168, 170-181) 

 that for several reactions one of a pair is particularly characteristic for one 

 of the zones of metamorphism. To illustrate, oxidation and its complement 

 desulphidation, carbonation and its complement desilication, and hydration 

 are particularly characteristic of the zone of katamorphism; sulphida- 

 tion and its complement deoxidation, silication and its complement decar- 

 bonation, and dehydration are particularly characteristic of the zone of 

 anamorphism. 



