84 A TREATISE ON METAMORPHISM. 



PRINCIPLES OF CHEMICAL REACTIONS APPLICABLE TO GROUND WATERS. 



GENERAL STATEMENT. 



DEFINITIONS. 



Before taking up chemical reactions it is advisable to give a number 

 of elementary definitions. 



"Compounds whose aqueous solutions contain the hydrogen ion (H) 

 are termed acids, and those which contain the hydroxy 1 ion (OH) bases."" 

 To illustrate, HC1 is an acid; NaOH is a base. When the hydrogen ion 

 united with one or more nomnetallic elements is mingled in solution with 

 the hydroxyl ion united with a metal a double reaction occurs, resulting 

 in the union of the hydrogen ions with the hydroxyl ions, forming water, 

 and the union of the nomnetallic parts of the compound with the metallic 

 parts. This latter union forms a salt. For example — 



HCl+NaOH=NaCl+H 2 0. 

 H 2 C0 3 +2NaOH=Na 2 C0 8 +2H i! 0. 



The acids and salts which contain only a single nonmetallic element are 

 called binary compounds. The acids and salts which contain two non- 

 metallic elements are called ternary compounds. For example, HC1 is a 

 binary acid; NaCl is a binary salt; H 2 C0 3 is a ternary acid; Na 2 C0 3 is 

 a ternary salt. Compounds having- the composition of acids, bases, and 

 salts may be separated from solution as solids, and of course all of these 

 solids may pass into solution. 



Some salts also contain a certain amount of acid, and such salts are 

 called acid salts. For instance — 



Na 2 C0 3 +H 2 C0 3 =2NaHC0 3 . 



The latter compound is acid sodium carbonate. On the other hand, some salts 

 contain some additional base, and such salts are called basic. For example, 

 Fe 2 (S0 4 ) 3 may be united with Fe 2 (OH) 6 , producing mFe 2 (S0 4 ) 3 .nFeo(OH) 6 . 

 This compound is basic ferric sulphate. 



DISSOCIATION. 



In explaining chemical reactions the theory of dissociation as advocated 

 by Arrhenius, Ostwald, Nernst, and others is followed for the most part. 



oOstwald, W\, The scientific foundations of analytical chemistry, translated by George McGowan, 

 Macmillan & Co., London, 1895, p. 117. 



