26 CHEMISTRY OF FARM PRACTICE 



(6) When in water solution, bases turn back to a blue 

 color litmus paper that has been made pink by the action 

 of an acid. 



(c) The stronger bases attack metals such as aluminium 

 and zinc, producing thereby water as one of the products 

 of the reaction. 



(rf) Generally they are insoluble in water. Those enu- 

 merated above are the only ones that will dissolve appre- 

 ciably in water. The three first mentioned above are 

 very soluble and are called the alkalies. 



(e) Bases all contain the radical, hydroxyl, OH, the 

 only other constituent being a metal. This hydroxyl is 

 easily separated from the metal. 



(/) Bases react easily with acids, the hydroxyl of the 

 base uniting with the hydrogen of the acid, producing 

 thereby water (OH+H = H2O). This action takes away 

 or neutralizes the characteristic properties of both acids 

 and base. 



(</) Bases are composed of a metal bound by means of 

 oxygen to hydrogen. For example: silver hydroxide, 

 AgOH; mercurous hydroxide, HgOH; copper hydroxide, 

 Cu(OH) 2 ; iron hydroxide, Fe(OH) 3 . 



25. Salts. Salts have no characteristic properties de- 

 fining them as a class. They may be best described by 

 their methods of production and by their composition. 



(rt) When the acid hydrogen of an acid is replaced by 

 a metal, the resulting compound is a salt. For example: 

 Replacing the two hydrogens of sulphuric acid, HoSO-i, 

 by the bivalent metal zinc, a salt, zinc sulphate, ZnSO-i, 

 is produced; replacing the hydrogen of nitric acid, HNOs, 

 by the univalent metal silver, a salt, silver nitrate, AgNOs, 

 is produced. 



(6) When the hydroxyl of a base is replaced by a non- 

 metal or by a non-metallic radical, the resulting com- 

 pound is a salt. For example: When the hydroxyls of 

 the base, zinc hydroxide, Zn(OH)2, are replaced by the 



