162 PHYSIOLOGY FOR NURSES 



while we have two new substances, we have exactly 

 the same number of atoms. Such changes result when 

 the chemical affinity of one element is stronger than that 

 of another. In this example nitrogen, an inert sub- 

 stance whose chemical affinities are not strong, is re- 

 placed by chlorine whose affinity is strong and active. 



Acids. "An acid is a substance consisting of hydro- 

 gen and a nonmetallic element or radical, which usually 

 has a sour taste, turns litmus red, and is capable of 

 reacting with a base to form a salt and water." In the 

 example given above the radical (the nonmetallic ele- 

 ment which combined with hydrogen) is made up of 

 one atom of nitrogen and three of oxygen. When, 

 therefore, acids combine with bases to form salts, it is 

 the radical which thus combines, i.e., in silver nitrate 

 AgN0 3 , the nitric acid having lost its hydrogen which 

 combined with to form water and was replaced by 

 an atom of H. 



Acids which have but one element of H to be replaced 

 in combination with bases are called monobasic, those 

 with two, dibasic, etc. 



Bases. "A base is a compound in which a metallic 

 element is linked to hydrogen by means of oxygen, 

 turns litmus blue, and is capable of reacting with an 

 acid, forming a salt and water." 



Bases have a group of oxygen and hydrogen (OH) 

 atoms called Jiydroxyl and the bases themselves are called 

 hydroxides. If there is one OH group the base is mono- 

 acid, if two, diacid, etc. 



Salts. These substances are "products of the inter- 

 action of acids and bases." A base like sodium hydrox- 

 ide may be converted into common table salt (sodium 

 chloride) and water. The change is expressed in the 

 following formula : 



