60 PRINCIPLES OF CHEMISTRY. 



Physical properties of elements. Most elements are, at the 

 ordinary temperature, solid substances, two are liquids (bromine 

 and mercury), five are gases (oxygen, hydrogen, nitrogen, chlo- 

 rine, and fluorine). Most of the solid elements may be con- 

 verted into liquids and gases by the action of heat. Some 

 solid elements, however, have so far resisted all attempts to 

 change their state of aggregation. 



Most, if not all, of the solid elements may be obtained in the 

 crystallized state ; a few are amorphous and crystallized, or 

 polymorphous. The physical properties of many elements in 

 these different states differ widely. For instance : Carbon is 

 known crystallized as diamond and graphite, or amorphous as 

 charcoal. The property of elements to assume such different 

 conditions is called allotropic modification. 



Some of the gaseous elements are also capable of existing in 

 allotropic modifications. For instance : Oxygen is known as 

 such and as ozone, the latter differing from the common oxygen 

 both in its physical and chemical properties. The explanation 

 given for this surprising fact, that one and the same element has 

 different properties in certain modifications is, that either the 

 molecules or the atoms within the molecules are arranged dif- 

 ferently. Ozone, for instance, has three atoms of oxygen in the 

 molecule, while the common oxygen molecule contains but two 

 atoms. 



Most of the elements are tasteless and odorless ; a few, how- 

 ever, have a distinct odor and taste, as, for instance, iodine and 

 bromine. 



Relationship between elements and the compounds formed by their 

 union. The properties of the compounds formed by the com- 

 bination of elements are so various that it is next to impossible 

 to give any general rule by which they might be indicated. It 

 may be said, however, that nearly all of the gaseous compounds 

 contain at least one gaseous element, and that solid elements, 

 when combining with each other, generally form solid sub- 

 stances, rarely liquids, and never compounds showing the gas- 

 eous state at the ordinary temperature. 



Nomenclature. The chemical nomenclature of compound sub- 

 stances has undergone considerable changes within the last 



