GENERAL REMARKS REGARDING ELEMENTS. 131 



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 substances, rarely liquids, and 

 never compounds showing the gaseous state at the ordinary tem- 

 perature. 



Nomenclature. The chemical nomenclature of compound sub- 

 stances has undergone considerable changes within the last twenty- 

 five years. These changes were made in conformity with our present 

 views of the constitution of the compounds. 



Whenever the syllable ide is used to replace the ending of a non- 

 metallic element it designates that this element has entered into com- 

 bination with another element or with a radical. Thus, we speak of 

 <>x/Vcs, sulphicfos, carbides, chlorides, etc., when referring to compounds 

 formed by the union of oxygen, sulphur, carbon, or chlorine with 

 another element or with a radical. 



When two elements combine in one proportion only, little difficulty 

 is experienced in the formation of a name, as, for instance, in iodide 

 of potassium or potassium iodide, KI, chloride of sodium or sodium 

 chloride, NaCl. 



When two elements combine in more than one proportion, the 

 syllables, mono, di, tri, tetra, and penta are frequently used to designate 

 the relative quantity of the elements. For instance : Carbon mon- 

 oxide, CO, carbon dioxide, CO 2 , phosphorus tfn'chloride, PC1 3 , nitrogen 

 t< '//-oxide, N 2 O 4 , phosphorus >entachloride, PC1 5 . 



In many cases the syllables ous and ie are used to distinguish the 

 proportions in which two elements combine ; the syllable ous being 

 used for the simpler or lower, the syllable ic for the more complex or 

 higher form of combination. For instance : Phosphorous chloride, 

 PC1 3 , and phosphoric chloride, PC1 5 ; ferrous oxide, FeO, ferric 

 oxide, Fe 2 O 3 . 



The syllable sesqui is used occasionally to indicate that a compound 

 contains one-half more of an element than another compound formed 

 from the same elements. Thus, ferric chloride, FeCl 3 , is sometimes 

 called sesgiiichloride of iron, as it contains one-half more of chlorine 

 than does ferrous chloride, FeCl 2 . 



The syllables proto or sub and per have also been used as prefixes 

 to differentiate between compounds formed by the same elements. 

 For instance, mercurous chloride, HgCl, is called protochloMe or 

 sw6chloride, while mercuric chloride, HgCl 2 , is often designated as 

 jwchloride of mercury. 



When two oxides of the same element ending in ous and ic form 



