CHEMICAL NOMENCLATURE AND NOTATION. 103 



relations in composition, of the same kind as the use of figures 

 in the comparison of arithmetical sums. 



Symbols of the elements. Each elementary substance is re- 

 presented by the initial letter of its Latin name as will be seen 

 by reference to Table I, page 94; but when the names of 

 two or more elements begin with the same letter, a second in a 

 smaller character is added for distinction ; thus oxygen is re- 

 presented by the letter O, the metal osmium by Os, fluorine by F, 

 and iron (ferrum) by Fe ; small letters, it is to be observed, never 

 being significant of themselves, but employed only in connexion 

 with the large letters as distinctive adjuncts. These symbols 

 represent, at the same time, certain relative quantities of the 

 elements, the letter O expressing not oxygen indefinitely, but 

 100 parts by weight of oxygen, and Fe, 339 parts by weight of 

 iron, or any other quantities of these two substances which are 

 in the proportion of these numbers ; 8 parts of oxygen, for in- 

 stance, and 27-18 of iron. It will immediately be explained 

 that the elementary bodies combine with each other in certain 

 proportional quantities only, which may be expressed by one 

 or other of the two series of numbers placed against the names 

 of the elements in the tables (pages 94, 95, 96). These quanti- 

 ties are conveniently spoken of, as the equivalent quantities, or 

 equivalents, combining proportions or proportions of the elements. 

 The symbol or letter, of itself representing one equivalent of the 

 element, several equivalents are represented by repeating the 

 symbol, or by placing figures before it, thus Fe Fe, or 2 Fe, and 

 3 O, which mean two equivalents of iron and three of oxygen ; 

 or small figures are placed either above or below the symbol, 

 and to the right, thus Fe*, O 3 , or Fe 2 , O 3 , which expressions 

 are of the same value as the former, but are used only when 

 Symbols are placed together in the formulae of compounds. 

 Two equivalents of an element are often expressed by placing a 

 dash through, or under its symbol, as 2C, by -? or C, but such 

 abbreviations will not be made use of in the present work. The 

 substance represented by any symbol, which occurs to the reader 

 in the following pages, may be learned by reference to the alpha- 

 betical arrangement of symbols, page 96. 



Formulae of compounds. The collocation of symbols ex- 

 presses combination ; thus Fe O represents a compound of 

 one equivalent or proportion of iron, and one of oxygen, 

 or the protoxide of iron; SO ;i , a compound of one cquiva- 



