xiv THE ATOMIC THEORY 313 



except fluorine combine directly with oxygen, whilst the 

 formation of hydrides, at least in the case of the metals, is 

 the exception rather than the rule. The figure 8 is chosen 

 because it gives for hydrogen a value, i *oo8, which approxi- 

 mates very closely to unity. 



Table of equivalents of elements. The following table 

 shows the equivalents or combining weights of some of the 

 common elements. 



Hydrogen . . . I'OoS Lithium . . .6*94 



. 20-03 

 . 23 - oo 

 . - 3178 

 . 39'iQ 



. 100-3 

 103-55 

 . 107-88 



The table shows at a glance the composition of lime as 

 containing 20*03 parts of calcium combined with 8 parts of 

 oxygen, whilst litharge contains 103-55 parts of lead com- 

 bined with 8 parts of oxygen. Muriate of lime or calcium 

 chloride contains 20-03 parts of calcium combined with 35*46 

 parts of chlorine, whilst common salt contains 23-00 parts of 

 sodium combined with 35-46 parts of chlorine. 



In drawing up a table of equivalents it is customary, 

 when multiple proportions are observed, to tabulate the 

 equivalent of the element as deduced from the analysis 

 of one compound, selected as typical, and to represent the 

 composition of the others by multiples of the tabulated 

 equivalents. Thus, in the table, carbon and oxygen are 

 shown as uniting together in the ratio 3*00 to 8 to form 

 carbonic anhydride ; but they also unite in the ratio 

 2 x 3-00 to 8 to form carbonic oxide. Again carbon and 

 hydrogen unite in the ratio 3*00 to 1*008 in marsh gas, but 

 in the ratio 2 x 3*00 to roo8 in olefiant gas. Such multiple 



