88 



THE WONDERFUL CENTURY. 



smallest portion that has the properties of the element, 

 and the atom of each element has a different weight, 

 Hence, when one element combines with another, the 

 proportions must be either those represented by the 

 atomic weights, or some multiple of those weights, since 

 the atoms are assumed to be indivisible. This will be 

 made clearer by another example. The atomic weights 

 of nitrogen and oxygen are as 14 to 16, and these ele- 

 ments combine in five different proportions, as shown by 

 the following figures, each circle representing an atom of 

 the elements indicated by their initial letters : 



Chemical 

 Symbol 



= Nitrogen monoxide N 2 O 

 = Nitrogen dioxide N 2 O 2 

 = Nitrogen trioxide N 2 O 3 

 = Nitrogen tetroxide N 2 O 4 

 O J= Nitrogen pentoxide N 2 O 6 



The atomic or combining weights of all the elements 

 having been carefully determined by numerous experi- 

 ments, a beautiful system of chemical symbols has been 

 formed which greatly facilitates the study of the in- 

 numerable complex substances that have to be investi- 

 gated. Each element is indicated either by one or two 

 letters, being the initial letter, or some two characteris- 

 tic letters, of its chemical name, so that nearly seventy 

 elements are thus clearly defined. But these symbols 

 represent not only the element, but a definite propor- 



