21 



The quantity, therefore, <f each clement remains constant in all 

 chemical changes ; which fact may be deduced as a consequence of the 

 la\\ of the indestructibility of matter, and uf the conception of elements 

 themselves. Thus the equation expressing the law of the indestructi- 

 bility of matter acquires a new and still more important signilication. 

 If we know the quantities of the elements which occur in the acting, 

 it may be compound, substances, and if from these substances there 

 proceed, by means of chemical changes, a series of new compound sub- 

 stances, then the latter will together contain the same quantity of each 

 of the elements as there originally existed in the reacting substances. 

 The essence of chemical change is embraced in the study of how, 

 and with what substances, each element is combined before and after 

 change. 



In order to be able to express various chemical changes by equations, 

 it has been agreed to represent each element by the first or some two 

 letters of its (Latin) name. Thus, for example, oxygen is represented by 

 the letter O ; nitrogen by N ; mercury (hydrargyrum) by Hg ; iron 

 (ferrum) by Fe ; and so on for all the elements, as is seen in the tables 

 on page 24. A compound substance fe represented by placing the 

 symbols representing the elements of which it is made up side by side. 

 For example, red mercury oxide is represented by HgO, which shows 

 that it is composed of oxygen and mercury. Besides this, the symbol 

 of every element corresponds with a certain relative quantity of it by 

 weight, called its ' combining ' weight, or the weight of an atom; so that 

 the chemical formula of a compound substance not only designates the 

 nature of the elements of which it is composed, but also their quantita- 

 tive proportion. Every chemical process may be expressed by an equa- 

 tion composed of the formulae corresponding with those substances 

 which take part in it and are produced by it. The amount by weight 

 of the elements in every chemical equation must be equal on both sides 

 of the equation, because no element is either formed or destroyed in a 

 chemical change. 



On pages 24, 25, and 26 a list of the elements, with their symbols 

 and combining or atomic weights, is given, and we shall see afterwards 

 on what basis the atomic weights of elements are determined. At 

 present we will only point out that a compound containing the elements 

 A and B is designated by the formula A M B" 1 , where m and n are the 

 coefficients or multiples in which the combining weights of the 



they conduct an electric current without decomposing) which allow them to be distin- 

 guished at a glance from other kinds of matter. Besides, there is no doubt (from the 

 results of spectrum analysis) that the elements are distributed as far as the most 

 distant stars, and -that they support the highest attainable temperatures without 

 decomposing. 



