24 SMITHS' INTERMEDIATE CHEMISTRY 



did. Nature, however, has no free will, and cannot tell why she 

 presents certain phenomena, and not others. 



On examining the explanation, we find that it simply shows 

 that when iron rusts it combines with oxygen from the air. This 

 is an additional fact. It shows how iron rusts, namely, by taking 

 up oxygen, but not why it is able to unite with oxygen. We 

 simply do not know why iron can combine with oxygen gas and 

 platinum cannot. 



Explanations in chemistry are of three kinds. (1) We usually 

 try to show that the phenomenon is not an isolated one. Thus, 

 we show that other metals rust. This reconciles us to some ex- 

 tent to the fact that iron rusts, and we feel some mental satisfac- 

 tion. This is the method of showing that the fact to be explained 

 is a member of a large class of similar facts. (2) Next, we try 

 to get more information about the fact to be explained. Thus, 

 when, to the acquaintance with the outward manifestations of 

 rusting, we add the further information that there is an increase 

 in weight, and that this is due to union of oxygen from the air 

 with the iron, we feel increased satisfaction, and say that the 

 fact has been " explained." (3) If we are still dissatisfied, and 

 can discover no further useful facts, we imagine a state of affairs 

 which, if true, would classify the fact or add to what we know 

 about it. This step we call explaining by means of an hypothesis. 

 We then devote our attention to trying to verify the hypothesis. 



The formulation of laws and the making of attempts to explain 

 facts are part of what is called the scientific method. The purpose 

 of this method is to convert the subject matter into a science, that 

 is, into an organized body of knowledge. 



Summary. In this chapter we have learned: (1) that, 

 while there are many substances, there is a limited number of 

 entirely different kinds of matter (elements) ; (2) that, in addition 

 to definite specific properties, each substance has a constant 

 composition by weight. We have also learned that physical 



