CHEMICAL PHENOMENA 55 



If this mixture is placed in a test tube and heated 

 in the flame of a Bunsen burner, a very striking change 

 takes place. The mixture begins to glow at the bottom 

 of the tube, and then the glow rapidly extends through 

 the entire mass. If the test tube is now broken and 

 its content examined, it will be found to be a brittle 

 substance, which in no way resembles the sulphur or 

 the iron with which we started. The magnet will no 

 longer attract the iron, neither can the sulphur be 

 separated by any physical process. A new substance 

 has been formed, resulting from the action of the heat 

 upon the mixture of iron and sulphur. This new sub- 

 stance is iron sulphide. Such a substance is called 

 a chemical compound. When two or more substances 

 unite in such a way as to lose their characteristic 

 properties, and to form a new substance with new 

 properties, such a substance is called a chemical 

 compound. 



Elements. It has been seen that iron sulphide is 

 composed of two entirely different substances, iron 

 and sulphur. The question now naturally arises: do 

 these substances each contain different substances, that 

 is, are they also chemical compounds? 



Chemists have tried in a great many ways to decom- 

 pose them, but all their efforts have failed. Substances 

 which can not be decomposed into other substances are 

 called elements. It is not always possible to prove that 

 a given substance is an element. It is always possible 

 that by some yet untried method the supposed element 



