CHAPTER II 

 CHEMICAL CHANGE AND THE METHODS OF STUDYING IT 



WE must now take up two new examples of chemical change. 

 They will aid us in introducing one or two additional conceptions 

 and laws. These are continually used by the chemist, and without 

 them we cannot begin the systematic study of the science. 



Another Case of Combination: Iron and Sulphur. 



Since oxygen is an invisible gas, there is a slight difficulty in real- 

 izing that rusting consists in the union of two substances this 

 gas and a metal. The present example is less interesting historic- 

 ally, but it is simpler because both substances are visible and are 

 easily handled. The case of iron and sulphur will enable us to 

 illustrate the same point of view and to 

 practice the application of the same tech- 

 nical words. It will also introduce us to 

 two manipulations filtration and evap- 

 oration which are frequently used by 

 the chemist. 



We begin by observing and contrasting 

 FIG. 7 the specific properties of the two sub- 



stances. Sulphur is a pale-yellow sub- 

 stance of low specific gravity (sp. gr. 2). It is easily melted (m.-p. 

 114.5 C.). It does not dissolve in water that is, it does not 

 mix completely with and disappear in water, as sugar does on 

 stirring. It does dissolve readily in certain other liquids, such as 

 carbon disulphide, however. It crystallizes in rhombic forms 

 (Fig. 7). It is not attracted by a magnet. Iron is a lustrous 

 greyish substance of much higher specific gravity (sp. gr. 7.8). 



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