CHAPTER I 

 Composition of Matter 



i. Physical and Chemical Changes. All substances 

 in nature are subject to change in form and composition. 

 At a low temperature, water is converted into ice, and by 

 the application of heat into steam. The three forms 

 which water may assume solid, liquid, and vapor are 

 simply different conditions in which it is capable of ex- 

 isting. When water is changed into steam or ice, noth- 

 ing is either added to or taken from the particles of water, 

 simply a change of form or a physical change takes place. 

 When, however, an electric current is passed through 

 water, the water is decomposed and two gases are pro- 

 duced. When such a change takes place, the water par- 

 ticles are subjected to a change in composition called a 

 chemical change. 



Limestone may be pulverized until it is as fine as wheat 

 flour, and when examined with a microscope, each frag- 

 ment is in all respects like the original piece, except in 

 size. The crushing has resulted in simply dividing the 

 limestone into a large number of particles. If, however, 

 a piece of limestone is burned in a lime kiln, the product 

 is entirely different in its properties from the original 

 lime rock. When water is added to burned lime, it 

 slakes, heat is generated, and steam is given off, while, 

 when water is added to lime rock, no appreciable change 

 takes place. 



Changes, which affect the form but not the composition 

 of matter are known as physical changes. The produc- 

 tion of steam from water, the freezing of water, the pul- 



