FORCE AND MOTION 67 



weight is 145 grams. The apparent loss of weight is 85 

 grams. 230 g. -=- 85 g. = 2.7 (specific gravity). Therefore, 

 the weight in air is 2.7 times the weight of the water dis- 

 placed, or 2.7 times the weight of a volume of water equal 

 to that of the marble. (LABORATORY MANUAL, Exercise 

 IX.) 



69. Physical States of Matter. There are three states 

 or conditions of matter: solid, liquid, and gaseous. Most 

 substances have been obtained in all three states. 



Matter is said to be solid, or in the solid state, when it 

 opposes any change in its shape. Much energy is required to 

 separate the molecules of a solid. Wood, iron, nails, and 

 sand are solids. 



Matter is said to be liquid, or in the liquid state, when it 

 has no definite shape of its own, but will take the shape of 

 any vessel into which it is poured. It will oppose strongly, 

 however, any change in its volume. Water, milk, kerosene, 

 and mercury are liquids. 



Matter is said to be a gas, or in the gaseous state, when 

 it has no definite shape or volume of its own; if put into 

 a vessel, it will distribute itself throughout all the space in 

 the vessel, whatever the size or form. Air, hydrogen, illumi- 

 nating gas, and steam are gases. 



70. The Effect of Heat on Physical State. Many 

 solids, on being heated, are changed into liquids. Examples: 

 ice, lead, lard. When these liquids are cooled, they change 

 back to the solid state. Many liquids, on being heated, 

 change into gaseous substances called vapors. Vapors are 

 gases which condense at ordinary temperatures. Steam, the 

 gas made by boiling water, is a vapor. The gas from boil- 

 ing alcohol is a vapor. The gases of which the air is com- 

 posed are not vapors. 



The temperature at which a solid begins to be liquid is 

 called the melting point of the substance. Every substance 

 that can be melted has its own melting point. Iron melts 



