EXPANSION AND CONTRACTION 



II 



in the cork of a flask, and applying heat to the flask (Fig. 4). 



The ink is forced up the tube by the expanding air. Even 



the warmth of the hand is generally 



sufficient to cause the drop to rise 



steadily in the tube. This means that 



the air in the flask occupies more 



space than formerly, and since the 



quantity of air has not changed, each 



cubic inch of space must hold less 



warm air than it held of cold air ; 



that is, one cubic inch of warm air 



weighs less than one cubic inch of 



cold air, or warm air is less dense 



than COld air. All gases, if not COn- FIG. 3 As the airing is heated, 



fined, expand when heated and con- J* expa f nds .^ d escapes in the 



form of bubbles. 



tract as they cool. 



Heat, in general, causes substances to expand 

 or become less dense. 



3. Amount of Expansion and Contraction. 

 While most substances expand when heated 

 and contract when cooled, they are not all 

 affected equally by the same changes in tem- 

 perature. Alcohol expands more than water, 

 and water more than mercury. Steel wire 

 which measures \ mile on a snowy day will 

 gain 25 inches in length on a warm summer 

 day, and an aluminum wire under the same 

 FIG. 4. As the conditions would gain 50 inches in length, 

 ft^ex^ifd^lmi 4' Advantages an( * Disadvantages of Expan- 

 forces the drop of sion and Contraction. We owe the snug fit of 

 lbe ' metal tires and bands to the expansion and con- 

 traction resulting from heating and cooling. The tire of a 

 wagon wheel is made slightly smaller than the wheel which 



