CHAPTER V 

 EXPANSION AND HEAT MEASUREMENT 



EFFECTS OF HEAT 



Experiment to Show Expansion of Gas. Fill a bottle half full of water 

 colored with a little red ink; close with a one-hole rubber stopper through 

 which runs a hollow glass tubing extending into the liquid. Place the hands 

 on that part of the bottle which contains the air. The air will become warmer, 

 expand, and force the liquid up the tube. 



If air is heated 1 F., it expands ^Jr of its volume. Suppose 

 a room contains 3000 cubic feet of air, and the temperature 

 changed from 32 F, to 65 F., making a difference of 33. The 

 air would expand until there were about 3214 cubic feet of air; that 

 is, 214 cubic feet of air would be forced out of the doors and windows. 



Air is called a gas. We may apply to all gases the same rule for 

 expansion. 



In some countries the unit of measure for the expansion and contraction of 

 a gas is -^Tf f its volume at for every degree on the centigrade thermometer. 

 (A thermometer to be studied later.) 



The Use of Expansion of Air in Cooking. The expansion of 

 air is an important factor in cooking. We beat our various baking 

 mixtures, such as graham flour mixed with water or milk, to fill them 

 with air, which expands when exposed to the heat of the oven, and 

 renders the cooked product " light." Some cakes, as genuine sponge 

 cake, are made light solely by the introduction of air in the vigorous 

 beating of the eggs. The " beaten biscuits " of the south illustrate 

 how to make food light with no other aerating agent than air. The 

 dough is beaten or kneaded, rolled or pounded, and folded over 

 many times, until it contains large quantities of air. 



Because a cold liquid contains more air than a warm one, we use 

 ice water to mix up pastry dough. Eggs, when beaten to a froth, 

 retain great quantities of air. Eggs are beaten in cool dishes and, 



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