86 



(b) Liquids water evaporation condensation. 



(c) Solids rock disintegration of rock. 



1. Gases. 

 Experiments. 



(1) Half fill a bladder with air, tie securely, and place in front of 



the fire. It begins to swell, almost at once, and is soon 

 quite full. Heat expands gases. 



(2) Half fill a rubber balloon with air and tie securely. Place in 



water and heat gradually. The balloon enlarges. Plunge 

 it into cold water. It becomes smaller. Why? Cold con- 

 tracts gases. 



(3) Blow thistle down or milkweed pappus over a hot stove or 



register. They rise. Why? The air is heated, expands, 

 and is forced up by cold currents. 



(4) Observe the direction of sparks, smoke and cinders of a bon- 



fire; the disturbance of the leaves around the fire. Account 

 for the result. The air is heated, expands, thus carrying 

 sparks, smoke and cinders. The cold air coming from all 

 sides to replace the heated air, forms currents carrying the 

 scattered leaves toward the fire. 



Eelate these experiments to absorption and radiation of 

 heat by earth's surface and production of winds. 



2. Liquids. 



(1) Fit a glass tubing through a cork. Fill a test tube with col- 



ored water. Press in the cork, causing the water to stand 

 in the tube just above the cork. Heat the water. It rises 

 in the tube. Why? Heat expends liquids. Cool the tube. 

 The water falls. Cold causes liquids to contract. Water is 

 the exception. It contracts until it reaches freezing point 

 and then expands. Put a bottle filled with water in a cold 

 place where the water will freeze. What causes the bottle 

 to burst? What causes the rocks to crack in winter? Ob- 

 serve ledges of rocks; do you see any effects of freezing? Ob- 

 serve the upheaval of soil in damp places in winter. What 

 effect does freezing have upon wet, clay soil? W T hat effect 

 does this freezing have upon the disintegration of rock? Re- 

 late this disintegration to liberation of plant food in the 

 rock. 



(2) Put one-half pint of water into vessels 4x4x4 inches, 4x8x2 



inches, 4x2x8 inches, 4x4x2 inches. Expose to great heat, 

 cold, wind, for twenty-four hours and measure the water in 

 each vessel. Relate the amount of evaporation in the deep 

 and shallow vessels to deep and shallow bodies of water. 

 Relate the amount evaporated in pi arcs of different tempera- 

 tures to places of different altitudes and latitudes. 



Boil a gill of water until all passes off as vapor. Put a 



