ROCK WEATHERING 279 



solved substances deposited. The tremendous power of 

 freezing water, the weathering power of the atmosphere, 

 the wearing and transporting power of the wind, the scour- 

 ing and pulverizing power of moving ice, and the never- 

 ending processes of growth and decay have also greatly 

 affected the earth's surface. 



Experiment 84. Allow a test tube filled with water and tightly 

 corked to freeze. What happens? If the temperature of the air 

 is not cold enough, place the test tube in a mixture of chopped ice 

 and salt, or better, chopped ice and ammonium chloride (sal am- 

 moniac), arid allow it to remain for some time. 



Water getting into the cracks of rocks and expanding 

 when it freezes splits them apart and aids much in their 

 destruction. Plant roots penetrate into the crevices of 

 rocks and by their growth split off pieces of the rock. Water, 

 especially when it has passed through decaying vegetable 

 matter, has the power of dissolving some rock minerals. 

 Certain minerals of which rocks are composed change when 

 exposed to the air somewhat as iron does when it rusts. 



Rock 'Weathering. Experiment 85. Weigh carefully a piece 

 of dry coarse sandstone or coquina. Allow this to remain in water 

 for several days. Wipe dry and weigh again. Why has there 

 been a change in weight? 



Experiment 86. Fill a test tube or small glass dish about half 

 full of limewater, made by putting about 2 ounces of quicklime into 

 a pint of water. Blow from the mouth through a glass tube into 

 the limewater. There is formed in the limewater a white sub- 

 stance which chemists tell us is of the same composition as lime- 

 stone. 



Experiment 87. Continue to blow from the mouth for a con- 

 siderable time through a tube into a dish of limewater. The 

 white substance disappears. The carbon dioxide of your breath 

 dissolved in the water, forming a weak acid, and caused the change. 



