NATURE AND FORMATION OF SOILS. 9 



has little chemical effect, but moist air is very 

 active. The oxygen, which is now known to 

 combine with nearly every other element, seeks 

 to unite with the minerals of the exposed rocks.* 

 Iron, which in some form is contained by most 

 rocks, unites readily with oxygen in the presence 

 of moisture, forming rust, which stains, softens, 

 and ultimately causes the disintegration of the 

 rock. 



Carbon dioxide (CO 2 ), though present in a 

 comparatively small quantity, is a powerful 

 agent both in moist air and in rain-water. It 

 acts upon the rocks, especially upon limestone, 

 causing them to crumble away or to be entirely 

 dissolved. 



EXPERIMENT i. Before beginning to perform any experi- 

 ment in this book, read over the entire directions for it, get 

 necessary apparatus ready, and know what you are going to 

 do and why you are going to do it. Record your observations 

 at the time they are made, not after leaving the laboratory. 



Throughout this book, wherever the word "note" is 

 used, it means to observe and record your observations or 

 explanations. 



(a) Break pieces of limestone, marble, or clam-shells 

 into tiny bits, and place a small quantity in a wide- 

 mouthed bottle. 



(&) Pour in small successive portions of dilute hydro- 

 chloric acid (HC1). Note what takes place as the acid 

 comes in contact with the stones or shells. Both the 

 hydrochloric acid and the calcium carbonate of the 

 stones or shells are decomposed, and calcium chloride 



* Gilbert and Brigham, Physical Geography, p. 78. 



