42 LESSONS IN CHEMISTRY. 



CHAPTER III. 



MATERIALS EXISTING IN THE SOIL. 



40. We have considered the nature of the materials which 

 the living plant obtains from the air and water, the impor- 

 tant gaseous elements with which the Creator has stored the 

 immense expanse of the atmosphere, and which in every part 

 of the world are accessible to the vegetable tribes. I trust 

 that you have received such clear ideas of the properties of 

 these gases that you will be prepared to understand some 

 remarks which I purpose making on the part assigned to 

 them in building up the structure of your crops. We will, 

 however, in the first place, direct our attention to the ingre- 

 dients which the earth in which plants ai*e fixed — the soil, 

 as it is termed — supplies for their support. 



41. Suppose a stack of hay or of corn in one of your fields 

 should accidentally be consumed by fire, you would find upon 

 examination that the greater portion of the stack had burned 

 away, had- vanished into the air, and that there remained 

 merely a small quantity of ashes which had resisted the fire. 

 If you were to take a ton weight of sea-weed, and, after 

 drying it, set fire to it in the rude furnace or kelp-kiln which 

 is used by the farmers along our coasts, you would find that 

 the great bulk of it would vanish into the air, but that there 

 would remain in the kiln about 100 lbs. of a grey ash in a 

 solid mass, Hke the slag of the iron-smelter, which could be 

 ftised by heat, but not consumed. 



42. When the ash left upon burning a stack of grain or a 

 heap of sea- weed is examined by the chemist, he finds that 

 it is not a simple substance like iron or charcoal, but is made 

 up of nine or ten different substances, with the names and 

 appearance of most of which you are probably familiar. You 

 may remember that I stated (31) that iron when it unites 

 with oxygen gas becomes coated with rust, which is a com- 

 pound of that metal and oxygen, forming what chemists term 

 " an oxide of iron." In the ashes of plants we discern several 



