EXPERIMENTS IN SOIL CHEMISTRY 267 



potassium chlorate to give out some of the oxygen that 

 was in the combination in it. A good test for oxygen is to 

 hold a glowing splinter in it, and the splinter will burn very 

 brightly. 



Where does the plant get the oxygen that it uses in 

 making starch ? It probably gets it, as well as the hydrogen, 

 from the water which it gets out of the soil. What must 

 first be done with the water ? 



If you wish to obtain hydrogen, place in a glass jar or 

 wide-mouthed bottle (an olive or pickle bottle will serve 

 the purpose) a number of small pieces of zinc, and cover 

 with a solution of sulphuric acid and water; about a sixth 

 or seventh as much acid as water. The bubbles that are 

 given off are hydrogen. Be very careful not to allow the 

 sulphuric acid to touch your hands or clothing. Place in 

 the bottle in which the hydrogen is being generated a 

 stopper through which a glass tube passes and extends two 

 or three inches above. After the hydrogen has been com- 

 ing off for several minutes apply a lighted match to the end 

 of the tube. What happens? The hydrogen gas burns. 

 This is a good test for hydrogen. Care should be taken 

 not to apply the match until all the air is out of the 

 bottle. 



Where does the plant get the carbon? This is ob- 

 tained from the air. How do we know that plants contain 

 carbon ? Place a small piece of wood (hard wood is best) 

 on a piece of wire screen, or on a tin pie plate, or in a test 

 tube. Heat by holding the flame of the alcohol lamp under 

 it. When it stops smoking note what is left. This char- 

 coal is mostly carbon. What is its color ? Think of other 

 plants which you have seen heated or partially burned, 



