EXPERIMENTS IN SOIL CHEMISTRY 269 



How can we show that plants contain potash ? Place 

 some unbleached wood ashes in a dish or pan and cover 

 with water. Stir thoroughly several times. Allow the 

 mixture to settle, then pour off the water. Place some of 

 the water in a cup and boil till all the water is evaporated. 

 The yellow ash substance that is left is potash. Test it by 

 moistening and rubbing between your thumb and finger. 

 It feels like lye or soap. 



We have seen that the first three elements named above 

 are supplied to the plant from the water and air. Then all 

 the rest must be obtained from the soil. 



At this point it will be worth while to take at least one 

 recitation period to discuss what soil is, its origin, and the 

 agents that have aided and are aiding in making it. 



How many of the things furnished the plants by the soil 

 may be found as elements in the soil ? Can you find sul- 

 phur or phosphorus as such in the soil? (Sulphur may 

 be found as an element in volcanic regions.) If not, then 

 in what form must they exist? 



Examine some sulphur, and then some calcium sulphate 

 or plaster of Paris. It is in this form that much of the 

 sulphur that is used by plants exists in the soil. Sulphuric 

 acid is also found in many soils. 



The compounds that exist in the soil may be acids, 

 alkalies, or salts. We may make some simple tests to 

 determine which one of these three any chemical com- 

 pound is. 



Test for Acid. — Litmus paper is one of the simplest 

 tests. Place a small piece of litmus paper in weak vinegar. 

 What color does the paper take on ? Put a few drops of 

 sulphuric acid in half a glass of water and test with the 



