CHAPTER XXXIII 



SIMPLE EXPERIMENTS IN SOIL CHEMISTRY 



In the preceding chapter it was brought out that plants 

 manufacture certain plant products. Now, if plants are 

 factories, what equipment must they have? Machinery, 

 power, and raw material out of which to make the starch, 

 sugar, etc. What is the source of this raw material ? 



By discussion it may be brought out that the environ- 

 ment of the plant is air, soil, and soil water; hence these 

 are the only available sources from which the plant may 

 obtain raw material to make the plant products. 



Just how the plants procure the raw material, and how 

 they make the foods, we shall take up for consideration in 

 some later lessons. At present we are concerned chiefly 

 in finding out what the materials are that the plants use in 

 making foods and plant tissues. 



We know that we cannot find starch as starch in the 

 environment of the plants. We also know that starch is 

 made up of several substances which are united to form 

 what we call a chemical compound. 



What is a chemical compound ? 



Here is some table salt which is a good illustration of a 

 compound. It is made by the chemical union of two things, 

 sodium and chlorine. Let us look at these. Do either 

 of them resemble salt? Yet chemists can separate salt 



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