EXERCISE 69 

 WHAT IS THE NATURE OF THE PARTICLES WHICH MAKE UP THE SOIL? 



Materials. Glass tubing ^ inch in diameter and 2 feet or more in length ; cork stoppers ; soil. 



Directions. Close one end of a glass tube with a cork stopper. Different students may perform 

 the following experiment by use of different kinds of soils. Mix some soil with water to the con- 

 sistency of a thin mud, and pour in enough of the mixture to fill the lower end of the tube 3 or 4 

 inches. Add water to fill the tube. Close the upper end with a cork stopper, invert the tube, and 

 stand it in a vertical position. Watch the particles as they settle through the water. 



What differences are there in the materials which settle first and those which settle later ? Why 

 do some particles settle before others ? Describe the sediment with reference to the various-sized 

 particles and the parts of the sediment in which the particles are too small to be seen with the un- 

 aided eye. Do you suppose that there may be some of the particles which have not yet settled ? If 

 so, where are they and why have they not settled ? If allowed to stand for several days, will all 

 particles settle ? 



Do the samples of soil used contain both rock materials and organic materials ? 



Additional problems. If a very long tube (5 or 6 feet) is used, a more complete separation of materials 

 will be made. Such a demonstration will prove instructive. 



If a microscope is available, small pieces of soil should be studied under magnification. Such studies 

 will enable students to determine the form and structure of soil particles. 



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