CLASSIFICATION AND PROPERTIES OF SOIL 49 



C. PHYSICAL PROPERTIES. 



EXPERIMENT 4. PART i. (a) Collect a quantity of 

 dry sand, and one of dry clay, and one of dry garden 

 loam, and one of dry humus. Keep these in a.dry place 

 in separate boxes, for use in the following experiments. 



() Get four small, similar-sized boxes, and fill each 

 box with one of these soils. 



(f) Weigh each one separately. Which is heaviest? 

 Which lightest ? 



(d) How many cubic inches of soil in each box ? 

 What part of a cubic foot ? How many square feet in 

 an acre ? How much would an acre of soil to the depth 

 of one foot weigh if each cubic foot weighed the same 

 as a cubic foot of your sample of garden soil ? 



(e) If this acre produced a crop of twenty-five bushels 

 of wheat and 2,500 pounds of straw, how many pounds * 

 has this crop taken from one acre of soil ? This may 

 seem a very small amount to be taken from the soil, but 

 it must be borne in mind that some soils contain a very 

 small per cent., or fraction of a per cent., of some of the 

 very essential plant-foods (as, potash, phosphoric acid, or 

 nitrates), while plants vary in their demands for these 

 different foods. So it is that certain essential plant- 

 foods, as nitrogen, may be nearly exhausted from a given 

 soil by repeatedly growing certain plants which make 

 large demands of that particular element from the soil, 

 and yet the same soil may be abundantly able to sustain 

 other plants which demand less of that element from 

 the soil f 



PART 2. (a) Place these four boxes (Part i, b] of soils 

 in a cool, dry place. With them place three similar 



* At least 95 per cent, of the material composing the plant is 

 obtained from the air and water, and but 5 per cent, from the 

 soil. 



f See " Leguminous Plants" and " Fertilizers." 



