194 SOILS AND FERTILIZERS 



the resulting grades and calculate the proportion of the original 

 sample passing through the different mesh sieves. Try to make a 

 relative estimate of the value of the various samples on this basis. 



Exercise III. — Effect of lime on biological action. 



Materials. — An acid soil from under sod, two 8-ounce, wide- 

 mouth bottles, hydrate of lime, large vessel for mixing soil and 

 water, funnel and filter paper, evaporating dishes, water bath, 

 phenoldisulphonic acid, ammonia, flame, two 100 c.c. graduated 

 cylinders. 



Procedure. — Place 50-gram samples of the acid soil in each of 

 two 8-ounce bottles. Add and mix well with one gram of carbonate 

 of lime. Bring the soils in each bottle up to optimum moisture 

 content. Plug mouths lightly with cotton and set aside at opti- 

 mum temperature for a week. 



Now estimate nitrates in manner described in Exercise I, Chap- 

 ter IX. A comparison of the results will show the influence of lime 

 on nitrification. Apply these results to practical problems. 



Exercise IV. — Flocculation by lime. 



Materials. — Ground limestones and hydrate of lime ; large 

 bottle for preparing soil suspension, two 100 c.c. graduated cylinders. 



Procedure. — Prepare a soil suspension by shaking a heavy 

 clay soil for 15 minutes in a bottle partially filled with water (one 

 of soil to ten of water) after adding a few drops of strong ammonia. 

 Allow to stand for two or three hours and then pour suspension into 

 the cylinders. Fill to 100 mark. Now add to one a pinch of hy- 

 drate of lime and to the other the same amount of ground lime- 

 stone. Shake well and allow to stand. 



Watch closely and explain results. Apply the principle involved 

 here to actual field practice. 



Exercise V. — Flocculation by lime. 



Materials. — Clay soil and hydrate of lime. 



Procedure. — Prepare from one portion of clay soil a well-puddled 

 ball. Add hydrate of lime to another portion of the clay soil (rate, 

 1 of lime to 500 of soil), and work into a ball after adding sufficient 

 water. Allow the two samples to dry thoroughly. Crush each one. 

 Note difference in crushing resistance and the structural character 

 of each soil. Apply results to actual field practice. 



Exercise VI. — Lime and the rotation. 



The place of lime in a rotation depends on a number of factors. 

 Discuss these with the student. Take a number of standard rota- 



