262 SOILS AND FERTILIZERS 



19. The nitrogen of soils. — Place in a strong test-tube a mixture 

 of 5 grams of soil and an equal bulk of soda-lime. Connect the 

 test-tube with a delivery-tube which leads into another test-tube 

 containing distilled water. Heat the test-tube containing the soil for 

 five or ten minutes. Then test with litmus paper the liquid in the 

 second test-tube, neutralize with standard acid as in Experiment 30. 



20. Nitrates. — Examine laboratory samples of the following 

 nitrates: Potassium, calcium, and sodium. Place in separate test- 

 tubes y z gram of each, add 10 cc. of water, and heat gently. To 

 each when cool add a few drops of sulphuric acid, then a few drops 

 of an indigo solution. 



21. The Nitrogen of Blood. — Repeat Experiment 19, using 100 

 milligrams of dried blood in place of the soil. 



22. Organic Nitrogen Soluble in Pepsin. — Prepare a pepsin solu- 

 tion by dissolving 5 grams of commercial pepsin in a liter of water, 

 adding 1 cc. of strong hydrochloric acid. Place in separate test- 

 tubes 5 grams each of dried blood, tankage, and horn meal. Add 

 25 cc. of pepsin solution and place the test-tubes in a cylinder con- 

 taining water at a temperature of 40 C. Shake the test-tubes occa- 

 sionally, and at the end of one-, two-, and five-hour periods observe 

 the amounts of insoluble matter remaining in the test-tubes. 



23. Testing for Nitrates. — Dissolve some sodium nitrate, not 

 exceeding 100 milligrams, in 10 cc. water. Add 2 cc. of a dilute 

 solution of ferrous sulphate, and place the test-tube in a cylinder 

 of water. Sulphuric acid is then added by means of a long stemmed 

 funnel. Observe the dark ring formed. 



24. Water in Manure. — Dry 100 grams of fresh manure in a 

 water-oven for four hours. Determine the loss of weight and the 

 per cent, of water. 



25. Leaching Manure. — Place 5 kilos of manure, the same as 

 used in Experiment 24, in a box provided with small holes in the 

 bottom, so that the manure can be leached. Place the box over a 

 sink or a receptacle for receiving the teachings. Percolate 3 gallons 

 of water through the manure, daily, for five days. Finally weigh 

 the manure, determine the per cent, of water, and the total loss of 

 dry matter. 



