270 SOILS AND FERTILIZERS 



Experiment No. 18. 

 Extraction of Humus from Soils. 



Ten grams of soil are placed in a bottle (preferably a glass stop- 

 pered one) and 200 cc. H 2 O and 5 cc. HC1 added. Shake aad 

 allow 10 to 24 hours for the acid to dissolve the lime so that the 

 humus can be dissolved by the alkali. Filter the acid and wash 

 the soil on the filter with distilled water until the washings are no 

 longer acid to litmus paper. Transfer the soil to the bottle again, 

 add loo cc. H 2 O and 5 cc. KOH solution. Shake, and after two to 

 four hours filter off some of the solution, which is dark-colored 

 and contains dissolved humus compounds. 



To 10 cc. of the filtered humus solution, add HC1 until neutral. 

 The precipitate that is formed is mainly humic acid and soil 

 humates. Evaporate a second portion of 10 to 20 cc. to dryness ; 

 the black residue obtained is humus material extracted from the 

 soil. 



Experiment No. 19. 

 Nitrogen in Soils. 



Mix 5 grams of soil and an equal bulk of soda lime in a mortar ; 

 transfer to a strong test tube. Connect the test tube with a deliv- 

 ery tube which leads into another test tube containing distilled 

 water. Heat cautiously the test tube containing the soil and soda 

 lime with the Bunsen burner, for from 5 to 10 minutes. Test the 

 liquid with litmus paper and note the reaction. Soda lime aided 

 by heat decomposes the organic matter of the soil and forms CO 2 > 

 H 2 O and NH 3 . The nitrogen in the form of ammonia is distilled 

 and absorbed by the water in the second test tube ; the reaction 

 is due to the presence of the ammonia. 



Experiment No. 20. 



Testing for Nitrates. 



Dissolve about 50 milligrams of sodium or potassium nitrate in 

 loo cc. H 2 O. To 15 cc. of this solution, add 2 cc. of a dilute and 

 clear solution of FeSO 4 , and place the test tube in a cylinder. 

 Through a long stemmed funnel add 2 or 3 cc. H 2 SO 4 . Observe 

 the dark brown ring that is formed ; H 2 SO 4 liberates HNO 3 as a 

 free acid, which in turn changes the iron from the ferrous to the 

 ferric state ; the dark brown color is due to the nitric acid forming 

 intermediate iron compounds during this operation. 



