32O SOILS AND FERTILIZERS 



Experiment ITo. 17 

 Absorption of Gases by Soils 



Weigh 50 gms. of soil into a wide-mouthed bottle, add 50 cc. of 

 water and i cc. of strong ammonia. Note the odor. Cork the 

 bottle, shake, and after 24 hours again note the odor. To what is 

 the fixation of the ammonia due? Is this a physical or a chemical 

 change? Define fixation. 



Experiment No. 18 

 Acid Insoluble Matter of Soils 



Weigh 10 gms. of soil into a beaker, add roo cc. hydrochloric 

 acid (50 cc. strong acid and 50 cc. H 2 O) ; cover the beaker with a 

 watch glass ; heat on the sand bath in the hood for two hours, re- 

 placing the acid solution in case excessive evaporation takes place. 

 Filter, transfer, and wash the residue, using 50 cc. distilled water. 

 Note the appearance and quantity of insoluble residue. Of what 

 does it consist? What is its value as plant food? How does it 

 resemble the original soil and in what ways does it differ? Save 

 the filtrate for the next experiment. 



Experiment No. 19 

 Acid Soluble Matter of Soils 



Divide the filtrate from the preceding experiment into three 

 equal portions, (i) To one portion add ammonia until alkaline. 

 The precipitate formed consists of iron and aluminum hydroxide and 

 'phosphoric acid. Note the color and gelatinous appearance of this 

 precipitate. When dried it occupies only a small volume. Filter 

 and remove this precipitate which contains lime, magnesia, potash, 

 and soda. To the filtrate add 20 cc. of ammonium oxalate ; warm 

 on the sand bath, and note any precipitate of calcium oxalate 

 that is formed. (2) Evaporate the second portion nearly to dry- 

 ness. Add 20 cc. distilled H.,0 and 3 cc. HNO 3 ; warm to dissolve 



