PHOSPHORIC ACID FERTILIZERS 111 



8. Compare floats and acid phosphate as sources of phosphoric 

 acid when fertilizing land. 



9. Describe the effects of phosphoric acid on plant growth. 



10. Name the plants that are particularly benefited by fertili- 

 zation with phosphoric acid. 



LABORATORY EXERCISES 



Exercise I. — In Exercise V, Chapter I, an experiment was 

 described that was designed to show the importance of some plant- 

 food materials to plant growth. If this test has been properly con- 

 ducted it should now be ready to show the actual effects of the 

 phosphoric acid on crop development. 



Exercise II. — Examination and identification of phosphate 

 fertilizers. 



Materials. — Set of fertilizers (consisting of ground bone, raw 

 rock phosphate, basic slag and acid phosphate), hydrochloric acid, 

 nitric acid, litmus paper, flame, test tubes, funnel and filter paper, 

 ammonium molybdate solution. 



The ammonium molybdate solution is made as follows : 

 Dilute 50 c.c. of ammonia (sp. gr. .9) with 75 c.c. of distilled water. 

 Dissolve in this 25 grams of molybdic acid. Pour this into a solu- 

 tion consisting of 175 c.c. of nitric acid (sp. gr. 1.42) diluted with 

 250 c.c. of water. Make the addition slowly with constant stirring. 

 Allow to stand in a warm place for two days and then decant the 

 clear supernatant liquid for use. 



Procedure. — The fertilizers should be tested as described below 

 and examined until their identification is easy and positive. 



Ground Bone  

 Bone is usually ground to a coarse powder. It is dry and has a 

 decided and characteristic odor. It is light gray in color, insoluble 

 in water and has a characteristic appearance under the hand lens. 

 Its physical characters are sufficient for identification. 



Ground Phosphate Rock 



Floats appear on the market as a light gray powder, insoluble 

 in water and with little odor. 



Dissolve a small amount in hydrochloric acid, heat and filter. Add 

 ammonia until a precipitate appears. Dissolve it with a small 

 amount of nitric acid. Then add ammonium molybdate. Heat gen- 

 tly. A yellow precipitate indicates the presence of phosphoric acid. 



N 



