32 PRACTICAL AGRICULTURAL CHEMISTRY [79-81 



test-tubes introduce equal quantities respectively of coprolite 

 powder (which contains bone phosphate), basic slag (which 

 contains slag phosphate), and superphosphate. About as 

 much as can be held on a sixpence will be sufficient. Half 

 fill each test-tube with distilled water and shake up. Filter 

 each one into a clean test-tube through separate filters. If 

 the solutions do not come through clear, pass them through 

 the filters again. Now test each solution for phosphoric 

 acid. This is done by adding an excess of ammonium 

 molybdate solution and boiling ; a yellow precipitate 

 shows that phosphoric acid is present. It will be found 

 that the liquid from the superphosphate contains phos- 

 phoric acid, but that the others do not, showing that 

 superphosphate of lime is the only one of the three 

 substances that is soluble in water. 



* 70. Action of Ammonium Citrate on Phos- 

 phates. — Place small quantities of superphosphate, slag 

 and coprolite powder in separate test-tubes, as in paragraph 

 78. Shake up with ammonium citrate solution. Filter 

 and test with ammonium molybdate as before. This time 

 the liquids from both the slag and the superphosphate will 

 be found to contain phosphoric acid, whilst that from the 

 bone phosphate will not, showing that both superphosphate 

 and slag phosphate are soluble in ammonium citrate, whilst 

 bone phosphate is not. 



80. Action of Dilute Nitric Acid on Phosphates. 

 Proceed exactly as in the two previous experiments, 

 treating the different phosphates with dilute nitric acid. 

 Filter and test as before. All three phosphates will be 

 found to be soluble in nitric acid, and will therefore give 

 the molybdate test. 



81. Reversion of Superphosphate.— When a super- 

 phosphate is placed on the soil the rain dissolves the soluble 

 substance and thoroughly impregnates the soil with it. If 

 it were to remain soluble, a quantity would eventually be 



