264 SOILS AND FERTILIZERS 



33. Marl. — Test a sample of marl for lime and carbon dioxide, 

 as directed in Experiments 16 and 17. Observe the nature of the 

 insoluble residue. Test the marl with litmus paper. 



34. Testing Land Plaster. — Test for carbon dioxide as directed 

 in Experiment 17. There should be but little carbon dioxide in 

 the best grades of land plaster. Digest 1 gram of gypsum in a test- 

 tube with 10 cc. dilute hydrochloric acid. Observe the nature and 

 the amount of insoluble matter. 



35. Mixing Fertilizers. — Mix in a large box 



200 grams acid phosphate (saved from 28), 

 50 grams kainit, 

 50 grams sodium nitrate. 

 Calculate the approximate composition of this fertilizer and its 

 trade value. 



36. Testing Fertilizers. — Test the above fertilizer for water- 

 soluble phosphoric acid, as directed in Experiment 27. Test for 

 nitrogen pentoxide, as directed in Experiment 19. 



37. Calculating Results. — A fertilizer is said to contain 3.1 per 

 cent, ammonia, 12 per cent, bone phosphate of lime and 6 per cent, 

 potassium sulphate ; calculate the equivalent amounts of nitrogen, 

 phosphoric acid, and potash. 



