44 



PRACTICE 21. 

 DETERMINATION OF TOTAL PHOSPHORUS IN FERTILIZERS. 



Each group of students will work upon one of the following materials : 



1. Bone Ash. 5. Raw Rock Phosphate. 



2. Raw Bone Meal. 6. Acidulated Rock Phosphate. 



3. Steamed Bone Meal. 7. Double Superphosphate. 



4. Acidulated Bone Meal. 8. Basic Slag Phosphate. 



For materials containing more than 9 percent of phosphorus use i gm., 

 for lower percentages use 2 gm. Ignite in a crucible to destroy organic 

 matter. Transfer to a beaker and dissolve in 15 cc. of hydrochloric acid 

 (concentrated hydrochloric acid plus an equal volume of ammonia-free 

 water) by the aid of gentle heat. Transfer to a 250 cc. measuring flask, 

 cool, and dilute to exactly 250 cc. Mix well, transfer to a dry bottle, and 

 let settle. 



Place 25 cc. in a 250 cc. beaker, add 5 cc. of nitric acid (concentrated 

 nitric acid plus an equal volume of ammonia-free water), just neutralize 

 with ammonia, and clear up with a few drops of nitric acid, using heat if 

 necessary but avoiding more than a few drops in excess. Heat to so-6o p 

 on a water-bath, add 35 cc. of the clear molybdate solution, stir, keep at 

 50? -60 for two hours, let stand in the desk over night. Filter, wash twice 

 by decantation, using 25 cc. portions of distilled water, stirring thoroughly, 

 and then allowing the precipitate to settle before decanting upon a 9 cm. 

 filter. Transfer the precipitate to the filter, and wash the beaker and filter 

 seven or eight times with small amounts of ammonia-free water until free 

 of acid. Place the filter containing the precipitate in the beaker and add 

 standard potassium hydroxid in 10 cc. portions until the precipitate is dis- 

 solved. Titrate the excess alkali with standard nitric acid, using phenol- 

 phthalein as an indicator. 



cc. HNO 8 cc. KOH to mg. P % 



used dissolve ppt. 



Ave. 



