PRACTICE XX 



DETERMINATION OF PHOSPHORUS IN FARM PRODUCE 



Each group of students will work upon one of the following 

 products : 



1. Wheat. 5. Oats. 



2. Corn. 6. Oat straw. 



3. Corn stover. 7. Red-clover hay. 



4. Corncobs. 8. Alfalfa hay. 



Weigh out 2 g. of the material in a 25-cc. crucible, moisten with 

 a 15 per cent solution of calcium nitrate, dry carefully, and ignite 

 in a muffle furnace at a low red heat for two hours. Transfer to a 

 250-cc. beaker, digest in about 15 cc. of nitric acid, dilute to about 

 40 cc., filter, and wash. Evaporate the filtrate and washings to about 

 25 cc., add 5 cc. of nitric acid, 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 50-60 on a 

 water bath, add 10 cc. of the clear molybdate solution, stir, keep 

 at 50-60 for one hour, and allow to stand over night. Filter, wash 

 twice by decantation, using 25-cc. portions of cold water, stirring 

 thoroughly, and then allowing the precipitate to settle before decant- 

 ing 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 cold water until free from acid. Place the filter containing the pre- 

 cipitate in the beaker and add standard potassium hydroxid in 10-cc. 

 portions until the precipitate is dissolved. Titrate the excess alkali 

 with standard nitric acid, iising phenolphthalein as an indicator. 



cc. HXO 3 cc. KOH to mg. P Per Cent P 



used dissolve 



ppt. 



Av.... 



Calculate the results obtained, and record with these the results 

 obtained by three members of each group as indicated on the fol- 

 lowing page. Value phosphorus at 12 cents per pound. 



How many pounds of steamed bone meal will be required to replace 

 the phosphorus removed from the soil in a 100-bushel crop of corn, 

 a 100-bushel crop of oats, a 4-ton crop of clover hay, and a 50-bushel 

 crop of wheat ? (See Practice V.) 



40 



