48 



PRACTICE 23. 

 DETERMINATION OF CITRATE-INSOLUBLE PHOSPHORUS. 



Use the same amounts and materials as in Practice 21. If the material 

 is acid, wash the weighed sample on a 9 cm. filter with water until free 

 of acid. 



Heat in a water-bath 100 cc. of the neutral ammonium citrate solution 

 to 65 in a 200 cc. Erlenmeyer flask, loosely stoppered with a stopper hold- 

 ing a ioo- thermometer. When 6s p is reached put in the sample and shake 

 thoroughly. Place in the bath at 65 and let stand for 30 minutes, shaking 

 every five minutes. At the end of 30 minutes filter and wash thoroughly 

 with water at 65 until all soluble phosphorus is removed (test for soluble 

 phosphorus with I cc. of ammonium molybdate solution). Transfer the 

 filter and its contents to a crucible, dry, and then ignite until all organic 

 matter is destroyed, transfer to a beaker, add about 15 cc. of hydrochloric 

 acid, and heat until all phosphorus is dissolved. Make up to 250 cc., mix 

 well, transfer to a dry bottle, and let settle. Determine phosphorus in 25 

 cc. portions according to the directions given in Practice 21. 



cc. HNO 3 cc. KOH to mg. P %P 



used dissolve ppt. 



Ave 



Calculate the results obtained in Practices 21 and 23 and with these 

 record the results obtained by three members of each group as indicated 

 in the table on the following page. Value citrate-soluble phosphorus at 12 

 cents and insoluble phosphorus at 5 cents a pound. 



