124 AGRICULTURAL ANALYSIS 



centimeters with the sulfuric-nitric acid mentioned and the 

 mixture placed in a flask of 250 cubic centimeters capacity. The 

 mixture is heated and there is added thereto, 50 cubic centimeters 

 of the ammonium molybdate reagent. After standing five minutes 

 the mixture is stirred vigorously for one minute. The precipi- 

 tate is allowed to stand for from three to 18 hours and then 

 separated on a gooch under pressure, not through asbestos felt, 

 but as recommended by Kilgore, through a disk of ash- free filter 

 paper. The last traces of the yellow precipitate are brought 

 into the filter and washed several times with the two per cent, am- 

 monia nitrate solution. The precipitate is washed three times 

 with alcohol and as many times with ether, sucking the filter dry 

 after each addition of the washing liquids. When washed and 

 dried as described the crucible with its contents is placed in a 

 partial vacuum desiccator without CaCl 2 or H 2 SO 4 for 30 min- 

 utes and weighed. The ammonium phosphomolybdate prepared 

 in this way contains 3.295 per cent, of P 2 O 5 . 



112. Method of Woy. The direct weighing of the yellow pre- 

 cipitate in the determination of the phosphoric acid in slags ex- 

 tracted by citric acid is accomplished by Woy in the following 

 manner. 02 



To 50 cubic centimeters of the solution obtained from basic 

 slags by treatment with a two per cent, citric acid solution are add- 

 ed 30 cubic centimeters of nitric acid of 1.153 specific gravity, and 

 45 cubic centimeters of ammonium nitrate solution containing 340 

 grams of the salt in one liter of water, the mixture boiled and the 

 phosphoric acid precipitated by the addition of 100 cubic centi- 

 meters of a boiling aqueous six per cent, solution of ammonium 

 molybdate. After standing for 15 minutes the supernatant liquid 

 is decanted, the precipitate washed with 50 cubic centimeters of 

 a solution of 50 grams of ammonium nitrate and 40 cubic centi- 

 meters of nitric acid in one liter at a lukewarm temperature and 

 then collected on a gooch crucible, dissolved in 10 per cent, am- 

 monia, 20 cubic centimeters of ammonium nitrate, 30 cubic centi- 

 meters of water and one cubic centimeter of ammonium molybdate 

 added to the filtrate, boiled and the yellow precipitate re-formed by 

 n Chemiker-Zeitung, 1903, 27 : 279. 



