614 EXPERIMENT STATION RECORD. 



complete until the ignited product is uniformly black and crystalline on both the 

 ujiper and under surface. Directions for preparing reagents and carrying out the 

 method are given in detail. 



The determination of phosphoric acid in superphosphates, mixed fer- 

 tilizers, and precipitated phosphates by precipitation in the cold as ammonium, 

 phosphomolybdate, L. Ledoux {Bui. Assoc. Beige Chim., 15 {1901), No. 3, pp. 

 135-129; abs. in Chem. Centbl, 1901, I, No. 25, p. 1341; Bui. Soc. Chim. Paris, 3. ser., 

 25 {1901), No. 15, p. 766). — The author points out that phosphoric acid may be 

 determined in form of phosphomolybdate by the citro-mechanical method pro\'ided 

 the solutions contain a sufficient amount of ammonium nitrate and a sufficiently large 

 amount of molybdic solution be added. The solutions must also be heated with nitric 

 acid to convertall of the metaphosphates into orthophosphates. The molybdic reagent 

 used is made up of 150 gm. of molybdic acid, 600 cc. of 0.96 sp. gr. ammonia, and 1,070 

 cc. of nitric acid of 1.22 sp. gr. The method of procedure recommended is as follows: 

 Treat 2 gm. of superphosphate or 4 gm. of phosphatic fertilizer in the usual way with 

 water and citric acid; make the solution to 250 cc. ; heat 50 cc. of this solution for 5 

 minutes with 15 cc. of nitric acid (1.4 sj). gr. ); cool; add 15 cc. of ammonia (0.92 

 sp. gr. ), and shake vigorously for 30 minutes, adding 100 cc. of molybdic solution. 

 Titrate the yellow precipitate according to Pemberton's method or convert into 

 ammonium-magnesium phosphate in the usual way. 



Determination of phosphoric acid as ammonium phosphomolybdate, H. 

 Pellet {Ann. Cliim. Anabjt., 6 {1901), j)p. 24S-251; abs. in Chem. Centbl., 1901, II, No. 

 7, p. 50i).— The author points out the danger of incomplete precipitation of phos- 

 phoric acid in the presence of much iron and other impurities when Ledoux's method 

 (see above) of shaking for one-half liour in the cold is followed. He recommends as 

 more accurate the direct weighing of the ammonium phosphomolybdate without 

 converting it into magnesium pyrophosphate. He claims priority over Ledoux as 

 regards discovery and announcement of conditions under which a pure ammonium 

 phosphomolybdate may be obtained. 



Determination of phosphoric acid, De Molinari {Bui. Agr. \_Br^lsseh'], 17 

 {1901), No. 2, pp. 154-157). — Comparisons of the so-called citro-mechanical method 

 and Pemberton's titration method are reported. Tests of the method based upon 

 titration of the ammonium-magnesium phosphate precipitate according to De Koninck 

 are also reported. 



Determination of phosphoric acid by titration of ammonium phospho- 

 molybdate, Nyssens {Bui. Agr. [Brussels], 17 {1901), No. 2, pp. 142-146).— Tests 

 of precipitation in the absence of citric acid and in the presence of a large quantity 

 of this substance are reported. The composition of the yellow precipitate was found 

 to vary with the quantity of precipitant and the manner of adding it to the solution. 

 The author precipitates in the cold, using a shaking apparatus making 100 revolu- 

 tions per minute. By this method 10 minutes suffices for complete i)recipitation. 

 With more vigorous shaking 5 minutes suffices, but the precipitate is very fine and 

 difficult to retain on the filter. When citric acid is present it is oxidized by means 

 of potassium permanganate before i^recipitation. The author is attempting to work 

 out a method by which complete precipitation in the cold may be effected without 

 destroying citric acid. This is based on the use of nitro-molybdate of potash as a 

 precipitant instead of nitro-molybdate of ammonia. 



The transformation and purification of magnesium pyrophosphate with 

 the object of weighing as magnesium pyrosulphophosphate, H. Pellet {Ann. 

 Chim. Analyt.,6 {1901), p. 211; abs. in Chem. Centbl, 1901, II, No. 3, jy. 233).— In 

 order to obtain a perfectly white ignition product the author treats the magnesium 



iZtschr. Analyt. Chem., 19 (1880), p. 450; 21 (1882), p. 353. 

 ^Ztschr. Angew. Chem., 1890, p. 43. 



