RECENT WORK IN AGRICULTURAL SCIENCE. 



AGRICULTURAL CHEMISTRY. 



A contribution to the determination of phosphoric acid by the citrate 

 method, a hitherto overlooked source of error and a modification to avoid it, 

 V. Schenke (Landw. Vers. Stat., 62 {1905), No. IS, pp. 3-10).— This is an account 

 of comparative tests on bone meal, Thomas slag, and soils of Miircker's molybdic 

 method, the official citrate method of the German Association of Agricultural Exper- 

 iment Stations, and a modified citrate method in which the acid solution of the 

 material was neutralized with concentrated ammonia before the citrate solution and 

 magnesia mixture were added. 



The results obtained by the modified citrate method agreed more closely with 

 those obtained by the molybdic method than was the case with the ordinary citrate 

 method. It is pointed out that the citrate method is a "compensation method" in 

 which the errors due to impurities of silica, lime salts, etc., are supposed to be bal- 

 anced by those due to solubility of the magnesium-ammonium phosphate precipitate 

 in ammonium citrate. The modified citrate method apparently gives a more perfect 

 balance in this respect, due to the fact that less ammonium citrate is used (50 to 

 64 cc. as against 100 cc. in the ordinary method). 



On the determination of phosphoric acid in Thomas slag, F. Westhausser 

 {Ztschr. Analyt. Chem., 44 {1905), No. 3-4, pp. 187-191; abs. in Chem. Centbl., 190.',, 

 I, Xo. 19, j>. 1434). — Comparisons of the official method of the Association of German 

 Agricultural Experiment Stations, the original Kellner-Bottcher method, and of the 

 Kellner-Bottcher method using Hal lens ammonium citrate solution. The methods 

 proved very unreliable in case of substances like Wolter phosphate containing large 

 amounts of silica. 



Phosphoric acid determination, F. Raschig (Ztschr. Angew. ('hem., IS (190-5), 

 Xo. 10, ])}>. 374-376). — A series of tests are reported to show that the amount of water 

 used in washing the magnesium-ammonium phosphate prior to its titration with 

 tenth-normal hydrochloric acid may with safety and advantage be reduced to 10 cc. 

 The details of manipulation in carrying out the method are described. 



The Pemberton method of determining phosphoric acid, D. J. Hissink and 

 H. Van dee Waerden (Chem. Weekblad, 2 (1905), pp. 179-184; abs. in Chem. Centbl., 

 1905, I, Xo. 16, pp. 1188, 1189). — A modification of the method insuring uniform 

 composition of the precipitate and fixed requirement of sodium hydroxid solution 

 for titration is described. 



Quick methods for the determination of lime, potash, and phosphoric acid, 

 E. H. Schultze (Chem. Ztg., 39 (1905), Xo. 37, pp. 508, 509).— Titrimetric methods 

 for the determination of calcium oxid in calcareous substances and phosphoric acid 

 in phosphates, and a short method of determining potash as potassium platinic 

 chlorid are described. 



Maercker-Biihring solution, Wagner's citrate magnesia mixture, and iron 

 citrate magnesia mixture, H. Svoboda (Chem. Ztg., 29 (1905), Xo. 33, pp. 453- 

 456). — A series of comparative tests of these mixtures with reference to the error due 

 to their solvent action on glass is reported. 



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