RECENT WORK IN AGRICULTURAL SCIENCE. 



CHEMISTRY. 



The determination of phosphoric acid, S. W. Johnson {Jour. 

 Amcr. Clam. ^Soe., 16 {1S91), Xo. 7,P2). 1G:3-M5). — Tests by the author, 

 Wells, and Osborne of the citrate method as compared with the molyb- 

 dic iiietliod, already reported in full in the Report of the Connecticut 

 State Station for 1889 (E. S. R., 2, p. 480), are briefly reviewed. The 

 author concludes that — 



"The citrate iiiethod only gives good results by lomponsation of its errors and under 

 exactly defined conditions, which must be cnipiiically deteriained. A procedure good 

 for calcium phosphates is (jiiite inapplicable to ferric and aluminum phosphates. 



"Again, the molybdic method, when carried out rapidly at temperatures higher than 

 50 ', or as Ligli as 65' C, in presence of trivalent iron, aluminum, or manganese, 

 gives results too high, and in presence of great excess f>f nitric acid may give results 

 too low, unless the filtrates from the yellow precipitate are mixed with additional 

 molybdic solution and further digested until no more precipitate can be thrown 

 down." 



On the determination of phosphoric acid as magnesium pyro- 

 phosphate, il. Nexibax'EK {Jot(r. Amrr. Clicm. iSoc, Id (i.S'yj), No. 5, 

 pp. 289-207. — This is a translation and condensation by K. P. McElroy 

 of an article read before the World's Chemical Congress at Chicago, 

 which discusses in detail investigations already briefly noticed (E. S. 

 R., 4, p. 584). 



Systematic determinations were made of the errors due to volatil- 

 ization of phosphoric acid involved in Wagner's modification of the 

 molybdic method, and a table giving corrections to be used in phos- 

 phoric-acid determinations was calculated from the results. 



The method of procedure recommended is as follows: 



"Separate the phosphoric acid in the form of the yellow precipitate, and wa.sh this 

 latter in the usual way. Too high a heat should not be emjjloyed, nor should the 

 solution be allowed to stand too long, lest excess of molybdic acid separate. Dissolve 

 the phos])homolybdate in 100 cc. of cold 2.5 per cent ammonia and add as many cc. of 

 the usual magnesia mixture (55 gm. magnesium chlorid and 70 gm. ammonium chlo- 

 rid dissolved in a liter of 2.5 per cent ammonia) as there are centigrams of phosphoric 

 acid present. Addition .should not be made faster than 10 cc. per minute. Stir dur- 

 ing the addition. After the precipitation stir briskly once more and then allow to 

 stand at least 3 hours. AVash with 2.5 j)er cent ammonia till the chlorin reaction 

 disapi'ears, dry the filter and introduce into a Avell-cleaned crucible wliich has lieen 

 thoroughly ignited. Place the lid at an angle, carbonize the filter, and gradually 

 raise the heat, though not liigher than -a medium red heat, till the pyrophosphate 

 becomes completely white. When this happens bring the blast into action and 

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