RECENT WORK IN AGRICULTURAL SCIENCE. 



CHEMISTRY. 



A new gravimetric and g-asometric modification of the molybdic metliod 

 for tlie determination of phosphoric acid and mag'nesia, E. Riegler (Ztschr. 

 Anaiyt. Chem., 41 {I'M^), No. 11, pp. 675-686, fig. i).— The gravimetric method for 

 phosphoric acid rests upon the fact that barium chlorid produces in an ammoniacal 

 sohitiou of ammonium phosphomolybdate a precipitate, perfectly insoluble in water, 

 containing 1.75 per cent of phosphoric anhydrid and 45.5 per cent of barium, corre- 

 sponding to to thefornmla Ba.^- (MoOi).^! P,,Og + 24H2O. The weight of the precipi- 

 tate, ilried at 100° C'. nudtiplied by 0.0175, gives the weight of pliosphoric anliydrid. 

 In the gasometric method an excess of barium chlorid is added and this excess 

 determined by conversion into iodate by addition of hydrociodic acid, the iodate 

 being decomposed by addition of hydrazin sulphate with evolution of nitrogen, 

 which is measured and furnishes a basis for calculating the excess of barium chlorid. 

 This subtracted from the total amount of chlorid used gives the amount required 

 for precipitation. The 2 methods may be used on the same i)ortion of the original 

 solution and thus serve as a check on each other. They were found to give very 

 concordant results in a numljer of tests. A table containing factors for correcting 

 results for different barometric pressures and temjjeratures is given and the apparatus 

 used is described. For determination of magnesia this substance is first precipitated 

 as anmionium-magnesium phosphate, which is dissolved in nitric acid and precipi- 

 tated as ammonium phosphomolybdate, the further treatment being the same as 

 that just described. 



Determination of phosphoric acid in fertilizers, A. G. Woodman {Engineer. 

 and Mining Jour., 74 {1902), j'- 781; abs. in Chem. Ztg., 27 {1903), No. 3, ReperL, 

 p. 5) .■ — In the method described 2 gm. of substance is heated in a covered beaker 

 with 10 cc. each of strong hydrochloric acid and water and 1 to 2 gm. of sodium 

 chlorate until the chlorin is driven off. The volume is made to 250 cc, and to 25 cc. 

 of this solution in an Erlenmeyer flask 15 cc. of ammonia (0.9 sp. gr.) is added and 

 neutralized with strong nitric acid. The solution is heated to 65° C, and 25 to 75 

 cc. of ammonium molybdate is added, shaking vigorously. The precipitate, which 

 settles quickly, is collected on a filter and washed. The filter and contents are 

 returned to the Erlenmeyer flask and standard potash solution added until the pre- 

 cipitate is almost dissolved. Phenolphthalein is added and the addition of the potash 

 solution is continued until the color remains for 1 minute. If the potash solution 

 used consists of 323.81 cc. of normal solution diluted to 1 liter, each cul)ic centimeter 

 corresponds to 1 mg. of phosphoric acid. 



The valuation of Thomas slag, B. S.iollema {Jour. Landir., 50 {1902), No. 4, 

 IJ}). 367-370). — I'hosphoric acid was determined in a sample of Thomas slag by treat- 

 ment with (1) strong nitric acid, (2) Wagner's method, and (3) repeated extraction 

 with 2 per cent citric acid. In the latter case the slag was ( 1 ) shaken in a flask with 

 successive portions of 150 cc. of acid, allowed to stand some hours, and the solution 

 filtered, and (2) mixed with sand, placed in a tube, and washed with the acid. Two 

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