RECENT WORK IX AGRICULTURAL SCIENCE. 



AGRICULTURAL CHEMISTRY. 



Some observations on the determination of citric-acid soluble and total 

 phosphoric acid in Thomas slag-, F. M.\< u ( Landw. Vers. Stat., 68 | 1905), No. 1-2, 

 pp. 81-91; abs. in ('hen. Centbl., 1906, T, No. 1, pp. 85,86; Jour. Chem. Soc. [London], 

 an | 1906), No. 519, II. p. 50).- Comparative tests of Wagner's method and of the 

 official method of the German association of experimenl stations fox determining 

 citric-acid soluble phosphoric arid arc reported. 



The resulte by the two met Ik ids as a rule agreed quite closely, but occasionally the 

 Wagner method gave higher results than the official method, in which silica is 

 removed before precipitation of the phosphoric acid, and higher than the molybdic 

 method, especially in slags rich in silica. The method of evaporating only to a sirupy 

 consistency proposed by A. Bomer gave similar results. The thorough removal of 

 silica previous to precipitation of phosphoric acid is considered essential to accuracy. 



The Schenke lification of the citrate method for determining total phosphoric 



acid | E. S. \[.. 17. p. 6) was found to give results in the author's opinion too high, 

 indicating thai it should he further tested before it is substituted tor the ordinary 

 method. 



A simple method of determining phosphoric acid, potash, sodium, calcium, 

 and magnesium in hydrochloric-acid soil solutions, II. Nedbaueb ( Landw. Vers. 

 Stat.. >;.; (1905), No. 1-2, pp. 141-149; abs. in Chem. Centbl, 1906, I. No. 1, p. 

 The method described is based upon the fact that when the hydrochloric-acid boIu- 

 tion of a soil is evaporated to dryness and carefully heated the iron and aluminum 

 chlorids are converted into insoluble oxids, the calcium and magnesium chloride are 

 hut slightly affected, and the chlorids of the alkalis are not altered. 



The evaporation to dryness | with addition of a small amount -if calcium carbonate 

 if this constituent is deficient in the soil) removes iron, phosphoric acid, and silicic 

 acid, and furnishes a solution in which potash and soda may he determined directly 

 hy the author's method." Phosphoric acid is determined hy the molybdic method 

 in the residue from the potash determination. For tin- determination of calcium 

 and magnesium another portion of the hydrochloric-acid solution is evaporated to 

 dryness and heated until all trace of acid disappears and calcium is determined in 

 the water extract of the residue by precipitation with ammoniac -a I ammonium oxalate 

 and magnesium in the filtrate from the calcium precipitate by precipitation with 



sodium phosphate. 



The method is not reliable in case of soils containing large amounts of sulphates. 

 The rv is danger of injury to ['latin urn dishes due to the formation of free chlorin in 

 the heating of the chlorids in the residue from evaporation. The results of the 

 potash determinations are not very satisfactory in case of soils poor in potash. The 

 addition of a small amount of potash-free calcium chlorid to the soil solution before 

 evaporation u a- found to increase the accuracy of the potash determination-. 



"Zts.hr. Analyt. Chem., 89 (1900), p. 481. 

 23786— No. 8— OH 2 731 



