RECENT WORK IN AGRICULTURAL SCIENCE. 



AGRICULTURAL CHEMISTRY. 



Chemical method for the determination of the available phosphoric acid 

 in soils, A. De 'SiGMor<D {Jour. Aiiier. C'heiH. Soc, 29 (1901). Xo. (>. iip. 929-936, 

 fifj. 1). — The author here l)rieH.v describes the method which he has used for the 

 determination of the available phosphoric acid in soils in connection with an 

 elaborate study of the fertilizer requirements of Hungarian soils for which he 

 was awarded a prize by the Hungarian Academy of Sciences. The method is as 

 follows : 



" 1. The (letcnni)i(ttio)i of flir hasicity of the soil. — Titrating 2.5 gm. of soil 

 with a standard solution of nitric acid, containing 100 mg. NoOs per liter, and 

 boiling the soil, to drive out all the carbonic acid, we get at the basicity of the 

 soil, that is the amount of nitric acid neutralized by the soil. The author uses 

 the term basicity for the number of milligrams N^Os for complete neutraliza- 

 tion of 2.5 gm. of the soil. 



" Weigh 25 gm. air-dried soil in a beaker, add a small amount of water and 

 10 cc. of the standard nitric-acid solution. Then boil the solution until the 

 carbonic acid escapes, test with litmus paper, and if the reaction is not dis- 

 tinctly acid, add again 10 ec. of nitric acid, boil, and test again with litmus 

 paper. Repeat this until there is a distinct excess of acid. Then pour the 

 whole contents of the beaker into a standard flask of .500 cc, fill up, shake, 

 filter, and determine in .50 cc. the excess of acid with a standard solution of 

 potassium hydroxid such that 1 cc. neutralizes 10 mg. NoO,. Use methyl 

 orange as indicator. By calculating tbe junnber of milligrams of N2O5 neutral- 

 ized by 25 gm. of soil, we get the basicity of the soil. 



" With soils which on adding some acid effervesce distinctly, the author has 

 found it better to use only 5 gm. instead of 25 gu. 



" 2. Making of the soil solution. — In making the soil solution, we wish to get 

 a solution with an end acidity ranging 200 to 1.000 mg. N2O5 per liter of the soil 

 solution. The end acidity means the acidity of the soil solution after the solu- 

 tion is ready for the determination of phosphoric acid. 



" From the basicity of the soil we can nearly calculate the amount of stand- 

 ard acid wanted for the soil solution, namely : 



"(1) If the soil contains practically no traces of carbonates, or the basicity 

 runs below the value of 1.000 mg. N.O5. use l)ut 10 cc. of the standard nitric 

 acid solution to 25 gm. of soil. 



"(2) If the soil contains carbonates, but the basicity ranges but 1,000 to 4.000 

 mg. N2O5. use just as many cubic centimeters of the standard acid as are required 

 for the full neutralization of the basicity of the soil to 25 gm. of soil. 



"(3) If the soil is very much loaded with carbonates or the basicity runs above 

 4.000 mg. N2O5, and the soil is almost loamy or clay, use 5 to 10 cc. less of the 

 standard acid than would be required for the complete neutralization of the 

 basicity. But in the case of sandy and loose peaty soils the author has found 

 it best to use the amount of acid according to (2), 



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