2OO AGRICULTURAL ANALYSIS 



173. Dutch Method for Basic Slag. Heat 10 grams of the 

 sample with 50 cubic centimeters of sulfuric acid (1.84 specific 

 gravity) till white vapors are evolved, shaking or stirring con- 

 stantly. After cooling, make the fluid up to 500 cubic centi- 

 meters with water, taking no account of the undissolved sub- 

 stance. Filter, and to 50 cubic centimeters of the filtrate add 

 100 cubic centimeters of the ammoniacal citrate solution, and 

 after cooling, 25 cubic centimeters of magnesia mixture. Stir or 

 shake for a sufficient time. After the lapse of two hours the 

 precipitate is to be separated by filtration and treated in the usual 

 manner. 



174. Estimation of Citrate-Soluble Phosphoric Acid in Basic 

 Slag. Experience has shown that the manurial value of basic 

 slags does not depend alone on their content of phosphoric acid. 

 Slags may contain tri- as well as tetracalcium phosphate, and 

 even this latter salt may exist in states of differing availability. In 

 determining the availability of basic slag for manurial purposes, 

 its solubility in ammonium citrate is considered the best stand- 

 ard. But this solubility will evidently be influenced by the basicity 

 of the sample or, in other words, by the quantity of lime present. 

 A slag rich in calcium oxid would deport itself differently with 

 a given ammonium citrate solution from one in which the lime 

 had been chiefly converted into carbonate. If possible, therefore, 

 all samples should be reduced to the same state of basicity before 

 the action of any given solvent is determined. 



Wagner proposes to neutralize the basicity of a slag in the 

 following manner : 50 Five grams of the slag are placed in a half- 

 liter flask, which is then filled up to the mark with a one per cent, 

 solution of citric acid and placed for half an hour in a rotating 

 shaker. After filtering, 50 cubic centimeters are titrated with a 

 standard soda solution, using phenolphthalein as indicator. This 

 gives the quantity of citric acid necessary to neutralize the slag. 

 To a second portion of five grams of the sample in a half-liter 

 flask are added 200 cubic centimeters of water and enough five 

 per cent, citric acid solution to neutralize the lime, and then 200 

 cubic centimeters of acid ammonium citrate made as indicated 

 60 Chemiker-Zeitung, 1894, 18 : 1153- 



