2l8 AGRICULTURAL ANALYSIS 



In the sulfuric acid method, 10 grams of phosphatic slag, pre- 

 pared as above described, are covered with a few cubic centi- 

 meters of sulfuric acid (one to two) and well shaken. After the 

 addition of 50 cubic centimeters of concentrated sulfuric acid, the 

 mixture is heated at first to boiling and afterwards just to the 

 boiling point, until the mass is evaporated to a thick fluid and vio- 

 lent bumping begins. After cooling, water is gradually added to 

 the mark and the phosphoric acid determined either by the citrate 

 or molybdic acid method. 



Estimation of Citric-Acid-Soluble Phosphoric Acid in Basic 

 Slag. The method of estimating the citric acid soluble phos- 

 phoric acid in basic slag is that of Wagner, which has already 

 been described. 



191. Estimation of Lime. When the lime is to be determined 

 in basic slags, some difficulty may be experienced by reason of 

 danger of contamination of the oxalate precipitate with iron and 

 especially manganese, which is often present in slags. 



Holleman proposes to estimate the lime in basic slag by mod- 

 ification of the methods of Classen and Jones. 72 The manipula- 

 tion is as follows : Fifty cubic centimeters of an acid solution 

 of slag, from which the separated silica has been removed by fil- 

 tration, equivalent to one gram of substance, are evaporated to a 

 small volume, 20 cubic centimeters of neutral ammonium oxalate 

 solution (one to three) added to the residue and heated on a 

 water bath, with frequent stirring, until the precipitate is pure 

 white and free from lumps. The time required is usually about 

 10 minutes. The precipitate is collected on a filter and washed 

 with hot water until the filtrate contains no oxalic acid. The 

 precipitated calcium oxalate must be snow-white. The filter is 

 broken and the calcium oxalate washed through, first with water 

 and finally with warm, dilute hydrochloric acid (one to one), 

 The calcium oxalate is dissolved by adding 15 cubic centimeters 

 of concentrated hydrochloric acid, the solution evaporated to a 

 volume of about 25 cubic centimeters, and 10 cubic centimeters 

 of dilute sulfuric acid (one to five), and 150 cubic centimeters 

 of 96 per cent, alcohol added. After standing three hours or 

 72 Chetniker-Zeitung, 1892, 16 : 1471. 



