=31. Lime Method of Immendorff.=—The tedious processes required to determine the lime in the presence of iron, alumina, and large quantities of phosphoric acid are well known to analysts. Immendorff has published a method, accompanied by the necessary experimental data, based on the comparative insolubility of calcium oxalate in very dilute solution of hydrochloric acid. He has shown in the data given that the lime is all precipitated in the conditions named and that the precipitate, when properly prepared, is not contaminated with weighable amounts of the other substances found in the original solution[22]. The ease with which oxalic acid can be determined volumetrically with potassium permanganate solution aids greatly in the time-saving advantages of the process. In a hydrochloric acid solution of a mineral phosphate an aliquot part of the filtrate representing about 250 milligrams of calcium oxid, usually about twenty-five cubic centimeters, should be taken for the analysis. Ammonia is added in slight excess and then the acid reaction restored with hydrochloric until shown plainly by litmus. The solution is then heated and the lime thrown down by adding a solution of ammonium oxalate in excess. In order to secure a greater dilution of the hydrochloric acid after the precipitation has been made, water should be added until the volume is half a liter. Before filtering, the whole should be cooled to room temperature. The precipitate should be washed first with cold and afterwards with warm water. The well-washed precipitate is dissolved in hot dilute sulfuric acid and the solution, while hot, titrated with a standard solution of potassium permanganate set by a solution of ammonio-ferrous sulfate. If one cubic centimeter of the permanganate represent 0.005 gram of iron it will correspond almost exactly to 0.0035 gram of calcium oxid. _Example._—Sample of rather poor mineral phosphate, five grams in half a liter. Strength of potassium permanganate, one cubic centimeter equivalent to 0.00697 gram of iron and to 0.003484 gram of calcium oxid. Twenty-five cubic centimeters of the solution, representing one quarter of a gram, in which the lime was precipitated as above described, required 9.6 cubic centimeters of the potassium permanganate to saturate the oxalic acid. Then 9.6 × 0.003484 = 0.0334464 gram, or 13.38 per cent of calcium oxid. The method is also applicable to basic slags.