No. 1. Florida rock 1.45 1.32 “ 2. “ “ 4.40 4.53 “ 3. Sodium phosphate 19.78 19.99 “ 4. “ “ 19.72 19.73 “ 5. Florida rock 37.28 37.22 This near agreement shows the reliability of the method. The comparison of the Pemberton volumetric method with the official gravimetric method was investigated by the reporter of the Association of Official Agricultural Chemists in 1894.[87] The individual variations were found to be greater than in the regular method but the average results were nearly identical therewith. The method works far better with small percentages of phosphoric acid than with large. Where the average of the results by the official methods gave 12.25 per cent, the volumetric process gave 11.90 per cent, whereas in the determination of a smaller percentage the results were 2.72 and 2.73 per cent, respectively. Kilgore proposes a variation of the method which differs from the original in two principal points.[88] First the temperature of precipitation in the Pemberton process is 100°; but in the modified form from 55° to 60°. At the higher temperature there is danger of depositing molybdic acid. The second difference is in the composition of the molybdate solution employed. The official molybdate solution contains about sixty grams of molybdenum trioxid in a liter while the Pemberton solution contains sixty-six grams. There is therefore not much difference in strength. The absence of nitric acid, however, from the Pemberton solution favors the deposition of the molybdic acid when heat is applied. Kilgore, therefore, conducts the analysis as follows: The solution of the sample is made according to the official nitric and hydrochloric acid method for total phosphoric acid. For the determination, twenty or forty cubic centimeters are taken, corresponding to two-tenths or four-tenths gram of the sample. Ammonia is added until a slight precipitate is produced and the volume is then made up, with water, to seventy-five cubic centimeters. Add some ammonium nitrate solution, from ten to fifteen cubic centimeters, but this addition is not necessary unless much of the nitric acid has been driven off during solution. Heat in water-bath to 60° and precipitate with some freshly filtered official molybdate solution. Allow to stand for five minutes, filter as quickly as possible, wash four times by decantation using from fifty to seventy-five cubic centimeters of water each time, and then wash on a filter until all acid is removed. The solution and titration of the yellow precipitate are accomplished as in the Pemberton method. The agreement of the results obtained by this modified method was much closer with the official gravimetric method than those obtained by the Pemberton process.