At 48° At 50° At 52° At 54° At 55° B. B. B. B. B. Tricalcium phosphate 1.590 1.517 1.446 1.382 1.352 Iron phosphate 1.630 1.558 1.485 1.420 1.390 Aluminum phosphate 2.025 1.930 1.839 1.756 1.721 Calcium carbonate 1.640 1.565 1.495 1.428 1.411 Calcium fluorid 2.006 2.010 1.916 1.830 1.794 Magnesium carbonate 1.940 1.860 1.775 1.690 1.660 _Example._—Suppose for example a phosphate of the following composition is to be treated with sulfuric acid; _viz._,[124] Moisture and organic 4.00 per cent. Calcium phosphate 55.00 “ Calcium carbonate 3.00 “ Iron and aluminum phosphate nearly all alumina 6.50 “ Magnesium carbonate 0.75 “ Calcium fluorid 2.25 “ Insoluble 28.00 “ Using sulfuric acid of 50° B., the following quantities will be required for each 100 kilograms. Kilos of acid required. Calcium phosphate, fifty-five kilos 83.44 “ carbonate three and a half kilos 5.48 “ fluorid, two and a quarter “ 4.52 Aluminum and iron phosphate, six and a half kilos 12.55 Magnesium carbonate, three-quarters of a kilo 1.40 ----- Total 107.39 =142. Phosphoric Acid Superphosphates.=—If a mineral phosphate be decomposed by free phosphoric in place of sulfuric acid the resulting compound will contain about three times as much available phosphoric acid as is found in the ordinary acid phosphate. The reaction takes place according to the following formulas: (1) Ca₃(PO₄)₂ + 4H₃PO₄ + 3H₂O = 3[CAH₄(PO₄)₂·H₂O]. (2) Ca₃(PO₄)₃ + 2H₃PO₄ + 12H₂O = 3[Ca₂H₂(PO₄)₂·4H₂O]. In each case the water in the final product is probably united as crystal water with the calcium salts produced. The monocalcium salt formed in the first reaction is soluble in water and the dicalcium salt in the second reaction in ammonium citrate. Where fertilizers are to be transported to great distances there is a considerable saving of freight by the use of such a high-grade phosphate, which may, at times, contain over forty per cent of available acid. The phosphoric acid used is made directly from the mineral phosphate by treating it with an excess of sulfuric acid. AUTHORITIES CITED IN PART FIRST. [1] Day, Mineral Resources of the United States 193, pp. 703, et seq. [2] Massachusetts Agricultural Experiment Station, Bulletin 51, March, 1894. [3] Brown, Manual of Assaying, p. 24.