Chapter Xiii.--Superphosphates.

Discovery of superphosphate by Liebig 382 Manufacture of superphosphate 383 Nature of the reaction taking place 385 Phosphates of lime 385 Reverted phosphate 389 Value of reverted phosphate 391 Composition of superphosphates 391 Action of superphosphates 392 Action of superphosphate sometimes unfavourable 395 Application of superphosphate 395 Value of insoluble phosphates 396 Rate at which superphosphate is applied 397

APPENDIX TO CHAPTER XIII. NOTE I. The formulæ, and molecular and percentage composition, of the different phosphates 398 II. Reactions of sulphuric acid and phosphate of lime 398 III. Table for conversion of soluble phosphate into insoluble phosphate 399 IV. Action of iron and alumina in causing reversion 399 V. Relative trade values of phosphoric acid in different manures 400