| 423 / | HD | CHEMISTRY OF INORGANIC COMPOUNDS |
| 299 | DF | PHOSPHORUS OR COMPOUND THEREOF {5} |
| 304 | DF | .~ Oxygen containing {2} |
| 316 | DF | .~.~ Ternary compound containing hydrogen {1} |
| 317 | | .~.~.~ Orthophosphoric acid {3} |
| 318 | DF | .~.~.~.~> Utilizing reactant containing silicon or carbon |
| 319 | DF | .~.~.~.~> Reacting an acid and phosphate rock {1} |
| 321.1 | DF | .~.~.~.~> Purification or recovery {1} |