| 423 / | HD | CHEMISTRY OF INORGANIC COMPOUNDS |
| 351 | DF | NITROGEN OR COMPOUND THEREOF (EXCEPT AMMONIUM SALT OF NON-NITROGEN ACID) {5} |
| 352 | DF | .~ Ammonia or ammonium hydroxide {6} |
| 359 | DF | .~.~ From elemental hydrogen and nitrogen {3} |
| 362 | | .~.~.~ Utilizing metal containing catalyst {1} |
| 363 | DF | .~.~.~.~> Alkali or alkaline earth metal |