| 423 / | HD | CHEMISTRY OF INORGANIC COMPOUNDS |
| 210 | DF | MODIFYING OR REMOVING COMPONENT OF NORMALLY GASEOUS MIXTURE {11} |
| 220 | DF | .~ Carbon dioxide or hydrogen sulfide component {9} |
| 226 | DF | .~.~ Utilizing organic reactant {2} |
| 228 | DF | .~.~.~ Amine {1} |
| 229 | | .~.~.~.~ Ethanolamine |