| 661.1 | Special chemical industries |
| 661.2 | Production of sulphur and its derivatives |
| 661.3 | Production of soda and potash, alkalis |
| 661.4 | Production of halogens and halogen compounds, inorganic peroxo-compounds |
| 661.5 | Production of nitrogen compounds. Fixation of nitrogen. Nitrogen industry in general |
| 661.6 | Production of various nonmetals and semimetals (metalloids), and their compounds |
| 661.7 | Production of organic substances. Organic chemicals |
| 661.8 | Metallic compounds in general. Salts. Mineral compounds |
| 661.9 | Production of gases |
