| Sample | Sulfuric acid/mL | Temperature/˚C | Time/h |
| 1 | 0 | 200 | 24 |
| 2 | 1 | 200 | 24 |
| 3 | 2 | 200 | 24 |
| 4 | 3 | 200 | 24 |
| 5 | 4 | 200 | 24 |
| 6 | 5 | 200 | 24 |
| 7 | 3 | 180 | 24 |
| 8 | 3 | 200 | 12 |