Table 1 Range and levels of laboratory independent variables
Variable | Axial bottom (−α) | Low factorial (−1) | Central point (0) | High factorial (+1) | High axial (α) |
|---|---|---|---|---|---|
Concentration (ppm) | 2 | 5.75 | 9.5 | 13.25 | 17 |
Dosage (g) | 0.01 | 0.03 | 0.05 | 0.07 | 0.09 |
pH | 3 | 4.5 | 6 | 7.5 | 9 |
Time (min) | 5 | 35 | 65 | 95 | 125 |
Temp (°C) | 20 | 25 | 30 | 35 | 40 |