| Item | No. of samples of solution | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Distilled water | Citric acid solution (0.5%) | NaCl solution (1%) | ||||||||
| 0.5 h | 2 h | 6 h | 0.5 h | 2 h | 6 h | 0.5 h | 2 h | 6 h | ||
| Stainless steel | Pot | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 |
| Hard aluminium | Pot | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 |
| Soft aluminium | Pot | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 |
| Fluorocarbon resin | Pan | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 |