1) Fill one of the two containers (containing the indicator) with 10 ml of the oil to be examined.
2) Using the pipette, slowly add and shake 0,5 ml of neutraliser at a time.
3) Stop when the solution became purple.
The acidity will result:
- low if we add only 0,5 ml of neutraliser (purple coloration reached after one step);
- average if we add 1 ml of neutraliser (purple coloration reached after two steps);
- high if we add from 1,5 ml to 5 ml of neutraliser (purple coloration reached from 3 to 10 steps).
If the purple coloration is reached after putting in the indicator container more than 5 ml of neutraliser (>0,5 x 10 steps) we need proceed with the substitution of the oil and the complete washing of the system.