How do you make an experiment when investigating the time taken for a mixture of oil water and emulsifier to separate depending on the volume of emulsifier?

Equipment:
Measuring cylinders
Water
Boiling tubes
Vegetable oil
Emulsifier solution
Marker pen
Stopwatch
Boiling tube rack
Ruler

Method:
1. Place six boiling tubes in a boiling tube rack;
2. Label the boiling tubes in order: control, 1 cm³, 2 cm³, 3 cm³, 4 cm³, 5 cm³;
3. Measure out 10 cm³ of water into each boiling tube
4. Add 10 cm³ of vegetable oil into each of the boiling tubes.
5. The first boiling tube is a control. To the second boiling tube add 1 cm³ of the emulsifier solution, and to the third boiling tube add 2 cm³ and so on until the sixth boiling tube has 5 cm³ of the emulsifier solution in it;
6. With the marker pen draw a line 1 cm below the top of the oil.
7. Insert the stopper into the first boiling tube and invert 10 times to mix the solutions;
8. Once you have completed the inverting, start the stop clock and time how long it takes for a
1 cm high layer of oil to form on top of the solution;
9. Repeat this inverting and timing process with the other five boiling tubes, recording your results as you go along in a table.