The magnetic particles need to be coated with a surfactant so that they won't stick together when magnetized. Finally, the coated particles will be suspended in a carrier so the magnetic solution will flow like a liquid. Since you are going to be working with ammonia and kerosense, prepare the carrier in a well-ventilated area, outdoors or under a fume hood.
- Heat the magnetite solution to just below boiling.
- Stir in 5 ml oleic acid. Maintain the heat until the ammonia evaporates (approximately an hour).
- Remove the mixture from heat and allow it to cool. The oleic acid reacts with ammonia to form ammonium oleate. Heat allows the oleate ion to enter solution, while the ammonia escapes as a gas (which is why you need ventilation). When the oleate ion binds to a magnetite particle it is reconverted to oleic acid.
- Add 100 ml kerosene to the coated magnetite suspension. Stir the suspension until most of the black color has been transferred into the kerosene. Magnetite and oleic acid are insoluble in water, while oleic acid is soluble in kerosene. The coated particles will leave the aqueous solution in favor of the kerosene. If you make a substitution for the kerosene, you want a solvent with the same property: the ability to dissolve the oleic acid but not uncoated magnetite.
- Decant and save the kerosene layer. Discard the water. The magnetite plus oleic acid plus kerosene is the ferrofluid.
