1. Dissolve 67.58g FeCl 3.6H 2 O in 250ml of 2M HCl. Dissolve 39.76g FeCl 2.4H 2 O in 100ml of 2M HCl. Ferrofluids 1 Modified from Berger et al, Journal of Chemical Education, 1999, 26, 7, 943-948

2. 1M FeCl 3 should be used within one week of preparation. 2M FeCl 2 should be used within one week of preparation. Ferrofluids 2

3. Combine 3ml of FeCl 2 solution and 12ml of FeCl 3 solution and fill a burette with 150ml of 0.7M ammonium hydroxide solution. Add ammonia very slowly whilst stirring. A black precipitate of magnetite will form. Ferrofluids 3

4. After addition is complete, stop stirring and use a strong magnet (Nd 2 Fe 12 B) to settle the black precipitate to the bottom of the flask. Decant off the water and add fresh water. Rinse the precipitate and again decant off the water. Repeat three times to remove excess ammonia. Ferrofluids 4

5. Transfer the viscous liquid to a weighing boat using a little extra water if necessary. Use a magnet on the base of the weighing boat to remove excess water. Add 24ml of tetramethylammonium hydroxide (25% solution) and stir with a glass rod Ferrofluids 5

6. Hold a magnet on the base of the weighing boat and let the solid settle to the bottom. Decant off any excess liquid to leave a very viscous black liquid. The viscous liquid should form spikes if a magnet is held underneath the weighing boat. You may need to adjust the amount of water. Ferrofluids 6