Ferrofluid

Ferrofluids are made up of tiny magnetic fragments of iron suspended in oil (often kerosene) with a surfactant to prevent clumping (usually oleic acid). 

Day 26: Interesting Facts About Iron
Atomic Symbol: Fe; Atomic Number: 26; Atomic Mass: 55.847 

1. Iron has been well known since ancient times. In fact, Indians were one of the first people to master the art of extracting and smelting iron many years before Europeans. The Iron Pillar located in Delhi is said to be over 1600 years old and in all its time it has not corroded or rusted.
2. Iron is another element whose atomic symbol may not make sense to English-speakers. Its symbol of Fe is derived from its Latin name of ferrum. This name also gives rise to the term ferromagnetic, which is a property of A Allotrope iron.
3. Iron is one of the most frequently used metals in the world. In its pure form, it is actually a rather soft metal, so it is usually combined into alloys to produce stronger metals. However, upon prolonged contact with oxygen, the majority of these iron alloys will rust and corrode, necessitating processes such as galvanization and painting.
4. It is an essential element in biological processes, as plants use iron in chlorophyll and humans use iron in hemoglobin molecules in blood to allow for the transport of oxygen to tissues throughout the body. Yet, too much of it is extremely toxic. Unabsorbed iron in the blood reacts with peroxides to form free radicals that damage DNA, protein, lipids and other cellular components, leading to illness and sometimes death. 

Image: This is a photograph of various forms of high-purity elemental iron. Iron is a blue-gray metal found in steel and many other alloys as well as in pure form.