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Ferrofluid is a suspension of tiny iron nanoparticles in mineral oil that behaves like a moving liquid magnet when placed in a magnetic field. It can now be inexpensively <a href="https://www.apexmagnets.com/ferrofluid-kit-neodymium-magnets-dish-dropper" target="_blank">purchased</a> at magnet supply stores like Apex magnets. It has some fascinating and beautiful behavior. You can use it make a liquid piston with no moving parts, unless you count the liquid moving. Since this could be made very small, researchers have been interested in trying to make small pumps with Ferrofluid for the purpose of manipulating tiny samples for chemical analysis, perhaps by making a “<a href="https://infoscience.epfl.ch/record/55930/files/98.pdf" target="_blank">lab on a chip</a>”.