How to build machines from liquid metal

GEARS ABRADE, pistons crack, pumps clog. If engineers had their way, machines would have no moving parts at all. Alas, a sedentary lump of metal would be a paperweight, rather than a useful machine. So, perhaps just one moving component would be an acceptable compromise.Such machines are now beginning to appear. The component in question is a cleverly chosen liquid, any one of a number of alloys of gallium that melt below room temperature. These have three alluring properties: the highest surface tensions of any known liquid (nearly ten times that of water), good electrical conductivity, and extreme chemical reactivity, in the form of a willingness to donate electrons—a process known as oxidation—to nearby compounds.