Although it's the most abundant element in the universe, hydrogen is most commonly found locked in water here on Earth. In the 19th century, a researcher named William Grove found that applying electricity to water -- aka electrolysis -- separated it into its basic components of hydrogen and oxygen. In the resulting gas, hydrogen and oxygen are intermingled but not bonded together.
Researcher Yul Brown delved into practical research on using this gas, now known as Brown's or HHO gas, as a fuel. Today, kits can carry out this kind of conversion in internal combustion engines to increase gas mileage.