Hydrogen

Hydrogen is so easy to make by adding a metal to an acid that it was known as early as the late fifteenth century. Paracelsus (1493?-1541) made it by adding iron to sulfuric acid, but it wasn't until 1766 that it was recognized as a distinct substance, different from all other gases, or what were then called "airs." Henry Cavendish (1731-1810), an English chemist, gets the credit for this realization and hence for the discovery of hydrogen. Only in modern times, however, were isotopes of elements discovered. In 1932 Harold Urey (1893-1981) discovered deuterium by separating out the small amounts of it that are in ordinary water. This was the first separation of the isotopes of any element.

Hydrogen can be prepared in several ways. Many metals will release bubbles of hydrogen from strong acids such as sulfuric or hydrochloric acid. Hot steam (H₂O) in contact with carbon in the form of coke reacts to produce a mixture of hydrogen and carbon monoxide gases. Both of these products are flammable, and this so called" water gas" mixture is sometimes used as a fuel, although it is dangerous because carbon monoxide is poisonous. Passing an electric current through water—electrolysis—will break it down into bubbles of oxygen gas at the anode (positive electrode) and hydrogen gas at the cathode (negative electrode).