(Gr. hydro, water, and genes, forming) Hydrogen was prepared many years before it was recognized as a distinct substance by Cavendish in 1776.

Named by Lavoisier, hydrogen is the most abundant of all elements in the universe. The heavier elements were originally made from Hydrogen or from other elements that wereoriginally made from Hydrogen.

Hydrogen is estimated to make up more than 90% of all the atoms or three quarters of the mass of the universe. This element is found in the stars, and plays an important part in powering the universe through both the proton-proton reaction and carbon-nitrogen cycle-- stellar hydrogen fusion processes that release massive amounts of energy by combining Hydrogen to form Helium.

Production of hydrogen in the U.S. alone now amounts to about 3 billion cubic feet peryear. Hydrogen is prepared by

• steam on heated carbon,
  
• decomposition of certain hydrocarbons with heat,
  
• action of sodium or potassium hydroxide on aluminum
  
• electrolysis of water, or
  
• displacement from acids by certain metals.

Liquid hydrogen is important in cryogenics and in the study of superconductivity, asits melting point is only 20 degrees above absolute zero.

Tritium is readily produced in nuclear reactors and is used in the production of the hydrogen bomb.

Hydrogen is the primary component of Jupiter and the other gas giant planets.  At some depth in the planet's interior the pressure is so great that solid molecular hydrogen is converted to solid metallic hydrogen.

In 1973, a group of Russian experimenters may have produced metallic hydrogen at apressure of 2.8 Mbar. At the transition the density changed from 1.08 to 1.3 g/cm3. Earlier, in 1972, atLivermore, California, a group also reported on a similar experiment in which they observed a pressure-volume point centered at 2 Mbar. Predictions say that metallic hydrogen may be metastable; others have predicted it would be a superconductor at room temperature.