A gas, and one of the elements. It is the lightest gas known, hydrogen excepted. It weighs just twice as much as that gas, and only one-seventh as much as air. Helium is extracted from natural gas which is tapped from the ground in certain parts of the United States and Canada. As it cannot take fire it is ideal for inflating balloons; but, owing to the great expense of separating it, it has been used for this purpose only in a few American airships.