Sodium is named from the English soda, and was isolated in 1807. Sodium is fairly abundant in the sun and stars. Sodium is the sixth most abundant element on earth, comprising about 2.6% of the earth's crust. It is the most abundant of the alkali group of metals. The most common compound is sodium chloride (salt) but it occurs in many other minerals, is very reactive and is never found free in nature. It is obtained commercially by the electrolysis of absolutely dry fused sodium chloride. Sodium is a soft, bright silvery metal which floats on water, decomposing it with the evolution of hydrogen and the formation of the hydroxide. It may or may not ignite spontaneously on water depending on the amount of oxide and metal exposed to the water. The metal may be used to improve the structure of certain alloys, to descale metal, to purify molten metals and as a heat transfer agent. Sodium compounds are important to the paper, glass, soap, textile, petroleum, chemical and metal industries.