Acetylene is a colorless and extremely flammable gas at standard temperature and pressure with a garlic-like odor. Acetylene can violently decompose if the pressure of the gas exceeds 100 kPa in its free state, so it is shipped and stored dissolved in acetone. The majority of acetylene's chemical energy is contained in the carbon-carbon triple bond.
Above 400 °C (what is really low for a hydrocarbon), the pyrolysis of Acetylene will start. The main products are the dimer vinylacetylene (C4H4) and benzene. At higher temperatures above 900 °C the main product will be soot.
Calcium carbonate (limestone) and coal are the principal raw materials for acetylene manufacture. The calcium carbonate is first converted into calcium oxide and the coal into coke, and then the two are reacted with each other to form calcium carbide. Calcium carbide and water are then reacted by several methods to produce acetylene. Acetylene can also be manufactured by a process employing the partial combustion of methane with oxygen and by the thermal or arc cracking of hydrocarbons.
Approximately 80 percent of the acetylene produced annually in the United States in used in chemical synthesis. The remaining 20 percent is used primarily for oxyacetylene welding and cutting. Combustion with oxygen produces a flame of over 3300 °C, releasing 11,800 J/g.
Acetylene is also used in the acetylene lamp or carbide lamp, formerly found in mines and on cars (automobiles), and still sometimes used by cavers. Acetylene is generated by adding calcium carbide (CaC2) pellets to water and then burnt, producing an intense flame. The lamp was first patented in Duluth, Minnesota on October 21, 1902 (U.S. Patent No. 711 871).
Nowadays acetylene is used for carburization (i.e. hardening) of steel. Research in the last ten years came to the conclusion, that acetylene is the best hydrocarbon available for this purpose.