Acetylene is an endothermic compound, its heat of formation being nearly 50kg.-cal. g. mol. Both the gas (tc, 37°; Pc, 62 atm.) and the liquid (b.p.,83.6°) are highly explosive, particularly under pressure. Acetylene is a colourless inflammable gas obtained by the action of water on calcium carbide. When pure, it has a slightly ethereal odour, but when produced from commercial calcium carbide, it has a distinct unpleasant odour due to the presence of traces of phosphene, etc. Colorless, flammable gas, odourless when pure, but ordinarily has a garlic like odour because of impurities. Mol. wt. of acetylene is 26.04. One pound of acetylene is equivalent to 14.5 cu ft. Soluble in acetone (2500 cc gas per 100 g, 30000 cc gas per 100 g at 12 atm), alcohol ( 600 cc per 100 g), water (100 cc per 100 g), and liquid ammonia at room temperature. Ignition temperature is 635°F and Vapor density (air = 1) : 0.91. The first commercial use of acetylene is as illuminant. Though superseded to a large extent by electricity, acetylene is still widely used as an illuminant for marine and aeronautical purposes in buoys, light houses, signaling lamps, etc. Large cylinders holding, in some cases, 500 c.ft. of dissolved acetylene and provided with automatic control and lighting devices are fitted to buoys. At present the most important use of acetylene is in the welding and cutting industry. Acetylene is also used very extensively as a fuel gas for the oxygen cutting process. Its high calorific value, ready portability and ease of manipulation, particularly in the dissolved state, make it superior to most other fuel gases. It is also employed in blowpipes called pistols to melt wires used in metal spraying. There are at present 86 plants producing dissolved acetylene gas with an installed capacity of 22 million cubic metre has been approved be issue of industrial licenses /letter of intents. Most of these approvals are integrated with the approval given for oxygen gas plants as acetylene gas is consumed along with oxygen gas for high temperature cutting/welding purpose. Dissolved Acetylene gas is one of the biggest users of Calcium Carbide. Dissolved Acetylene gas is used in helping of various metals and therefore widely used by various Engineering industries. It has been estimated that future production of dissolved Acetylene gas would increase at the rate of 8%. It is assumed that the production of dissolved Acetylene gas would increase at the rate at which engineering industry is expanding. It is understood from inquiries that 250 cum of Acetylene gas can be produced from 1 ton of Calcium Carbide.