Acetylene

ACETYLENE has the chemical formula C₂H₂ (structural formula H-C≡C-H) and is a colorless, poisonous gas at ordinary conditions, condensing into a liquid at 0°C and 26 atm. 1 liter of A. at 0°C and 760 mm weighs 1.165 g. At ordinary temperature, 1 volume of A. dissolves in 1 volume of water. A. is an endothermic compound and therefore possesses strong explosive properties (especially liquid A.); in this case, an explosion can be caused by impact, an electric spark, etc. A. is obtained from calcium carbide by its interaction with water: CaC₂ + 2H₂O = C₂H₂ + Ca(OH)₂. The acetylene obtained in this way contains as impurities ammonia, hydrogen sulfide, hydrogen, carbon monoxide, and phosphine. Therefore, acetylene is purified by passing it through water, alkali, calcium chloride, and copper chloride. In qualitative determination of acetylene, its reaction with an ammoniacal solution of cuprous chloride is used: Cu₂Cl₂ + C₂H₂ + H₂O = [(Cu₂C₂H₂)O] + 2HCl₂. The gas in which the presence of A. is to be detected is passed through a tube with cotton wool soaked in the reagent; in the presence of A., the wool turns pink. -- A. has great practical significance and is used for lighting, metal melting, etc. A. is sold in the form of acetone solutions, in steel cylinders embedded in a porous clay mass. A. is a poisonous gas, causing on the organism the same phenomena as carbon monoxide. According to Vogel, staying in an atmosphere containing 2⁰/₁₀₀ acetylene for half an hour causes severe poisoning associated with loss of consciousness. Therefore, there must be regular control of the air in rooms where acetylene lighting is used and work with acetylene is performed, etc.

S. Vovenessensky. Acetylene welding is performed by the flame of acetylene burning in oxygen (initially according to the formula: C⁺ + C^- = H₂ + 2CO, and then: CO + O = CO₂ and H₂ + O = H₂O). The installation for acetylene welding consists of 1) reservoirs for oxygen and A., 2) gas piping, and 3) a burner in which A. is mixed with oxygen and gives a concentrated flame. Oxygen is supplied to the gas piping from cylinders in which it is under high pressure, the pressure being reduced by a reducing valve. Oxygen cylinders must be protected from impact, jolts, and heating to avoid explosion. On the other hand, an explosion can occur from the ingress of insignificant amounts of fatty substances into the fittings, for which reason the cleanliness of the fittings must be attended to with the utmost seriousness. Acetylene is supplied to the gas piping either from cylinders in which it is under pressure in acetone, or is obtained in special apparatus by the decomposition of water of carbide. These apparatuses are stationary and portable (small ones, with a loading of not more than 2 kg of carbide). According to the principle of action, the apparatuses are divided into two types: "carbide on water," when the carbide is gradually fed into a reservoir with water, and "water on carbide." The second type is safer, as it is easier to regulate. The installation consists of an apparatus, a purifier, and a gas holder. It must be located in a separate room made of fire-resistant material with a light roof, separated from neighboring rooms by a blind fire wall. The removal of acetylene penetrating into the room must be ensured by proper ventilation (possibility of poisoning and explosion). Electric lighting must have hermetically sealed fittings; in other lighting methods, the light source must be placed outside. In the same way, the furnace must be fired from outside. All these measures aim to prevent the possibility of an explosion of a mixture of acetylene with air. The pressure of the gas in the generator must not exceed 0.5 atm. (a water manometer is used to measure it), and the excess must be removed outside away from sources of fire. The same safety measures are required for the gas holder. Due to the insufficient purity of the carbide, acetylene usually contains impurities of other gases, in particular the poisonous phosphine. For this reason, the installation for acetylene welding must have a purifier for trapping gas impurities by means of chloride and chromate compounds. In addition, the gas should be washed with water. A great danger is represented by the sludge obtained as a result of carbide decomposition, due to the possibility of containing small particles of carbide in it and, consequently, the possibility of acetylene being released upon contact with water. For this reason, special precautions must be observed when removing sludge and it must by no means be discharged into public water bodies, etc. Special pits must be arranged for the sludge in the open air, with fencing and warning signs prohibiting smoking. The pipeline through which acetylene enters the /b> welding room must have carefully made joints and must be protected from corrosion. The hoses to the burners must be made of thick rubber and have a corresponding length for safe operation. In every place of gas consumption, a water seal must be installed, which does not allow oxygen or air to penetrate the apparatus and neutralizes possible backfires of flame from the burner. Special attention must be paid to the good construction of the burner and to its correct handling. Since oxygen goes under greater pressure than acetylene, in case of clogging of the burner's outlet with metal splashes, oxygen can penetrate into the acetylene gas piping with the formation of an explosive mixture. To prevent this, in addition to the water seal, special cartridges with a porous mass that softens the impact and a check valve that interrupts communication with the acetylene gas piping in case of increased pressure are also used. - During the welding itself, a flame rich in ultraviolet rays (see) is obtained, which is harmful to the workers' vision. For this reason, welders must be equipped with protective goggles or special protective glasses of a special construction. To protect against splashes of molten metal, the welder must be equipped with appropriate special clothing (see). Safety rules for acetylene installations were published by the NKTruda of the USSR on January 14, 1926. In addition, there are NKTr rules for the production of repairs in steam boilers by acetylene welding.

P. Sinev. Acetylene lighting, see Lighting.