Linnert, Welding Metallurgy, ( Oxygen from torch) (Oxygen from Air) This is a representation of the oxy-acetylene welding torch. Note that acetylene gas and oxygen are provided from tanks to the torch where they a re mixed and burned. Depending upon the amount of each, the flame produced may be either neutral, reducing (with an excess of carbon from the acetylene present) or oxidizing (with an excess of oxygen present). The burning actually takes place in a two step process where acetylene combines with the oxygen from the tank to form carbon monoxide and hydrogen in the first step. This produces the inner flame. Then the carbon monoxide and hydrogen combine with oxygen from the air to finish the burn. In the neutral flame they are completely reduced so that the final reaction products are just carbon dioxide and water vapor. Linnert, Welding Metallurgy, AWS, 1994