The flame is lighted by first turning on the acetylene, lighting it, and then turning on the oxygen. The acetylene burns with a bright, smoky flame. As the oxygen jet increases, an indefinite-shaped cone appears at the nozzle; it first has two points, one beyond the other. More oxygen reduces it to a clearly defined single cone of blue flame. If there is too much oxygen, the flame will sputter and roar and the point of the cone become ragged and violet-colored. For this reason the operator can always tell by appearance when his flame is right. It is always safer to have too much acetylene, rather than too much oxygen. Oxygen will burn and rust the metal; acetylene will keep it from burning.

1 Henry Cave, The Horseless Age, Dec. 2, 1908.

The low-pressure flame consumes acetylene and oxygen in the ratio of 1 to 1. 50; the high-pressure in ratio of 1 to 1.28.

As to pressure for the gases, the operator will soon learn by trial what pressure of oxygen is necessary to use to keep the flame from back-firing. The low-pressure torch needs higher oxygen pressure to draw in the acetylene; at least 30 pounds for welding and 125 pounds for cutting. Pressure is regulated by turning on the full initial supply of the gases and then setting the constant-pressure regulators. Different kinds of work may take different pressures.

The hottest part of the flame is at the tip of the cone and a fraction beyond. Never hold the cone against the work, because it will burn the metal. Only the tip should be allowed to touch.