The extinction point of acetylene was determined by burning a vertical he under constant pressure and in an atmosphere consisting of O2 and N2 of constant composition which could be altered at will. The length of flame, the diameter of the combustion chamber, the velocity of the gas mixture through the combustion chamber, and the percentage excess air all affect the extinction point. The results under specific conditions are given in the conclusions. The presence of CO2 in the inlet gas mixture increases the value of the extinction point but to a lesser extent then that previously found for other hydrocarbon gases, e.g., methane.