To make a Bunsen burner for acetylene the tube must be extremely narrow, and it is even then found to be very liable to flash back, while it requires a high pressure to bring about satisfactory combustion of the gas with an absolutely non-luminous flame. One of the chief difficulties to be overcome is due to the range over which mixtures of air and acetylene are explosive, and which lies between the limits of 3 per cent, and 82 per cent. of acetylene. The propagation of the explosive wave down the burner tube cannot be satisfactorily stopped by the ordinary device of using wire gauze, on account of the low igniting point of mixtures of acetylene and air; while ii nigh pressures are used so that the rate of flow shall be greater than the propagation downwards, more air is sucked in by the uprush of the gas and the velocity of the explosion is again increased. The best results in acetylene Bunsens have been obtained by taking a Bunsen burner in which a constriction in the air-tube creates a high velocity at the particular point where the explosive wave starts to propagate downwards.