7561. Harrop, G. March 27. Incandescent gas burners. - In inverted incandescent gas burners, the burner tube is either provided w i t h rifling grooves, or is rifled by twisting it upon itself, from or near the point of admission of air to the point where the gas and air mixture is ignited. A rifled nozzle may be employed in combination with a mixing-tube rifled throughout its length.