1. IN AN INCENDIARY DEVICE, A SELF-IGNITING AGENT OF THE TYPE WHICH RAPIDLY INCREASES IN TEMPERATURE OF THE KINDLING POINT WHEN EXPOSED TO THE AIR, AN ENCLOSING CASING INITIALLY PROTECTING THE AGENT FROM THE ATMOSPHERE BUT COMPOSED AT LEAST IN PART OF THE MATERIAL SLOWLY DEFORMABLE UPON CONTINUED EXPOSURE TO THE ATMOSPHERE TO ADMIT AIR TO THE AGENT TO INITIATE IGNITION.