If an incendiary bomb should fall on the Academy of Natural Sciences in Philadelphia it would be smothered quickly with a mixture concocted by the mineralogical staff. The ingredients - inexpensive and effective - are ten parts of ordinary salt and one part flaked coal-tar pitch, mixed dry. Containers for the mixture are paper shopping bags taped shut with gummed paper. About 25 pounds are placed in each bag. In approaching a bomb the bag is held as a shield for the face, then dropped on the bomb which burns the paper to speed its own destruction.