"Fool Proof" - But It Can Explode -- Scientists of the E. I. Dupont De Nemours Co., have developed a dynamite which proved it would resist all efforts to explode it until it was set off by a special type of percussion cap. Sledge-hammer blows, red-hot irons and electric charges failed to detonate it, but when the special cap was set off, this blast resulted near Philadelphia, Feb. 20. At a demonstration test. February 20, 1935. (Photo by Associated Press Photo).