Another experiment with gun-cotton was then tried.  A piece not larger than a man's hand was fastened to an enormous iron chain fixed on the deck of the ship.  We were all ordered to go below, out of harm's way. Soon afterwards, the gun-cotton having been ignited by a train, we heard a loud report; and on returning on deck we found that the chain had been cut completely in two, the fragments having flown about in all directions.