560 TRANSACTIONS OF THE AMERICAN INSTITUTE 



endurance of guns and the efTect of heat upon metals from seven-eighths of 

 the eminent practical mechanics of the country. 



" I believe your views to be entirely correct on the subject of bursting 

 of guns. 



I was much struck by the coincidence of the result at Fort Fisher with 

 your prophecy to me that the 15-inch guns would burst whenever fired 

 rapidly. Of course I knew the Pari'ott guns would, and I always have 

 given them a wide berth when fired in my presence. They are liable to 

 burst at short notice. 



In ordinary machinery we have illustrations of your theory on guns, by 

 the spontaneous bursting of wheels and other castings: 



I believe your large skeleton gun will be successful in preventing these 

 accidents." 



In the course of the debate which followed this paper, Mr. Wiard gave 

 the following interesting account of the effects of unequal strain: 



Explosion of a Pile Hammer. 



"Some years since I cast a pile hammer weighing four tons. The man 

 for whom it was cast arrived at my place just after the mold was filled, and 

 wanted to take the hammer away that night. I told him that was impos- 

 sible. He was in a great hurry, and arranged with two of the men to sit 

 up with him all night to draw the sand away from the casting as it har- 

 dened, in order to cool it as rapidly as possible. The next day we hoisted 

 it out and got it upon the deck of a canal boat, the deck being protected 

 from the heat by two layers of brick. The man started off with his ham- 

 mer, but before night he came back and ordered another one cast. It 

 seems that the heat remaining in the casting set fire to the deck, and in 

 throwing water on the fire a little fell upon the hammer; seeing that this 

 hastened the cooling, the owner threw on more, when the casting burst 

 with a report that was heard two miles. One half flew forward, killing a 

 horse, and the other went towards the stern, falling through the bottom, 

 and sinking the boat." 



Bursting of a Large Plate. 



" In making the mold for my large cannon we cast a circular plate ten 

 feet in diameter, and three inches thick. To hasten the cooling we re- 

 moved the cope from the mold, when the large surface of hot iron made the 

 shop intolerably warm. To diminish the heat, the foreman threw sand-upon 

 the plate around the edge, leaving the middle uncovered. This caused the 

 middle to harden first, and the outside, cooling afterwards, was, of course, 

 drawn by its contraction into a state of tension upon the interior mass. 



"We had been at work upon this plate several days, drilling a series of 

 holes through it near the edge, and had it on a drill press over a pit which 

 communicated by a trench with the outer air. A very warni blast of wind 

 passed over Trenton, and the next morning when I went to the shop the 

 watchman said that the shop had been struck by lightning in the night. |I 

 went in and saw that the great plate had burst in two halves, one crashing 

 inward among the machinery, and the other flying outward and falling into 

 a pile of valuable castings. 



