i>ROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 433 



worth shells, before alluded to, did penetrate and explode behind 5| inch 

 iron plates. They were exploded by the heat of compression of the iron 

 in striking-. 



Mr. J. H. Churchill doubted whether the heat of compression was the 

 cause of firing-. 



Mr. P. Dibben alluded to the facts and theory with regard to large guns, 

 broug-ht forward by Mr. Wiard at a previous meeting. The heat he 

 (Mr. D.) thought could not expand the inside so as to very greatly affect the 

 strength of the gun. In the old way of testing guns by firing many times 

 with extra charges, more than half those failed on the first fire. He had 

 seen it in six different cases of trials at Kingston, N. Y. Iron is stronger 

 as it is heated up to 200° or 300° F. Experiments had as yet failed to 

 show how far the heating beyond these degrees would improve the strength, 

 but it had been determined that elasticity was of more value than actual 

 tensile strength in cast iron. Greenwood iron would spring very sensibly. 



Mr. Wiard remarked that wrought iron would bend still further. 



Mr. Dibben confessed that elasticity was not the only quality required. 

 Hardness and stiffness were also necessary. Mr. D. referred to the shortness 

 of the bore of Mr. Wiard's design for a spherical gun of three different 

 metals, and thought a longer bore, with slow-burning powder, would serve 

 more efficiently to project the ball. Mr. Wiard proposed to make his bore 

 only about five calibers long. The old plan for small arms was to make 

 them sometimes thirty calibers long. This was now shortened with good 

 effect, but he thought five calibers were too short. 



Mr. Wiard explained that he rated his guns to the length of cartridge. 

 He thought that about five times the length of cartridge was a good pro- 

 portion for nearly all arms, to get the best possible projectile force from the 

 powder. 



Mr. Dibben thought the heat produced by the burning of gunpowder in a 

 space absolutely confined, was about ten thousand degrees Fah., and pre- 

 sented several grounds for the opinion. Powder in firing and cooling down 

 the gases, occupies a space about 210 times that occupied when in a solid 

 state. If the cooled gas was again compressed suddenly in a non-conduct- 

 ing vessel to its original volume, its heat, by the known laws of heat due 

 to compression, would be about that above given, i. e., 10,000° Fah. 



Guns were often weakened by unequal cooling, due to the construction 

 of the flask in which they were cast. He had cast a number which on 

 extreme test burst along the lines of the junctions of the flasks. Guns 

 could be cast without trunnions in a one part flask. The heat of the inte- 

 rior, as at first stated, was not sufficient to burst or greatly weaken the gun. 



Mr. Bartlett explained the theory of Mr. Wiard and Mr. Reid, in ascrib- 

 ing the rupture of guns in part at least to heat. 



Mr. Wiard confirmed the estimate presented by Mr. Dibben, of the tem- 

 perature of the gases of powder, but differed from him in believing that it 

 had a very serious effect on the gun in expanding its interior. The tem- 

 perature of 10,000 or more, exactly 10,800° P., was many times that of 

 melted iron, and he had believed^ until recentl}', that he was the first to 

 show that it had or might have very great influence in bursting guns. 



Slow powder acts more equally on a gun, by reason of not fully burning 

 TAm. Inst.1 2S 



