PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 519 



Mr. Clinton Roosevelt, made a diagram on the black-board of the longi- 

 tudinal section of a gun, showing the peculiar fracture in guns that burst 

 and the place where it most occurs, and said : The principal point at which 

 guns burst is at the breech ; now if it was the heat that exploded them, 

 they should be torn apart through the whole length of the gun, and not at 

 the breech, for the heat is ever greater at the mouth than at the breech ; 

 the reason that they do not burst throughout goes to show that it was 

 pressure and not heat that produces this effect. 



Prof. Everett. — In regard to the remarks of Mr. Bartlett, in the early 

 part of the evening, as to the effect of burning gunpowder in the open air 

 and in a. close vessel, I should say that there would be a great difference in 

 the products, and it is strange that it has not been noticed before. And 

 therefore, to reason from Hansen's experiments would be very much like 

 the boy who is said to have asked his Professor how he found out the size 

 of the moon, and was told that he guessed the first half and multiplied that 

 by four. 



Mr. J. K. Fisher. — It appears strange to me that the pressure of gun- 

 powder should be put down at 150,000 and 200,000 pounds on the square 

 inch, when 150,000 pounds is the maximum strain that the best steel will 

 stand, and a pressure of 80,000 pounds will crush cast-iron. From this it 

 would seem that 200,000 pounds ought to blow a cast-iron cannon to pietes 

 almost instantly. 



Mr. Wiard. — Almost every one I have spoken to on the subject of the 

 pressure of gunpowder, attributes to it a far greater heat than would melt 

 the metal of which guns are made, and the reason that it does not do so is 

 that the heat acts on the metal for a very short time. We know that if a 

 piece of iron is put in the fire for a short time, it will be but slightly 

 heated, and if taken out can be handled without much difficulty, but if left 

 in the furnace very long it will become melted. 



Mr. Clinton Roosevelt. — I examined the fragments of the " Peacemaker," 

 a very large gun that burst several years ago, the crystals in the metal 

 were half an inch square, and they were afterwards worked over again and 

 made very good metal. 



Mr. N. Wiard. — The public imagine that we have some very large guns 

 doing wonders at Charleston, but I know that there were only three 800 

 pounders sent down thei'e, and I understand these have burst, and I may 

 say that so fai-, the charges used in our heavy guns are very small. 



The manufacture of tin-lined lead pipe, was selected as the subject for 

 the next meeting. 



Adjourned to Thursday evening, December 3d. 



