PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION.' 401 



foggotted, and being brought to a welding heat, are drawn from 

 the furnace and placed under a hammer. A heavy liammer, 

 moving slowly, so as to act on the whole mass of metal under 

 the hammer, and not merely on the surface, the heavier the ham- 

 mer the better the forging; other things being equal. Steel 

 cannon, seemingly of good quality are forged in this city. A 

 projectile like the Hotchkiss' projectile may obviate this difficulty 

 in a great measure. Much of the cast steel in use is very little 

 better than the cast iron from a common wind furnace ; and a 

 good cast-iron gun will probably stand as much as the semi-steel 

 or German steel. There must be a certain weight to prevent too 

 great recoil. The service field piece, made of bronze, is as light 

 as can well be made an account of the recoil. 



Mr. Babcock explained the construction of a gun, mad« in 

 Brooklyn, possessing the advantages of the steel gun. It is a 

 brass six-pounder, grooved out, and the grooves dove-tailed. 

 Pieces of steel were then fitted into these grooves, projecting a 

 little into the gun. This makes the bore smaller, and the pro- 

 jectile lighter ; which is especially an advantage in rifling can- 

 non for an elongated projectile which were only made heavy 

 enough for round projectiles. These bars can be made of a good 

 quality of steel, and will therefore wear longer and keep in order 

 better. 



Mr. Rowell exhibited a steel gun barrel, made in the Krupp's 

 steel works in Prussia, which had been tested at Harper's Ferry. 

 After various trials, upon putting in thirteen balls, the whole of 

 the powder escaped through the vent without affecting the bar- 

 rel. A heavier charge of powder was then used, and with six- 

 teen balls, and a charge of one hundred and sixty grains *bf 

 powder, the barrel burst. The balls are cylinders weighing one 

 ounce. The fracture shows that there is no fibre to this steel. 

 The gun is made upon the principle of having the crushing 

 strength and the tensile strength exactly equal. Upon a trial in 

 1849, two hundred shots wpre fired as rapidly as jDossible, 

 requiring four hours. The temperature, at the close, was only 

 109 deg. Fahrenheit in the interior. These cannon are made 

 with a mantle to prevent recoil. This barrel recoiled three 

 hundred feet at the charge with which it burst. 



Mr. Fisher explained the results obtained in a manufacturing 

 establishment, in which a tube had been expanded by the force 



[Am. Inst.] Z 



