MECHANICS AND USEFUL ARTS. 105 



Armstrong guns produced, not one, according to the testimony of Sir 

 William Armstrong, has yet burst explosively. Whitworth has also 

 had some success in the production of forged iron guns, although his 

 met hod is defective ; and Blakely in England and Ivrupp in Belgium 

 are now manufacturing superior ordnance from steel. The advantages 

 of wrought iron over cast iron consist in its greater tenacity, elastic- 

 ity, and ductility, which it preserves under heavy pressure. All gun 

 metals are said to possess a certain degree of elasticity; but the 

 ' elastic limit," in rapid firing, is always liable to be exceeded, and 

 when this happens, cast i 1*011, from its want of flexibility, easily cracks 

 and crumbles. In other words, after the limit of its elasticity is over- 

 come, any violent shock or sudden strain causes the gun to give way 

 at once, and explode without warning ; while a gun properly made of 

 wrought iron, under similar circumstances, would only widen a little, 

 and still be further from the point of bursting than it. was before. 

 The tensile strength of wrought iron is over 66,000 pounds to the 

 inch, while that of the best cast iron is only about 30,000 pounds per 

 inch. 



Artillery Experiments made under the Direction of the U. 8. Ord- 

 nance, Department. The Scientific American furnishes the following 

 resume of experiments whiclf have been recently made with guns and 

 targets, under the direction of the Ordnance Department of the U. S. 

 Government. The experiments in question were all made with the 

 11-inch gun, of Dahlgren, with an average, charge of 30 pounds of 

 powder, an average weight of spherical cast-iron projectile equal 

 to 160 pounds, and an average range of 80 feet. 



Under the above-named conditions, an experiment was made upon 

 a composite target of iron and India-rubber, backed with timber. 

 The iron was outermost, and was two inches thick ; the rubber came 

 next, and was 1% thick ; the timber was 19 inches thick, in all 22| 

 inches. The target was inclined at an angle of 15 ; and at the 

 first, fire the shot tore through the mass and penetrated the bank be- 

 hind (a solid clay) 17 feet, being but slightly damaged in its pas- 



sage. 



Another experiment was tried witli a 4^-inch solid scrap-iron plate, 

 backed with 20 inches of solid oak, and the iron faced with rubber, 

 four inches thick, the whole placed against a bank of solid clay ; this 

 resulted in the destruction of the target at the first fire, the charge be- 

 ing 30 pounds, the projectile, spherical cast iron, weighing 169 pounds, 

 and the range 87 feet. The shot did not go entirely through the tar- 

 get, but penetrated the plate and rubber, and lodged in the second 

 course of timber behind. The rubber was entirely forced off, by the 

 violence of the concussion, and fell 15 feet forward of the target. 



Still another target was made, of four 1-inch wrought-iron plates, 

 backed by rubber four inches thick in single sheets of one inch each; 

 the whole backed by 20 inches of solid oak. The first four inches 

 next the timber were composed of alternate rubber and iron, two 

 inches of each ; the wrought iron was on the outer surface of the tar- 

 get when fired at. The whole was placed against a bank of solid 

 clay. The charge was 30 pounds, the shot 169 pounds in weight, and 

 the range 84 feet ; at this distance, and under these conditions, the 

 target had two clean, handsome- holes bored through it, one of which 



