MECHANICS AND USEFUL ARTS. 51 



ance is made for fouling. The absence of smoke promotes rapid firing 

 and exact aim. There are no poisonous gases, and the men suffer less 

 inconvenience from firing in casemates, under hatches, or in closed 

 chambers. The fact of smaller recoil from a gun charged with gun- 

 cotton is established by direct experiment. Its value is of the recoil 

 from gunpowder, projectile effect being equal. To understand this 

 may not be easy. The waste of the solids of gunpowder accounts for 

 one part of the. saving, as in one hundred pounds of gunpowder sixty-eight 

 pounds have to be projected in addition to the shot, and at a much higher 

 speed. The remainder Von Lenk attributes to the different law of 

 combustion. But the fact is established. The comparative advanta- 

 ges of gun-cotton and gunpowder for producing high velocities are 

 shown in the following experiment with a Krupp's cast-steel gun, six- 

 pounder. With ordi nary charge thirty ounces of powder produced 1 ,338 

 feet per second. With charge of thirteen and one-half ounces, gun-cot- 

 ton produced 1,563 ft. The comparative advantages in shortness of 

 gun are shown in the following experiments, twelve-pounder : 



Velocity 

 Calibers. Charge. feet per second. 



Cotton, length 10 . . 15.9 oz. . 1,426 



Powder, " 13^ . 49 (normal powder charge) . . . 1,400 

 Cotton, " 9". . 17 1,402 



As to advantage in weight of gun, the fact of the recoil being less in 

 the ratio of 2 : 3 enables a less weight of gun to be employed, as well 

 as a shorter gun, without the disadvantage to practice arising from 

 lightness of gun. As regards durance of gun, bronze and cast-iron 

 guns have been fired 1,000 rounds without in the least affecting the 

 endurance of the gun. As regards its practical application to destruc- 

 tive explosions of shells, it appears that from a difference in the law of 

 expansion, arising probably from the pressure of water in intensely- 

 heated steam, there is an extraordinary difference of result, namely, 

 that the same shell is exploded by the same volume of gas into more 

 than double the number of pieces. This is to be accounted for by the 

 greater velocity of explosion when the gun-cotton is confined very 

 closely in very small spaces. It is also a peculiarity that the stronger 

 the shell, the smaller the fragments into which it is broken. As "re- 

 gards mining uses, the fact that the action of imn-cotton is violent and 



f^ *-^ ^j 



rapid in exact proportion to the resistance it encounters, tells us the 

 secret of its far higher efficacy in mining than gunpowder. The 

 stiongcr the rock, the less gun-cotton, comparatively with gunpowder, 

 is necessary for the effect ; so much so that while gun-cotton is stronger 

 tl .an powder as three to one in artillery, it is stronger in the propor- 

 tion of 6.274 to 1 in a strong and solid rock, weight for weight. It 



CT5 C^ ^j 



ia the hollow-rope form which is used for blasting. Its power of split- 

 ting up the material is regulated exactly as wished. As regards mili- 

 tary and submarine explosion, it is a well known fact, that a bag of 

 gunpowder nailed on the gates of a city will blow them open. In this 

 case gun-cotton would fail. A bag of gun-cotton exploded in the 

 same way is powerless. If one ounce of gunpowder is exploded in 

 scales, the balance is thrown down ; with an equal force of gun-cotton, 

 nothing happens. To blow up the gates of a city, a very few pounds 

 of gun-cotton, carried in the hand of a single man, will bo sufficient, 



