782 THE POPULAR SCIENCE MONTHLY. 



full of water, in which revolves a wheel having strips of steel upon 

 its rim, similar strips projecting from the bottom of the tub. As the 

 wheel revolves, the floating pieces are drawn between the steel strips 

 and thus reduced to a fine pulp. This is again washed for a long time 

 by mechanical means, after which it is taken to the press, where nearly- 

 all the water is expelled from it, the final pressure applied being about 

 fifteen thousand pounds to the square inch. When taken from the 

 press, it is in the shape of a disk or cylinder, of a close texture, easily 

 broken when dry, and capable of being cut in a manner not unlike 

 pasteboard. When a small quantity is ignited by a flame, it burns 

 quite rapidly, but quietly, if dry ; if wet, it is consumed very slowly. 

 If a large quantity is ignited, there may be sufficient confinement of 

 the inner portions by the outer shell to cause an explosion. If dry 

 loose gun-cotton be ignited, it burns with extreme rapidity, like a flash, 

 but without any violence ; in fact, a wisp placed on a small pile of gun- 

 powder and fired will not ordinarily cause its explosion. In order to 

 have a complete explosion of the dry material, fulminate of mercury 

 must be used, and this is accordingly employed in the primers made 

 for the explosion of that which is wet. Two pounds of the dry, de- 

 tonated by twenty-five grains of fulminate, will cause the detonation 

 of five hundred pounds of the wet. In this wet state it must be 

 carefully guarded from a low temperature, as the expansion of the 

 water in freeziug will tend to break up the disks. 



Many experiments have been made with a view to its adoption in 

 gunnery practice, but it is not at all likely that either it or any of the 

 high explosives will ever displace gunpowder ; their action is so vio- 

 lent and sudden that, before the projectile has time to take up its mo- 

 tion in the bore of the gun, the walls yield and the piece is burst. Its 

 use for military purposes must therefore be confined to mines and tor- 

 pedoes, as in the case of dynamite, or as a bursting-charge for shells, 

 for which purpose experiments show that it is most admirably adapted. 

 It is used in Europe for torpedo purposes, and is carried for that use 

 by war-vessels of the English and other navies. 



The explosive gun-cotton is not the only kind made ; another sort 

 (in which a less amount of the hydrogen of the cotton is displaced) is 

 used for making collodion, largely employed by photographers. This 

 variety, called collodion gun-cotton, combined with nitro-glycerine, 

 forms a new explosive* agent called gum-dynamite, or explosive gelatine. 

 Singular to relate, the ordinary gun-cotton used for explosive purposes 

 will not enter into this combination, and hence probably the late dis- 

 covery of the fact that it requires the collodion variety to do so. This 

 is finely shredded, generally by hand, and placed in small quantities at 

 a time in the nitro-glycerine, which is kept at a temperature of 80 

 Fahr. by means of a water-bath, the whole being constantly stirred with 

 a wooden spatula ; the proportion of materials is seven per cent by 

 weight of the gun-cotton to ninety-three per cent of the nitro-glycerine. 



