1864] 



Gun-cotton and Gunpowder. 



213 



of carbonic acid, carbonic oxide, hydrogen, and coal-gas. In operating with 

 pieces of gun-cotton-twist or thread of some length instead of employing 

 the material in loose tufts, the results obtained in the two last-named gases 

 were very different from those observed in atmospheres of nitrogen, carbonic 

 acid, and carbonic oxide. When ignited by means of a platinum wire 

 (across which it is placed) in vessels filled with either of those two gases, 

 and completely closed or open at one end, the piece of twist burned slowly 

 and regularly, the combustion proceeding much more deliberately than if 

 the same piece of gun-cotton had been ignited in the usual manner in air, 

 and being accompanied by only a very small jet or tongue of pale yellow 

 flame, which was thrown out in a line with the burning surface when the 

 gun-cotton was ignited. The same result was obtained in currents of those 

 gases when passed through a long, wide glass tube, along which the gun- 

 cotton twist was laid, one end being allowed to project some distance into 

 the air. The projecting extremity being ignited, as soon as the piece of 

 twist had burnt up to the opening of the tube through which the gas 

 was passing, the character of the combustion of the gun-cotton was changed 

 from the ordinary to the slow form above described. On repeating this 

 form of experiment in currents of hydrogen and of coal-gas, the ignited 

 gun-cotton burned in the slow manner only a very short distance inside the 

 tube, the combustion ceasing altogether when not more than from half an 

 inch to one inch of the twist had burnt in the tube. The same result 

 was observed when the current of gas was interrupted at the moment that 

 the gun-cotton was inflamed. It was at first thought that this extinction 

 of the combustion of gun-cotton by hydrogen and coal-gas might be caused 

 by the very rapid abstraction of heat from the burning surface of gun- 

 cotton in consequence of the difl^usive powers of those gases ; but when 

 the experiments were made in perfectly closed vessels, the piece of gun- 

 cotton-twist being ignited by means of a platinum wire, the combustion 

 also ceased almost instantaneously. These efl'ects, therefore, can only be 

 ascribed to the high cooling-powers, by convection, of the gases in question. 

 It was found, by a succession of experiments, that when nitrogen was mixed 

 with only one-fifth of its volume of hydrogen the combustion of gun-cotton- 

 twist in the mixture v/as very sIoav and uncertain (being arrested after a 

 short time in some instances), and that a mixture of one volume of hydrogen 

 with three of nitrogen prevented its combustion, like coal-gas. 



The slow kind of combustion of gun-cotton, in the form of twist, which 

 is determined by its ignition in currents or atmospheres of nitrogen, car- 

 bonic acid, &c. may also be obtained in a powerful current of atmospheric 

 air, the thread of cotton being placed in a somewhat narrow glass tube. 

 If, however, the air is at rest, or only passing slowly, the result is uncer- 

 tain. In employing very narrow tubes into which the gim-cotton fits 

 pretty closely, the combustion passes over into the slow form when it 

 reaches the opening of the tube, and occasionally it will then continue 

 throughout tli§ length of the tube. In that case, while the gun-cotton 



