MECHANICS AND USEFUL AKTS. 49 



there is no waste. The waste in gunpowder is sixty-eight per cent, of 

 its own weight, and only thirty-two per cent, is useful. This sixty- 

 eight per cent, is not only waste in itself, but it wastes the power of the 

 remaining thirty-two per cent. It wastes it mechanically, by using up 

 a large portion of the mechanical force of the useful gases. The waste 

 of gunpowder issues from the gun with much higher velocity than the 

 projectile ; and if it be remembered that in one hundred pounds of useful 

 gunpowder this is sixty-eight pounds, it will appear that thirty -two 

 pounds of useful gunpowder gas is wasted in impelling a sixty-eight pound 

 shot composed of the refuse of gunpowder itself. There is yet another pe- 

 culiar feature of gun-cotton. It can be exploded in any quantity instan- 

 taneously. This was once considered its great fault; but it was only a 

 fault when we were ignorant of the means to make that velocity anything 

 we pleased. Baron Von Lenk has discovered the means of giving 

 gun-cotton any velocity of explosion that is required by merely the 

 mechanical arrangements under which it is used. Gun-cotton, in his 

 hands, has any speed of explosion, from one foot per second to one foot 

 in YoVg- of a second, or to instantaneity. The instantaneous explosion 

 of a large quantity of gun-cotton is made use of when it is required to 

 produce destructive effects on v the surrounding material. The slow 

 combustion is made use of when it is required to produce manageable 

 power, as in the case of gunnery. It is plain, therefore, that, if we can 

 explode a large mass instantaneously, we get out of the gases so explo- 

 ded the greatest possible power, because all the gas is generated before 

 motion commences, and this is the condition of maximum effect. Itjs 

 found that the condition necessary to produce instantaneous and com- 

 plete explosion is the absolute perfection of closeness of the chamber 

 containing the gun-cotton. The reason of it is, that the first ignited 

 gases must penetrate the whole mass of the cotton, and this they do, 

 and create complete ignition throughout, only under pressure. This 

 pressure need not be great. For example, a barrel of gun-cotton will 

 produce little effect and very slow combustion when out of the barrel, 

 but instantaneous and powerful explosion when shut up within it. On 

 the other hand, if we desire gun-cotton to produce mechanical work, 

 and not destruction of materials, we must provide for its slower com- 

 bustion. It must be distributed and opened out mechanically, so as to 

 occupy a larger space, and in this state it can be made to act even more 

 slowly than gunpowder ; and the exact limit for purposes of artillery 

 Von Lenk has found by critical experiments. In general, it is found 

 that the proportion of eleven pounds of gun-cotton, occupying one cubic 

 foot of space, produces a greater force than gunpowder, of which from 

 fifty to sixty pounds occupies the same space, and a force of the nature 

 required for ordinary artillery. But each gun and each kind of projec- 

 tile requires a certain density of cartridge. Practically, gun-cotton is 

 most effective in guns when used as to ^ weight of powder, and oc- 

 cupying a space of l^th of the length of the powder-cartridge. The 

 mechanical structure of the cartridge is of importance as affecting its 

 ignition. The cartridge is formed of a mechanical arrangement of spun 

 cords, and the distribution of these, the place and manner of ignition, 

 the form and proportion of the cartridge, all affect the time of complete 

 ignition. It is by the complete mastery he has gained over all these 

 minute points that Von Lenk is enabled to give to the action of gun- 

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