468 NITRE. 



mixed, moistened and pounded in mortars, or ground, to the consist- 

 ence of a thick paste, by large wheels of stone or cast iron, shod with 

 copper. This mass is granulated, by passing it through a series* of 

 parchment or wire sieves, turned by cranks and covered by a heavy 

 piece of wood, usually lignum vitae, whose motion and pressure force 

 the powder through, in the form of grains. It is next sifted, and 

 then dried, in drawers with canvass bottoms, by hot cylinders or 

 stoves of iron placed on one side of the apartment, of which the 

 shelves occupy the other three ; or, as now practised in some manu- 

 factories, by steam, or by warm air thrown in from another apartment. f 



Gunpowder, although frequently injured by dampness, can be pre- 

 served a long time, as appears from the fact that, in 1782, "there 

 were discovered, at Purfleet, (England,) some barrels of very small 

 grained powder, manufactured by Sir Polycarpus Wharton, surveyor 

 of the ordnance in Charles the second's reign. "J 



(d.) Theory of its combustion. Gunpowder is merely a mechan- 

 ical mixture; no chemical action takes place between its ingredients 

 at common temperatures.^ Jit a red heat the oxygen of the nitre 

 acts on the sulphur and carbon, with which it is intimately blended ; 

 the combustion is therefore intensely rapid and violent, and it happens 

 equally in a vacuum, in a mephitic gas, or in a dry cavity under water, 

 and quite independently of air or of any foreign aid. The sulphur 

 produces a rapid combustion, the charcoal contributes largely to 

 the formation of gas, and a good gunpow r der cannot be made without 

 both these combustibles. The power is produced by the sudden 

 formation and disengagement of a vast volume of gases, greatly ex- 

 panded by the heat. 



Gunpowder , wet and crushed in the manner of a squib, maybe 

 safely although imperfectly burned in a gun or pistol barrel, and the 

 gases may be caught in an air jar filled with water. They are prin- 

 cipally carbonic acid, nitrogen and nitric oxide ; sulphurous acid gas 

 and sulphuretted hydrogen, and some ammonia ; perhaps also carbu- 

 retted hydrogen and oxide of carbon. Sulphuric acid is produced 

 and forms sulphate of potassa, which with some sulphuret, a little 

 carbonate of potassa and charcoal, remains. The smell of sulphu- 

 retted hydrogen gas is perceived in fire arms, especially when in 

 the act of being cleaned. 



(e.) The volume of gases produced from gunpowder is, at 60, 250 

 times, and at the moment of discharge 1000 times, greater than that 



* Said to be, in the Royal Mills of England, 24 in number. 



t For an account of the mode of making gunpowder in France, see Thenard, 5th 

 ed. Vol III, p. 251. 



t Gray's Op. Chem. 



See Am. Jour. Vol. XVII, p. 132, where it appears that it may sometimes ex- 

 plode in consequence of the heat given out by sudden compression of air, if not of 

 its own ingredients. 



