774 THE POPULAR SCIENCE MONTHLY. 



mula for " making thunder and lightning," are still in use, and in nearly 

 the same proportion now as at that early date. The three solid sub- 

 stances which, when properly and intimately mixed, form gunpowder, 

 are saltpeter, sulphur, and charcoal ; the first being three fourths, or 

 a little more, of the mixture, the two latter, in nearly equal but vary- 

 ing proportions, forming the remaining one fourth. The saltpeter 

 contains a large amount of oxygen, which it gives up with consider- 

 able readiness upon the application of heat ; this unites with the 

 carbon contained in the charcoal, forming a large volume of carbonic- 

 acid gas ; the potash of the saltpeter unites with the sulphur, while 

 the nitrogen is set free, adding to the volume of the gases evolved. 

 As these gases are given off with great rapidity, they are still further 

 expanded by the action of the heat produced by the change of the 

 solids into the gaseous form, until, under ordinary circumstances, they 

 occupy a volume nearly three hundred times as great as that occupied 

 by the powder itself. One can easily imagine that the expansion of a 

 pound of powder to a size (if we may so say) so much greater than 

 its original bulk would exert a tremendous pressure upon any object 

 in which it was confined. If a small quantity of powder is freely 

 exposed in the air and fired, the resulting explosive effect is small, as 

 the gases produced so rapidly can readily push aside the air; but if it 

 be confined in a large block of steel, in which is a cavity which will 

 just receive it snugly, the resulting pressure is nearly ninety-three 

 thousand pounds to the square inch. 



From this illustration it will at once be understood that confine- 

 ment, in a greater or less degree, is necessary, in order that the great- 

 est amount of work may be accomplished by the explosion. Those 

 explosives which give off their gases with intense rapidity require 

 but little restraint, while the slower ones require more confinement. 

 Among these less quick ones must be reckoned gunpowder, for, al- 

 though the explosion seems to follow immediately upon the applica- 

 tion of heat, yet an appreciable amount of time really elapses, in 

 which the combustion goes on. 



The ingredients of which gunpowder is composed are selected 

 with the greatest possible care : the saltpeter is procured chiefly from 

 India, being extracted from the soil by natural processes and then 

 secured by the natives, for marketing. It is also largely prepared by 

 artificial means, it being quite evident that it would not do for any 

 country to depend upon a supply without its own borders in case of 

 war. In this process, heaps of earth are mixed with decomposing 

 organic matter ashes, old mortar, and materials of like nature the 

 whole being wet with the liquor from stables sufficiently to keep it in 

 a moist condition ; the moistened heaps are worked over from time 

 to time, and the air allowed free access. A chemical reaction takes 

 place, and in time the crude saltpeter appears upon the exterior of the 

 heap, whence it is removed and treated for the extraction of the pure 



