OF GUN-POWDEE. 25

particular. These two properties, as well as the first andfourth, hold good in all fire-arms, and in every other cavitywhere powder is burned; they are also modified by the samecauses, (41.) and by others that will be hereafter men-tioned.

69. The second property is observable in all fire-arms,when, on applying fire to different quantities of the samepowder, either the whole or a part only of the grains takefire, in proportion to the strength of the fire, and the densityof the medium. For example, if a quantity of cannonpowder be all burned in a gun of large calibre, .the samequantity, in a piece of smaller calibre, will not be all burned.In the same piece, charged with different quantities of pow-der, the smaller charge will entirely explode, while a partonly of the larger will be consumed. If, in the largest charge,the resistance to the explosion be increased by a high wad,shot, &c. a greater quantity of powder will burn than whenthe piece is fired with a common wad, and without (hot.These varieties constitute the second property of powder.(44,45,46,47.)

70. The third property of powder is equally observable inall fire-arms. The inflammation of each grain, and of thecontiguous ones, being progressive in all kinds of powder, thevarieties that occur arise not only from the size of the grains,and the proportion of the ingredients, but also from thesize of the vestel in which the powder is fired. For example :if in two vessels, of unequal sizes, two equal quantities ofpowder be burned, the fire in the smallest vessel, being mostintense, accelerates the destruction of each grain, and all thepowder is consumed in less time than in the larger vessel.The same circumstance occurs, when two equal quantitiesof powder are burned in vessels of equal size ; one of whichresists the action of the powder, and the other bursts at thebeginning of the explosion : the heat being more intense inthe vessel that resists than in the other, the destruction ofeach grain is accelerated.

71. To prove that the inflammation of powder in fire-arms of all calibres depends on the density of the air con-tained between the grains, and the degree of fire that sur-rounds them, (69.) let a musquet or pistol barrel be filledwith powder to four or five diameters; let a small wad, madeof a substance not easily combustible, be lightly comprefledupon the powder; and let the piece be fired into a vessel made

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