OF GUN-POWDER.

I 9

53. The grains of powder are generally of a very irregularform and uneven surface ; whence arise many varieties inthe quickness of its inflammation and explosion. To re-medy these inconveniencies, some manufacturers put thepowder into a barrel suspended by two pivots; and havingturned it for some time, separate, by means of a screen, thedust from the grains; which are, by this operation, suffi-ciently smoothed and rounded. On comparing powdermade in this manner with powder of an irregular form anduneven surface, the latter is found to take sire more quickly,though the proportion of ingredients be precisely the same inboth. Nevertheless, as the interstices between the roundgrains are larger than between grains of an irregular figure,and as upon them the quickness of the inflammation greatlydepends, the round grains may be so small, that the intersticesbeing equal in both, the fire may be able to spread itselfequally, and consume the powder with the same rapidity5and as powder of an irregular grain takes fire more easilythan smooth-grained powder, a proportional size mi^ht befixed on which would cause the latter to inflame with greater,

, or at least equal promptitude.

54. As these properties are common to all kinds of pow-der (40.) that are well made, of proper materials, andequally dried, varieties in their effects can only result fromthe different proportion of the ingredients, the size of thegrains, their figure, and smooth or uneven surface. If theingredients, however good in quality, are not well mixedtogether, the powder will not so readily burn, and the dif-ference of the effects will be very sensible.

55. The following experiment will prove, that from firedpowder a permanent elastic fluid (35. N° 4.) is produced ingreat quantity, upon which depends its principal force.(Fig. IV.) AB C Z is a hollow cylinder of bronze, witha screw at B C to receive OFF. G G is a key to openor stiut the communication between the parts of the funnelH H. To the spiral F F, fix the air-gun M M, to receivethe elastic fluid generated in the cavity B P j and screw D Einto B C. Put the powder into the cavity; and screw I K L,made of bronze, into A P. Lm is the vent; no a smallmoveable plate of iron, to which is fastened a fuse 0 p, andjoined to the pin K, Lcc. q r is a smooth bar of iron, madeto slide in a groove by the spring Vy, which keeps it in theposition ts, when not forcibly held back; and closing thevent, totally prevents the passage of the air; so that, when

B 2 the