THE PROPERTIES
H
H to Ij shorter than the funnel ABC by half a diameterD D. The part K L of the iron rod K L M, fits the co-nical part A H so exactly, that no air can pass: the cylin-drical part is a little longer than H I. The capital N N Oof brass, of which the aperture O O is less than D D, canbe fastened by the spirals N N to B B.
Let the space D F be so diminished by the ring G, that theremaining part D P be entirely filled with the powder used inthe experiment; and let the powder be retained by a hog’sbladder tied fast to the thread of the screw B B. The fun-nel, thus charged, is screwed into V V of the receiver,placed upon the base X Z, which keeps the funnel perpen-dicular. Then if the iron rod be made red-hot, and pressedforcibly into the funnel, the point M coming below the bot-tom of the funnel I, without touching the bladder, willnevertheless set fire to the powder, and the bladder willburst. If this experiment be made with 24 grains of can-non powder, when the receiver is placed so that the loweraperture X Z fits a large tub or other vessel, no unfiredgrains of powder will be found; but if the receiver be placedupon the plate of the pneumatic machine, and the air behalf exhausted, } or i of the grains will be found unfiredupon the plate after the explosion; and if the receiver be ex-hausted, y or 4 of the grains will be found untouched by thefire.
In these three modifications of the air in the receiver, thefunnel is always charged in the fame manner, and with thefame quantity of powder; and the bladder tied fast in B Bentirely prevents any communication between the receiverand the part D P of the funnel; so that when the receiver isexhausted, no change takes place in the part of the funnelthat communicates with the external air by means of thelittle canal A H I; and consequently, when the rod is intro-duced into the canal, the powder inclosed in the funnel, andthe air contained between the grains, remain in the famestate, whatever alteration be made in the air of the receiver;wherefore, the bladder bursting at the beginning of the in-flammation of the powder, the air which is between thegrains in DP, spreads itself into the receiver; and in pro-portion as it becomes more rarefied, less powder is fired.In each of these three different states of the air in the re-ceiver, it may be observed, that the insides D P of the fun-