20

THE PROPERTIES

the several parts are properly adjusted, and the bar of iron q ris in the position t s, the elastic fluid inclosed in the cavityB P, though very much condensed, cannot escape. Q_Q.are pivots,' or trunnions, to support the machine.

In this experiment the machine must be placed vertically,that the powder contained in the space B P may rest on B X;the little funnel H b having been previously filled with hog’slard, that the powder, when fired, may not act immediatelyon the key G G, and prevent it from being drawn out. Bymeans of a thread of silk, fastened with two little nails atthe hole ot, the iron q r is held back, the fuse is chargedwith powder, and the vent L m primed. Then I K isscrewed into A P, and fire applied at L ; which, communi-cating by ot, sets fire to the fuse in o ; and burning, at thesame time, the thread of silk, sets at liberty the iron q r ;which, pressed by the spring V y, slides into s t, and closesthe holem. The fuse burns from o to p, and sets fire to thepowder in B X : the vent being closed in ot; and, for greatercertainty, a little screw introduced into L.

(Fig. V.) When it is judged that the powder in B X isfired, which can only be known by the heat of the cylinderA B C Z, as no motion can be perceived, let a bullet be putinto the air-gun, and the machine be pointed against a plank,by means of the semicircle of iron B B, which can be stoppedby C in any direction; then .giving a half turn to the keyG G, that. the cavity B P may communicate with the boreof the air-gun, on touching the trigger A the bullet is dis-charged with velocity; and impinges on the plank with thefame force as would have been produced by a very great con-densation of air.

The cavity B P will contain ten ounces of powder, butwith one ounce only, sixteen or eighteen bullets may be dis-charged successively, and at the distance of forty paces, eachbullet will pass through a fir plank half of an inch thick.After these discharges, if the key G G be turned as it was atfirst, the air-gun be unscrewed, a large bladder fastened inits place, and the key again turned, the bladder will be filledwith an invisible fluid ; which, being close tied up for severaldays, will not sensibly diminish in bulk. In the coldest wea-ther it is equally elastic ; so that, considered relatively to itselasticity, it may be compared to the atmospheric air. Un-screwing K. I, the inside B P X will be found covered withsaline particles j which, collected and examined, form a fixed

Alkali