OF THE VENTS.

*5 3

CHAP. VIII.

Of the Vents of Guns.

i ig. TPH E position of the vent contributes also to mo-dify the inflammation and explosion of the charge. (PI. 3*Fig 8) If in the gun ABM the vent QP correspond to halfA N of the charge, it will be the most advantageous posi-tion for obtaining the greatest force from the given quantitybf powder; but then the motion of the breech, though ofthe proper weight (84) will be so violent, as to render thefiring totally irregular, and of course the fire-arm useless.The vent should be placed at A C corresponding to the bot-tom of the bore, which will obviate the ill consequncesattending the former position; and if the bottom of the boreinstead of being hemi-spherical be plane, the charge will bebrought nearer to the vent, more powder will take fire, andthe explosion be more violent, without causing such an irre-gular motion in the breech.

120. Chambers in guns are liable to great inconveniencesfrom the alteration of their figure, as happened at the expe-riments with the Sarcophagus (36). This gun had at thebottom of the bore a small cylindric chamber A H C D(PI. 3, Fig. q) of which the diameter A C was 1 inch andthe length AB 2 inches, the communication F to the ventF G was distant from A i-£ 0 -: the part F Ni of the ventmade in the gun itself was in length 3^ the remainderG N was filled with an iron screw HLMK 2-,\ in length,which had been well worked and tempered. After 500rounds the metal was much corroded at F, and round theorifice A C of the chamber; and the upper part PA BFwas considerably damaged towards N. This increased verymuch in the next 300 rounds; the clefts extending towardsN were 1 £ inch in length; the pricked line Q_Q_Q_shewsthe alteration that took place in the figure of the chamber.The part N G of the vent formed by the iron screw was regu-larly enlarged to nearly twice the original diameter: but by theassistance of this bouch the piece might yet have been frequentlyfired, without apprehending any great increase in the size of the

vent j