OF GUNS. I $3

tnetal containing tin in the ratio of 16 to 17 in the 100 cor-bodes more easily than assayed goid; but at 4 to 5 in the 100it resists more than German brass; for which reason, as wasbefore remarked, soft gun-metal was for a long time ingreat credit. But these resistances are merely relative andcan only apply to determined circumstances; for if the qualityor quantity ot the powder be altered, the wads rammed withmore force, or the piece much heated by frequent siring, themetal will be the sooner corroded and the vent enlarged.

124. The first method adopted for repairing the ven s ofguns that had run, was the application of a bouch : afterwardin hopes of totally preventing or at least deferring this accident,they put into the mould a piece of copper or iron at the placewhere the vent would be: this expedient was soon aban-doned, on finding that the liquid metal on coming in con-tact with a cold body, bubbled and formed cavities con-tiguous to the vent: and one of the four following methodswas universally adopted.

The first consisted in enlarging the vent A B C D (PI. 3,Fig. 10) when damaged towards the middle F G and fillingup 1 he cavity with gun-metal; the metal when cold wasperforated to form a new vent.

The second method differed from the first, only in fillingthe cavity with pure copper.

In the third method, the vent A B C D (PI. 4, Fig. 11)was enlarged as before, and an iron bouch P applied withthe projection Q_Q_; melted metal was then poured intoL M which when cold held the bouch P very firmly ; after-ward a new vent H K was drilled.

(PI. 4, Fig 12) The fourth method was to enlarge the ventvery considerably in form of a troncated cone A M K E, thefides of which Q.RDBLE served as a female screw to receivean iron bouch; in the axis of which was drilled a new ventF G. These different methods of repairing the vents of gunsmay be applied according to the damage that the piece has sus-tained but are not equally good. In the first method thevent may run a second time, if there be too much tin in themetal. By the second, the vent is less liable to corrode;but the copper from its great ductility may spread andlengthen, and being detached from the sides of the cavity,the whole bouch may be blown into the air. The thirdmethod is preferable to the two former, since the bouchgives more resistance, and is less liable to the above accidents.

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