OF GUN-METAL.

I18

not the least alteration could be observed in any of the guns }this degree of hardness may then be looked upon as suffi-cient, and this conclusion has been fully justified by subse-quent experience.

42. The third method, by which the powder tends todestroy guns (32, No. 3) new remains to be considered.In the wars of 1733 and 1742, there was an opportunity ofexamining guns of different nations, that had been renderedunserviceable by the Ihot striking against their sides, andmaking cavities, furrows, cracks, and swellings, which hadcaused some of the shot to break to pieces in the guns, andcut the metal very deep ; as appears from the reports madeby the officers of artillery, appointed to examine them be-fore they were recast.

These accidents may be accounted for by the general cus-tom the nations of Europe had before the middle of thepresent century, of leaving it entirely to the foundets to mixthe metals; they, not aware of the necessity of having a certaintenacity and hardness, proceeded without any regular system:whence frequently arose a remarkable difference in the resist-ance of guns cast by the fame founder. In proving newguns, the charges occupied a great length of the bore; at thefirst round, the powder was equal to \ of the weight of theshot; at the second to A; and at the third, was equal to it inweight: so that if the metal were not of sufficient hardness,an orbicular cavity was formed at the position of the wadbetween the powder and shot, without the least attentionbeing paid to it: less charges being afterwards used on ser-vice, the shot was placed in this very cavity, which caused itto take an oblique direction, and strike against the sidesunder angles of incidence, so much the greater as thecavity was the deeper; thus by degrees the gun was renderedunserviceable.

43. The result of experiments made in May 1753, andin July 1759) will further shew the inconveniences arisingfrom the formation of orbicular cavities in guns. For thefirst experiments, three 16 prs. were cast of the commonmixture (38) at the fame time, and from the fame fur-nace, to render the metal homogeneous, and for greateraccuracy constructed with the fame proportions; the onlydifference being in the calibre : for the diameter of the shotbeing divided into 8290 parts, the calibre of the smallest gunwas 8463 of those parts, that of the second 8505, and that