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60. Are brass cannon liable to external injury, caused by service?
They are little subject to such injury, except from the bending of the trunnions sometimes, after long service or heavy charges.
Note.—Recent experiments at Fort Monroe show that brass guns, when rifled, and fired with large charges and heavy shot, expand so much that the projectile does not take the grooves.
61. What are the causes of internal injury?
Internal injuries are caused by the action of the elastic fluids developed in the combustion of the powder, or by the action of the shot in passing out of the bore.
62. Name the injuries of the first kind.
Enlargement of the bore by the compression of the metal; corrosion of the metal at the inner orifice of the vent, or at the mouth of the cylindrical chamber; cracks, from the yielding of the cohesion of the metal; cavities, cracks enlarged by the action of the gas, and by the melting of the metal, observable especially in the upper surface of the bore.
63. Name those of the second kind.
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