To the above defects in a less degree than brass, except the corrosion of the metal, by which the vent is rendered unserviceable from enlargement. The principal cause of injury to iron cannon is the rusting of the metal, producing a roughness and enlargement of the bore, and an increase of any cavities or honeycombs which may exist in the metal.
69. How may you judge of the service of an iron gun?
Generally by the appearance of the vent.
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70. What rules are laid down for the preservation of artillery?
Cannon should be placed together, according to kind and calibre, on skids of stone, iron, or wood, laid on hard ground well rammed and covered with a layer of cinders or of some other material to prevent vegetation. In case of guns and long howitzers, the pieces should rest on the skids in front of the base ring and in rear of the astragal, the axis inclined at an angle of 4° or 5° with the horizon, the muzzle lowest, the trunnions touching each other; or the trunnion of one piece may rest on the adjoining piece, so that the axis of the trunnions may be inclined about 45° to the horizon; the vent down, stopped with a greased wooden plug, or with putty or tallow. The pieces may be piled in two tiers, with skids placed between them exactly over those which rest on the ground; the muzzles of both tiers in the same direction and their axes preserving the same inclination. In case of short howitzers and mortars, the pieces should stand on their muzzles, resting on thick planks, the trunnions touching, the vents stopped.
71. What additional precautions should be observed in case of iron pieces?
They should be covered on the exterior with a lacker impervious to water; the bore and the vent should be greased with a mixture of oil and tallow, or of tallow and beeswax melted together and boiled to expel the water. The lacker should be renewed as often as necessary, and the grease at least once a year. The lacker and grease should be applied in hot weather. The cannon should be frequently inspected, to see that moisture does not collect in the bore.
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