. Annual report of the American Institute, of the City of New York. Science. PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 401 HOW GUXS BURST. When gunpowder is fired from a gun, two prominent phenomena are to be observed; namely, the wonderful expansive force which ejects the shot, aud the heat which results from the combustion of the powder. Let us exhibit the eifect of heat on metals by a familiar experiment. T^^l. Pour boiling water into a glass tumbler; the heat, com- municating more quickly to the thin sides than to the thick bottom, breaks the glass from unequal expansion. If v. e wish th
. Annual report of the American Institute, of the City of New York. Science. PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 401 HOW GUXS BURST. When gunpowder is fired from a gun, two prominent phenomena are to be observed; namely, the wonderful expansive force which ejects the shot, aud the heat which results from the combustion of the powder. Let us exhibit the eifect of heat on metals by a familiar experiment. T^^l. Pour boiling water into a glass tumbler; the heat, com- municating more quickly to the thin sides than to the thick bottom, breaks the glass from unequal expansion. If v. e wish the tumbler to withstand the sudden communication of heat, we must make it everywhere thin alike, so that the heat may pass through it uniformly and quickly. Hot water may then be poured into it with impunity. But it we wish it to withstand a pressure of cold fluid, it will be -^y^- necessary to make the walls equally thick; it will then withstand a considerable pressure on its interior surface, even if communicated suddenly. But if, after having pre- T!<j-3. pared it to withstand the pressure, we wish to communicate a pressure accompanied by U^ j) •heat, as of a considerable height of col- ^— =^ umn of melted metal, although the thickness of the walls would be sufficient to withstand the pressure, the heat communicated to the inner surface of the wall would \ y expand it within the outer metal, before the heat reaches the outside, and it would be broken by this unequal communication of the heat. Now, this unequal communication of heat has a similar effect upon large guns. This may, also, be illustrated by a glass model of a gun, which, although strong enough to withstand a pressure on the inner surface of 400 lbs. to the inch, would be broken by the insertion of a heated rod of iron of smaller diameter than the bore, even though so inserted as not to come in contact with its sides, and not accompanied by any pressure against the surface. Three models might thus be brokon
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