STEAM GUN

A contrivance by which balls, or other projectiles used in warlike operations, may be projected by the expansive force of steam. This invention, which is due to Mr. Jacob Perkins, so well known for various ingenious and useful contrivances in the mechanical arts, having been first brought forward since the general peace which succeeded the battle of Waterloo, has never been submitted to the test of actual experience either in military or naval operations, and consequently has not received the benefit of that stimulus to improvement which is always so nece ary to bring mechanical contrivances of a novel kind to perfection, and \vhich can only be derived from their practical application on a large scale. Of the probable or po ible utility of the steam gun nothing, therefore, can be inferred from that safest source of information — experience; and we are left to judge of it by the general properties of vapour, and by the experiments on a small scale to which it has been submitted. If a strong close iron ve el, having two valves, one opening ipwards and the other outwards, the latter being loaded with some definite pre ure, be completely filled with water, such a ve el may be heated to the temperature corresponding to the pre ure with which the valve is loaded without causing any portion of the water in it to be converted into steam. To render the effect more feasily understood, let us suppose that the valve is loaded with a pre ure of fifty atmospheres. The temperature of water evaporated under that pre ure being 510° {see Steam), the ve el may be raised to any temperature not exceeding 500°, without having any of the water contained in it converted into steam. If the temperature to which the water is raised be 600°, and a cubic inch of water at common temperature be forced into the ve el through the valve which opens inwards, water being sensibly incompre ible, a cubic inch of water at 500° will be forced out at the valve which opens outwards. This water being no longer subjected to the pre ure which kept it in the liquid state, will suddenly expand and flash into steaig, which at first will have a pre ure of 45 atmospheres, but as it expands will have its pre ure diminished in nearly the same proportion as the volume into which it swells shall be increased. Since, however, fiOQP is not sufiicient heat to enable the whole of the water thus ejected to pa into steam {see Steam), that part of it which will take the vaporous form will take the requisite amount of latent heat from the sensible heat of that portion which remains in the liquid state. As this latter portion will still retain a considerable temperature, it may be conducted to a ve el containing the feed for the heated ve el just mentioned, from which it will be again forced into that ve el. Such was the principle of Mr. Perkins's generators; by which term he denommated those close ve els in which water was raised to a high temperature without being converted into steam. Now if the valve through which the heated water is ejected be supposed to be in communication with the 116G STEAM NAVIGATION. barrel of a gun or piece of ordnance, in the same manner as the barrel of an air gun is in communication with the hollow metallic ball in which air is compre ed, a ball may be projected by the expansive force of the water ejected from the valve, in the same manner exactly as the ball of an air gun is projected by the expansive force of the compre ed air. As the water may be ejected from the valve either in a constant stream or by a rapid succe ion of jets, the balls may be discharged from the barrel as rapidly as it is po ible for them to be brought under the action of the steam; and since the heating of the barrel only tends to increase the elastic force of the steam, there appears to be no other practical limit to the action of such an engine of offence except that which may be imposed on the heating power applied to the generator. Of the abstract practicability of applying steam in this manner as an offensive engine there can be no doubt. Both theory and experiment conspire to establish it; but of the comparative efficacy, convenience, and economy of it, compared with gunpowder, many doubts will present themselves to all who duly reflect on the circumstances and purposes of war on the one hand, and the phenomena attending the explosion of gunpowder and the evaporation of water on the other. Not to mention any other, the fact that the steam gun cannot be brought into action until the generator has been raised to a high temperature by the application of an adequate furnace, would at once give to gunpowder an advantage over steam which would limit the application of the latter to a very few cases indeed, such as those of siege and other protracted military operations. In naval warfare it might po ibly be more frequently available; but even in that case, great improvements in the details of its mechanism should be made before its use could be attempted with any reasonable prospect of advantage. The steam gun is exhibited on a small scale in most mechanical museums and other exhibitions of a like kind; and such will probably be the limit of its use for a longjjeriod to come. [s. 1179]