Page:The American Cyclopædia (1879) Volume III.djvu/632

626 CALORIC ENGINE don constructed such an engine, in which a gas flame was used to generate the heat. Niepce of France, the colaborer of Daguerre in his photographic researches, also entered the field ; and in 1833 Lieut. John Ericsson, while resid- ing in England, brought out his first caloric en- gine. The principle on which caloric engines are based is that when air is heated, and by confinement prevented from expanding, it will exert a pressure against the walls of the vessel in which it is contained, increasing with the temperature exactly in the same ratio as the air would expand if not confined. As air at 32 F., under a pressure of one atmosphere, expands to double its volume when heated to 522% it exerts then a pressure of two atmos- pheres; at 1011, of three atmospheres, &c. The air being enclosed in a cylinder with a movable heavy piston, this pressure will raise the piston with the force of 15 or 30 Ibs. per square inch ; and if then the air below is cooled or allowed to escape, the piston will move back downward by its own weight. This is the sim- plest form of caloric engine, and entirely simi- lar to the oldest (Newcomen's) steam engines. As the specific heat of the air is very small, it takes little heat to expand it, compared with that required to make steam from water ; and this is the chief reason why in later times many practical minds have given their attention to the solution of this problem ; several kinds of engines have resulted. The first caloric engine of Ericsson consisted of two cylinders and pis- tons of different sizes; the piston rods were so connected by a walking beam, that the ascent of one corresponded with the descent of the other (see fig. 1). The air in the small cylin- der A was by the descent of its piston driven into the larger cylinder, but during its passage heated and thus expanded in a proper appa- Fio. 1. Ericsson's First Caloric Engine. ratus by a fire ; this expansion being more than necessary to fill the large cylinder B, it exerted a pressure on its piston exceeding that on the smaller piston A. At the return stroke the hot air escaped from B, and a new supply of cold air was taken up in A by proper valves. The improved Ericsson caloric engine, which he introduced in 1850, is represented in fig. 2. The cylinder A contains the fire box B, out of which the products of combustion pass through Fie. 2. Ericsson's Improved Engine. the channel G around the cylinder in the jacket H, and after heating those parts goes up the chimney J. The cylinder A is open at the other end, and possesses two pistons, the sup- ply piston C, protected by non-conductors, and carrying a cap of light metal e e, fitting over the fire box B ; and the working piston D, with two valves Tc. Two rods, not visible in the figure, are attached to the latter piston, which set the fly wheel I in motion by means of cranks acting on its axle c, and which at the same time, by an ingenious system of levers, move the rod E C and the supply piston C in such a manner that it moves through twice the length of stroke of the working piston D, and is always slightly ahead in its stroke. The working piston carries also a valve ring g, which alternately closes and opens the commu- nication of the space between the pistons D and with the space A. The valves k in the piston D are opened by an excess of pressure from without, and vice versa ; the valve F, on the contrary, is opened by a projection on the axis c and closed by the spring /'. If now the pistons are moving from left to right, the space between D and C enlarges by the more rapid motion of 0, and the valves k admit cold air, while the air in the space A and around the cap e e escapes by the valve F. At the return stroke from right to left this valve F closes; the valve ring g opens and permits the air be- tween the pistons to flow into the space A, but in order to reach it, the cold air must pass the space between the cap e e, the outer cylinder, and the hot sides of the fire box B. Notwith- standing the short time that this contact lasts, the air takes a temperature of about 480 F., and this causes an increase of bulk of nearly double the volume, without pressure on the piston C, as the air passes by the annular valve g and fills the space between the pistons C and D. The pressure of this heated air on the pis- ton D increases rapidly with the motion of the