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Gunpowäer and Vapor Engines. [Book IV.

muzzle of the other barrel. Now let that musket with whose breech theplug of its ramrod is in contact be first fired, and the rod will instantly beforced like a bullet up the barrel, and by its connection with the beamwill cause the other rod to descend. The musket in which this last rodmoves is then in its turn to be fired and the rod forced up in the same way.Thus the Operation is continued. The reciprocating motion of the beamis converted, if required, into a continuous rotary one by means of a crankor some analogous device.

Engines on this plan have not succeeded, nor is there any probabilityof their success. There are apparently insuperable objections to them,but which need not here be detailed. The explosion of gunpowder hastherefore been more frequently employed to produce a partial vacuum ina cylinder when its piston is raised, in Order to excite the pressure of theatmosphere to force it down. Suppose one or more openings, covered byvalves or flaps, were made near the upper ends of the muskets mentionedabove, i. e. just beneath the pistons or plugs of the ramrods when at thehighest point in the barreis, and the powder exploded when they are inthat position : the sudden expansion would drive out through the valvesmost of the air previously in the barrel, the valves would instantly close,and the atmosphere would push down the rod and thus raise the other;which in its turn might be caused to descend by exploding the chargeunder it, and so on continually. Instead of openings in the cylinders forthe escape of the air, some experimenters have made large openings inthe pistons and covered them with flaps, (like the suckers of commonpumps) so that when the explosion ceased the flaps closed and preventedthe air’s return. Others have used solid pistons and removed the bottomsof their cylinders, and covered the openings with leather flaps so as tooperate as valves and give a freer exit to the air and heated gases. Thiswas the plan adopted by Mr. Morey. Papin used hollow pistons. Thevacuum produced in this manner by gunpowder has always been veryimperfect. Instead of obtaining a pressure of 14 or 15 pounds on the inch,Papin could not realize more than six or seven.

Gunpowder has also been applied to raise water directly, by explodingit in close vessels like the receivers of Savery, with a view to expel theircontents by its expansive force, and also to produce a vacuum in Order tocharge them—but with no useful result.

Explosive mixtures, formed of certain proportions of an inflammablegas and common air, have been found to produce a better vacuum thangunpowder; for a volume of air equal to that of the gas used is displacedfrom the cylinder by the entrance of the gas previous to every explosion,and when this takes place nearly the whole of the remaining air is expelled,As yet, however, the best of explosive engines have had but an ephemeralexistence. Besides other disadvantages, the heat generated by the flameattending the explosion expands the air that remains, so as to diminishconsiderably the effect.

Of vapor engines, the most promising at one time were those in whichthe moving force was derived from ether and alcohol. The former boilsat about blood heat, or 98° of Fahrenheit’s scale, and the latter at 174°,while water requires 212°. The vapor of alcohol, it has been stated,exerts double the force of steam at the same temperature ; and if to this itbe conceded that the same quantity of fuel produces equal temperature?on both alcohol and water, then the former would seem to be more econo-mical than than the latter. Moreover, in consequence of the different spercific gravides of water, alcohol and ether, the cost of vaporizing equalvolumes of each varies in a still greater ratio than their boiling points—r