. The Locomotive . her along in the cylinder and the pressure-volumechange may be represented by the line BC of Fig. 3 which is similarto the line BC of Fig. i. In Fig. I we had the engineexhausting to the atmosphere whichis a space of constant pressure. Inthe present arrangement we shallsubstitute a condenser which, beingconstantly cooled by water at auniform temperature, reduces theexhaust steam to water and pro-vides a space of constant temperature of the coolingwater will determine what this pressure will be. Furthermore, inFig. I w^e had release taking place slightly before t
. The Locomotive . her along in the cylinder and the pressure-volumechange may be represented by the line BC of Fig. 3 which is similarto the line BC of Fig. i. In Fig. I we had the engineexhausting to the atmosphere whichis a space of constant pressure. Inthe present arrangement we shallsubstitute a condenser which, beingconstantly cooled by water at auniform temperature, reduces theexhaust steam to water and pro-vides a space of constant temperature of the coolingwater will determine what this pressure will be. Furthermore, inFig. I w^e had release taking place slightly before the end of thestroke of the piston. In this case, as will be noticed, we do not openthe exhaust valve until the completion of the forward piston pressure in the cylinder then drops approximately to that in thecondenser and, with the return stroke of the piston, we get the lineCDE. This line also differs from the corresponding line of Fig. iin that we have continued it back to the end of the return Fig. 3. 238 THE LOCOMOTIVE. [October, In this we have differed a Httle from the actual engine of Fig. i inwhich some of the steam was retained in the cylinder for the cushion-ing effect. The zveight of steam so retained, however, is compara-tively small and the difference between the real and this imaginaryengine is without relative importance. We now have the piston back to the starting point in contactwith the sliding gate and, with the exhaust valve closed, this gate maybe opened when the pressure against the piston (we could also saythe pressure in the cylinder) is raised. This change can be repre-sented by the line EA. -By means of the pump shown in Fig. 3 the condensed steam maybe taken from the condenser and returned to the boiler. In so doingit should be noted that the volume changes but very little, while itspressure is raised from that in the condenser to that in the boiler. In the above discussion we have been considering one pound ofwater or steam. Durin
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