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M.CLAPEYRON ON THE MOTIVE POWER OF HEAT. 353 
drawn and the dilatation continued.. A fresh quantity of liquid will 
then pass into the gaseous state, and a part of the sensible caloric be- 
coming latent, the temperature of the mixture will diminish as well as 
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the pressure. Suppose the dilatation to be continued until the tem- 
perature diminishing gradually becomes equal to the temperature ¢ of 
the body B; let A F be the volume and F G the pressure corresponding 
to it. The law of the variation of the pressure will be given by a curve 
E G, which will pass through the points E and G. 
During this first part of the operation which we are describing, a quan- 
tity of action will be developed represented by the surface of the rect- 
angle B C E D, and that of the mixtilinear trapezium E G F D. 
We will now bring forward the body B, put it in contact with the 
mixture of liquid and vapour, and successively reduce its volume; a 
part of the vapour will pass into the liquid state, and as the latent heat 
disengaged in its condensation will be absorbed by the body B, the 
temperature will remain constant and equal to ¢ We shall thus con- 
tinue to reduce the volume until all the heat furnished by the body A 
in the first part of the operation has been conveyed to the body B. 
Let A H then be the volume occupied by the mixture of vapour and 
liquid ; the corresponding pressure will be K H equal to G F: the tem- 
perature remaining equal to ¢. during the reduction of the volume from 
AF to AH, the law of the pressure between these two limits will be re- 
presented by the line K G parallel to the axis of the abscisses. 
Arrived at this point, the mixture of vapour and liquid upon which 
we are operating, which occupies the volume A H under a pressure K H, 
