$62 M. CLAPEYRON ON THE MOTIVE POWER OF HEAT. * 
of the liquid corresponding to the temperature ¢ of the body A, and fg 
that which corresponds to the temperature ¢ — dé of the body B; bh 
the increase of volume due to the vapour formed in contact with the 
body A, 4’ that which is due to the vapour formed after the body A 
has been removed, the formation of which has reduced the temperature 
by the quantity d¢; we have seen, I say, that the quantity of action de- 
veloped by the transmission of the latent caloric furnished by the body 
A, [and transmitted ] from that body to the body B, is measured by the 
quadrilateral figure cdef. Now this surface is equal, if we neglect the 
infinitely small quantities of the second order, to the product of the vo- 
lume cd by the differential of the pressure dh —ek. Naming p the 
pressure of the vapour of the liquid corresponding to the temperature ¢, 
p will be a function of ¢, and we shall have dh — ek = = dt. 
ed will be equal to the increase of volume produced in water when it. 
passes from the liquid into the gaseous state, under the pressure p, at a 
corresponding temperature. If we call p the density of the liquid, 6 that 
of the vapour, and v the volume of the vapour formed, 6 v will be its 
weight, and ay will be the volume of the liquid evaporated. The in- 
p 
crease of volume owing to the formation of a volume v of vapour will 
therefore be 
(los! 2) 
enike=i Sais 
Pp 
The effect produced will therefore be 
7) yp P 
1— — d 
( ae FFM 
The heat, by means of which this quantity of action has been pro- 
duced, is the latent caloric of the volume v of vapour formed; let & be 
a function of ¢ representing the latent caloric contained in the unity 
of volume of the vapour furnished by the liquid subjected to experiment, 
at a temperature ¢, and under a corresponding pressure, the latent ca- 
loric of the volume v will be &v, and the ratio of the effect produced 
to the heat expended will ( expressed by 
(1-5) art “Pat 
We have demonstrated that it is we greatest which can possibly be 
obtained ; that it is independent of the nature of the liquid employed, 
and the same as that obtained by the employment of the permanent gases: 
now we have seen that this is expressed by ‘3 C being a function of ¢ 
independent of the nature of the gases; we shall therefore also have 
