SATURATED STEAM. 21

Furthermore, the value of the entropy at M is repre-
sented by that of the liquid at e and the a;th part of
the entropy of vaporization, or



om=om+^ — >

J M



and the total heat at M equals the heat of the liquid
plus the a;th part of the heat of vaporization, or

Hm = <lM +XmTm,

and is represented by the area OaeMN.
T

In a similar way the distance ^ for several tem-
peratures can be divided into the same number of
equal parts, and then if all these corresponding points
are connected by smooth curves, each curve will repre-
sent a change during which the fractional part of the
water vaporized is constant. These are known as the
x-curves.
In place of having separate scales of pressure and
temperature for the ordinates of the T^-diagram,
it is often convenient to take the values of p and t from
the steam-tables and to plot Regnault's pressure-
temperature curve in the second quadrant, as shown in
Fig. 9.
Then given any pressure pi the corresponding tem-
perature t^ may be found as indicated or vice versa.
22



THE TEMPERATURE-ENTROPY DIAGRAM.
Let pi be the pressure and x^ the dryness fraction
of a pound of mixture, then on the chart its condi-




PlG. 9.
