. The steam-engine and other heat-motors . ofthe indicator-card is given by m4^ of the entropy diagram. Second Method of Drawing the Constant-volume Curve.—Lett3s3 and t2s2, Fig. 121? represent two of any number of entropy-lines of steam at constant pressure. Let OT and OE be the absolute temperature and entropy TO and lay off on the prolongation OF a scale of scale must be so chosen that OV is at least equal to the volumeof one pound weight of steam at the lowest pressure. Since the ENTROPY. 221 diagram deals with one weight of steam only, it is convenient totake the
. The steam-engine and other heat-motors . ofthe indicator-card is given by m4^ of the entropy diagram. Second Method of Drawing the Constant-volume Curve.—Lett3s3 and t2s2, Fig. 121? represent two of any number of entropy-lines of steam at constant pressure. Let OT and OE be the absolute temperature and entropy TO and lay off on the prolongation OF a scale of scale must be so chosen that OV is at least equal to the volumeof one pound weight of steam at the lowest pressure. Since the ENTROPY. 221 diagram deals with one weight of steam only, it is convenient totake the volumes from the tables for one pound, since it is easyto change the scale to give the volumes for any other the quadrant TOE, ordinates represent absolute temperatureand abscissas represent entropy; in the quadrant VOE, the ab-scissas represent entropy as before, but the ordinates representvolume. The line /3s3 gives the increase of entropy due to the formationof one pound of steam. At ts the volume of the steam is zero, and. Fig. 121. the entropy is found by dropping the perpendicular £3<?3. Simi-larly, dropping a perpendicular s3e4 from s3 and laying off on theprolongation e4V3 equal to the volume of one pound weight ofsteam at temperature ts (in accordance with the scale laid off onOV), we obtain the point F3. Draw e373. This is a straight line,as the entropy measured from the water-line is directly propor-tional to the volume of steam formed. Suppose e4F3 = cubicfeet. If we wished to find the entropy corresponding to any othervolume, as three cubic feet, find that number on OF; draw aparallel to OE. At the intersection, t3, erect a perpendicular toOE. The intersection of this perpendicular with £3s3 at c3 givesthe required entropy £3c3. In a similar manner draw 62^2, e\Vi9 222 THE STEAM-ENGINE AND OTHER HEAT-MOTORS. and find C2 and Ci. Draw the curve Cic2c3. The line so found willrepresent the entropy at constant volume of 3 cubic feet of steam. We
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