80 



PROF. c. FI:K\\KX JENKIN AND MR. D. R. PYE ON THE 



V-,hi, of fy between the 700-lb. and 900-lb. pressure curves and the limit curve 

 were calculated in this way and are given in Table VIII. From this table we see 

 that the 700-lb. and 900-lb. pressure curves cut the C. temperature line at 

 = --IM.-J4 and = -'0049 respectively. These two points serve as the starting 

 fur plotting the two constant-pressure curves (700-lb. and 900-lb.) on the 00 



diagram. . 



The corrected 00 diagram may now be constructed. Ihe result is shown in 

 fig. 12. This diagram was drawn as follows : Starting at the points just found, 

 the 700-lb. and 900-lb. pressure curves were drawn as before, remembering that the 

 area under each curve on the 00 diagram between any two temperatures equals the 

 difference of I for the same temperature range. The liquid-limit curve was then set 

 off on the right of the pressure curves by plotting the small values of $<f> given in 



Table VIII. 



The gas-limit curve was then plotted by measuring off the values of L/0, taken 

 from Table VI., to the right of the liquid-limit curve. 



To plot the constant I lines it is first necessary to find a starting point. At the 

 origin (0 = 273, = 0) the value of lo is given by the equation I = Apv, where 



p is the saturation pressure at C. = 508 Ibs. per sq. in. = 73,200 Ibs. per sq. ft., 

 v is the volume of 1 Ib. of liquid = "0173 cub. ft.,* 

 A = T^jVo J therefore Io = '905 thermal unit. 



The point on the 700-lb. curve having the same I was then calculated as follows : 

 The change of temperature at C. is taken from the curve, fig. 9, p. 76, viz., '24 C. 

 per 100 Ibs. difference of pressure. The difference of pressure is 700 508 = 192. 

 Therefore the temperature of the required point is '24x1 '92 = '46 C. In other 

 words, I = '905 at a point + '46 C. on the 700-lb. pressure curve. Similarly, 

 I = '905 at a point + '94 G. on the 900-lb. pressure curve. 



Having found in this way the true value of I for one point on each of the pressure 

 lines, we can mark the true zero on the scale of the I curves, so that they shall give 

 absolute values of I instead of only differences (see p. 72). Using the new scales, 

 the points on the 700-lb. curve corresponding to I = 0, 5, 10, 15, 20, and 25 

 were marked off on the 00 diagram; also the points on the 900-lb. curve corre- 

 sponding to 1 = 45, +10, and +15. The corresponding points on the limit curve 

 were then calculated from the difference of pressure multiplied by the rise or fall 

 of temperature, given in fig. 9. Having found these points, the rest of the I curves 

 within the saturated area are easily constructed. Draw a horizontal (constant 

 temperature) line through one of the points, say, where I = 0, on the limit curve. 

 This is at temperature -1 C. = 272 abs. Along this line, starting at the limit 

 curve, mark off a series of points, equally spaced, at distances S<j> = ^ apart. These 

 will be points on the +5, +10, &c., I lines. 



* BHN's(6) value of the density of liquid C0 2 at C. is -925. 



