366 PROF. C. FEE WEN JENKIN AND MR. D. R. PYE ON THE 



Cor. 4. The slopes of all the constant-pressure curves are the same at the points 

 where they are cut by any one temperature curve. Thus every constant-pressure 

 curve on the CO 2 chart has the same slope at the point where it is cut by the 35 C. 

 temperature curve, viz., 308. 



Cor. 5. The slope of the constant-temperature curves is a convenient measure of 

 the " imperfectness " of the gas, for the slope is equal to the difference between the 

 reciprocals of the dilatation of a perfect gas and of the gas represented, i.e., 



slope = - 



dilatation of perfect gas dilatation of actual gas 

 CM. \ _ fl idj 



jUi 



(4) The slope of any I curve in a Q<f> chart may be expressed in any of the following 

 forms : 



( 1Q\ = A l~1 _0 AMI 

 di/Ji ~~ C ; , L v W#/ J' 



p v 



j.0 (de\ ,. . 



. -J-) ......... (ivc) 



Equations (iv6) and (ivc) are particularly useful in the saturated area, where they 

 reduce to : 



'de\ ._ e 2 Vs-V, 



and 



f de\ J0 de 



, , / - --, --^- (ivc?) 



d(f>/i V Lj-l! 



7 J i . , .......... (ive) 



d(j>/i v dp 



of which the first is the more convenient. 

 Cor. 1. Equation (ivd) may be written : 



dj?\ = e 2 V 3 -V 1 



~' 



where x is the dryness fraction. Thus the slope of I lines varies with x across the <ty 

 chart from one limit curve to the other. 



Cor. 2. The forms (iva), (iv6) and (ivc) become indeterminate at the critical 

 point, but (ivd) or (ive) may be used. For CO 2 the slope of the I line at the critical 

 point is about 3730. 



