18 



SATURATED STEAM, AND OTHER VAPORS. 



It is apparent that the errors of this formula are much larger than the 

 probable errors of the thermo-dynamic method. 



The following table, giving the volumes in cubic metres of one kilogramme 

 of saturated steam, shows the comparison of the two methods : 



By equatioa o" c. so* c. 100* c. iw c. 200* c. 



~ + <r , . 211.5 12.11 1.660 0.3875 0.1277 



, 54.97 11.43 1.643 0.3706 0.1343 



From equation 

 V = 25.62 + 



Steam Entropy. From the second law of thermo-dynamics may be 

 deduced the equation 



* = $ 



In which <f> is the entropy, dQ is the heat applied or withdrawn, and T is the 

 absolute temperature. Since the entropy depends on the state of the sub- 

 stance only, and not on the method of arriving at that state, we may calculate 

 the increase of entropy in one unit of weight of a given mixture <t 

 and steam, above the entropy of one pound of water at freezing point, in the 

 following method. Suppose that one unit of weight of water '. i from 



