KODUCTION. 21 



ii most important conclusion can be stated as follows: the heat 

 changed into work by a steam-engine working on Rankine's c> 

 equal to the d in the heat lonu-ntt of the steam supplied to and 



exhausted by the en/ 



This same expression is found in the discussion of steam turbines, 

 Problems of this nature can be solved immediately by aid of the 



.i-raturr Kntropy T.i 



Superheated Steam. A dry and saturated vapor, not in contact with 

 ,; uid from wlm h it is formed, may be heated to a temperature greater 

 than that corresponding to the given pressure for the same vapor when 

 saturated ; such a vapor is said to be superheated. When far removed 

 from the temperature of saturation, such a vapor follows the laws of 

 perfect gases but near the temperature of saturation the 



departure from those laws is too great to allow of calculations by them 

 for engineering purposes, 



All the characteristic equations that have been proposed have been 

 derived from the equation 



pv-RT, 



which is very nearly true for the so-called perfect gases at moderate tem- 

 peratures and pressures it k however, well known that the equation does 

 not give satisfactory result > at very high pressures or very low tempera - 



To adapt this equation to represent superheated gas, a corr 

 term is added to the right-hand side which may most conveniently be 

 assumed to be a function of the temperature and pressure, so that cal- 



. tions by it may be made to join on to those for saturated steam. 

 The most satisfactory chara< quation of this sort is that given 



Knoblauch,* Lindc, and KJebe* 



pv - BT - p (i - 



p the pressure is in kilograms per square metre, f is in cubic metres. 

 and T is the absolute temperature by the Centigrade thermometer. 

 The constants have the following values: 



B - 47.10, a - 0.000002, C - 0.031, D - 0.00 

 In the English system of units, the pressures being in pounds per 



liter Fr*KfrArt*ii. etc . Hrft ji. S. 33. 1905. 



