196 REPORTS ON THE STATE OF SCIENCE.—1914. 
The quantity 0°081 JK, represents the change of internal energy 
in foot-pounds per degree change of temperature per cubic foot as 
measured at standard temperature and pressure. When K, is variable 
and is a known function of T, say #(T), the term becomes 
T, 
0-081 J @ (T) aT. 
1 
Values of this expression in which the lower limit T, is 0 degrees 
Centigrade can be read off the curve given in fig. 10, which is taken 
from the first Report. 
HOLBORN & HENNING. 
CLERK CE es 
LANGEN! Po eg 
MALLARD & LE CHATEUER__._ 9 
ENERGY, FOOT-LBS. PER CUBIC FOOT 
TEMPERATURE 7 CENTIGRADE 
Fig. 15. 
To use this curve to find the internal energy corresponding to a 
given state-point it is necessary to measure the pressure P and 
volume V from a PV diagram, and also to determine the absolute 
temperature T. The corresponding volume at standard temperature 
and pressure is then calculated from the equation, 
peer A 
ea P, 
This calculated value of V, when multiplied by the internal energy 
as given by the curve for the temperature T gives the internal 
energy of the gas corresponding to the given state-point. 
Symbolically let 
E, = internal energy corresponding to the position of a state-point A. 
Va, = the corresponding volume measured at A reduced to standard temperature 
and pressure, and 
Y; = the ordinate of the curve measured at the temperature corresponding to 
the temperature of the state-point, then 
Ea = Va, Yz 
