124 CALORIFIC POWER OF FUELS. 



in which L is the latent heat in British thermal units in one 

 pound of steam of the observed pressure ; T the observed 

 temperature, and / the normal temperature due to the pres- 

 sure. This normal temperature should be determined by ob- 

 taining a reading of the thermometer when the fires are in a 

 dead condition and the superheat has disappeared. This tem- 

 perature being observed when the pressure as shown by the 

 gauge is the average of the readings taken during the trial, 

 observations being made by the same instrument, errors of 

 gauge or thermometer are practically eliminated. 



