Il6 CALORIFIC POWER OF FUELS. 



THE WATER EVAPORATED. 



The feed-water is preferably held in a gauged reservoir, or 

 else weighed, meters not being certain unless checked fre- 

 quently. Use jonly cold water or water whose temperature 

 will vary but little during the test, so as to avoid corrections 

 of temperature and expansion. The temperature usually 

 varies so little that no account of this variation need be taken. 

 Pump to the boiler with as much regularity as possible, and 

 keep accurate record. 



To have the same level at the end as at the beginning, 

 keep up the initial pressure and feed very carefully. The 

 mean temperature of the feed-water is referred to o C., con- 

 sidering that the specific heat is constant. Otherwise we may 

 use Regnault's formula, 



Q = t O.OOOO2/ 8 -f- O.OOOOOO3/ 1 . 



But when the temperature of the water varies no more than 

 10 degrees, no appreciable error will be made by calling t 

 equal to the temperature. 



TEMPERATURE OF THE STEAM. 



We may measure the temperature of the steam directly by 

 a thermometer in the boiler, or indirectly by observing the 

 pressure. Both methods should be used. . 



To take the temperature directly, the thermometer is 

 placed in an iron tube closed at one end and reaching to the 

 middle of the boiler. The tube should be filled with paraffin 

 or some analogous substance. The temperature of the 

 steam or the water may be taken as desired by changing the 

 position of the thermometer in the tube. See Figure 39. 

 Vertical maximum and minimum thermometers are very use- 

 ful, preventing too hasty observations. 



