CALCULATION OF THE HEAT UNITS. 



I6 7 



the most favorable conditions for smoke production the loss 

 does not exceed I per cent, and is generally less than one 

 half that amount. 



DISTRIBUTION OF CALORIES-LOSS. 



The difference between heat units accounted for and 

 those possible is considered as resulting from radiation by 

 surfaces not available for producing steam. The following is 

 taken from Scheurer- Kestner's results with a three -tube 

 steam boiler followed by a reheater. The first column gives 

 results obtained with Ronchamp coal in 1868, the second 

 results with Nixon's Navigation Co.'s coal in 1881. 



Ronchamp. Nixon. 



Calories in the steam 5 8 to 67$ 74. 5$ 



" " " waste gases 3.8 to 7.7 5.42 



" " " unburnt gases ... 2.4 to 9.7 traces 



" " " smoke 0.3 to 0.75 none 



11 " " aqueous vapor. . 2.0 to 3.7 2.81 



" not accounted for 19.4 to 24.7 17.27 



On September 20, 1895, Engineering published the results 

 of some experiments made by Bryan Donkin with Nixon's 

 coal on twenty different types of boilers. The following 

 table contains some of them : 



The calories in the steam varied from 63.8 to 78.5 per cent. 



" " " " waste gases " 6.5 to 22.5 " " 



" " " combustible gases " " o.o to 12.7 " " 



" '* not accounted for " 5.8 to 15.0 " " 



For the method of properly tabulating the heat balance, 

 see section XXI of the Steam Boiler Code on page 193. 



