31 |16.71|77.22|84.45|4.25| 3.04|1.28| .91| 6.07| .56| |---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----| | |Indiana| | | | | | | | | | | |Pa | Co. | |29.55|62.64|79.86|5.02| 4.27|1.86|1.18| 7.81| 2.90| |---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----| |W. | Fire | Rush | | | | | | | | | | |Va | Creek | Run |22.87|71.56|83.71|4.64| 3.67|1.70| .71| 5.57| 2.14| ========================================================================= Table 39 gives for comparison the ultimate and proximate analyses of certain of the coals with which tests were made in the coal testing plant of the United States Geological Survey at the Louisiana Purchase Exposition at St. Louis. The heating value of a fuel cannot be directly computed from a proximate analysis, due to the fact that the volatile content varies widely in different fuels in composition and in heating value. Some methods have been advanced for estimating the calorific value of coals from the proximate analysis. William Kent[38] deducted from Mahler's tests of European coals the approximate heating value dependent upon the content of fixed carbon in the combustible. The relation as deduced by Kent between the heat and value per pound of combustible and the per cent of fixed carbon referred to combustible is represented graphically by Fig. 23. Goutal gives another method of determining the heat value from a proximate analysis, in which the carbon is given a fixed value and the heating value of the volatile matter is considered as a function of its percentage referred to combustible. Goutal's method checks closely with Kent's determinations. All the formulae, however, for computing the calorific value of coals from a proximate analysis are ordinarily limited to certain classes of fuels. Mr. Kent, for instance, states that his deductions are correct within a close limit for fuels containing more than 60 per cent of fixed carbon in the combustible, while for those containing a lower percentage, the error may be as great as 4 per cent, either high or low. While the use of such computations will serve where approximate results only are required, that they are approximate should be thoroughly understood. Calorimetry--An ultimate or a proximate analysis of a fuel is useful in determining its general characteristics, and as described on page 183, may be used in the calculation of the approximate heating value. Where the efficiency of a boiler is to be computed, however, this heating value should in all instances be determined accurately by means of a fuel calorimeter. [Graph: B.T.U. per Pound of Combustible against Per Cent of Fixed Carbon in Combustible Fig. 23. Graphic Representation of Relation between Heat Value Per Pound of Combustible and Fixed Carbon in Combustible as Deduced by Wm. Kent.]