196 cox. 



The above figures perhaps show that there is an increase in the calorific 

 value of the volatile combustible matter with a decrease in the percentage, 

 but the difference in any event is very slight and there are many weak 

 points in such a deduction. I believe the assumption that it is constant 

 for all known Philippine coals to be equally accurate. Wlien a technical 

 problem is concerned and it is the desire to draw a general conclusion, 

 it is always necessary to attempt to determine a middle value whicli will 

 serve all samples equally well. If sufficient data were at hand we 

 probably would derive a slightly smaller value for "a" for the larger 

 percentages of volatile combustible matter in the above table. This 

 would give the highest degree of accuracy.'^- However, after considering 

 the remarkable regularity and similarity of the Philippine eoal,^^ the 

 data regarding which have been brought out in this paper, and which 

 also have been continually observed in the researches of this laboratory, 

 and using the data given by Table VI, an average value for "a" has 

 been derived for our coals, namely 53.6; that is, the -variable factor "a" 

 becomes a constant for coals of this Archipelago and is expressed by 

 the value 53.6. It is somewhat less than that applicable to coking coals 

 of the same grade. 



We now have all the factors for the development of an equation for 

 the calculation of the fuel value of a Philippine coal from its proximate 

 analysis. This formula is as follows : 



P=81C+53.6V, where 



P=^The calorific value in calories, 



C=The percentage of fixed carbon, 



V=Tlie percentage of volatile combustible matter. 



The coals must be analyzed Ijy the '"smoking-off method" ^^ which is 

 the only one giving reliable results with Philippine coals. In most 

 cases there is fairly close agreement between results calculated by the 

 \ise of the formula and those actually determined in the calorimeter; 

 this is shown by Table II, where they are given side by side. It is 

 possible to point out the limits of error by using the foregoing results 

 obtained directly by the calorimeter and calcidated by the use of the 

 formula. The average discrepancy between the determined and the 

 calculated heat of combustion of the coals is about "200 calories or nearly 

 four per cent, while the maximum deviation in the case of three or four 



'■= Results already published (Cox, A. J. This Journal (190G). 1, 892 et seq.) 

 show that the volatile matter of Philippine outcrop coals contains variable propor- 

 tions of noneonibustible matter other than water which probably accounts for 

 the observed irregularities. 



"" The results sometimes suggest the possibility of these beds all having been 

 continuous at one time, the differences in them as we now find them having been 

 produced by metamorphism and other conditions since the breaking up. 



■"'This journal, Sec. A. (1907), 2, 41. 



