1 1 8 Of the Management of Fire 



Dr. Crawford found, by an experiment contrived with 

 much ingenuity, and which appears to have been exe- 

 cuted with the utmost care, that the heat generated in 

 the combustion of 30 grains of charcoal raised the tem- 

 perature of 31 Ibs. 7 oz. Troy (= 181,920 grains of 

 water) i^fty degrees of Fahrenheit's thermometer, when 

 none of the heat generated was suffered to escape. 



But if 30 grains of charcoal are necessary to raise the 

 temperature of 181,920 grains of water i^Vfr degrees, 

 it would require 3 1 5 7.9 grains of charcoal to raise the 

 temperature of the same quantity of water 1 80 degrees, 

 or from the point of freezing to that of boiling ; for it 

 is 1.71 to 30 grains, as 180 to 3157.9 grains. Conse- 

 quently the heat generated in the combustion of i Ib. 

 of charcoal would be sufficient to heat 57.608 Ibs. of 

 ice-cold water 180, or to make it boil ; for 3157.9 grains 

 of charcoal are to 181,920 grains of water as i Ib. of 

 charcoal to 57.608 Ibs. of water. 



From the results of M. Lavoisier's experiments, it 

 appeared that the quantities of heat generated in the 

 combustion of equal weights of charcoal and dry oak 

 are as 1089 to 600. Hence we may conclude that 

 equal quantities of heat are generated by i Ib. of 

 charcoal and 1.815 Iks. of oak; consequently that the 

 heat generated in the combustion of 1.815 Ibs. of oak 

 would heat 57.608 Ibs. of ice-cold water, or i Ib. of 

 oak, 31.74 Ibs of ice-cold water 180, or cause it to boil, 

 were no part of the heat generated in the combustion 

 of the fuel lost. 



If now we suppose the quantities of heat produci- 

 ble from equal weights of dry oak and of dry pine-wood 

 to be equal, and there is reason to believe that this 

 supposition cannot be far from the truth, we can 



