22 ON THE HEAT EVOLVED 



The comparative numbers express the value of one A cord oi 

 each of the woods, one ton of the anthracite coals, and one 

 hundred hushels of the bituminous coals, charcoal and coak, 

 and although no one market is supposed to furnish for fuel 

 every kind of wood contained in the table, yet the principal 

 part will probably be found, and in markets where the woods 

 are much mixed, averages may easily b.e made adapted to those 

 markets. The column of comparative values was found in 

 the following manner. 



The value of a given quantity of fuel is directly proportional 

 to the time that a given weight of it maintained the air of the 

 room at a given temperature, and also to its weight. Hence 

 assuming shell-bark hickory for a standard, since one pound of 

 this wood maintained the air of the room at the given tempe- 

 rature 400 minutes, this being multiplied by 4469, the weight 

 of a cord of this wood, we obtain 1787600 minutes as the time 

 which the air of the room would have been maintained at the 

 given temperature, by consuming one cord of this wood. 



We then have the following proportion. As the product in 

 time corresponding to one cord of shell-bark hickory, ( 1 787600) 

 is to its assumed value (100) so is the product of the weight 

 of a given quantity of any other article into the time that one 

 pound of it would maintain the air of the room at the given 

 temperature, to the value of the given quantity of this article. 



Thus for a cord of white ash wood : 



As 1787600: 100 :: 3450x400 = 138000000 : 77 



For a ton of Lehigh coal, of 2240 pounds : 



As 1767600: 100 : : 2240x790=176960000 : 99 



For 100 bushels of cannel coal weighing 6525 pounds: 



As 1787600 : 100 : : 6525x630=41 10JT5000 : 230 



A few examples wiil be sufficient to show the facility with 

 which the comparisons may be made. For this purpose, we 

 will assume the price of shell-bark hickory wood as at six dol- 

 lars for a cord of 128 cubic feet, this being the average price 



