CH. VIT.] THE FRUIT AXD SEED. 2*27 



The specific heat of water being 1, and that of at- 

 mospheric air 0.00035, or o-rV*)^^' ^ *'^^ quantity 

 of fuel which will heat a cubic foot of water one de- 

 gree be multiplied by 0.00035, the product will be 

 the quantity of fuel requh'ed to heat a cubic foot of 

 air one degree., and twenty times that quantity vn\\ 

 heat it twenty degrees, thhty times will heat it 

 thuty degrees, and so on. Xow 0.0075 lbs. of best 

 coals will heat a cubic foot of water one degree, there- 

 fore, 0.0000026-25 lbs. of coal vdW heat a cubic foot of 

 air one degree. 



It is essential to good and profitable fuel that it 

 should be free from moisture ; for unless it be dry, 

 much of the heat which it generates is consumed in 

 converting that moisture into vapour ; hence the su- 

 perior value of old, dense, dry wood, to that which is 

 porous and damp. A pound of dry will heat thirty- 

 five pounds of water from 32° to 212', but a pound 

 of the same wood in a moist or fresh state, vdW not 

 similarly heat more than twenty-five pounds. The 

 value, therefore, of different woods for fuel is 

 nearly inversely as their moisture ; and this may 

 be readily ascertained, by finding how much a 

 pound weight of the shavings of each loses by 

 drying, during two hours, at a temperature of 

 212^2 



^ C. Johnson's Fanner's Encyc. p. 512. 



q2 



